STUDIES ON FACTORS INFLUENCING THE ABUNDANCE AND
DISTRIBUTION OF SOIL ARTHROPODS IN GRASSLAND
By
Ian Henry Haines
Thesis submitted to the University of London for the
degree of Doctor of Philosophy.
Entomology Department,
Rothansted Experimental Station.
June, 1975. ii -
ABSTRACT
Effects of temperature and moisture on arthropods in soil
under grass were studied in a field experiment in which populations of animals in plots exposed to normal weather were compared with those in plots -inwhich- condrtians were artificially changed.-
Compared with total numbers of animals in normal soil, numbers in heated but unwatered soil decreased. This did not
occur in heated soil which was watered, so the major influence on
numbers was desiccation.
Certain groups within the total fauna reacted differently.
Acarid mites, especially Tyrophagus sp., always increased in number
in heated soil, whether moist or dry. Other mites, such as
certain uropodids, increased in number only in heated watered soil.
The Oppiidae decreased in number in heated soil, regardless of
watering. Total Prostigmata, total hypogastrurid and isotomid
,Collembola and lsotomodes productus were unaffected by the
treatments.
Numbers of sminthurid and entomobryid (especially
Lepidocyrtus spp.) Collembola, and of Oppia c.f. minus increased
or decreased in response to treatments, depending-am the - period
of exposure.
Most invertebrates decreased in number in the upper layers
of heated soil; often, numbers decreased by an order of magnitude,
especially in soil which was heated and allowed to dry. Possibly
these changes were due more to differences in mortality or
fecundity between the various layers than to vertical migrations.
The rates of population change during and after the treatment
period were determined, and studies on rates of recovery in
heated but unwatered soil allowed crude estimates of intrinsic — iii — rates of natural increase of certain microarthropods to be made.
Rates/head/week were between 0.01 and 0.06.
The influence of climate on populations of certain soil arthropods was studied in five sites ranging from Scotland to Devon, but effects were difficult to establish because physical conditions in soil were much too similar.
An attempt was made to define, in terms of "moisture-degrees", the limiting influence of temperature/moisture interactions on soil arthropods in general. It was suggested that values below about 240 or 250 might indicate unfavourable conditions for their survival.
- iv -
CO 'TT Title par e Thstract . • PO 00 00 00 00 00 00 00
C ontents o. 0. Oa O. 0. iv GENERAL INTRODUCTION 1 1. THFORTMS OF POPULATION GRMTTIT AND RE0rULTION 1 2. SO !1" PMFSICAL FACTORS INFLUENCING ATZTHROT;Ori POP-
ULATIONS O. .0 2 Climate and weather 2 a) Temperature • 5 (i) Resistance to low temperature 3
(ii) Resistance to high temperature .. Of (iii) Preferred temperature • • OP •O .. 6 (iv) Effects of temperature on physiology and
behaviour 00 .0 00 00 O. 4.6 6
b) Moisture 0. 7 (i) Resistance to desiccation 7 (ii) Resistance to excessive moisture (iii) Preferred moisture conditions 9 (iv) Effects of moisture on physiology and be- haviour .. 9
3. ARTHROPODS IN SOIL .. .• Oa 9
a) The soil as a habitat 00 00 4.0 PO 10 b) The arthropod fauna of soil 4. 11
c) The biology of certain arthropods O. 14 (1) Some effects of temperature and moisture
on population size and distribution O. 14 1) Spatial distribution of soil arthropods 15
Vertical distribution OG .. .. 15 Vertical movements of soil arthropods 15
Horizontal distribution 0* • • .. 19 Horizontal movements of soil arthropods 20 2) Population change in relation to time 21 Seasonal fluctuations ...... 21
Longer-term fluctuations 00 .0 00 23 (ii) Other aspects of the biology of selected soil arthropods in relation to temperature
and moisture .. .. 00 O. 0• e a 24
1) Egg production .. .. 00 O. • 0 24
v
Development ...... 25
3) Survival 06 00 00 .6 #8 .0 26
Lethal temperatUres .. DO •• 00 27 Optimum and preferred conditions .. 28
.. O. 60 4. THE SCOPE OF THIS THESIS .. .. 30 PART 1. A FIELD EX-7==NT UNDER CONTROLLED CONDITIONS 33 1. PRELIMINARY INVESTIGATIONS 07 THE STRUCTURE OF IN- VERTEBRATE COMMUNITIES IN THE SOIL OF THE EXPERI- MENTAL SITE • • • • • . • • • . .. • • 33 Sampling • • • • • • .• .• •. • • • • 33 Results and discussion • • • • • . •• • • 34 (i) Abundance of fauna .. . . • . • • • • 34 (ii) Size of sample unit .. .. • • • • .34 (iii) Number of sample units .. • • • • • • 33 (iv) Spatial distribution of fauna • • • • 40 Conclusions • • • • • • • • • • • • • • 43 2. THE EXPERIMENTAL PESIDN ANDPROCEDURE • • • • 43 (i) Design • • • • .• • • • • • • • • 43 (ii) Sampling • • • • • • • • • • • • 44 (iii) Extraction of fauna • • • • • • • • 48 (iv) Sorting of fauna • . • • .• • • • • 51 (v) Sub-sampling within the sorting dish • • 54 Method .. • • • • • • • . • • • • 55 Results .. • • • • • • • . • • • • 55 Discussion • • • • • 0 • • • • • 0 59 Conclusions .. • • 0 • • • • • • • 62 3. PHYSICAL MEASUREMENTS AT THE SITE . . • . • • 63 (i) The measurement of soil water • • • • 63 Water content of soil .. • • • • • • 64 Energy status of soil water: the use of tensiometers • • • • • • • • • • 66 (ii) The long-term recording of temperatures 69 4. SOIL ANALYSIS OF THE SITE • • • • • • . • 71 Methods • • • • • • • • • • • • • • • • 73 (i) Particle size distribution • • • • .• 73 (ii) Particle density • • • • • 0 • • • 0 74 (iii) Bulk density • • • • • • • • • • • • 74 (iv) Pore space • • • • • • •• • • • . 74 (v) Total orrranic carbon • • • • • • • • 74 (vi) Soil reaction (pH) .. . • • . • • • . 75 Results and discussion • • • • •• • • .• 75
vi
Conclusions •• .. •• 5. TIOTA.,:TC.',L ANALYSTS OP TU.-F 32 o2 Methods • • •• •• • . • • • • o-
Results and discussion • .. .. •• 83
Conclusions • • •• .. .. •• •• •• 95 6. WEATHER CONDITTONS AT ROTHAMSTED AND TUE MICRO- C=ATE AT GARDEN PLOTS DURING TILE EXPERIMENT .. 96
(i) General weather conditions .. 00 .. 96 (ii) Microclimate at Garden Plots .. 99
a) Temperature .. O. .0 0. 99 Seasonal distribution of temperature 99 The distribution of heat across the
plots •• •• . • •0 •0 _ 108 The vertical distribution of temper-
ature in the plots .. .. W. 00 109
b) Moisture .. 00 00 00 00 00 113 Seasonal changes in the water content'
of the soil in the plots 00 .0 113 The effectiveness of the watering
technique 00 00 00 00 06 113 7. CHANGES IN POPULATIONS 07 ARTHROPODS IN THE GAR-
DEN PLOTS EXPERIMENT ...... 00 00 117 (i) The statistical treatment of data .. 117
Transformations 40 00 0. 00 .0 118 (ii) Fluctuations in arthropod numbers in res- ponse to the treatments .• 120 Results •• •• •• •• •• •• 120 Discussion ...... • _ 134 (iii) Proportional changes in the composition of the soil fauna in response to treatment 148 Results ...... 149 Discussion .. •• .. • • •• •. 149 (iv) The results of pitfall trapping .. .. 160
Results and discussion 0,0 00 160 (v) The effect of the treatments on the phen- ology of some species of mites .. .. 162 PlatynothruF peltifer ...... 162 Pelops tardus ...... • . 166 Perr7amasus spp, .. •. .. .. • • 168 (vi) Some effects of the treatments on the rate
of change of numbers of arthropods .. 170
vii
8. TJTE 1-'ThITRTPUTIO'.1 CT TTT1. 7 ATTN.P., TN TUV PI,OTS 176 (i) NorizoiNtal clistr41-lution • . 176
(ii) Vertical distribution • • • • • • • • 132 Discussion • • • • • • • • 194 195 9. GEN7RAL SUMMARY OF PART 1 .. • • • • PART TI. THE SURVEY: Ps cf,TTFTYY OF C.;"\"\MES IN POPULATION NUMBERS OF CERTAIN FAUNA IN REL.PTION TO CLIMATE IN VAR- IOUS PARTS OF RTTAIN • • • • • . • • •• • • 197 1. Method • • • • • • ...... 197 2. Description of the sites ...... 199 3a) The results of temperature recordinps •• .. 209 3b) Population fluctuations at the sites: results of counts of animals extracted from soil cores .. 209 3c) Sampling for leatherjackets •• ...... 221 3d) The results of pitfall trooping ...... 223 3e) The vertical distribution of the soil fauna .. 226 Initial comparisons of the sites ...... 226 Changes in the vertical distribution of certain soil arthropods in autumn and winter .. .. 234
3f)The results of light tranoing .. .. 0* Of 2411. 4. General summary of Part II ...... 256 GENERAL DISCUSSION AND CONCLUSIONS •• .• •. 257
SUMMARY .. •.. • • •• • • •. 0 • ■ • • • • 268 ACKNOWLEDGEMENTS ...... • 271 REFERENCES .,...... 272 APPENDIX T • • • • .• .• •• •• •• •• 288 APPENDIX 2 • • • • . • • • •. •. •. •• 289 APPENDIX 3 • • •• •• • • •• •• •• •• 295 APPENDIX it • • • • •• • • •• .• •• •• 299 - 1 -
"To the lover of prescribed routine methods with the certainty of
'safe' results the study of ecology is not to be recommended."
C. Elton, 1927.
GENERAL INTRODUCTION
Malthus (1803), in his studies on the human population, pointed out that reproductive increase of successive generations followed a geometric, rather than an arithmetic progression.
This idea was taken further by Darwin (1859) when he proclaimed that "every organic being increases at so high a rate that, if not destroyed, even a single pair could produce enough progeny to cover the earth." Clearly, some form of natural regulation of animal populations must occur.
1. Theories of population growth and regulation
The type of unchecked growth (with a stable age distribution) envisaged by Malthus and Darwin is exponential and may be represented by the general equation:-
rt Nt = N oe
(Macfadyen, 1963; Southwood, 1966), where N is the number of organisms at any given time, t; and e is the base of natural logarithms. The parameter, r, is constant under the above conditions and is generally considered to represent the intrinsic rate of natural increase of the population (Andrewartha and
Birch, 1954). In natural populations, such geometric growth does not occur unchecked.
Verhulst in 1839 (Andrewartha and Birch, 1954; Macfadyen, 1963) proposed the use of the "logistic curve" to describe population growth in a limited environment. This curve is represented by the equation:-
E . N er(K-11 K \t t o where K is the asymptotic value which N approaches as time t approaches infinity. The equation is relatively simple and widely used because it has many theoretical and practical advantages.
do not propose to re-state theories on population growth, as they are many and have been adequately discussed (Andrewartha and Birch, 1954; Davidson, 1944; Elton, 1949; Solomon, 1949, 1957; Nicholson, 1954; Milne, 1957; Wigglesworth, 1972).
Macfadyen (1963) presented a useful critique of some aspects of these theories.
2. Some physical factors influencing arthropod populations
There has been much work on factors which influence arthropod populations but most of this concerns populations above ground, probably because soil populations are unseen and more difficult to study.
Climate and Weather:
The influence of climate and weather on the behaviour and outbreaks of pest insects has been reviewed by Graham (1956) and Wellington (1957). Both Wellington (1957) and Messenger - 3 (1959) stressed the importance of studying mieroenvironmental, as well as macroenvironmental, physical conditions in relation to insect population dynamics. Wellington (1957) also pointed out that "the microenvironment is the one part of the total environment that can be most easily manipulated for the partial control of insect pests." The susceptibility of insects to climate and weather was emphasized by Uvarov (1931); he included insects living in soil.
a) Temperature: Temperature is an important physical factor influencing animal populations (Andrewartha and Birch,
1954; Birch, 1957; Belehradek, 1935; Allee et al., 1949) and influences the speed of development, the duration of life, the fecundity and the behaviour, of the animal concerned (Andrewartha,
1970). (i) Resistance to low temperature: Theories concerning resistance to cold in insects and poikilotherms are given by
Allee et al. (1949), and Andrewartha and Birch (1954), but ,these will not be considered in much detail here. Briefly, for insects at least, three groups can be discerned according to the response of the insect to low temperatures (Kozhantshikov, 1938):-
(1) Those which cannot become dormant and must either develop or die; (2) those which can become 'quiescent', and (3) the diapause stage by which species from temperate climates
survive adverse conditions. The mechanisms of cold resistance in insects and other
invertebrates are not fully understood (Wigglesworth, 1972). - 4 -
Those organisms accustomed to warm surroundings often die at temperatures well above freezing point, possibly because of the accumulation of toxic products which, at normal temperatures, would be eliminated.
Most insects are killed when their tissues freeze
(Wigglesworth, 1972) and their death has been attributed usually
to dehydration of the tissues, or to mechanical injury by the formation of ice crystals, or both. A few insects can withstand complete freezing, but they die from unknown causes when the temperature is lowered even further.
The work relating to cold-hardiness in insects, and
poikilotherms has been summarised by Payne (1933), Sacharov,
(1930), Uvarov (1931), Mellanby (1939), Luyet and Gehenio (1940),
Allee et al. (1949), Andrewartha and Birch (1954), and
Wigglesworth (1972).
Increased resistance to cold is usually, but not necessarily, associated with loss of water, but in some insects,
contact with free moisture prevents undercooling (Wigglesworth,
1972). This factor may be important in the survival of some
invertebrates in soil where very cold conditions can occur, and some hibernating insects have been reported to withstand
temperatures as low as -50°C (Wigglesworth, 1972; Andrewartha and Birch, 1954; Allee et al., 1949).
(ii) Resistance to high_LeEperature: Useful background
information regarding tolerance of high temperatures in insects and other invertebrates has been given by Uvarov (1931), -5-
Andrewartha and Birch (1954), and Allee et al. (1949).
Wigglesworth (1972) points out that the resistance of insects to high temperatures_is complicated_by the interaction of factors_ such as moisture so that, in nature, insects may be in places which are cooled by evaporation and so survive where the ambient temperature would seem to be lethal.
An insect, or other arthropod, can effectively cool itself by evaporation only when it is above a certain size; below a certain size it can only cool its body by the evaporation of water it can not afford to lose (Wigglesworth, 1972).
The maximum temperature which invertebrates can withstand varies from one species to another, but Wigglesworth (1972),
Andrewartha and Birch (1954), Uvarov (1931) and Allee et al.
(1949) give many examples of insects surviving temperatures of around 5000.
How high temperatures kill insects is unknown, but it is probably related to a disturbance in the metabolic processes of the organism and an associated accumulation of chemicals
(Wigglesworth, 1972).
There are many examples of invertebrates becoming acclimatised to changes in their environmental conditions
(Andrewartha and Birch, 1954; Allee et al. 1949; Wigglesworth,
1972; Mellanby, 1939, 1959) and this can have an important influence on the ability of the organism to withstand extremes of temperature. Thus, for many animals, the upper and lower -6- lethal temperatures depend largely on the previous conditioning of those animals.
(iii) Preferred temperature: Although the body
temperature of poikilothermic animals normally follows that
of their environment fairly closely, poikilotherms generally show a preference for certain temperatures within their viable range. Humidity may affect the temperature preference of an organism and, again, the previous conditioning of the animal often influences the 'preferred' temperature (Andrewartha and Birch, 1954; Wigglesworth, 1972). The 'optimum' temperature of an insect, or of any
poikilotherm, is difficult to define. One may regard the optimum
_temperature as either that at which the greatest percentage
of individuals complete their development; or, that at which
the time of development is shortest (Wigglesworth, 1972).
(iv) Effects of temperature on physiology and behaviour:
There is a vast literature on the effects of temperature on
factors such as growth rate, fecundity, longevity and the
behaviour of animals (Uvarov, 1931; Belehradek, 1935;
Andrewarth and Birch, 1954; Allee et al., 1949; and Wigglesworth, 1972).
Attempts have been made to relate temperature and its
effects in terms of simple mathematical equations, but the
influence of temperature on organisms is complex. Responses
to chances in temperature are the result of many varied chemical -7- and physical reactions, many of which must be differently affected by such changes (Wigglesworth, 1972).
Cook (1927) in his studies on cutworms found that fluctuations in temperature accelerated development, and he stressed the importance of the period of exposure to the various temperatures.
b) Moisture: Moisture, together with temperature, have important influences on the physiology and behaviour of animals.
These two physical factors always interact, and many authors have confirmed the necessity of considering them together
(Wigglesworth; 1972; Andrewartha and Birch, 1954).
(i) Resistance to desiccation: The length of time insects and other invertebrates can survive drying conditions depends not on the rate of desiccation along, but also on factors such as temperature and the nutritional stage of the organism.
The time of exposure to drying conditions is of extreme
importance in determining the ability of an organism to withstand desiccation. Few animals in an active stage of
their life cycle can survive even moderate desiccation for long
periods, but many can survive substantial loss of water for
shorter periods (Andrewartha and Birch, 1954).
Most quiescent and diapausing insects must retain a water
content of about 50./0- if they are to survive (Wigglesworth, 1972),
but some insects and other invertebrates are able to survive after
losing almost all of their water. They exist in a state of - 8 suspended animation or 'cryptobiosis' and in this state are also able to withstand extremely low temperatures,
This ability to survive almost complete desiccation is well known in invertebrates such as rotifers, tardigrades, nematodes and certain molluscs (Wallwork, 1970; Allee et al.,
1949), but occurs also in some insects, for example, in the larvae of the chironomid, Polypedilum sp. (Wigglesworth, 1972).
(ii) Resistance to excessive moisture: Andrewartha and Birch (1954) point out that because some animals do not spread to moist places, and even within their areas of distribution such animals are often more numerous during dry weather, excessive moisture must be adverse to them. The way in which excessive moisture restricts, or is harmful to a species is difficult to explain, but there are many examples where the abundance of insects has decreased because of such an excess.
For example, populations of the cutworm, Porosagrotis orthogonia, are reduced by wet conditions (Andrewartha and Birch, 1954).
It is probable that the main influence of excessive moisture is indirect, for example, moisture may prevent the species from becoming cold-hardy. Interactions between food and moisture can occur. Andrewartha and Birch (1954) considered that moisture influences the death rates in natural populations by inducing the spread of epizootics of bacterial, fungal, and virus diseases. Excessive moisture may also simply drown an organism.
Many animals living permanently in soil, and the immature - 9 - stages of insects and other invertebrates which spend part of their life-cycle in soil, can survive flooding, but the duration of flooding;is important (Kdhnelt, 1961).
Temperature also influences the ability of an organism to survive excess moisture. At low temperatures, elaterid larvae (wireworms) can survive flooding; but at higher temperatures, during summer floods for example, they may not survive (KUhnelt, 1961).
(iii) Preferred moisture conditions: The tendency of many animals to move in a definite direction along a gradient of humidity indicates that these animals have a preference for certain moisture conditions. The preferred range of humidity of an organism, just like the optimum humidity, is often difficult to establish, because temperature and also time are important considerations (Andrewartha and Birch, 1954; Wigglesworth, 1972):
(iv) Effects of moisture on physiology and behaviour:
Voisture, like temperature, influences most aspects of the physiology and behaviour of animals, and may affect their growth rate, fecundity and survival. Physiological and behavioural experiments on the moisture relations of invertebrates have been many (Andrewartha and Birch, 1954; Allee et al., 1949;
Wigglesworth, 1972; and Edney, 1957).
3. Arthropods in soil The ecology of arthropods living in soil has been very much neglected. The reasons for this are many, but probably most - 10-
important are (i) that soil animals are not easily visible,
(ii) that the problems associated with the separation of soil
fauna from the soil particles makes accurate population
estimations etc. difficult, and (iii) that environmental factors
acting on invertebrate populations above ground can fluctuate
widely, whereas similar factors in soil fluctuate less.
a) The soil as a habitat: Most soil types have
characteristic animal and plant communities (Kevan, 1962;
Ktlhnelt, 1961; Laub, 1962; Drift, 1951). Although the soil
does, to a large extent, moderate physical factors acting above
ground, some fluctuations in temperature and moisture do occur and these must influence the animals living there. The range of
temperature variation in soil, for example, depends on the
amount of solar radiation reaching the soil surface, on the
depth of the soil, and its water content (KUhnelt, 1961;
Waliwork, 1970). Surface layers of soil have a greater range of
temperature than the deeper layers; and wet soils, which warm
up more slowly than dry ones because of their increased thermal
capacity, have smaller fluctuations in temperature than drier
ones.
On a world scale, soil temperatures range from well below
freezing in the polar regions, to 60°C or more in the upper soil
layers of many deserts (Allee et al., 1949; Waliwork, 1970).
Arthropods are able to survive in areas with such extreme
conditions; for example, they are found in the cold soils of the arctic regions (Ohnelt, 1961; Block, 1966a; Macfadyen, 1954;
Hammer, 1944) and in the antarctic (Covarrubias, 1968; Janetschek,
1963); in the warm soils of the tropics (KUhnelt, 1961;
Belfield, 1956; Salt, 1952; Strickland, 1945) and in hot desert soils (Cloudsley-Thompson, and Chadwick, 1964; Buxton,
1923; Andrewartha and Birch, 1954). Some arthropods in Iceland
can even survive in soils around hot springs (Tuxen, 1944).
Moisture conditions in the soil range from those in arid deserts (Cloudsley-Thompson and Chadwick, 1964) to those in
tropical rain forests (Williams, 1941). Arthropods also occur
in saltmarshes (Luxton, 1967), where the salt water tends to desiccate them.
b) The arthropod fauna of soil: The arthropod fauna of soils can include Insecta (Pterygota and Apterygota), Myriapoda,
Arachnida, Crustacea, Onychophora and Tardigrada, and soil fauna
may be classified in terms of "ecological groups" as well as
taxonomically. Wallwork (1970) recognised four such major groups, based on body size, presence in the soil,-habitat
preference and activity.
The body size of soil invertebrates ranges from 20 microns
(Protozoa), to over 20 cm (earthworms). From this range,
three size groups have been distinguished; the microfauna,
mesofauna (= meiofauna) and macrofauna (Fenton, 1947; Kevan,
1962; Wallwork, 1970).
The size limits are somewhat arbitrary and the animal
groups making up the soil fauna overlap them. Furthermore, many - 12 - individuals change from one category to another during their normal growth pattern.
Jacot (1940) and Drift (1951) distinguished soil fauna which spent the whole of their lives in soil, from those which spent only part of their life cycle in soil; the permanent members of the soil were termed 'geobionts', and the temporary members
'geophiles'. The geophiles consisted of those animals which were in hibernation as adults and those which had part of their development in soil, usually as eggs or larvae. Kevan (1962) distinguished two types of geophiles; inactive forms, which he termed 'transients', and the active forms, which he further divided into 'periodic' and 'temporary'. Wallwork (1970) stressed the need for such a distinction between active and inactive geophiles, if the importance of the various types to the economy of the soil was to be realised.
Classifications based on preference of habitat are related to the structure and properties of the soil. Consequently, the fauna of the liquid phase of soil water are those animals (such as the microfauna and some of the mesofauna) living in films of water around soil particles and in the water-filled cavities.
The pore spaces and other air-filled cavities in the soil are inhabited by the bulk of the mesofauna and the macrofauna.
The soil fauna is often correlated with characteristics of the soil profile, and animals are then termed 'epedaphici ,
'hemiedaphic', or 'euedaphic', depending on whether they are found on the soil surface, in the organic layers or in the mineral - 13 - layers of the soil respectively (Kevan, 1962; Wallwork, 1970).
The term 'hyperedaphic' is sometimes used to define those
organisms normally inhabiting the vegetation above the soil surface, but this group is of lesser importance in contributing
to members of the soil fauna (Kevan, 1962).
The food available to animals in the soil is varied and ranges from fresh plant and animal material to organic, material in various stages of decomposition. As a result, the animals consuming their food can be divided into many categories including phytophages„ carnivores, saprophages, detritivores,
macrophages and unspecialised feeders etc. More details about
the food of soil animals are provided by Kilhnelt (1961), Kevan
(1962), and Wallwork (1970).
Classifications based on the method by which soil animals
move have distinguished between burrowers and non-burrowers;
the latter, which are unable to create channels of their own,
have to move through cavities which already exist in the soil.
Kevan (1962) gives a more detailed account of this system of grouping.
All these systems of defining 'ecological' or 'functional' groups of soil animals are essentially artificial, and it is not surprising that there is often much overlapping of the groups.
Nevertheless, such groups often provide a useful means of reasoning the reactions of the animals to various factors. For
example, the ability of animals to evade extreme conditions in
surface soil layers may depend on whether they can burrow or not; - 14 - the decrease in size with increase in depth of pore spaces and cavities in the soil may prevent some of the non-burrowers from escaping these factors, which may be lethal.
c) The biology of certain arthropods
(i) Some effects of temperature and moisture on
population size and distribution: It is difficult to assess how temperature and moisture influence populations of soil arthropods, because of the way the two interact (Shelford 1929, Gisin 1943, Macfadyen 1963, Wigglesworth
1972). For convenience, the factors have often been studied independently, but much care should be given to the interpretation of results (Macfadyen 1963).
Temperature and moisture conditions in soil can differ greatly and a wide range of microclimates is potentially available to the soil fauna. One might reasonably expect the soil fauna to distribute themselves in the soil according to their temperature or humidity preferences, or to their abilities to tolerate these conditions. For example, horizontal distributions of the animals could be related indirectly to either vegetation or topography, through the effects of these factors on the physical conditions in soil. Similarly, one might expect differences in the vertical distribution of soil fauna in relation to temperature or moisture differences in the soil profile. - 15 -
1) Spatial distribution of soil arthropods
The distribution of the arthropod fauna of soils has been studied by many workers (Kahnelt, 1961; Surges and Raw,
1967; Wallwork, 1970; Kevan, 1962: Murphy, 1962), but the factors causing these distributions have been much less studied. Temperature and moisture could well be important factors, but the availability of food, amount of pore space, and the distribution of predators could also be effective.
Vertical distribution
Generally, the numbers of animals in soil decrease with increase in depth; this is•well documented in the books previously indicated. Often the decrease in numbers is so marked that the majority of the animals occur in the upper
5 cm of soil (Macfadyen, 1968). Consequently, much of the soil fauna, especially in exposed soils, may be subjected to a relatively large range of temperature and moisture conditions.
Soil animals living in surface layers must either tolerate these changes, or move to more favourable conditions when necessary.
The distribution pattern of the fauna in the soil profile changes with time (Wallwork, 1967; 1970), partly because the animals in soil move from one layer to another (Wallwork,
1967), but also because there is probably a differential mortality (Hale, 1967) or birth-rate in the various layers.
Vertical movements of soil arthropods
Tarras-Wahlberg (1961), Metz (1970), Wallwork and - 16 -
Rodriguez (1961), Berthet (1964) and others have demonstrated regular vertical movements in the Acarina, especially the oribatid mites. Certain small oribatids (of size less than
0.32 mm) may not move in this -way (Lebrun, 1964a).
Relating these migrations to temperature tolerance, the greater the displacement, the more stenothermic seems to be the species concerned; lesser displacements indicate eurythermic reactions. With the possible exception of the smaller oribatids, the Oribatidae generally tend to be stenothermic (Lebrun, 1964b).
Soil Acarina are basically hemiedaphic (Wallwork 1967, 1970;
Kevan, 1962), but their distribution may also include the epigeal zone (Tarras-Wahlberg, 1961; Wallwork and Rodiguez,
1961), this activity probably being related to humidity fluctuations in the epigeal zone. Similar movements between organic layers within the hemiedaphon also occur (Tarras-Wahlberg, 1961) and these may be responses to local temperature conditions.
Vertical movements may be short-term or diurnal phenomena, or longer-term, e.g. seasonal movements. Many of the migrations relate to weather conditions (Wallwork, 1970) and of these, temperature and moisture are often the dominant factors.
Probably, such factors as the distribution of food induce movements, especially amongst the more active Acarina.
It does not seem necessary to differentiate between short-term and diurnal movements and longer-term seasonal movements because, - 17 - as Waliwork (1967) points out, all these movements are probably governed in a similar way. However, seasonal movements may be antagonistic to diurnal movements. For example, populations which normally move between the surface and deeper layers during a summer diurnal cycle may be restricted to deeper layers during the winter and thereby show little or no diurnal movement during this time (Waliwork, 1967).
The interpretation of vertical movements of soil animals should be considered with care. Only occasionally have actual vertical migrations of soil animals been directly observed.
Such movements have usually been implied from differences in vertical distribution which have been obtained usually by soil-sectioning techniques or other means of estimating the distribution of animals in the soil profile. Movements or migrations are not the only way changes in vertical distributions can be explained; often, differential mortality or birth-rate may also be important factors, especially in relation to the longer-term changes.
The use of marking techniques could illustrate these movements, and Berthet (1964) has used radioactive paint in his studies on oribatid mites to show that such movements do occur.
In general, the Collembola, like the Acarina„ are most abundant in the organic layers of soil, although they also occur in the deeper mineral layers of most soils.
Collembola have a range of morphological}. forms (' life-forms' - 18 -
or t Lebensformen' (Ktihnelt, 1961)) which are often related
to their habitat in the soil profile. Thus, forms living on
or near the surface of the soil, or on vegetation, are typically
well-pigmented, with long antennae, a well developed furcula,
large eyes with many facets and often with large bodies. Those
living in the deepest layers of soil usually lack pigmentation,
have greatly reduced antennae, a reduced or absent furcula, no
eyes, and are of small body size.
Distributions of other soil animals have also been described
according to their life-form, but generally with less success
than with Collembola (Jacot, 1936; Klima, 1956; Tarras-Wahlberg,
1961). Even with Collembola, the concept should not be applied
- rigidly to distribution patterns (Wallwork„ 1970).
Changes in the vertical distribution of Collembola in
relation to season have been reported by many workers (Hale, 1967)
and most of these changes were interpreted as vertical
migrations during periods of adverse climatic conditions.
Dhillon and Gibson (1962) found no evidence for seasonal changes
in the distribution of Collembola in undisturbed grassland, nor
did Frenzel (1936) in his studies on meadow soils. A possible
diurnal vertical movement in Collembola was reported by Leuthold
(Hale, 1967).
Temperature was considered to he the most important factor
influencing seasonal vertical migrations of large invertebrates
in the soil types investigated by Dowdy (1944). He found that - 19 -
the animals moved to the deeper layers in autumn and winter and returned to the surface in the spring; the times of the
movements being closely related to the times of temperature
inversions between surface and deeper layers of soil. The
possibility of differential mortality or birth-rate in the various soil layers cannot be excluded, because Dowdy used soil sections.
Seasonal changes in the vertical distribution of soil
invertebrates have also been shown by other workers (Cameron,
1925; Jacot, 1936; Belfield, 1956).
Edwards (1959c) reported seasonal vertical migrations of
Symphyla and these movements were shown to be initiated by
temperature and moisture changes, at least in the upper layers, and temperature was considered the dominant factor (Edwards, 1961).
Migration from deeper layers also occurred (from a depth not exceeding 1.8 m) but these were probably caused by endogenous factors,
because at these depths physical factors remain relatively constant
throughout the year. Seasonal changes in the availability of food, or of various chemicals in the soil(especially root exudates) may also have been of some influence.
Horizonal distribution
Microarthropod distributions (mainly mites and springtails)
have been studied in pasture and arable soils by Sheals (1957),
Belfield (1956), Morris (1922, 1927), Ford (1935), Curry (1968),
Edwards (1929), Wood (1966), Glasgow (1939), Weis-Fogh (1948), Dhillon and Gibson (1962), Salt et al., (1948); in forest soils by - 20 -
Agrell (1941), Drift (1951), Murphy (1955, 1955), Wallwork (1959), Poole (1961); and in moorland soils by Hale (1966), Block
(1965a, 1966b) and Wood (1967 a,b). Macfadyen (1952) investigated
the microarthropods of a fen; and the oribatid mites of a bog
were studied by Tarras-Wahlberg (1961). Buxton (1967) has
studied the ecology of saltmarsh Acarina.
This list is not complete, but shows the kinds of habitats
which have been investigated most. Fewer studies have
concerned comparisons between two or more types of habitat,
or of gradients from one habitat type to another and the
related factors influencing distributions, although the work
of Haarlft (1960) provides an important step in this direction.
Horizontal movements of soil arthropods
Movements of arthropods in soil occur in both horizontal and
vertical planes (Berthet, 1964). Many factors influence horizontal
movements, but the distribution of food is perhaps the most
obvious one; it is reasonable to expect that temperature
and moisture differences in the horizontal plane also affect
population distributions. Berthet (1964) showed that certain
oribatid mites move horizontally for considerable distances,
and that these movements are related to the moisture content
of the litter in which they occur. Probably, differences in
temperature also affect the horizontal distribution of much of
the arthropod soil fauna, for example, certain ants living in - 21 - soil tend to build nests under stones, where the temperature often differs from that of the surrounding soil (Wheeler, 1910;
Wilson, 1971).
Many workers have shown that soil arthropods are typically aggregated in their distribution (Haarlhv, 1960; Glasgow, 1939;
Macfadyen, 1957; Healy, 1962; Debauche, 1962; Poole, 1961); this may be due to egg batches, gregariousness, or related to acommon source of food (Hale, 1967), but also sometimes because of local physical conditions.
2) Population change in relation to time
Seasonal fluctuations
Acarina
Numbers of oribatid mites change greatly from season to season (Wallwork, 1967, 1970). Furthermore, because these mites are the most abundant of all mites in many soils (Salt et al.,
1948; Sheals, 1957; Haarlhv, 1960; Block, 1965a; Wallwork,
1970), changes in their numbers are often typical of the
phenology of the Acarina as a whole. But the efficiency of the
methods of estimating the population, or the methods of separating individuals from soil can give misleading results.
For example, population estimates based on Berlese-Tullgren extractions may be selective, in that some of the smaller forms
or the immature stages may be killed before they have left the soil or litter sample.
Mites belonging to the Mesostigmata and Astigmata change -22- less in numbers in relation to season than do the oribatids.
It is possible that the Mesostigmata, for example, being mainly predatory mites are more mobile than the oribatids and can move to more favourable environmental conditions in times of stress, particularly when sudden changes in environmental conditions occur.
Oribatid mites in temperate climates tend to reach population maxima during the autumn and winter and minima during summer (Wallwork, 1967, 1970). This is most clearly shown for mites with univoltine life cycles and the population peaks seem closely related to proportional increases in the number of immatures. In soils containing both univoltine and multivoltine species, the population peaks may be less clear or even indistinct, depending on the relative proportions of each type of species.
Thus, population changes are closely related to the length of life cycle and number of generations per year in the species concerned.
Collembola
Maximum populations of Collembola generally occur in autumn or winter in most temperate climates, and numbers in summer are low, although there are exceptions to this generalisation (Hale, 1967).
Most studies on population dynamics of microarthropods have been made on large groups of species, (Kuhnelt, 1963;
Christiansen, 1964; Butcher et al., 1971). This synecological approach is due usually to the difficult or poorly understood -23- taxonomy of the groups concerned, but such studies can provide a useful indication of population trends, especially when the statistical treatment_of_data is adequate. Very few studies on soil fauna have made proper allowances for the great variability often associated with the data.
When large groups of Collembola have been studied, the seasonal population trends have often been poorly defined, or even contradictory (Christiansen, 1964) and there is little doubt that autecological studies on such soil fauna provide much information to clarify the overall picture. Glasgow (1939) was one of the first to study the seasonal occurrences of species of Collembola. He showed that different species varied in the times of their peak population, and thereby explained previous discrepancies in timing of population maxima in Collembola.
Other invertebrates
Populations of other groups of invertebrates in soil also fluctuate in relation to season, and many workers have shown that temperature and moisture are dominant factors influencing these changes. Much information on the effects of weather on invertebrates, including those in soil, is given by Andrewartha and Birch (1954) and Allee et al. (1949).
Longer-term fluctuations
Very little is known of the patterns or trends of long-term fluctuations in populations of soil arthropods, especially of the microarthropods, because few ecological studies have been -24- conducted for more than a few years in succession. However, there is evidence of long-term (6-10 year) cycles of population maxima in tipulids, as results of the extensive sampling programme of A.D.A.S. show.
(ii) Other aspects of the biology of selected soil
arthropods in relation to temperature and moisture: In this section I shall discuss the Acarina and Collembola mainly, because these animals are the main subject of the research.
1) Egg production
Eggs of the Acarina and Collembola may be laid singly or o in clumps,/many substrates including old exuviae, detritus, and in soil pores. The eggs of oribatid mites are generally retained in the body of the female until they mature, they are then laid together. Clutch size varies, but the maximum number of eggs per clutch recorded for these mites is 16 (Woodring &
Cook, 1962). Probably, batches of eggs are laid by the majority of Collembola, and the number of eggs per batch may be over
100 for some species (Wailvork, 1970).
Temperature and moisture (or humidity) can affect egg production in various ways, e.g. by affecting the fecundity of the female or the rate of development of eggs. A range of behavioural responses and physiological changes are probably effected by various combinations of these two physical factors
(Madge 1964, 1966), but the nutritional state of the female is also important, especially in relation to fecundity. - 25 -
2) Development
Embryonic and post-embryonic development of,Acarina and
Collembola are greatly influenced by temperature, and most species
appear to have an optimum temperature for development which
is related to the ambient humidity.
There is evidence to suggest that under similar conditions,
small species of oribatid mites tend to have a shorter
development period than the larger species, and the more
primitive species of oribatids take longer to develop than
those belonging to the Circumdehiscentiae (Lebrun, 1970).
Lebrun (1970) and Wallwork (1970) gave tables indicating the
development times in relation to temperature for many species
of oribatids.
The smaller species of oribatids may have several generations
per year, whereas the larger ones are often univoltine. Thus
Euzetes globulus, /11a-timEtF tifer and Nothrus silvestris
may have one generation a year; Oppia nova and Minunthozetes
semirufus may have two generations a year and Tectocepheus velatus,
Oppia sapectinata and Hypochthonius rufulus can produce 3 - 5 generations per year under favourable conditions (Lebrun, 1964b).
Mites generally pass through a hexapod larval stage and
through one, two, or three nymphal stages having the normal
adult complement of eight legs, before reaching maturity
(Wallwork, 1970).
Collembola differ in the number of times they moult and the -26- time they take to reach maturity. The length of life is influenced by environmental factors, especially temperature and moisture or humidity. Within the range of tolerance of a given species, high temperatures reduce, and low temperatures increase, the length of instars. There is evidence that juveniles are more resistant to low temperatures and less resistant to high temperatures than the adults (Thibaud, 1968).
Collembola do not have a distinct metamorphosis, so the first instar juveniles usually resemble, but are smaller than, the adults.
At high altitudes and in arctic and sub-arctic conditions most Collembola have only one or two generations a year; in more temperate climates and at lower altitudes some species have several generations a year (Hale, 1967). Folsom recorded
3-4 generations in Hyoogastrura armata (Hale, 1967) and up to
12 generations a year occurred in this species at 24°C in the laboratory (Britt, 1951).
There tends to be an increase in the duration of each instar as development proceeds.' Much of the work on the development
of Collembola has been in laboratory studies under controlled conditions, and supporting field observations are relatively scarce.
3) Survival
Factors influencing the survival of populations of soil arthropods are many, varied and complex, and I cannot do more than
indicate the scope of studies in this context. - 27 -
The importance of temperature and moisture or humidity as factors influencing populations of soil arthropods has been the subject of much speculation, but the ability of species to tolerate extremes of these conditions is not well-documented.
Attempts have been made to determine the "optimum" conditions for survival, or the 'preferred' conditions of these animals.
In nature the 'preferred' conditions may not be the 'optimum' conditions for survival, so the results of experiments in the laboratory may be very misleading or inaccurate if applied to field conditions uncritically. The temperature preferendum of a mite may also be that of one of its major predators, and the maximum populations of that mite may therefore occur in habitats which are not those "preferred" on the basis of temperature.
Lethal Temperatures
Very little is known of lethal temperatures of most species of Acarina. Tuxen (1944) reported that certain oribatids could survive 4100 around hot springs in Iceland, so their range of tolerance was probably relatively large. Madge (1965) o stated that certain oribatids were killed at around 44 C, but others died at lower temperatures, and the lethal temperature varied with the humidity. The ability of mites to survive extreme low temperatures is even less documented, although mites do occur under polar conditions. Work on the oribatid Belba geniculosa (Madge, loc. cit.) has shown that this species can tolerate -5°C for one hour, and 3500 for twelve hours in saturated air. - 28 -
The upper lethal temperature for most species of Collembola appears to be about 34° - 40°C (Agrell, 1941; Pacit, 1956;
Bellinger, 1954; Davis and Harris, 1963), though some species can survive temperatures as high as 55°C (Willson, 1960;
Bunger, 1964). The Collembola are probably more resistant to cold than are the mites, because certain species of Collembola can survive temperatures as low as -50°C (Paclt, 1956; Pryor,
1962). According to Ktthnelt (1961) and Hale (1967), most
Collembola are still fully active just above freezing point, although not all authors agree (Agrell, 1941; An der Lan,
1963; Janetschek, 1963; Dunger, 1964). Isotomid Collembola can be active between -10 and -5°C (Kuhlmann, 1958; An der Lan,
1961). The ability of Collembola and other soil arthropods to survive or remain active under such extreme conditions depends largely on the environmental conditions normally experienced by the species (Wallwork, 1970).
It is likely that in nature, soil Collembola are rarely injured by extremely low temperatures, except when these temperatures are associated with desiccation (Stebayev, 1962;
Kahnelt, 1961), but the long-term effects of low temperatures on longevity and fecundity have not been studied.
Optimum and preferred conditions
Studies on temperature and humidity preferences and optimum conditions for development in Acarina have been restricted mainly to the oribatids. Madge (1966) reported that Belba -29- geniculosa "preferred" a narrow temperature range of 13 - 13.6C, even in harmful humidity gradients. Pauly (1956), also working on belbid mites, stated that they-'plleferiled' temperatures of 12 - 15°C, but these experiments were done without humidity controls.
Wallwork (1960) demonstrated that the 'preferred' temperature of certain oribatid mites could be changed by acclimation, but this may not occur for all oribatids, because Madge (Wallwork, 1970) could find no evidence that acclimation altered the temperature 'preferred' by
B. geniculosa.
The ability of mites to survive at various humidities differs with the species, but most soil mites 'prefer' saturated conditions.
Temperature and humidity interact, so that desiccation generally lowers the 'preferred' temperature and high temperatures usually induced a 'preference' for higher humidies.
Work on Collembola has shown that the temperatures required for optimum development differ with the species, and even related species may have marked differences in their requirements. For example, Sharma and Kevan (1963a) stated that Isotoma notabilis developed- best at 17°C;
but another isotomid, Folsomia similis developed best at 22°C (Sharma and
Kevan, 1963b). More closely related species of Collembola also responded differently to temperature: Sharma and Kevan (1963c) noted that
the entomobryid Pseudosinella petterseni survived (but did not reproduce) • at 4°C, whereas P. alba could survive at 0°C. Most Collembola are unable to withstand desiccation for more than
short periods, and in this respect, Collembola are probably more sensitive - 30 - to drying conditions than are the majority of the mites found in similar habitats, although there are exceptions to this generalization. Usually, Collembola need relative humidities of at least 90 to survive (Christiansen, 1964), and there is evidence that most species of springtails are able to survive flooding for relatively long periods (Kllbnelt, 1961).
4. The scope of this thesis Much of this review has considered the effects of temperature and moisture on soil arthropods and on the Acarina and
Collembola in particular, mainly because these are often the most numerous arthropods in soils. Many physical factors possibly influence populations, but temperature and moisture were emphasised most because the research described in the thesis relates to these factors.
In any project as broad as the one described in this thesis, it is necessary to limit the main investigations to only a small part of that which could be possible under this heading. It was decided that temperature and moisture were the most important factors and would be investigated in this work, although other factors are also considered, but in much less detail.
My research was confined to studies on those arthropods inhabiting grassland soils. This was partly to facilitate the experimental design, but also so that a more or less uniform habitat type and one which would contain plently of arthropods could be studied. The economic importance of grassland, and its - 31 - widespread occurrence, were further factors in the decision, because any information which may give a clearer picture of the dynamics of grassland, ecosystems is__potentially useful; especially if such information can be related to productivity.
Grassland in one form or another occupies about 700 of the surface mainland of Britain (Woodford, 1971; Woodford and
Morrison, 1971) and on a world scale has been estimated as covering over 33% of the total land area (Shantz, 1954).
In Britain, about 470 of grassland (total grassland occupying approx. 34 million acres) may be classified as rough grazing, 38% as permanent grass, and about 15% as temporary grassland up to seven years old (Harkness, 1969). Woodford (1971) considered that about 501 was classified as rough grazing, 17% was permanent grass and 30 was temporary grassland, but he included rotational grassland over twenty years old in the latter category.
Whichever criteria one may choose to classify grassland, clearly grass is widespread, and essential to the economy of
British and world agriculture. The French Minister for
Agriculture in 1950 (Semple, 1970) summarised the economic importance of grassland when he indicated that grass provided at least 50 of the sustenance for all farm animals in Europe and that grass occupied a larger area of land that all other current crops combined.
Semple (1970) considered that grass was one of the most - 32 conspicuous factors in creating and maintaining many of the more fertile soils. invertebrates in grassland soil were shown to accelerate the rate of herbage decomposition by an average of 2 to 3.5 times that which occurred by the action of bacteria and fungi alone; at the peak of invertebrate activity the rate was increased 6 to 9 times (Kurceva, 1971).
Probably, invertebrates play an important part in maintaining soil fertility through their effect on the breakdown of organic remains, and also by their assistance in promoting soil aeration and drainage (Harkness, 1970). The most important detritivores include earthworms and enchytraeid worms, and amongst the arthropods include the diplopods, Collembola, certain mites and many insect larvae (Wallwork, 1970). The breakdown of organic remains by most of these animals is probably mainly a mechanical process, rather than a chemical one; the act of comminution facilitating later chemical decomposition by fungi and bacteria (Kevan, 1962; Burgos and Raw, 1967;
Wallwork, 1970).
Factors influencing the abundance and distribution of any of these invertebrates may therefore indirectly affect the fertility of the soil, and there may be a possibility of manipulating such factors with the aim of increasing yield. — 33 —
Part I. A FIELD EXPERIMENT UNDER' CONTROLLED CONDITIONS
Studies on soil invertebrate populations involving artificial control of soil temperature and moisture conditions in the field were initiated at Rothamsted by Edwards (1969a) in an Unreplicated experiment. In 1970,7-a more elaborate experiment, with randomised block design, was begun in Garden Plots at Rothamsted and the account following concerns part of this latter experiment.
1. Preliminary investigations of the structure of invertebrate
communities in the soil of the experimental site
Initial sampling of the prospective site at Garden Plots was done on 6th May 1970, in order to determine which groups and species of animals were present in the soil, and to assess their relative abundance. An indication of the size and number of sampling units needed for population estimates was obtained, as well as information on the spatial distribution of the soil fauna.
Sampling;
A sample consisting of 16 soil cores (sample units) of diameter 10 cm x depth 15 cm was taken from the site, over the whole area. Even coverage was achieved by dividing the site into 16 sectors; the actual location of the core within each sector being determined at random (Healy, 1962; Debauche, 1962).
A further sample of 16 cores, but of diameter 5 cm x depth 15 cm, was taken alongside the 10 cm diam. cores. Animals were then extracted from the soil, over a 5-day period, using a modified
Tullgren apparatus described later in the thesis. -34-
Results and discussion:
(i) Abundance of fauna: Table 1 summarises the numbers
and systematics of the fauna collected from the two sets of
samples. Numerically, the dominant group was the Acarina,
with the Collembola second. The remainder comprised only 3.2A
of the total fauna extracted from the 5 cm diameter core sample,
and 4.1% of the total fauna from 10 cm diameter cores. The ratio
of mites/springtails was 2.86 from the 5 cm diam. cores and 2.58
from the 10 cm diam. cores,
Microarthropods are usually the most abundant arthropods
in most soils, and the predominance of Acarina in the soil
is typical of many grassland areas (Block, 1965a; Curry, 1968;
Davis, 1963; HaarljSv, 1960; Macfadyen, 1952; Salt et al. 1948;
Sheals, 1957; Strenzke, 1947, 1952; Weis-Fogh, 1948; Wood 1967a),
although some workers have reported Collembola to be more abundant
(Block, 1965a; Dhillon and Gibson, 1962; Ford, 1935). The
ratio mites/springtails may range from 0.03, as in the case of
Ford's meadows soil (Ford, 1935), to over 5.0 (Strenzke, 1947, 1952;
Macfadyen, 1952; Wood, 1967a) but comparisons of such ratios
are probably meaningless because of differences in the efficiency
of the methods used to extract the fauna from the soil, and
differences in the depths of the sample units taken.
(ii) SiaeofLaaLpleunit: The relative efficiencies or
precision of the two core sizes were compared, to determine
the most appropriate size of sample unit for the experimental - 35 -
Table I. The number'and systematics of animals collected from 5 cm diam. and 10 cm diam. cores
GROUP 5 cm 10 cm 5 cm 10 cm cores cores -GROUP core cores
Acarina (A) Araneae 2 5 Prostigmata + Symphyla 2 7 Heterostigmata 723 957 Pauropoda 1 Mesostigmata 218 218 Diplopoda 2 4 Astigmato 56 125 Chilopoda 5 13 Cryptostigmata 1671 1776 Enchytraeidae 31 18 TOTAL 2668 3076 Lumbricidae 1 Collembola (C) Nematoda 23 16 Onychiuridae 440 315 Diplura 1 Hypogastruridae 54 46 Thysanoptera 8 12 Isotomidae 369 465 Hemiptera 10 15 Entomobryidae 6 18 Hymenoptera 2 15 Sminthuridae 64 348 Coleoptera 20 51 TOTAL 933 1192 Diptera 10 14 Psocoptera 2 12 TOTAL OTHER ANIMALS 119 183 T-(A+C)
TOTAL FAUNA 3720 4451 - 36 - investigations. A statistical analysis of the presampling data is given in Table 2. The number of sampling units required to give the same overall precision are in the ratio of the squares of the statistic s/m (Healy, 1962). Thus, for total fauna, 100 10 cm diam. cores give the same precision as 2 100 x 0.58 /0.752, i.e. 60 5 cm diam. cores (See Table 2).
Similarlym 100 10 cm diam. cores give the same precision as Ay.
5 cm diam. cores for the Acarina; 96. 5 cm diam. cores for the
Collembola and 182 5 cm diam. cores for the non-microarthropods
(given as T-(ABC) ).
Because the 10 cm diam. core has a greater volume than that of the 5 cm diam. core (both cores being taken to a depth of 15 cm), it may be better to compare the amounts of soil examined in the two instances. The 10 cm diam. : 5 cm diam. core volumes are in the ration 4 : 1, hence, from the above figures, the volume of soil to be examined for equal precision are in ratios 100 : 15 for total fauna, 100 : 12 for Acarina, 100 : 24 for Collembola and 100 : 46 for the rest.
Comparisons of the two sample unit sizes, based on surface area, show that the 5 cm diam. core gave the greatest precision for the microarthropods, but not for the other groups.
On a volume basis, the 5 cm diam. core gave the greatest precision for all groups.
The optimum size of the sample unit depends on the size and behaviour of the animals to be extracted from it. A sample - 37 -
Table 2. Statistical analysis of sample data for major groups of soil fauna STAN- DARD GROUP MEAN DEVI- RATIO x2 xx __ _m ATION sim s
TOTAL FAUNA (T) 5 cm diam. cores 3720 232.5 134.5 0.58 8.82 1166.88 10 cm diam. cores 4451 278.2 208.5 0.75 12.50 2343.75
ACARINA (A) 5 cm diam. cores 2668 166.7 97.7 0.59 7.57 859.57 10 cm diam. cores 3076 192.2 166.3 0.86 11.99 2156.40
COLLEMBOLA (0 5 cm diam. cores 993 58.3 53.9 0.92 7.06 747.65 10 cm diam. cores 1193 74.5 69.8 0.94 8.09 981.72
T-(A+C) 5 cm diam. cores 119 7.4 6.3 0.85 2.32 80.74 10 cm diam. cores 183 11.4 7.2 0.63 2.13 60.05
sit = Disturbance Index of Lexis x2 = Dispersion Index of Fisher -3.8 - unit too small may be inefficient, and one too large may result in errors due to inefficient functioning of the extraction apparatus (Debauche, 1962). This latter point is probably important in explaining the greater precision when using the
5 cm diam. sample unit size than when using the 10 cm diam. size in the results given here.
(iii) Number of sample units: The question of the number of sampling units required to provide adequate information of the soil population at a given time is a crucial one and is difficult to solve practically. Debauche (1962).cimsidered that much of the published data relating to soil fauna were unreliable, because the samples taken were too few to be statistically adequate, owing to the large spatial variation encountered in natural populations. One of the principal causes of this variation he attributed to the aggregation of individuals, and for very aggregated populations the most representative sample would contain the largest number of sampling units. The counting and sorting of all the animals in such a sample would be a prohibitive task.
To illustrate this point, a quotation from Macfadyen (1963) seems appropriate " a thorough and complete count of a square
metre of English meadow soil using a microscope [is,] a process
which would require at least three years and would leave one in no
fit state for further scientific work...." Obviously, a compromise
is needed to choose a sample size offering a reasonable degree of - 39 - accuracy for an acceptable amount of work.
In theory, to obtain an estimate of a population mean with
the 95% fiducial limits -set at 5%-of that mean, one would
need to take n sample units, where n is given by Snedecor (1946) as :- n t2 s2 / (i m)2 and t is the value obtained from statistical tables for the chosen probability level (in this case 95%) for the d.f. of the initial sample; s is the standard deviation; and (7: m) is the difference between the unknown population mean and the sample
mean, it is pre-determined to obtain the required degree of accuracy, in this case at 5% of the sample mean. Hence,
(see also Table 2) the number of 5 cm diam. cores needed to
obtain the stated accuracy is:-
2 2 n = (2.131)2 x (134.5) / (11.625) = 608
Similarly, to approximate the 95% limits to 4. 10% of the sample mean, 153 sample units of diam. 5 cm. would need to be
taken.
It is clear that the number of 5 cm diam. cores required
to maintain the 95% limits to within even 10% of the sample
mean is too large to be maintained for an experiment of any
duration, because the number of sample units involved would
mean that the sorting of animals within a reasonable time
would be impossible.
For convenience of sorting (and especially as large numbers - 40- of animals are to be expected during the spring and autumn) decided to take on an empirical basis sixteen sample units of diam, 5 cm and depth 15 cm per treatment on each sampling date.
The results of the initial investigation using such a sample size of 16 sample units, showed the mean number of animals per 5 cm diem. core was 232.5, with calculated 950 fiducial limits of + 71.6 (i.e. approx. + 30% of the mean).
The mean, with 95-A fiducial limits for the 10 cm diam. core sample was 278.2 4- 111.1 (the limits being approx. 40A of the mean). However, better accuracy than this may be possible at certain times of the year when animals are more abundant.
Such large variability in data relating to sail fauna is common and is associated with the spatial distribution of the fauna (Debauche, 1962). Workers investigating soil populations, for practical reasons are seldom able to take enough sample units to satisfy the statistical requirements. The accuracy of my population estimations is acknowledged as being of the order determined in this initial investigation. Therefore, subsequent statistical treatment of the raw experimental data in relation to transformations and especially in obtaining an adequate estimation of the errors involved, required special attention.
(iv) Spatial distribution of fauna: The spatial distribution of most animals seems to be of an aggregated or contagious nature (Allee et al. 1949: Andrewartha and Birch, 1954; Elton, 1966; Lewis and Taylor, 1967; Odum, 1971;
Southwood, 1966) and this is especially so for the soil fauna (Healy, 1962;-- -Debauche, 1962). Estimation of the degree
of aggregation of a population is therefore important in determining the spatial structure of the soil communities. A
population of randomly dispersed individuals would show a distribution of the Poisson type (Healy, 1962; Debauche, 1962)
with a variance equal to the mean. This provides a useful estimate of randomness, departures from equally indicating regular or aggregated distributions. Aggregation tends to
increase the variance and the increase can be evaluated by
comparing the observed variance with that expected if the
distribution was random. A convenient index of aggregation
is the Disturbance index of Lexis and is given by
= Wm
Its significance may be tested by a transformation to the
Dispersion index of Fisher (1941-2), given in Healy (1962)
and Debauche (1962):-
2 X "
2 (n -1)
The index of aggregation is dependent on the number of
aggregates in the population and the density of individuals - 4-2- in the aggregates (Debauche, 1962). The index increases as the number of aggregates decreases and the density within aggregates increases. For a regular distribution X -4 0 and for a randomly distributed population X = 1.
Because the Lexis index is characteristic of a population at a given time, it will vary if the ecological tolerance of the species or group varies, or when conditions in the habitat alter. For example, a characteristic rise is usually observed at the time of reproduction (Debauche, 1962).
The results (Table 2) show that the spatial distribution of the soil fauna at Garden Plots is of the contagious type (h values exceeding 1) and that the microarthropods are the more aggregated, though the size of the sampling unit is important in evaluating indices of aggregation, as is shown by the different values of
X for 5 cm diam. and 10 cm diam. cores; 2 Results of the X analysis indicate that the aggregations are highly significant (P < 0.001) for all the groups of soil animals, whether estimated by 5 cm diam. or 10 cm diam. cores.
Because the spatial distribution of the soil fauna is not random, an alternative to the Poisson distribution must be found in order to treat certain experimental data statistically.
One which allows for aggregation is the Negative Binomial distribution, and the transformation of data into y = log10 (x + 1) is appropriate and commonly used. The transformation has the benefit of stabilising the variance and thereby facilitates the - 43 - use of parametric statistical techniques that would be otherwise inappropriate.
Conclusions
(1) The relative abundance of animals from the
Garden Plots site was typical of many grassland areas.
(2) A sample unit of diameter 5 cm and depth 15 cm
proved generally more efficient than one of similar
depth but of 10 cm diameter, probably because of the
reduced efficiency of the extraction apparatus
associated with the use of the larger sample unit.
(3) During the subsequent experiment, a sample of 16 sample
units was taken for each treatment on each sampling
occasion. The amount of time required to sort
the animals from larger samples would be too great to
be practical during this investigation.
(4) Working within the 95A fiducial limits, a
sample of 16 sampling units (5 cm diam. x 15 cm depth)
would provide an estimate of the mean in the order of
+ of the true mean.
(5) The spatial distribution of the soil fauna
investigated was of the contagious type.
(6) Statistical techniques used in later analyses
must be compatible with the non-random disposition
of the data.
2. The experimental design and procedure
(i) Design: The layout of the experiment, of randomised block design, is shown in Fig. 1 and Pl. 1 and 2. Six hexagonal plots of grassland, with each side 1.5 m long, were surrounded by sheet galvanished iron (22 gauge) 75 cm wide, bored in soil to half its depth to deter horizontal migration of soil animals. Four of these six plots were heated with 800 watt infra-red heaters (one heater being attached to each of the six metal sides) and two plots were left unheated as controls.
Two of the four heated plots were watered regularly to maintain the moisture content of the soil in these plots similar to that in the controls, in an attempt to separate effects of desiccation from those of temperature; the other two heated plots were unwAtered, except for natural rainfall. The electricity needed to operate the heaters was supplied from a nearby mains power source, through buried cables.
Soil (at depth 5 cm) and soil surface temperaturfflin one replicate of each plot were monitored using Cambridge thermographs with mercury-in-steel probes and Grant recorders with thermistors, the sensors being positioned 0.75 m from the centre of each plot. The temperature of the air, at height 1.5 al, in the vicinity of the plots was also recorded.
The soil moisture content within each plot was determined at regular intervals, the methods used being described elsewhere.
(ii) Sampling: On 7th October 1970, immediately prior to beginning the treatments, and on future sampling dates, — 45 —
- -- Workshop
Underground cable
I Road 35ft.
8Oft.
Arable
Fig. 1. Layout of the experiment at Garden Plots.
C - control, H unwatered heated and HW-heated plots which were
watered. H1 plot shows arrangement of heaters (F plots were flooded,
D plots were kept covered, but the results of these treatments were not studied). Plate 1. The experiment at Garden Plots, March 1972 View from east showing layout of plots.
Plate 2. View of experiment from WNW eight soil cores (5 cm diam.x 15 cm depth) were taken from
.each of the six plots. The cores (sample units) were taken
15 cm apart, along radial transects within each plot, the
direction of the radii changing with each sampling date to avoid
sampling the same area twice.
A random sampling method was not adopted, for two reasons.
Firstly, treatment effects on the soil fauna may vary from the
centre of a plot to the perimeter; sampling along a radius in
each plot would provide better information about such variability
than would random sampling. Secondly, the location of sampling
units taken by random methods would have to be marked to prevent
repeated sampling of the same place. This would necessitate the
use of pegs, since accurate mapping of the locations would prove
impracticable; further, the pegs could conceivably have
important local influence on the flora and fauna in the plot and
thus confuse the experiment. By using the method adopted here,
all that was required to locate previous sampling radii were marks
(in waterproof ink) on the barriers surrounding each plot. An
imaginary line drawn from any such mark to the centre of the
plot indicated the position of a sampling radius.
To maintain the plots as close to their original conditions
as possible, the holes left by the sample cores after each set of
samples had been taken were filled with other cores taken
from just within the perimeter of the same plot. Soil cores from
surrounding grassland were used to fill the holes in the perimeter
strips, so that any effects the organisms in the 'foreign' soil - 48 -
may have on the experimental populations would be minimal.
Populations of soil fauna were sampled on the following
twelve dates: 7th October 1970, 10th December 1970, 21st January-
1971, 18th March, 1971, 29th April 1971, 11th June 1971, 16th
September 1971, 9th December 1971, 10th February 1972,
30th June 1972, 2nd October 1972, and 29th March 1973. The
treatments began on 7th October 1970 and ended on 10th February
1972. The post-treatment samples were taken to follow changes in
the population during recovery of the soil fauna.
(iii) Extraction of fauna: Animals were extracted from sample cores, for 5 days, using a modified Macfadyen high-
gradient funnel apparatus (131.3 (i) and (ii)). This was designed by - Edwards and Fletcher at Rothamsted after they compared the
efficiences of various types of extraction equipment (Edwards and
Fletcher, 1967). The apparatus consisted of 162 units, each
comprising a funnel, a sample container and an overhead heat
source. The principle of Macfadyen funnels is to isolate the
upper surface of the soil sample from the lower, _and create a
controlled gradient through the sample. In the apparatus at
Rothamsted, each funnel is of anodised aluminium 25 cm deep
and 15 cm in diameter, tapering to an aperture of 1.2 cm at
the base, with the collecting tube attached by a clip. The sample
container, which rests above each funnel with a gap between it
and the funnel wall, was 8.75 cm deep and 12.5 cm. diam. with a
10-mesh stainless steel sieve in the bottom. Heat is from 25 watt (i)
Plate 3. The funnel apparatus: (i) model showing overhead heat source and section through sample container and funnel; (ii) complete funnel unit when not in use. - 50 -
pearl electric bulbs held in a hood above the samples and
which can be lowered by winding a handle. The temperature at the
surface of the soil samples was controlled at 50-55°C by a
rheostat and refrigerated air was used to cool the funnels to
between 5 and 10°C and so set up a consistent temperature
gradient through the soil. Samples were stored at 5°C for up to
five days whenever funnels were not immediately available, but
it is unlikely that this short storage significantly altered the
population of invertebrates in the cores (Edwards and Fletcher,
1967).
The sample cores were placed in the funnels as follows:
The surface mat of vegetation and the upper mineral soil
- layers (the first 5 cm approx.) were carefully removed from each
core and placed intact and inverted on the sieve. The rest of the
core was then gently crumbled and the soil spread over the
remainder of the sieve, ensuring that the whole sieve plate
was covered. Ideally, the sieve and its container should be of
about the same diameter as the sample unit - the sample unit then
being placed intact and inverted on the sieve (Edwards and
Fletcher, 1967). Here, because the diameter of the sample unit
chosen was less than that of the container, it was decided that soil
from part of the core should be crumbled, but that the rest, the
upper layers (often containing over 80/0 of the microarthropods),
should be left intact and inverted on the sieve.
The animals were collected into tubes containing 70,r0 denatured - 51- ethanol, with 5% glycerol added to prevent the catch drying out should all the alconol evaporate. After collection, the tubes were topped up with more alcohol and then placed in an o oven at 70 C for several hours. This made the animals sink in the collecting fluid (presumably because of a disruption of the cuticle in the animals concerned) and facilitated the identification of the individuals by preventing them from floating in the sorting dish. No changes in the morphological features of the animals were apparent after using this technique.
(iv) Sorting of fauna: The sorting of animals extracted from soil samples was done using a Nikon Stereoscopic Microscope fitted with a zoom lens, and a Cooke, Troughton and Simms Research
Microscope fitted with a phase contrast unit. The animals were usually separated at least into families, but rarely only the orders or similar groupings were identified.
Taxonomic literature used to identify the soil fauna was as follows:-
Acarina: The mites were identified to families mainly using the keys prepared by Evans and others for the courses in Acarology held at the University of Nottingham School of Agriculture. Other literature included:
General: Baker and Wharton (1952).
Prostigmata and ffeterostigmata: Thor and Willmann (1941, 1947),
Stammer (1959).
Mesostigmata: Evans (1957), Stammer (1963). 52
Cryptostigmata: Michael (1884-1888), Willmann (1931),
Hammen (1952), Balogh (1963).
Astigmata: Michael (1901-1903), Stammer (1957).
Collembola: The springtails were identified using keys given in Stash (1947-1963), Gisin (1960), Scott (1961) and Salmon (1964).
Insects: Most of the insects were separated only into families
or orders. In some instances, and especially where certain insects became very numerous as a result of the treatments,
the taxonomy was taken further. Keys used include those
by Fowler (1887-1888), Chu (1949), Peterson (1951-1953), Collingwood (1958), Arnett (1963), Brindle (1963), and
Lewis and Taylor (1967).
Symphyla: Edwards (1959a, b).
Biplopoda, Chilopoda, Isopoda: Cloudsley-Thompson and Sankey
(1961).
Many of the specimens were identified, or my identification of them was confirmed by specialists. Their help is gratefully acknowledged elsewhere. Animals were sorted under the low-power
binocular microscope, with incident lighting supplied by a Watson microscope lamp. A black background was normally
used, but a yellow background gave more definition for some samples. The contents of the collecting tube were washed with alcohol into a square Perspex sorting dish of side 60 mm
(internal dimensions), the underside of which was scored with lines -53 - approx. 8.5 mm apart, to form a grid. This grid divided the floor of the dish into 49 squares, thus making the quantitative assessment of the fauna easier and more accurate, since the
possibility of double counts or misses was reduced.
The size of the grid squares was designed to be such that a complete square was within the field of view of the microscope when a magnification of approx. x15 was used. This power was that normally used during sorting, and was one which offered a good degree of clarity and comfort. Whenever soil animals were too small to be identified at this magnification, the power could be
increased to x40 using the zoom lens. For the higher magnifications
initially needed to identify species, and to regularly confirm the accuracy of the identifications made by the binocular microscope,
the high-power research microscope was used. Permanent slide
preparations were made using a modified Heinz's PVA medium
(Boudreaux and Bosse, 1963).
Occasionally the collecting tubes contained a large
proportion of soil particles, especially when lumbricid and
enchytraeid worms occurred in the samples. These particles made
sorting extremely tedious and inaccurate, so the animals (and other
organic material) were separated from the mineral particles by
flotation in magnesium sulphate of sp. gr. 1.20 approx. It was
found that the animals occasionally lost by this treatment were much
fewer than those missed during the sorting of heavily-soiled samples,
even when samples such as these were sorted two or three times as
a check. - 54 -
(v) Sub-sampling within the sorting dish: The numbers of animals extracted from a single sample unit were often very large and took a long time to sort and count. For these, a method of sub-sampling was required that would give a reliable estimate of the number of animals within the sorting dish.
Solomon (1962), faced with a similar problem, used a sectored disc to count 1/30th of the total population in the dish. Mites were "distributed as evenly as possible over the (circular) dish" where they tended "to be distributed in a symmetrical rather than a random manner". In his work, a homogeneous sample of approx. 12,000 mites was used, the sectored disc after 10 counts providing an arithmetic mean of 12,036 and standard deviation of 1,074 or 8.9% of the mean.
Williams and Winslow (1955) in their estimation of nematode cyst contents, used modified Fenwick counting slides, and stated that the eggs and larvae were distributed in a Poisson form in the dilution fluid. The accuracy of their estimates depended on the number of organisms counted, and they recommended that enough squares should be covered to count at least 100 eggs and larvae, giving an estimate with S.D. 10% of the mean. They further recommended that the squares covered should form a symmetrical pattern in the grid area of the chamber. If the distribution in the chamber was truly of Poisson form, it would matter little which pattern was used, but perhaps random sampling would be more appropriate (Wedderburn, pers. comm., Statistics Dept. itothamsted). - 55 -
Method
The distribution pattern of animals in the dish was
determined by counting the animals present in each square and
then, using the statistics s and m, an index of
aggregation (the Disturbance index of Lexis) was determined. A
sample of 209 individuals in the dish gave an index of
aggregation of 1.53, and one of 524 individuals gave an
index of 1.66 X2 values of 112,39 and 132.81 respectively,
indicated that in both samples the aggregation was highly significant
(P < 0.001). Thus, animals in the sorting dish followed a
contagious distribution pattern.
It was thought that 10 squares counted out of the total
of 49 in the sorting dish would give a reasonable estimate of
the total population in the dish; thus, 1/5th of the total population
(approx.) was sorted. There were four squares at the corners of
the dish, twenty squares at the sides of the dish, and twenty-five
squares remaining; it was suggested that of the ten squares
to be counted, it would be preferable that one should be from
a corner of the dish, four from the sides and five from the
middle area (R. Wedderburn, pers. comm.). Within these
limitations, the actual positions of the squares were chosen
at random.
Results
Ten estimates of the population with 209 individuals
in the dish (sample unit code number 01.4 for 18.iii.71) gave
a mean estimate of 192.5 with s = 40.5 (i.e. 21/0 of the mean); - 56 with 524 individuals in the dish (sample unit code number
C1.1 for 18.iii.71), the mean estimate of ten counts was 506.5 with s = 49.89 (i.e. 9.80 of the mean). Thus, the accuracy of the estimate tended to be greater when there was a large number of animals in the dish.
The relationship between the estimated population and the actual population of animals in the dish was investigated further by comparing estimated numbers with known numbers of animals in the control plots for a single date, 18 March 1971.
Table 3 gives the actual and estimated values for the groups sorted, the results relating to the animals in 16 sample units.
The estimated total number of mites was 95.2A of the actual total number of mites, and that of Collembola 96.8A of the actual total for that group. Of the non-microarthropods, only the nematodes, thrips and ants were estimated (the other animals being too large in size and/or low in number to justify estimation) and the estimate was 116.0 of the actual total.
Fig. 2 consists of scatter diagrams of estimated against actual numbers of the major groups of soil fauna, the 'line of equality' being indicated. Sample unit counts plotted for total soil fauna indicate that there was good agreement between estimated and actual values, this was also so for the Acarina.
Estimated and actual values for the Collembola as a whole, show a more approximate relationship, but probably, too few were counted for a good relation. Plotted points for the numbers of non- Table 3 Actual and estimated numbers of animals in the 16 sample units of the control sample, taken on 18th March 1971 from Garden Plots. Number Number Group Actual Estimated Group Actual Estimated TOTAL ACARINA 5966 5680 Astigmata 81 80 Prostigmata + Acaridae 1527 1375 12 20 .Heterostigmata Unidentified Pyematidae 671 570 hypopi 69 60 Scutacaridae 565 515 Tarsonemidae 210 160 TOTAL COLLEMBOLA 775 750 Others (Prostigmata) 81 130 Onychiuridae 351 385 Mesostigmata 440 400 Hypogastruridae 40 30 Isotomidae 342 295 Parasitidae 31 40 Entomobryidae 9 5 Rhodacaridae 241 215 Sminthuridae 33 35 Digamasellidae 93 90 Phytoseiidae 3 0 Non-microarthropods 159 185 Ameroseiidae 5 0 Dermanyssidae 15 30 Nematoda 34 50 Pachylaelapidae 6 0 Thysanoptera 6 5 Hemiptera (ants) 119 130 Eviphididae 13 5 Ascidae 9 5 Uropodidae 10 0 6900 Unidentified 14 15 TOTAL FAUNA 6615 Cryptostigmata 3918 3825 Brachychthoniidae 162 120 Camisiidae 96 115 Pelopidae 55 85 Mycobatidae 1321 1335 Scheloribatidae 280 235 Oppiidae 1852 1780 Ceratozetidae 2 0 Carabodidae 1 0 Unidentified 148 155 immatures - 58 -
TOTAL FAUNA ACARINA
1000 1000
500 500
0 500 1000 0
COLLEMBOLA OTHERS, (A+c) 160
80
0
FIG. 2. The relationship between actual and estimated
numbers of animals in the counting dish.
Abscissae give actual numbers; ordinates, estimated numbers. The line of equality is drawn in each graph. - 59
microarthropods lay close to the line of equality, but again
their number was low.
Sample unit counts-for the different families of the
Collembola (except for the Entomobryidae, which were rare) are
plotted in Fig. 3. There was poor agreement between estimated and
actual values, because the number of individuals per sample unit
was small. Totals of families for the whole sample gave a
better indication of the reliability of the estimate.
Fig. 4 shows (A) sample unit counts (B) group totals
(family level) within each sample unit and (C) group totals for
the whole sample, for the major orders of the Acarina. Sample
unit counts indicated good agreement between estimated and
actual values, but the Mesostigmata and Astigmata were few in
number. The group totals within each sample unit showed a
greater scatter of points, but estimates within the Prostigmata and Heterostigmata, Cryptostigmata and Astigmata were still
closely related to actual numbers. The scatter of points for the
numbers of Mesostigmata was too great for the_estimate.of actual
numbers in the sorting dish to be good, but again, few mites
were present. For the Acarina, the estimated group totals for
the whole sample gave reasonable indication of actual totals.
Discussion
Problems associated with sub-sampling methods are many and
varied, and this is especially so where heterogeneous groups are
concerned. A thorough analysis in relation to these soil fauna 60 (1)
(v) 400
200
0 200 400
Fig. 3. The relationship between actual and estimated numbers of
Collembola in the counting dish. Sample unit totals for (i) Onychiuridae,
(ii) Hypogastruridoe, (iii) Isotomidae, (iv) Sminthuridae and (v) family
totals for sample. Abscissae give actual numbers; ordinates, estimated
numbers. The line of equality is given in each graph. (A) (c)
(1) • • .5 • • • .. • •• 06 •• 00
100 200 50 100
Fig. 4. The relationship between actual and estimated numbers of
Acarina in the counting dish.
Across
(A) Sample unit counts Prostigmata + Heterostipota (B) Group totals within each Mesostigmata sample unit Cryptostigmata (C) Group totals for sample Astigmata (Abscissae give actual values; ordinates, estimated values) - 62- would justify a thesis in itself, but even fairly complicated statistical tests to determine the accuracy of the procedure may in real terms be meaningless (L.R. Taylor, pers. comm.).
The statistics needed to determine the accuracy of the method, or the minimum size of the sub-sample required, would be enormous; even then, the sub-sample size would depend on the original size of the sample and on the size of the individuals comprising the sample (L.R. Taylor, pers. comm.).
Ideally, a different sub-sample size should be used for each species and its density within the dish. But, in practical terms, one must adopt some more simple sub-sampling technique, even though it may have many limitations.
Conclusions
(1) In general, the sub-sampling method gave a good
estimate of the actual number of animals in the sorting
dish, especially when many animals were present.
(2) Estimates of the total number of soil fauna and of
total Acarina were acceptable, but the number of Collembola
and non-microarthropods were too few in this sample to
draw further conclusions.
(3) Within the Acarina, the number of Prostigmata and
Heterostigmata and of Cryptostigmata were large and
estimated results were close to actual values, so the
estimate may be considered reliable.
(4) When the number of animals was low, the estimate was - 63 -
unreliable; thus, for some groups within the Mesostigmata,
the sub-sampling method was not used. Most of these
mesostigmatids were relatively large and easily seen and
identified under the binocular microscope, so the sub-sampling
method would not be necessary for them anyway. This also
applies to the non-microarthropods, except where occasional
large numbers of such insects as aphids or ants occur;
then the method of estimation can be used.
(5) 1 used this method of sub-sampling only where the number
of any group of animals in the dish appeared, from eye estimate,
to be large enough to be accurately estimated. Low numbers
of animals and large animals were counted.
(6) The more even the distribution of animals in the dish,
the greater should be the accuracy of the estimate
(L.R. Taylor, pers. comm.), so care was taken to ensure
that the animals were spread over the dish as evenly as
possible.
3. Physical measurements at the site (i) The measurement of soil water: There are basically two types of information relating to soil water; firstly, that concerned with the water content of soil, its measurement requiring gravimetric sampling or neutron moderating equipment; secondly, there is the energy status of soil water, requiring measurements of soil suction (Wadsworth, 1968). - 64-
Water content of soil
Routine estimates of the water content of soil in the plots were made initially using a "Speedy" Moisture Tester, which measures the pressure of acetylene given off when a known weight of soil is mixed with an excess of calcium carbide in a sealed aluminium container. A dial on the pressure gauge is calibrated to indicate directly the percentage content, on a vet weight basis, of water in the soil. Results obtained by this method and the oven-drying method are compared in Fig. 5 (1). Soil moisture was also determined using a
Sauter MPRT-U 160/100 balance, which gives a direct reading of moisture content (again on a wet weight of soil basis) using an infra-red lamp to dry the soil. Comparisons of results obtained by the Sauter method with both the "Speedy" and oven dry methods are given in Fig. 5 (ii and iii).
Measurements of the water content of soil are conventionally expressed as a percentage of the dry weight of soil. This was not done in the routine estimates of the soil water content, because the instruments used were calibrated in relation to the wet weight of soil. In this investigation, comparisons on a wet weight basis are valid, because the soil type within the plots is similar (see later). For comparison with other areas, the scatter diagram in Fig. 5 (iv) shows the relationship between the moisture content when expressed as percentage wet and dry weights of soil, and this gives more information about the
properties of the soil at Garden Plots. 65 -
(1)
50
+A -0 CO -C
° 25 0C E U >. 0) -0 +A 0 O 0 • 0-
0 25 50
% water content % water content oven dry method Sauter method
50 50
+A 4-, "0 C ri CO 0) 444 0)C +A 0 44 +A C C O.) 0 0 I) 44— • 25 0 25 $4 5.4 0 +A 0 -0 +I 3 +A 0) O a) • CL 5.4 1.:
0 25 50 0 25 , 50 % water content % water content Sauter method (wet wt of soil)
Fig. 5. (i)-(iii). Comparisons of the moisture content of soil using the Sauter, "Speedy" and oven dry methods. The line of equality is indicated in each graph. Soil moisture is expressed as the wet weight of soil.
(iv) Scatter diagram showing the relationship between moisture content of soil expressed as percentages of wet and dry weights of soil. - 66 -
Energy status of soil water; the use of tensiometers
Measurements of the water content of soils may be of only
limited value in relation to the ecology of soil animals
because such measurements provide little information on the amount of water which is available to animals. A more useful
concept in this connection relates to the amount of energy or
suction' required to draw water from the soil. Soil suction may
be expressed as, cm Hg suction pressure, or these units may be
transformed using a logarithmic scale (to the base 10) to give
pF values. The 'permanent wilting point' of plants occurs
at about pF 4.2 and the 'field capacity' of soils varies from 2
to 3.2 (Burges and Raw, 1967; Macfadyen, 1963; Kuhnelt, 1961;
Wadsworth, 1968), depending on soil type.
Soil suction can be measured in the field for any particular
soil type using tensiometers (Macfadyen, 1963) and these were
used in the control plots and in the heated plots which were
watered as a quick method of comparing the water status of soil
within these plots, to indicate when watering was necessary.
The use of tensiometers to monitor the need for irrigation
was proposed by Richards and Marsh (1961). Duration of an
irrigation was judged by comparisons with instruments reading
soil suction in deeper soil; if readings at this depth were low,
a short period of irrigation was required and vice versa. In the
Garden Plots experiments the tensiometers (Gallenkamp Bench
Model SE-085) were placed in the centres of the four plots - 67 -
concerned and the porous pots were buried to a depth of
8.5 cm (measured from the soil surface to the centre of the
pot). Comparisons between tensiometer readings from control
and heated plots to be watered indicated when watering was
necessary.
Fig. 6 gives the relationship between the water content of
soil and soil suction, the regression of y on x being shown.
The coefficient, r = -0.7889, indicated a highly significant
correlation (P < 0.001 for 102 d.f.). A change in soil moisture
content of TA corresponded to a change in tensiometer reading
of approximately 2.6 cm Hg.
It was calculated that approximately 3 gallons of water were
needed to raise the water content of the soil within a plot by 1%.
This approximation was made as follows:- The weight of an
average soil, to a depth of 6 in, was taken as 2 million lb/acre
(Lilly, 1956). As the area within each plot was 63.75 sq. ft,
the weight of soil (to a depth of 6 in) was 2930 lb. 1% of this total is 29.3 lb, and this weight of water is-approximately 3
gallons. Thus, for a difference of 2.6 on the tensiometer scales,
3 gallons of water were required to bring the heated plots
to a moisture regime similar to that in the controls.
Stblzy et al. (1959) pointed out that to measure soil
suction and obtain water content values from calibration curves
on typical soil samples (or vice versa) may be unreliable.
The relationship between soil suction and water content values for
a given soil was not a single value, but depended on the soil - 68 -
60 • • •
50 •
ty) 40 E U
30 • LuU) a_ • 0 20 1-1 •
171 10 ul0
0 10 20 30
% SOIL MOISTURE (WET WI OF SOIL)
Fig. 6. Regression of soil suction on percentage soil moisture content (method of least squares; y = -2.61x + 84.6). Percentage variance accounted for = 61.9 - 69 - structure and degree of compaction. Even when as many variables were controlled as possible, drying and wetting curves were different, indicating an hysteresis effect. Although these differences were recognised, it was assumed that the tensiometers used at Garden
Plots provided a good indication of when and how much water was required. During the course of the experiment, the effect of adding water by this method was also monitored by soil moisture content measurements.
There is a serious restriction to the use of the tensiometer, due to the limitation in range of the instrument.
The vacuum gauge indicates partial vacuum relative to the atmosphere, hence the highest reading theoretically possible is equivalent to atmospheric pressure. The practical limit of the tensiometer is about 0.8 of this, i.e. 60 cm Hg. A zero reading on the scale indicates a condition of 'free water' in the soil, and readings increase as the soil is dried, until the upper limit is reached. Thus, the range 0 to 60 on the tensiometer scale corresponds to a fall of from 32.25% to 9.5% moisture content of soil as shown by the regression in Fig. 6. Values of moisture content outside this range cannot be detected by the tensiometer, and this restricts the use of tensiometers to soil water conditions not limiting to plant growth. The use of tensiometers and other methods of determining water status are further discussed in Wadsworth (1968) and by Macfadyen (1963).
(ii) The long-term recording of temperatures: Soil - 70 -
(at depth 5 cm) and soil surface temperatures, within one replicate of each treatment, were recorded using Cambridge thermographs with mercury-in-steel probes, and Grant recorders with thermistors. The unwatered heated plot probes (for the major part of the experiment) and the control plot probes were of the mercury-in-steel type; the heated and watered plot probes were of the thermistor type. In the control and in the heated plots that were watered, the surface probes were always covered by vegetation. The vegetation in the heated plots that were not watered often became very dry and, in summer, bare patches of soil occurred, exposing the surface temperature probe to direct sunlight. Direct solar radiation reaching temperature probes causes a false and exaggerated indication of actual ambient temperature (Long, 1968), so the problem arose of how to obtain realistic measurements of the soil surface temperatures in the heated plot. Conventionally, a Stevenson's screen is often used to shade temperature sensors, but a modification of this arrangement was not thought advisable here, because the vegetation under the screen would also be shaded and would then possibly grow at a rate not representative of the rest of the vegetation in the plot. Apart from thereby modifying the soil surface temperatures, the change in vegetation could also influence the soil fauna locally.
It was decided to compare exposed probe temperatures with simultaneously recorded shielded probe temperatures. The shield - 71 - chosen comprised a U-shaped tube of aluminium of diam. 5 cm and length 25 cm, which was polished on the outside. The probe shield was set up over a second surface probe in the heated plot, for two weeks, in order to obtain enough data to calculate a regression between exposed probe values and corresponding shielded probe values. In this way, the influence of the shield on both vegetation and soil fauna within the plot was minimised. Fig. 7 shows two regression lines fitted to the plotted co-ordinates. The straight line is the regression of y on x for the untransformed data; the curve is derived from a log10 transformation of the data and is more representative of the scatter (L.H. Taylor, pers. comm.). The correlation coefficient, r, was 0.9734, and indicated a highly significant correlation
(P < 0.001 for 178 d.f.) between exposed probe and shielded probe temperatures.
Temperatures recorded when the surface probe was exposed to direct sunlight are indicated in various parts of this thesis, and information is also given as to whether the data have been
corrected using the above regression. Problems relating to the
measurement of soil surface temperatures, and to the measurement
of environmental factors in general, have been considered in
detail by Platt and Griffiths (1964).
4. Soil analysis of the site
Physical and chemical analyses of soil samples taken from
each plot were made (the sample unit, except for special purposes, Fig. 7.Regressionofshieldedprobetemperaturesonexposed log the untransformeddata(y=4.554.0.62x);curveisderived temperature (methodofleastsquares).Thestraightlineisfittedto variance accountedfor=94.7 10 transformationofthedata(a=0.13, b=0.84). SHIELDEDPR OBE TEMPERATURE°C 50 40 30 20 10 10
EXPOSED PROBETEMPERATURE 20
7 30
4 0
Percentage ° 5 0 C.
from 60 a - 73 -
being a soil core of diam. 5 cm and depth 15 cm) to provide
information on the nature of the soil at the site, and to see
whether any differences in properties could be detected which
could be attributed to differences in treatments. The physical
analysis consisted of a particle size distribution analysis
of the soil, particle and bulk density determinations and
consequent estimations of pore space. Chemical analyses were
confined to estimations of organic carbon content and soil
reaction.
Methods
(i) Particle size distribution: Air-dried soil
passing through a 2 mm sieve was used for this analysis, the
silt-and clay content being determined using the hydrometer method
of Bouyoucos (1927a, b), the sand content using a nest of
sieves. The actual techniques were those used by Bascomb
(unpub.) of the Soil Survey of England and Wales, but more
general accounts of these techniques and the theories involved
are given in Piper (1942) and Black et al. (1965). The particle
sizes are defined here, since there are several conflicting
definitive systems (Buckman and Brady, 1960; Black et al., 1965);
Particle description Particle size (microns)
Clay <2
fine silt >2 <20 silt >20 <50
fine sand >50 <200
coarse sand >200 <2000 - 74 -
From the results of the particle size distribution analysis, the soil class was determined using the triangular diagram of soil texture used by the USDA (Buckman and Brady,
1960).
(ii) Particle density: Particle density is defined as the mass of a unit volume of soil solids, and is usually expressed in gm/cc. The method used here to determine particle density was that given by Black et al. (1965), using volumetric flasks. Determinations were made from sample units, sectioned
to correspond with field depth layers of 0-2 cm and 2-7 cm, after removal of the surface vegetation mat.
(iii) Bulk density: Bulk density is defined as
the mass of a unit volume of dry soil. The mass (weight) was determined after oven drying at 105°C and the volume was that of the sample fresh from the field. Bulk density determinations were made on soil from the 0-2 cm and 2-7 cm layers.
(iv) Pore space: The pore space of a soil is that
portion of the soil not occupied by soil solids. The percentage
pore space was therefore calculated, for the two depth layers, as:
% pore space = 100 - (bulk density X 100 / particle density).
(v) Total organic carbon: The method of estimating organic carbon content was basically that of
Schollenberger (1927) involving the partial oxidation of organic
matter with chromic acid, but with the modification of ;:ialkley - 75 - and Black (1934) which gives a more selective estimation of the active organic carbon, over 90% of the elemental carbon being excluded. Back-titration with potassium permanganate was used (Smith and Weldon, 1940) to facilitate end-point determination.
The method has been briefly summarised by Madge and Sharma (1969) and a more detailed account, with some theoretical considerations, is given by Hesse (1971).
The expression of results obtained by partial oxidation methods is difficult because of the assumptions that have to be made (Hesse, 1971). To express the results obtained (uncorrected carbon totals) as total organic carbon, an arbitrary conversion factor must be used: the conventional factor for the Walkley-Black method being 1.33. Percentage organic matter may be found by multiplying uncorrected values by 2.29, though Hesse (1971) points out that this correction factor is variable, because different soils contain different sorts of organic matter. It was decided to express results here as total organic carbon, because the conversion factor 1.33 is well substantiated for the
Walkley-Black method. Organic carbon content was determined for the depth layers 0-2 cm and 2-7 cm.
(vi) Soil reaction (pH): The pH of the field soil was determined using a BDH Barium Sulphate Soil Testing Outfit, determinations being made at several dates.
Results and Discussion
The results of the analyses are given in Table 4. The - 76 -
Table 4. Analysis of soils at Garden Plots (underlining indicates
2liLA29LT12LfaL2nlbITJ-R_-_-_)5-catj
ANALYSIS CONTROL HEATED HEATED + WATERED (1) (2) (1) (2) (1) (2)
Particle size (7o content) coarse sand 7.2 8.2 6.4 fine sand 7.8 7.0 7.6 silt 18.0 18.0 15.1 fine silt 26.5 25.7 29.3 clay 29.8 29.3 28.7 difference 10.7 11.8 12.9 Soil class CLAY LOAM CLAY LOAM/LOAM CLAY LOAM Particle density (gm/cc) 0-2 cm layer 2.08 2.09 2.0 2.32 2.3 2.41 2-7 cm layer 2.31 2.29 2.25 2.31 2.35 2.22 Bulk density (gm/cc) 0-2 cm layer 0.81 0.66 0.60 0.79 1.17 0.86 2-7 cm layer 1.22 1.04 1.16 1.18 1.22 1.08 Pore space CO 0-2 cm layer 61.1 68.4 70.0 64.6 49.1 64.3 2-7 cm layer 47.2 54.6 48.4 48.9 48.1 51.4 Organic carbon (%) 0-2 cm layer 7.63 7.98 6.04 6.13 4.88 6.96 2-7 cm layer 4.31 4.85 4.24 4.07 3.83 5.01
Soil reaction (pH) 0-2 cm layer 5.75-6.0 6.0-6.5 5.75-6.0 6.0-6.25 6.0-6.25 6.25-7.5 2-7 cm layer 6.25-6.5 7.0-7.25 6.25-8.0 7.75-8.0 7.0-7.25 7.25-7.5 - 77 _
textural classes of the soils within the plots are in accordance with the method of Cooke and Williams (1971) and
Avery et al. (1971), who indicated that Rothamsted soils were
mostly clay foams and silt foams. Soils from the control and
heated plots that were watered were classified as clay foams;
those from the unwatered heated plots as clay loam/loam types.
These differences in soil texture were marginal, because the newer M.I.T. System of textural classification, intended as a replacement for the conventional USDA system (Rothamsted Report for 1972, Part 1, 311), would classify the soils from all
plots as clay bowls.
Soil texture and soil structure are important physical characeristics which help to determine the nutrient status
of the soil, its water and air-holding properties. Because
the texture of the soil within the treatments was similar, this variable may be eliminated from the factors possibly having a differential effect on the population of soil fauna within the
various plots.
The structure of a soil concerns the arrangement of the
soil particles into groups or aggregates and soil conditions such as water movement, heat transfer, aeration, bulk density and
porosity are all influenced by soil structure. The particle
density determinations (necessary to determine porosity of the soil) showed a range of densities from 2.0 to 2.41 gm/cc in the
plots examined.
These values probably underestimated the true densities - 78
of the particles in the samples, because Cook and Williams
(1971), using more sophisticated techniques, found that nearby grassland soils at Rothamsted had a particle density averaging
2.46 gm/cc. The particle densities I determined have been used
in the estimations of porosity, because small variability
between replicates have then at least relative representation.
Particle density figures for most mineral sails range between 2.6 and 2.67, according to Smith (1943) and Buckman and Brady
(1960); but Madge and Sharma (1969) recommended 2.5 as a workable specific gravity for the average soil. Chappell et al.
(1971) found that their chalk grassland had a particle density
of 2.4 gm/cc, and Williams (1970) who tested 37 grassland soils, found that the average particle density was 2.46 gm/cc , the range
being from 2.17 to 2.63 gm/cc.
The method used here for carticle density determinations
is precise if weights, and especially volumes, are measured
carefully. A weighing error of 10 mg on a 30 gm sample
would give an error of only 0.001 gm/cc. Greater errors can
result from lack of precision in the volume measurement (Black et al.,
1965). The relatively low values obtained here were probably due
to the differing amounts of organic matter in the samples,
because the trend (as expected) is for the particle density to
be greatest with increasing depth; and for organic matter to
decreaSe with increasing depth.
The bulk density of the soil varies with the structural
condition of the soil and is therefore often used as a measure -79 - of soil structure (Black et al., 1965). In all the plots, the bulk density increased with depth. The 2-7 cm layers had similar average bulk densities for all treatments, but at 0-2 cm _ depth in the heated plots that were watered, the bulk density was, on average, markedly greater than that for other treatments.
The increase in bulk density of the 0-2 cm layer in the heated plots that were watered is associated with the decrease in
percentage pore space and this could have an important influence on the soil fauna, especially with regard to their vertical distribution. The decrease in porosity was probably caused by the frequent waterings necessary to maintain the moisture content of the soil in these plots at levels similar to those in the controls. It is interesting that heating alone tended to increase the porosity of this 0-2 cm layer, the average percentage pore space for control, unwatered heated and heated plots that were watered being 64.75%, 67.3% and 56.7% respectively. At depths
2-7 cm the porosity in all plots was less than that in the.related
0-2 cm layer. Further the average porosity at the greater depth layer was remarkably constant, the between treatment differences not exceeding 2.25%.
Organic matter contributes to the physical condition of the soil by retaining moisture and affecting soil structure. It also
provides (with the help of soil fauna and microbial activity) a direct source of plant nutrients and is directly involved in the availability of elements by affecting cation exchange capacity
(Hesse, 1971). Therefore, an assessment of the organic matter so - in the plots is important, because it can affect, both directly and indirectly, the soil fauna. The organic matter was determined in terms of percentage organic carbon, for reasons expressed earlier.
At depth 2-7 cm, the average percentage organic carbon was 4.58% in the controls and 4.15% in the unwatered heated plots.
The average value for the heated plots that were watered was
4.42%, but, because the replicates for this treatment showed a greater range of values (from 5.83A to 5.01%) than average treatment values, conclusions about treatment effects cannot be made.
The 0-2 cm layers in each plot showed greater variability in their organic carbon content, but a trend towards a decrease in organic carbon in the heated plots was indicated because values in all of these plots were lower than in any of the controls.
Average percentages of organic carbon were 15.61%, 12.17% and
11.84% respectively for the control, unwatered heated and heated plots that were watered.
The pH of soil from the 0-2 cm layers was generally lower than that of soil from the 2-7 cm layers, the greater acidity of the upper layers being possibly due to a greater proportion of humic substances in these layers. The range of pH in the surface layers was from 5.75 to 7.5, values above 6.5 (the maximum pH recorded in the controls at that depth) were found only in the heated plots that were watered. In the 2-7 cm layers a pH range of from 6.25 to 8.0 was recorded, the highest pH values being found in the unwatered heated plots. - 81 -
Samples for pH analyses were also taken outside the plots, but within the general area of the site. As the pH varied from
5-75 to 8.0, general conclusions on the effect of the treatments on soil reaction cannot be made with certainty, It was noticeable that the maximum pH of 8.0 occurred in both of the unwatered heated plots at 2-7 cm depth and in no other plot.
The use of colourimetric test kits for field pH determinations has been recommended by Hesse (1971) who stated that the accuracy of the measurements may fall within 0.1 or 0.2 of a pH unit if the method was used carefully. In practice, the standard BDH kit seemed unsatisfactory for detecting values above'8.0 because of the limited range of the indicator supplied.
Because pH values of about 8.0 were found at the site, an indicator with a wider range in the alkaline part of the scale was tested, but still no values above pH 8.0 were found.
Conclusions
(1) The soil within the plots was of a clay loam/loam
texture and typical of those soils generally found at
Rothamsted.
(2) The decrease in the porosity of the surface layers of
the heated plots that were watered was probably caused by .
the watering. This reduction in porosity could have an
effect on the soil fauna, especially with regard to
their vertical distribution.
(3) In the 0-2 cm layers of all heated plots there was a - 82. -
trend towards a decrease in organic carbon content.
This could possibly have been caused by a difference in
the vertical distribution of the fauna (the fauna contributing
to the organic carbon content) as a result of the treatments.
(4) The effects of treatments on soil reaction were
inconclusive, but the effect of heating soil without
adding water may have caused a tendency for the soil at
depth 2-7 cm to become more alkaline.
5. Botanical analysis of the site A list of plant species found during the experimental period was compiled in order to obtain a general qualitative description of the site. It became apparent (in the spring of 1971) that the
treatments were affecting the vegetation. In July of that year, the floral spectrum was assessed within each replicate using a presence or absence criterion. A more detailed botanical analysis was made later that month using quadrats. On 22nd May
1972 (after termination of the treatments) a further, but less
time-consuming comparison of the flora was made using subjective estimations of cover and abundance.
Methods
Plants were identified using the Excursion Flora of the
British Isles (Clapham, Tutin and Warburg, 1559), The Concise
British Flora In Colour (Keble Martin, 1965) and Grasses
(Hubbard, 1954). - 83 -
2 The July analysis was made using a 25 cm quadrat, 2 with sub-divisions of 5 cm The quadrat was thrown at random into each 'quartile' of each plot and the presence or absence of shoots of each species within each of the 25 sub-divisions of the quadrat was noted. The local frequency of plants within each plot was then determined by averaging the results of the four randomised quadrats (Kershaw, 19
Post-treatment estimations of cover and abundance of plants in each plot were made using the procedure proposed by
Braun-Blanquet (1932). The method incorporates a six- part scale as follows:-
+ = sparsely or very sparsely present; cover very small
1 = plentiful but of small cover value
2 = very numerous, or covering at least 1/20 of the area
3 = any number of individuals covering * to 2 of the area
4 = any number of individuals cover i to * of the area
5 = covering more than * of the area
The scale combines abundance with cover; the smaller numbers relating mainly to abundance and the larger numbers to cover.
eesults and Discussions
The list of plant species identified in the Garden
Plots experiment is given in Appendix 1. Table 5 shows the flora identified in July 1971, after ten months treatment.
Of the grasses, Agropyron repens and Arrhenatherum elatius were found only in heated plots which were not watered; Table 5 Systematics of the flora identified at Garden Plots in July, 1971. Species indicated (*) were seen at the site, but not within the treatment plots.
PLOT SPECIES Cl C2 H1 H2 HW1 HW2 GRAMINEAE - Agropyron repens + + Agrostis gigantea + + A. stolonifera + + + + + + A. tenuis + + + + + + Arrhenatherum elatius + Cynosurus cristatus + + Dactylis glomerata + + + + Festuca ovine + + + + + F. rubra + + + + + Holcus lanatus + + + + + + Lolium perenne + + + + + + Phleum bertolonii + Poa trivialis + + Trisetum flavescens + + CARYOPHYLLACEAE Cerastium glomeratum + + + COMPOS ITAE Achillea millefolium + + + + Bellis perennis + + + + Centaurea nigra + Hypochoeris radicata + + Leontodon hispidus + + + + + + L. taraxacoides + + + + + Picris hieracoides + Senecio vulgaris + + + Sonchus asper + Taraxacum officinale + + + +"- + CONVOLVULACEAE Convolvulus arvensis* LABIATEAE Prunella vulgaris + + PAPILIONACEAE Lotus corniculatus + + + + Trifolium pratense + + + + + T. repens + + + + + + T. striatum + + + PLANTAGINACEAE Plantago lanceolate + -+ + + + P. media + POLYGONACEAE Rumex acetosa + + + + ROSACEAE Potentilla reptans -85-
Cynosurus cristatus and Phleum bertolonii occurred only in the control plots, and Agrostis gigantea was identified in one control plot and in a heated plot which was watered, but not in plots which were heated but not watered.
Of the Compositae, Centaurea nigra and Hypochoeris radicata were found only in the controls; Picris hieracoides occurred only in a heated plot which was watered; and
Sonchus asper only in a heated plot which was not watered.
Seneoio vulgaris was absent from the controls but present in one or both of the two treatment replicates.
Of the other families, Prunella vulgaris was found in one of the control plots and in one of the heated plots which was watered; Plantago media occurred only in one of the heated plots not watered; and Potentilla reptans occurred in one control plot. All other species listed in the table occurred in either or both of each treatment replicate.
It is probable that the presence or absence of plant species
(Table 5) may be somewhat fortuitous, rather than caused by the treatments, because the spatial distribution of plants in nature is almost always aggregated (Brawn-Blanquet, 1932;
Kershaw, 1964). Hence, most importance should be attached to quantitative differences in the flora, and the results of the quadrat counts reveal differences in vegetation more closely related to differences in treatments.
In Table 6, the average percentage frequency of grasses was - 86 - Table 6. Quantitative botanical analysis of plots, July 1971. Figures,indicate the number of squares per quadrat occupied by taxon (quadrat size 25 cm2, with sub-divisions of 5 cm2). % fre uenc of taxon within each re licate is also indicated.
REPLICATE DEAD BARE GRAMINEAE COMPOSITAE OTHERS PLANTS GROUND
C1 Quadrat 1 25 3 7 - - 2 25 4 13 - - 3 24 12 1 - - 4 25 2 16 - - % frequency 99 21 37 0 0 C2 Quadrat 1 25 22 19 - - 2 25 1 21 - - 3 22 3 20 - 4 25 21 - - % frequency 97 26 81 0 0 H1 Quadrat 1 17 4 2 9 2 13 8 4 3 23 6 5 4 15 - 10 - % frequency 68 10 7 27 4 H2 Quadrat 1 5 5 - 15 4 2 15 8 25 - 3 25 12 10 - - 4' 22 22 6 - - % frequency 67 47 41 15 4 HW1 Quadrat 1 25 1 - - 2 25 8 5 3 16 10 7 1 4 21 4 1 4 % frequency 87 23 4 11 1 HW2 Quadrat 1 11 3 5 10 - 2 25 8 - 3 15 9 13 2 - 4 25 9 8 - - % frequency 76 21 34 12 0 - 87 -
98% in the controls, 67.5A in the unwatered heated plots and 81.55-0 in those heated plots which were watered. Average percentage frequencies of Compositae in the control plots, unwatered heated plots and heated plots which were watered were 23.5%,
28.5% and 22/0 respectively; corresponding values for 'other plants' were 59%, 24% and 387g. The average frequencies of dead plants and of bare ground were nil in the control plots,
21% and 4% respectively in the unwatered heated plots, and
11.57:, and 0.5% respectively in the heated plots with added water.
Table 7 gives the percentage frequency of plant species within each replicate. Agrostis stolonifera was more frequent in unwatered heated plots than in any other; A. tenuis tended to be more common in the treated plots than in the controls, though the differences in frequencies of A. tenuis were small.
Occurrences of Festuca rubra, Holcus .lanatus and Lolium perenne were fewer in plots which were heated, compared with the controls; that of H. lanatus being least in the unwatered heated plots but that of L. perenne least in the heated plots with added water. Comparisons of other species of grasses cannot be made with validity because their frequencies were rather low, but it is interesting to notice that Trisetum flavescens, whilst having an average frequency of 19A in the control plots, was uncommon in all heated plots, even though this species was shown to be present in at least one replicate of each treatment.
Among the Compositae, Bellis perennis and Centaurea nigra were most abundant in the controls, though C. nigra did not occur in any of the heated plots. Achillea millefolium (found in most replicates) was on average most abundant in the unwatered heated plots -- its occurrence being least in the controls.
- $8 - Table 7 Percenta•e fre uenc of lant s•ecies within •lots July, 1971.
SPECIES C1 C2 H1 H2 HW1 GRAMINEAE Agropyron repens 4 Agrostis stolonifera 10 16 21 25 7 A. tenuis 12 10 17 11 17 Cynosurus cristatus 1 Dactylis glomerata 3 5 8 7 Festuca ovina 1 Festuca rubra 37 43 16 10 10 Holcus lanatus 68 51 23 16 34 Lolium perenne 48 46 39 28 28 Poo trivialis 1 Trisetum flavescens 22 16 3 COMPOSITAE Achillea millefolium 3 28 19 Bellis perennis 10 3 1 Centaurea nigra 20 Hypochoeris radicata 1 Leontodon hispidus 1 4 9 22 1 L. taraxacoides 3 2 Picris hieracoides Senecio vulgaris Taraxacum officinale 4 3 9 2 OTHERS Cerastium glomeratum 1 Lotus corniculatus 9 Plantago lanceolate 7 2 4 3 Potentilla reptans 10 Prunella vulgaris Rumex ocetosa 4 2 Trifolium pratense 28 40 7 12 T. repens 10 48 31 1 T. striatum 4
AA - 89 -
Leontodon hispidus was more frequent in the unwatered heated plots than in the other plots.
Trifolium_spp—were, on average, more common in the controls_ than in the other plots, with much fewer in the heated plots which were watered.
Plate 4 (i) to (iii) shows the plots in the winter of
1972 a few weeks before the termination of the treatments.
Control plots were snow-covered at this time, but the heated and watered and unwatered heated plots were not. Note that even in winter there were some patches of bare ground in the unwatered heated plots (pl. 4 (iii)) and the surface temperature probe was exposed to direct solar radiation. A sparse vegetation cover was also seen in the heated plots which were watered (Pl. 4 (ii)), but the surface temperature probe was never exposed. Many field mushrooms (Agaricus campestris) grew in heated plots at this time (especially in the unwatered heated plots, as Pl. 4 (iii) indicates). The underground mycelium of these fungi could have provided additional food for the invertebrate fauna in these plots.
The post-treatment assessment of the floral composition of the plots (in May 1972) is summarized in Table 8. The
Gramineae were still more abundant in the control plots; less than half of the area in the heated plots being covered with grass. Table 8 also shows the improved status of the
Compositae in the heated plots, and especially in those plots k Aid
Plate 4. (i) control plot, snow covered, tensiometer seen in centre; (ii) heated and watered plot; (iii) unwatered heated plot - note the exposed temperature probe, and the presence of Agaricus campestris. Photographed in Jan 1972, a few weeks before termination of treatments. - 91 -
Table 8. Subjective assessment of plant abundance using Braun- Blanue.. - ..noiratio. 22nd May 1972. (See text for explanation of figures)
Plot Species or Group C1 C2 H1 H2 HW1 HW2
GRAMINEAE 5 5 3 3 3 3 CARYOPHYLLACEAE Stellaria media 2 2 COMPOSITAE Achillea millefolium 1 2 1 Bellis perennis 1 1 1 2 1 Hieracium sp. 2 Senecio vulgaris 2 2 1 Taraxacum officinale 2 1 2 2 others 1 2 2 2 CRUCIFERAE Capsella bursa -pastoris 1 PAPILIONACEAE Trifolium spp. 2 2 2 3 2 3 PLANTAGINACEAE Plantago spp. 1 1 1 2 POLYGONACEAE Rumex acetosa 1 2 2 2 R. obtusifolius 1 2 2 2 RANUNCULACEAE Ranunculus repens 2 2 1 (dead plants and bare ground) 3 2 2 - 92 - with added water. Of the other plants, Rumex spp. differed most between plots, the control plots being very sparsely populated. The occurrence of patches of dead plants and bare ground was still obvious in some of the plots, so ratings have been given to emphasise this. The unwatered heated plots were especially patchy, though patches were also plentiful in the heated plots which were watered. Plates 5 (i) - (iii) and 6 (i) (iii) illustrate the recovery process of the flora after treatment. Pl. 5 (i) (iii) shows the differences between the vegetation cover in the plots in March
1972, one month after the treatments ended. The control plots
(Pi. 5 (i)) contained a complete cover of grasses, but in plots which were heated and watered (P1. 5 (ii)) Compositae were still common. Plots which were heated but not watered (Pl. 5 (iii)) also contained many Compositae and patches of bare earth were still visible.
In June 1972, the differences between vegetation were less marked (P1.6 (i) - (iii)) and grasses were again becoming dominant in plots which had been heated.
The vegetation in the plots was occasionally allowed to grow to the state shown in P1. 6 to facilitate the identification of the flora. In this way the list in App. 1 was made as complete as possible. In June 1973, after all the arthropod sampling was completed, the vegetation in the plots was very closely cropped and weighed. These weighings were as follows:- (1)
Plate 5. The plots in March 1972. (i) control plot; (ii) heated and watered plot; (iii) unwatered heated plot. Note the increased abundance of Compositae in heated plots. Plate 6. The plots in June 1972: (i) control plot; (ii) heated and watered plot; (iii) unwatered heated plot. The soil in heated plots has regained its grass cover. - 95 -
Control plots 5.80 kg
Heated and watered plots 10.91 kg
Hated plots 11.02 kg
There is thus some indication that even 16 months after
the treatments ended, some treatment effects on the vegetation remained.
Conclusions
(1) Qualitative differences in the botanical
composition of the plots could be due to the natural
spatial pattern of the flora, rather than to treatment
effects, but quantitative differences were related to
treatment.
(2) During treatment (in July 1971), the average
percentage frequency of grasses and of 'other plants',
(see Table 6) was lowest in plots which were heated;
the unwatered heated plots having the lowest frequency
of grasses and the heated but watered plots the lowest
frequency of 'other plants'. The average percentage
frequency of Compositae at this time was greatest
in the unwatered heated plots; numbers in the control
plots and heated plots with added water were approximately
equal.
(3) Heating killed plants and caused patches of bare
earth to appear. This effect was most marked in the - 96 -
unwatered plots.
(4) The growth of fungi was enhanced during winter
oy the heating. This may have caused an increase
in the amount of food available to certain soil fauna
in these plots, and thereby possibly influence their
abundance.
(5) The effect of the treatments on the flora in the
plots was relatively long-lasting, differences between
the botanical composition of plots being obvious three
months or so after termination of the treatments and
possibly even 16 months afterwards.
6. Weather conditions at Rothamsted and the microclimate at Garden Plots during the experiment
(i) General weather conditions
The general weather conditions at Rothamsted during the experiment are summarised in Rothamsted Reports,Tart 1, for 1970 - 1973. Table 9 gives a summary of some aspects of these data. 1972 was, on average, a colder year than the others, the air temperature and soil temperature at depth 10 cm being the lowest recorded for those four years. There were fewer hours of sunshine and the total evaporation was less in
1972, but 1970 was the wettest year.
Fig. 8 gives more details of weather conditions for part Table 9. Summary of some weather conditions at Rothamsted from 1970-1973
Latitude 51° 48' 30" N; longitude 0° 21' 10" W; altitude 128 m.
MEAN MEAN EVAPORATION SOIL GROUND SUNSHINE RAIN YEAR AIR TEMP (°C) (mm) TEMP AT DAYS OPEN WATER °C 10 cm
1970 9.1 (+0.1) 9.0 117 1464 (-46) 710 (+12) 194 570 1971 9.3 (+0.1) 9.1 107 1455 (-56) 622 (-78) 144 596 1972 8.9 (-0.1) 8.5 113 1337 (-169) 639 (-72) 167 554 1973 9.4 (+0.3) 8.9 128 1618 (+114) 518 (-176) 141 592
(Departures from long-period averages are shown in brackets) - 98 - 20- O MEAN AIR • • MEAN SOIL 0 • • AT DEPTH • 10 cm • O e 10'= 2 • • a. 0 6 • 9 ti • s :
20-
10- o RAIN DAYS • GROUND 0 FROSTS 150- O RAINFALL • EVAPORATION
100-
a C 50,
0
200, SUNSHINE
100-
OD F A J A 0 D F A J A 0 D F
1970 1971 1972 1973
Fig. 8. Some weather conditions at Rothamsted during the Garden Plots Experiment. - 99 - of this time, during the experiment on Garden Plots. The mean air temperature and mean soil temperature (under bare soil) at a depth of 10 cm followed very similar patterns, but this does not mean that soil and air temperatures were similar at any given time. The daily temperature wave moves through the soil at roughtly 2.5 cm per hour (Penman, 1973) so, at a given time, temperatures at different depths will be at different phases of the cycle. Over a large uniform area, annual mean soil temperatures should be similar at all depths, and in Britain should be the same as annual mean air temperatures to within a fraction of a degree Centigrade (Penman, 1973). This trend is seen in the figure giving monthly means.
There was no obvious seasonal trend in the number of rain days during the experimental period, nor in total rainfall.
The seasonal trend in the occurrence of ground frosts is clear.
Evaporation and sunshine also showed seasonal trends, maxima generally occurring in mid-summer and minima in mid-winter.
(ii) Microciimate at Garden Plots a) Temperature Seasonal distribution of temperature
Figs. 9 (1) (iii) give the soil surface and soil temperatures (at depth 5 cm) in the control plot, unwatered heated plot and heated plot which was watered, respectively (one replicate of each plot only was used for obtaining measurements of temperature). In each graph, the monthly range of temperature - 100 - SURFACE
Fig. 9 (i). Surface and soil(at depth 5 cm) temperatures in a control plot. Arrow indicates when treatment ended.
- 101 - 40 1 1 1 I i 1 SURFACE I 1 I I 30 1 I 1 I 1,1k ; 1‘ 1 20 I I /1 7 11 1 1I Ik1 1 t' 1 i 41 I , ■1„..‘i 1 It 1 1 I 1 I t. 1 1 10 1 I I ki 1 i 1 i 'II I i
—10
40 O
0 w 30
20
10
—10 O D F AJAODF A J A
1970 1971 1972
Fig. 9 (ii). Surface and soil (at depth 5 cm) temperatures in an unwatered heated plot. Arrow indicates when treatment ended. - 102 -
SURFACE
-10 0()
z 30 SOIL
20
10
-10 OD F A J A O D F A J AD
1970 1971 1972
Fig. 9 (iii). Surface and soil (at depth 5 cm) temperatures in a heated plot which was watered. Arrow indicates when treatment ended. - 1 03-
is indicated by the vertical bars, and monthly mean temperatures
(calculated as the mean of the average of daily maxima and minima) are also shown; the arrows show when the treatments were
terminated.
In the long-term, true mean air temperature (integrated over
the day) differs little from the mean of the average of maxima and
minima, and Penman (1973) considered that, for a year, the error
may be only 0.100 over-estimate. There is no reason to believe
that mean soil temperature, calculated in this way, should
provide a less accurate estimate of integrated mean soil temperature.
Mean soil surface temperatures, similarly calculated, also give a reasonable estimate of the true mean soil surface temperature,
but the accurate measurement of surface phenomena is notoriously difficult.
Fig. 9 (i) shows that the monthly range of temperature at the soil surface in the control plots was greater than that within the soil, and this effect was most marked in summer. The
monthly mean temperatures were more similar, although there was a trend for mean soil temperatures to exceed mean soil surface temperatures during the winter, and for the reverse to
occur in summer. Inversions in the temperature profile occurred around April/May and September/October and this pattern
is typical of air/soil temperature relationships (Macfadyen, 1963).
It is interesting to observe that the inversions in the temperature profile relating air and soil temperatures recorded - 104-
by the Rothamsted meteorological station (Fig. 8) also
occurred at similar times of the year, but that the profile was
an inverse one, -compared-with that in the experiment. In Fig. 8,-
the mean soil temperatures were slightly higher than mean air
temperatures during summer and slightly lower in winter.
These differences are probably because air temperatures, rather
than soil surface temperatures were recorded and also because
temperatures under bare soil, not under grass, were measured.
In Fig. 9 (ii), temperature recordings for the unwatered
heated plot are summarized. Again, the temperature range at the
surface of the soil was greater than that within soil, but mean
temperatures were similar. In the graph of soil surface
temperatures, corrections have been made whenever necessary
(using the regression line in Fig. 7), to allow for times when
the surface probe was exposed to direct sunlight. Corrected
ranges and means are indicated by the broken lines. Pl. 7 shows an exposed thermistor probe used to record
temperatures in an unwatered heated plot.. For moat of-the
experiment, mercury-in-steel-probes and a Cambridge recording
thermograph were used in this plot, but later it was necessary
to change to thermistors. The regression in Fig. 7 is based on
values obtained using the mercury-in-steel probes, but comparative
tests indicated that corrections using this regression for
recordings made with thermistors were unlikely, on average, to be o more than 1 C in error. Plate 7. Probes in the unwatered heated plot, recording temperatures at the soil surface and at depth 5cm.
Plate 8. Probes recording the distribution of temperature in the soil profile. - 106-
Pig. 9 (iii) summarizes the heated and watered plot temperatures for the soil and soil surface. Inspection shows that the mean soil surface temperatures in this plot were often very similar to those of the unwatered heated plot, except during the first winter of the experiment, when mean temperatures differed by up to 8°C. The range of soil surface temperatures also showed similar trends, except just before and after the end of the treatments. This difference may have been related to the cumulative differential effect of the treatments on the flora in the plots and on soil structure, as indicated earlier. Mean soil temperatures in the heated plot which was watered, were closely related to mean soil surface temperatures in that plot, although the range of temperature in soil was reduced.
Table 10 compares certain temperatures within each plot during the time of treatment. On average, soil (at depth 5 cm) and soil surface temperatures in heated plots were 7 to 9°C higher than in the control. The range of monthly mean temperatures was 14°C in soil and 18°C at the soil surface in the control plot; and corresponding temperature ranges in the unwatered heated plot were 22°C and 21°C respectively, and in the heated plot which was watered 15°C and 18°C respectively. In terms of overall average soil and soil surface temperatures, those in heated plots were similar, but the ranges of mean temperature in the heated plot which was watered were more closely related to those in the control. These differences must be related to the water content of the soil in the plots, the extra water in the - 107 -.
Table 10. Summary of some overall temperatures during the treatment
time of the Garden Plots Experiment
PLOT TEMP. °C CONTROL HEATED HEATED + WATERED
SOIL SURFACE OVERALL MEAN 10 17 (19) 18 MAX. MONTHLY MEAN 21 27 (36) 27 MIN. MONTHLY MEAN 3 6 (6) 9 MAX. TEMPERATURE RECORDED 34 38 (57) 38 MIN. TEMPERATURE RECORDED -6 -3 (-3) -2
SOIL AT DEPTH 5 cm: OVERALL MEAN 9 18 16 MAX. MONTHLY MEAN 17 30 24 MIN. MONTHLY MEAN 3 8 9 MAX. TEMPERATURE RECORDED 23 38 27 MIN. TEMPERATURE RECORDED -1 3 4
(uncorrected soil surface temperatures in unwatered heated plot given in brackets) -108- heated and watered plot moderating the effect of the heating.
This effect is more clearly seen when the absolute range of temperature recorded in soil (at depth 5 cm) in the unwatered heated plot (35°C) is compared with that in soil of the heated plot which was watered (23°C); the temperature range in the soil in the control plot was 24°C.
Soil surface temperatures in the unwatered heated plot, corrected by means of the regression in Fig. 7, are perhaps lower than expected, so I have also included the uncorrected temperatures for comparison. One might have expected the range of monthly mean and the absolute monthly range of soil surface temperatures in this plot to be greeter than those in the heated plot which was watered, but the effect of the extra moisture in the soil of the heated plot which was watered could possibly extend the range of temperature at the soil surface, but inducing lower minimum temperatures. In fact, inspection of Fig. 9 (i) (iii) shows further that, although the temperature of the soil surface in treated plots was higher than that in the control, the monthly range of surface temperatures in summer was generally greater in the control than in treated plots. Probably the true soil surface temperatures lie somewhere between the corrected and uncorrected temperatures, but close to the corrected values.
The Distribution of heat across the lots
A check was made that the distribution of heat across the treated plots was as even as possible, and this was repeated -109 -
periodically during the experiment, and the bias of the heaters
was altered accordingly. Typical measurements of the temperature
profile across the plots, when the heaters were set to give out
heat as evenly as possible, are shown in Table 11. The period
covers November 1970. At that time, three probes (at depth
5 cm) were placed in one replicate of each of the treated plots,
the probes being positioned at equal distances from the barrier
(excluding the perimeter strip) to the centre of the plot.
There was, on average, about 1°C difference in soil
temperature across each plot at this time, so the distribution
of heat was considered adequate. The maximum differences
recorded were 3.5 C in the unwatered heated plot and 1.5°C iin
the heated plot which was watered.
The vertical distribution of temperature in the plots
In Britain, the long-term average temperatures through the
soil profile should be similar for a given uniform habitat type. The
range of temperatures within these layers is usually not similar,
because of differences in the thermal capacity of the different
layers. The range of temperature in soil usually decreases with
increasing depth.
In Table 12, typical temperature profiles in the control
plot and unwatered heated plot during various periods in winter
are shown. Limitations in the availability of temperature
recording equipment prevented studies in similar detail being made - 110 -
Table 11. The horizontal distribution of heat in treated plots.
Temperatures are those recorded in soil at depth 5 cm,
for the month of November 1970.
H PLOT HW PLOT TEMP. °C PROBE POSITION PROBE POSITION 1 2 3 1 2 3 Overall mean 12.0 13.0 12.5 13.5 13.0 12.5 Max. monthly mean 13.0 14.0 13.5 14.5 14.0 13.5 Min. monthly mean 11.0 12.0 12.0 12.5 12.0 11.5 Max. temp. recorded 18.0 17.0 17.0 17.0 16.0 15.0 Min. temp. recorded 6.0 8.0 9.5 8.5 10.0 9.0
(probe position 1-3 from barrier to centre of plot.) Table 12 Some measurements of the soil temperature profile in control end unwatered heated plots.
PLOT TIME SOIL LA= TIP71W-URE "C MAX. NIN. RANGE
C WINTER STMPACE 18.25 -0.5 18.75 14-27 Dec, 1971 1 cm 8.75 0.0 8.75 and 3-19 Jan, 2 cm 9.0 1.0 8.0 1972 3 cm 9.0 1.75 7.25 4 cm 8.5 1.0 7.5 5 cm 8.5 1.0 7.5
4.0 -2.0 26.0 H WINTER SURFACE (31.0) (-2.0) (33.0) 21 Nov-3 Dec, 1 cm 21.75 -1.5 23.25 1971 and 30 Jan- 2 cm 21.5 -0.5 22.0 28 Feb, 1972 3 cm 21.0 0.5 20.5 4 cm 20.75 0.25 20.5 5 cm 21.0 0.5 20.5
C SUMMER SURFACE 33.5 8.25 25.25 July, 1971 5 cm 22.5 14.0_ 8.5_
38.0 17.5 20.5 H SUMMER SURFACE (56.0) (21.0) (35.0 July, 1971 5 cm 36.5 21.0 /5.5
(uncorrected soil surface temperatures in unwatered heated plots are given in brackets). -112- during the summer, but an indication of summer temperature
profiles can be obtained from temperatures recorded at the soil surface and -in--s-oil-(at-depth 5 cm) by the probes recording long-term temperature changes.
In winter, the ranges of temperature in the layers of soil tended to be inversely proportional to depth, although in the 3-5 cm Dryers, temperatures were more or less equivalent.
This equivalence was probably related to the amount of moisture in the soil at this time and it is likely that the temperature profile in summer would be more marked, when soil became drier.
Excluding soil surface temperatures, the range of temperature in the top 5 cm of soil varied by about 1°C in the control plot in winter, and in the heated plot by about 3°C. No corresponding profile values are available for summer temperatures. The soil surface in the control plots showed a greater range of temperature in summer than in winter, but in the unwatered heated plot this trend was reversed. This difference waa_also. reflected in the range of temperatures at depth 5 cm in the respective plots.
Rainfall and snow cover tend to equilibrate temperatures in soil layers (Mail, 1932). This effect was noticed, for example, in January 1972 when snow fell and the temperature in control plot soil varied by only 0.25°C in the top 5 cm of soil. The soil surface temperature range was also reduced, being 2.75°C when under snout but up to 6.75°C just before and after snow-fall. - 1 1 3 -
b) Moisture
Seasonal changes in the water content- of the soil in the plots
Routine estimations of the water content of the soil in the plots were made during the experiment. Fig. 10 (i) shows the seasonal changes in the water content of the soil (expressed as a percentage of the wet weight of soil) in these plots, the values for each treatment being the average of those for the replicates.
The wettest times of the year were generally in winter and the driest times in late summer. According to soil moisture content determinations, the control plot soil was wetter than heated plot soil during the time of treatment (the unwatered heated plots being, of course, the driest).
The relative effectiveness of the watering in bringing the soil moisture content closer to that in control plots is shown more clearly in Fig. 10 (ii) in which the moisture content of soil in treated plots is expressed as a difference between treated plot values and those in controls. It will be shown later (in relation to the heated plots which were watered) and these differences do not follow a similar pattern to those obtained when the moisture regime in the soil was assessed in terms of soil suction.
The effectiveness of the watering technique
As described earlier, tensiometers were used to maintain the water status in the soil, in heated plots which were watered, - 1 1 4 -
0 D F A J A O D F A J A OD F
1970 1971 1972 1973 Fig. 10(i). The water content of soil in the plots during the experiment. Arrow indicates when treatment ended.
-15- DRY X v1T (n ei —10- X \ \ / X / X.--X-"X II-I 5- / \X 1.0 X••••• X ti X-X NW C
WET
Fig. 10(i1). The water content of soil in treated plots, expressed as a difference between treated plot values and control. Time axis as in 10(i). 0 -115- at levels similar to those in controls. This technique was moderately successful (see Fig. 11 (1)), though there were some differences between the amounts of water in the plots, as is clearly shown in Fig. 11 (ii).
According to tensiometer readings, the soil in heated plots which were watered was sometimes drier and at other times, wetter, than the soil in control plots. The results do not agree with those obtained by determinations of soil moisture content (Fig. 10 (ii), in which the soil in heated plots which were watered was always drier than control soil, at least during the time of treatment).
It is not clear why this discrepancy should exist, but it is probably related to the times when the various tensiometer readings and moisture determinations were made. Tensiometer readings were usually taken daily, and they also include those readings taken just before and after each watering procedure.
The values plotted are the monthly averages. Soil moisture content determinations were made at less frequent intervals (during the treatment period this was generally once a week; sometimes once every two weeks) and never immediately after the watering procedure. Thus, soil moisture content determinations may have a tendency to underestimate the amount of water in heated plots which were watered. - 1 1 6 - 60 O C • H W 10 o (1) a (1) 0.- 5 40 -11413, o tr) 0 9 © " 1-4 0 r- CO LU .1 6 V) 0 —I I-. a h- o L4,1 20 • 171 1‘4.• CI 0 • 0 U.)z LLI • rn 30? 32.25
D F A J A 0 F A J
Fig. 11(1). The water status of soil in control and heated plots which were watered, as indicated by tensiometers. Arrow indicates when treatment ended.
rn U) ed L.0 h- LO DRY 2: +1 0 V) + 5 C) 0-4 E W 0 •"' 5 z +25 NI W • Irl W % "` 1 0 WET fr. +5 os li w
Fig. 11(ii). The water status of soil in control and io heated plots which were watered, expressed as
a difference between treated plot readings and nis a
control. 3 D NO I N3 I. - 117 -
7. Changes in nonulations of arthropods in the Garden Plats
Experiment
(i) The statistical treatment of data
Changes in arthropod populations are summarised in
Figs. 12 - 46. Before these are studied, a brief note on the
statistical treatment of the raw data is required. I am
particularly indebted to R.A. Kempton (Statistics Dept.,
Rothamsted) for advice on the analysis and help in processing
the data.
The general pattern of fluctuations in arthropod numbers
was obvious, but estimates of the natural sampling variability
were required for comparison with observed treatment
differences. Individual statistical analyses (analysis of
variance) done at each sampling date were poor in indicating
treatment differences because the low number of replicates
did not give an accurate estimate of the between plot error.
Estimates of the error were therefore pooled for the different
dates to obtain a single estimate of the error at each level
of the analysis.
The sample error usually increased with the number of
arthropods present, but this effect was largely eliminated
by using a log10 transformation. The variability of the logarithm of the counts appeared fairly uniform, both for the different
treatments and dates, and a pooled measure of this variability
seemed justified.
The analysis allowed the calculation of an L.S.D. for
comparison of treatment effects for each date (or dates for each - 1 1 8- treatment), in addition, it was also possible to test for effects of the position of sample units (i.e. to test whether there were differences in the horizontal distribution of the fauna in relation to treatments).
Because of the large number of comparisons made, and of the objections made to the indiscriminate use of the L.S.D. method in significance tests (Snedecor and Cochran, 1957), the use of a stricter significance level than the normal 5A is recommended; in the graphs the L.S.D.'s giving both the
1% and 5% levels of significance are drawn. The L.S.D. method of comparing means increases the likelihood of making a Type 1 error (i.e. that differences are declared significant when, in fact, they are not) when many comparisons are made. The frequency of such declarations may be reduced (at the cost of increasing Type 2 errors) by comparing means using techniques based on the Studentized
Range (Snedecor and Cochran, 1967). 1 considered that the
L.S.D. method was the most appropriate for these data, as there is probably little to choose between the various methods when the F (variance ratio) values are large. However, more care with the L.S.D. method is required in interpreting results when F values are small.
Transformations
Soil arthropod populations are usually aggregated.
Counts from field samples, when plotted as a histogram, are -119- skewed. However, if a log-transformation of counts is used, N the distribution is closer to the normal form, suggesting that normality exists on a multiplicative, rather than an additive scale.
When an untransformed additive scale is used, the variance is not a constant property of the data, but increases with the mean
(often the increase is roughly proportional to the square of the mean). Thus, if one population of arthropods is twice as large as another, the variance in sample counts from the one is often roughly four times that in sample counts from the other.
A log-transformation eliminates this and allows a single measure of variability to be applied to the whole of the logged data.
The average count per sample may be represented by the mean or the median, according to requirements. For a symmetrical distribution these two statistical measures of average are equivalent, but if the distributions are very skewed they may be quite different. For skewed distributions the median is often maatsatisfactory for the average or typical count and better than the mean (Snedecor and Cochran, 1967). The median (a distribution-free or non-parametric statistic) also has the useful property that it is invariant under transformation, e.g. log (median count)= median (log count). Thus, if the analysis is done using a log transformation of the data, one may transfer back the means of the logged data (which are equivalent to the medians of the logged data assuming the logged data to be normally distributed) to obtain the median counts. Should -1 20 - confidence intervals be required for this median, they are found by first constructing them for the logged data and then transforming back. The confidence intervals after transformation are not symmetrical about the median and, further, increase with the median count. With such distributions, the analysis of variance and parametric tests of significance should always be made on the transformed data, because these statistical procedures require constant variability and normality of the data.
In a later part of the analysis, changes in the proportion of one group of arthropods, relative to another were investigated in relation to treatment effects. Here, an angular transformation of percentages was used, also to equalise the variability
(Snedecor and Cochran, 1967). In untransformed data, variability between samples is greatest when the mean is about 5O and falls as it approaches 10 or 10 0 because of the influence of these bounds. The transformed values may be transformed back to obtain median % using Fisher and Yates (1943).
(ii) Fluctuations in arthropod numbers in response to the treatments
Results
Figs. 12 to 46 summarise how the numbers of various arthropods changed as a result of the treatments. In the graphs, the 1% and 5% Least Significant Differences (for comparing differences between treatments for any given date) are included. - 121 -
Figs. 12 to 46. calls2222222atiEL122221.2-....±Le abundance of eeleSllSLIYLt222iEjIIUatL22SLTILL.
In each graph, the abscissa gives the mean log (n + 1) count and the ordinate, the date. To keep the graphs as uncluttered as possible, the years are indicated at the bottom of each page only, and the key symbols at the top of each page. The bars in each graph give the 1% and 5% LSD's for comparing differences between treatments for any given date; the arrows indicate when the treatments were discontinued. — 122 — C TOTAL FAUNA * HW X H
FIG. 12
OCT NOV MC JAN FM MR MR INT MI JUL CNC OF OF NOV In JON KO MR OFN Tiff MI JA RUC MP OCT NOV MCC JIMI INIL ttwt
C
-J 2 w z NOV CO JAN Pa MR NPR MAY JIM Al ex gar ocr tar acc JUAt FCII MAR AM MT 4111 AL RUC $0 OCT NOV MC 4110 FM MN COLLEMBOLR 1
FIG. 14 a • OCT MT FIN MR MR tclf JUN Jat RUC UP OCT MY CO JCS FO NM MR My JUN JR MC s I= tar MC JAN Fe MR 0 1970 1971 1972 1973 — 123 —
C ♦ HW X H
OCT my CCC JAN MC MAR NON MY JUN 411 MC MOs OCT MV Oft AIN MI MR MR MY JIM Jlt MR CC OCT MT CCC Ai MN MR PRT I MITA + HET.
FIG. 16
t 1 f I 1 1 1 1I11111111111 OCT NCI OM 4111 MC MR OM MY JUN JIA MC Mr OCT MV CCC JON MS INN MR MY JUN JA ass *TP OCT MV CCC Jet MC MR
PROST I GMRTA
FIG. 17
OCT NOV MC JIM MO MR MR MY JUN JUL MC 01? OCT M4V QCC MI FCC Mit MR MY JUN JUL MC MP OCT MV Oft JAN I MN
1970 1971 1972 1973
- 1 21-1- C MESOST I OATH * H W X H
FIG. 18
OCT NOV WC JON WO MI AMA NAY JUN Jut RUC CCP OCT NW CRC al NO NW NPR Wff JI I Jtt 00 OW OCT NOY OCC JRN WS MI
CRYPTOST I CIIRTA
6
FIG. 19
OCT NOV WC .80 FON MI NM NOT JUN JUL RUC WP OCT Nov CCC a4 WI MI AMR .010 JUL WC CCP OCT 07V WC JAN RU NW
!", AST I GMATR
FIG. 20
1 I I I I I i E 1 /J1111111111111 si; OCT NOV RTC JON WS TAR MR MY JUN JUL WC WP acT tor INC JAN Rd MR VA ttAY 4t1N JUL OW 6VP OCT NOV OCC JAN fC8 IR 1970 1971 1972 1973 -125— PYEMOT I DRE C HW III X H
1111 OCT NOY OW JAM WO SIA APR NM JUN JAR ANAL MP OCT WA OW JAN FASO MR APR MY JUN JO. MC CCP OCT Nov WC JAN FRO AM
SCUTACAR 1 DRE
FIG. 22
MY WC OE WO MR NPR MY JUN XL WC CCP M MY MC .a ca MR MR MY JUN JUL MC WP OCT MY OW JAN Fa MR D I GRIRSEL L. I DRE
FIG. 23
• act ter WC JAN Ffle NM NW MY JR4 JR. WC CCP OCT Nov WC JAR fli MR APR NTT JUN JUL RUC VP OCT MY WC JAN Fti MR ffi 1970 1971 1972 1973 - 12 6 - c RHODIRCAR 1 EIRE 411 X H
FIG. 24
VW OCT NOV aEC 411 FIN WIN N9R nnr JUN JUI twc WP OCT WM MC JAN WO WA RPM MY AV JUL OX ocr NOV OCC JAN FRO tal eW ffi RHODACRRUS ROSEUS FIG. 25
MY NW WC JON Fa nna WO MY JUN JUL ntx OW OCT ter ow JAR FUO non wit rot JUN JUL WC WP OCT saw urr JiN roc
OCT NOV Ler JPS FiO NOR APN KW JUN JUL WJJC OCT NOV occ JAN TO f NPR INN JUN JUL FAX WP OCT NOV MC JAN KO IMMk
1970 1971 1972 1973 — 127 —
FIG. 27
OCT NOV ccc MA MS OM APR OW MN JUI. Ate MT NW MC MI rca IMO NM AM JUN Jut MX c ocr NOV OCC at rca Ftilt
MT .cv OCC AM MO Olt OM MN AM JA MX SW MT WM JR rca rMNi MM WN at a MX MP MT NM OM rca NM
I MATURE C I RCUMDE1-1,1
FIG. 29
1111111111 OZ MR 0EG at Rat Me MM lMiT AM a XX WY 017 FRY MX JR4Th MU WM AM a AUC CEP MI MT Mt JO OM MO 1970 1971 1972 1973 - 128 -
• C MYCOBFIT I DIRE • HW X H
ROT OCC JAN Fit MR IN MY JUR AIL Ott OCT MY MC JNM Fit MAR AM MT JLW JUL RUC UP OCT MY MC AR MI II
M I NUNTHOZETES
I
FIG. 3 1
CCT ION OM Jati ct MAR APR Rift JUN A. RUC CCP OCT MY OM JAN 1-43 MR APR MAY .AX1 JUL AM ACP OCT MY OEC JAM MO OAR PUNCTOR I BATES
FIG. 32
OCT M1Y OCC JAN FM MM APR RN( ACP OCT FOY ow V i 1101 ORR gm MRY JUN X. RUC • SEP a ROY OM J PEG MR 1970 1971 1972 1973 - 129 - SCHEL OR I BAT I DRE • C • HW FIG. 33 X H
OCT WY KC JON F178 NPR PIM NAY JUN JUL OM PEP OCT NOV OCC JOI PO ticit PPR INN JUN JUL liUt UP OCT NOV OM JRN RR NM
OPP I I DAE 1 1 I FIG. 34
OR
C.4
OCT NOV OM JRN KO NPR RP* NAT JIM JUL RUC POI OCT NOV INC JAI( Fel MR we ter JUN JUL RUC COI OCT NOV OCC at FOS MO IA CS. CLAD.
FIG. 35
g® OCT NOV GEC Jiti FEB NV HPR MI JIM JUL NX PCP OCT NOY OW JIM FEN NOR APR MI Mt JUL MC PCP OCT NOV MC JAN TO MR
1970 1971 1972 1973 — 130 — OPPIR C.F. MINUS I II .HWc X H FIG. 36 -tea C•1
111111111111J1111j CO OCT .M. RUC CCP OCT WY DEC JFAI MI MAR APR RAY JUN JA. RUC SEP OCT NOY DEC JRK ETA MR ONYCH 1 UR ORE III FIG. 37
OCT MY DEC al MO IOU APR PAT JIM JIA. WC UP OCT WY DEC JAR KA MAR NPR NAT .AN ,*L RuG CEP OCT MT ACC JAR FES IVA HYPOGASTRUR I DRE FIG. 38
a (11111111111111 es; xi. NOV OCC .1N4 TOO YR% ROR RAT JUN .Ad RUC SIP OCT MT oct JAI PCS An APR MAY JUR .11.1 AUC ACP OCT RCP KC JAR FOS MAR 1970 1971 1972 1973 - 1 3 1 - I SOTOM I DRE
FIG. 39
OCT HOT WC 41118 Fte WA MI Off JUN JUl RUC Wil* OCT NOV OCC MI Fee MN NM MY AN PL 0VC VIP OCT NOV aot ai FCS NiNe
I SOTOMA SPP Q +11 FIG. 40
8—
a l 1 1 1 1 1 1 1 1 1 I 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 ts; OCT NW MC NI TS NA PP TN ON AL VC CCP OCT' NOY MC JAN Eta NOR NPR MV JUN o. MX CFA OCT NOT OM Jai FM ORR
I SOTOMODES FIG. 41
a• FEB 1MW 1.2 NNV JIX JUL RUC CEP OCT NOT CRC JAN FEN TM NM MY JUN JUL 010 CRP OCT NOV OW AN Fite TAN 1970 1971 1972 1973
— 133 —
C THYSFINOPTERA • HW FIG. 45 1 X H I
I I 1 1 1 1 I I I I I I I _I I I 1 ET NOW MC JAM FEE MRR RFR PIRY AN M. RUC ACP OCT NOV TEC J1111 FEB MIR APR NO JUR JUL fitC CEP OCT NOV KC JIM MI MR
Aim
FIG. 46
ts; ICY PM ORR APR NO JUL FOX EP OCT NOW JAN FCI RPO FOR IWO .UM JUL RUC CEP OCT ROY OW XII FEE RFC 1970 1971 1972 1973 ITVI -
A comparison of the significance and size of the differences between populations in response to treatment is made in Table 13, and the direction of each difference is also indicated, as explained in the table.
The analysis also provided standard errors of differences for comparing dates for any given treatment, but the derived
L.S.D.'s have not been included in the graphs in Figs. 12 to
46 in order to keep these graphs as simple as possible. The omitted. L.S.D.'a can be derived from the data in App. 2.
A list of species of Acarina and Collembola identified from the Garden Plots experiment is given in App. 3.
Discussion
Fig. 12 shows that the general trend was for a reduction in the total population of soil invertebrates in unwatered heated plots; whereas the population in heated plots which were watered remained at a level similar to that in controls.
The overall implication was that the reduced population (whether brought about by effects on fecundity, mortality, or migration) was related to reductions in the amount of water in the soil (i.e. to some degree of desiccation).
The Acarina (which numerically made up over 70$ of the total soil invertebrate fauna extracted), were mainly responsible for this trend (Fig. 13), although the Collembola
(Fig. 14), which comprised nearly 25g of the total fauna, also changed in a similar way. No obvious effects of treatments were noticed in the remaining invertebrate fauna
(Fig. 15), except in December 1971, when the numbers in unwatered heated plots were less than those in heated plots Table 13 Comparison of differences between arthropod numbers in relation to treatmnt. Untransformed values are given in the table:scores underlined indicate P=0.01, otherwise P=0.05. Treatment comparison 1, 2 and 3 were control c.f. heated, control c.f. heated + watered, and heated c.f. heated+watered plot populations respectively. The sign of the difference indicates the direction of the difference (for example, a negative difference under treatment comparison i indicates that the population in the control plOts was smaller than that in the unwatered heated plots; a positive sign indicates that the control population was larger),
TREATMENT SAMPLING DATE GROUP COMPARISON 1 2 3 L. 5 6 7 8 9 10 11 12 OCT DEC JAN MAR APR JUN SEPT DEC FEB JUN OCT MAR 1970 1970 1971 1971 1971 1971 1971 1971 1972 1972 1972 1973 TOTAL 1(c:11) 1.22 +197 +125 FAUNA 2(C:HW) 3(H:HW) -144 -146 -100 ACARINA 1 (C :H) ...ta. +t36 +74 (C:HW) 3(H:HW) -109. -120 -73 .... .b...... COLLEMBOLA 1(C:H) +29 +52 2(0:HW) 3(H:HW) -33 OTHERS 1(C:H) +9 T-(A+C) T:H1 3 H:H PROSTIG.+ 1(C:H) HETEROSTIG. 2(C:Hi +72 +16 3(H:HW PROSTIGMATA 1p:H) 2 C:H1 3(H:HW Ta 1e 1,1 continued
TREATMENT SAMPLING DATE 40 GROUP COMPARISON 1 2 3 4 5 6 7 8 9 10 11 12 OCT DEC JAN MAR APR JUN SEPT DEC FEB JUN OCT MAR 1970 1970 1971 1971 1971 1971 1971 1971 1972 1972 1972 1973 MESOoT1GMA 1(0:11) 142- +12 +17 +26 -TA :11 32p:HW H -29 -21 CRYPTO- 1p:H) +51 +117 +61 STIGMATA 2(0:11W 3(H:HW -77 -9 ------7 7.5..4 ASTIGMATA 1(0:H) -12 -8 -41 -x1 2p:Hl -6 7 3 H:HW 17E -8 PYEMOTIDAE t(C:H) -32 +21 -6 20:11 +25 +5 3(H:liw +34 SCUTAC- 1(0:H) +5 +5 ARIDAE 2(C:HW) +45 +7 +6 3(H:HW) -6 DIGAMAS- 1(0:H) +8 MLIDAE 2(0:1 3(H:HW -11 RHODAC- 1(0:H) +29 -28 ARIDAE 2(0:HW) 3(H:HW) -97 hHODACARUS 1(0:H) +5 ROSEUS 2(C:HW3 -9 3(H:HW -12 -10 -10 'rabic, 11 continued TREATMENT SAMPLING DATE GROUP COMPARISON 1 2 3 Li- 5 6 7; 8 9 10 11 12 OCT DEC JAN MAR APR JUN SEPT DEC FEB JUN OCT MAR 1970 1970 1971 1971 1971 1971 1971 1971 1972 1972 1972 1973 RHODACAR- ELLUS 1(C:H) -12 z.L +13 2p:HW) 1 - 4 +1 4 3 H:HW -15 +10 UROPODINA 1 (C :H) 2(C;HW -6 — 9 3(H:HW 7 -2 -2 =2 -2 =a -2 ADULT 1(C:H) CIRCUMDEH. 2p:Hi (EXCEPT 3 H;HW -55 OPPIIDAE)
IMMATURE 1(C:H) +15 CIRCUMDEH. 2(0:11 3(H:HW 11 -25
MYCOBATIDAE 1(C:H) +36 :116. 2r:H1 3 H:HW -27 MINUNTHOZET- 1(C:H) +44 ES IC:H SEMTRUFUS 3 H:H1 _ PUNCTORIB- 1(C:H) -34 +12 ATES 2(0:Hi -15 PUTTCTUM 3(H:HVi -20 SCHELORIB- 1(C:H) +10 ATIDAE 2p:H1 3 H:HW -18 -13 Table 13 continued
TREATMENT SAMPLING DATE 41 GROUP COMPARISON 1 2 3 4 5 6 7 8 9 10 11 12 OCT DEC JAN MAR APR JUN SEPT DEC FEB JUN OCT MAR 1970 1970 1971 1971 1971 1971 1971 1971 1972 1972 1972 1973 OPPIIDAE 1(C:H) -125 +39 +21 +26 2(C:H1 +41 +20 +12 3(H:Hw +127 -7 OPPIA c.f. 1(C:H) +40 +23 +19 CLAVIP. 2(C:HW) 2(H:HW) -11 OPPIA 1(C:H) =52 -173, MINUS GP 2(C:111 -33 la- -12 3(H:Hw +129 ONYCLIUR- 1(C:H) +21 IDAE 2p:H1 3 H:HW -5 -12 1 HYPOGAST- 1(C:H) RURIDAE 2r:H1 3 H:HW ISOTOid- 1(C:H) IDAE 2(C:H1 3(H:HW ISOTOA 1(C:H) -11 -21 -19 -19 +7 +9 SPP 2(C:HW) Z/1 =21 =1/ =II 3(TI:Hta ISOTC.,(A) ;b l(C:H) PRODUCTUS 2(C:H1 3(H:HW Table 13 continued
TREATMENT SAMPLING DATE GROUP COMPARISON 1 2 3 14- 5 6 7 8 9 10 ii 12 OCT DEC JAN MAR APR JUN SEPT DEC FEB JUN OCT MAR 1970 1970 1971 1971 1971 1971 1971 1971 1972 1972 1972 1973 ENT OMOBR- 1(C:H) =1 -71 .:2-. '....F +8 -18 YIDAE 2(C:HW) -2 -11 3(H:fivi) =2 -11 +18 LEPIDOCYRTUS 1(C:H) -3 -3 -5 +8 -12 SPP. 2(C:HW) Z1 =LI +3 -6 3(H:iivi -:k -8 ' +13 SMINTH- T:H) -0.2 =1 +10 +18 URIDAE 2 C:Hi -2 +8 +18 3(H:HW -2 THYSAN- IC:H) +4 OPTERA 2 C:HW) +4 3 H:HW HEMIPTERA T:H) -40 -12 2 C:Hi -14 3(H:HW) , - 140 which were watered (P = 0.05). Too much emphasis must not be
placed on this difference, because the effect did not persist, and the number of animals involved in this group was less than
5% of the total invertebrate soil fauna collected over the whole of the experiment.
A breakdown of the changes in numbers of various groups within the Acarina is given in Figs. 16-36. Four of the major orders are considered in Figs. 17 to 20 and in Fig. 17 the
Prostigmata excludes the Heterostigmata. The previously recognised grouping of 'Prostigmata' included the Heterostigmata (=
Tarsonemoidea); In Fig. 16 this grouping is included for comparison.
There were no consistent differences between the populations of 'Prostigmata' (Fig. 16) in relation to treatment. In June 1971, the numbers in controls were greater than those in heated plots which were watered (P . 0.05), but a difference of this level of significance also occurred at the beginning of the experiment, making the interpretation of the results difficult. It is noticeable in this group that there was a decrease in numbers, independent of treatment, during much of the treatment period.
During this time, sampling and grass-cutting was most frequent, so the population decline may be related to sampling pressure or cropping. When the treatments ended, the sampling and cutting occurred less frequently as the population recovered.
There were no differences in numbers of Prostigmata
(Fig. 17) related to treatment, but the population did not decline in the same way as the Prostigmata and Heterostigmata together
(Fig. 16). This suggested that the Prostigmata (a large 141 -
heterogeneous group) were less affected by sampling and cutting
than the Heterostigmata, possibly because many of the Prostigmata
live in the deeper layers of soil.
The Mesostigmata (Fig. 18) includes many predacious species, and the main effect of the treatment was to reduce the population
of these mites in unwatered heated soil; thus suggesting that
desiccation was a major factor in reducing their numbers. The
numbers of Cryptostigmata (Fig. 19) fluctuated in a similar way to that of the Acarina as a whole, and again the major influence
of the treatments was probably due to some measure of desiccation.
The Astigmata (comprised almost entirely of members in the
Acaridae) reacted quite differently (Fig. 20) and numbers of these mites
were increased by heating (whether extra water was added or not).
These increases first occurred during the latter part of the
treatment, and continued throughout the post-treatment observations.
The increase in numbers of astigmatid mites could have been directly
related to the heating, through effects on fecundity; or indirectly
through reductions in predator pressure, or due to an increased food
supply (it was shown earlier that the frequency of Agaricus campestris, a possible food source for many soil invertebrates, increased in
heated plots).
Population fluctuations of mites belonging to different
orders varied according to the treatments but it seemed that the
Mesostigmata and Crytostigmata were most susceptible to desiccation,
whereas the Astigmata increased in numbers in heated soil,
irrespective of the prevailing moisture conditions. No obvious
changes in numbers due to treatments occurred in the Prostigmata,
nor in the Prostigmata Heterostigmata. -
The effects of treatments on the Acarino were investigated further (Figs. 21 to 36) in an attempt to determine the response of species, genera and families (and other small taxonomic groups). The changes in numbers of two major families in the
Heterostigmata (the Pyemotidae and Scutacaridae) are shown in
Figs. 21 and 22. The Tarsonemidae were poorly represented quantitatively in Garden Plots soil, so these are not considered. No clear patterns of change in numbers due to the treatments occurred with either the Pyemotidae or the Scutacaridae, although in April
1971 the number of pyemotids in the unwatered heated plots was less than that in controls (P = 0.01). The overall effect of the heating was to decrease the number of scutacarid mites. It is likely that the effect of the sampling and of cropping had a large influence on the population of Heterostigmata, because many of these mites were found at the soil surface and on vegetation. The true effects of the treatments may therefore be confused. Effects of treatments on numbers of species belonging to
the Mesostigmata are summarised in Figs. 23 to 27. Numbers of the
Digamasellidae (Fig. 23) were not greatly influenced, though heating without adding water caused populations of these mites
to decrease in March 1971, compared with the population in heated
plot soil which was w,,tered, and in April 1971, compared with
digamasellid numbers in control soil. Therefore, it is likely
that the main influence of high temperatures on theSe mites is by
increased desiccation.
There was some indication that a similar effect influences
the Rhodacaridae (Fig. 24) in the long-term, but initially the
heating caused an increase in t're number of rhodaca rids, so that
in March 1971 the population of these mites in unwatered heated
plot soil was larger than that in controls (P . 0.05). However, - 14'3 - at the start of the experiment the rhodacarids in the controls were also much more numerous, the significance of the difference exceeding P = 0.01 at that time. Rhodacerus roseus was the dominant species of_rhodacarid and_ohanges in numbers of this species are summarised in Fig. 25. The most obvious effect of the treatments was that heating soil without adding extra water decreased the number of these mites, and this effect was persistent.
The effect of treatment on Rhodacarellus sp. (probably
R. silesiacus) was not so obvious. Initially, the heating increased the population compared with that in control plots, but later this effect disappeared (Fig. 26).
All the mesostigmatid mites considered so far belong to the
Gamasina, a group generally believed to be predacious (with the possible exception of certain of the Rhodacaridae). The other group of mesostigmatid mites, the Uropodina, are considered to be mainly non-predatory. The Uropodina from Garden Plots comprised several species, of which the most frequently occurring was possibly Olodiscus minima, although species of Uropoda and Dinychus, were also found. As no species or genus occurred consistently in sufficient numbers to enable a thorough statistical analysis to be made, the uropodids have been considered as a whole. The most striking observations (Fig. 27) were that heating without adding water did not decrease the population of uropodid mites as compared with controls, and that heating and watering usually increased the population. This may explain why large numbers of uropodid mites are commonly found in compost heaps (D. Macfarlane, pers. comm.) where the microclimate is often very warm and moist.
Fluctuations in numbers of the Cryptostigmata are summarised in Figs. 28 to 36. The changes in number of adult
Circumdehiscentiae (except Oppiidae) in relation to the treatment are shown in Fig. 28, Effects were not seen until just before the treatments ended, and by that time (December 1971) the number of these mites in heated plots which were not watered was less than that in other plots. Thus, the reduction in numbers was probably related to the cumulative effect of desiccation. A similar pattern of change was seen in the immature Circumdehiscentiae
(including Oppiidae) (Fig. 29). The general indication is that most 'higher oribatids' can tolerate relatively high temperatures, unless they are influenced by desiccation.
The Mycobatidae were well represented in Garden Plots soil.
Changes in numbers of the adult Mycobatidae showed similar trends to those of the mites as a whole, i.e. heating without adding water caused a decline in the population (Fig. 30), but no differences were observed between the numbers in the control and in heated plots which were watered. Similar patterns occurred in populations of adults of Minunthozetes semirufus (Fig. 31) and of
Punctoribates punctum (Fig. 32), the two dominant species in the Mycobatidae in Garden Plots.
The Scheloribatidae (Fig. 33) here comprised two major species, Scheloribates laevigatus and Liebstadia similis. Here also, the effect of desiccation probably had the most important influence on change in numbers.
Changes in numbers of Oppiidae (Fig. 34) showed trends which depended on the length of the treatment. In the spring of 1971,
(6 months from the beginning of the experiment) the population of oppiids in the unwatered heated plots was greater than that in the control or in the heated plots which were watered (the - 145 significance was- marginal at the 5Y, level). Later, the pattern changed and by the end of the treatment period the population
in control plots was greater than those in either of the
treated plots. An interaction between increased temperature and desiccation (through effects on fecundity and mortality)
obviously influenced these mites, but as the family Oppiidae is a
large one, the exact causes of population changes at this level
are difficult to ascertain and different species probably reacted
to the treatments in different ways. Fig. 35 summarises population
changes in a group of medium-large sized oppiids. This group was
dominated by Oppia c.f. clavipectinata, but other species were also present, although in low numbers. Heating without adding water
decreased the population of these mites and this group was
possibly the most susceptible to desiccation. Oppia c.f. minus
(Fig. 36), a small oppiid, often occurred at greater depths
in the soil than 0. c.f. clavipectinata. Therefore, it is possible
that a comparison of the effect of treatments on these two groups
of mites is unjustified, because the temperature and moisture
conditions each was exposed to may not have been similar. It is
probably fair to imply that 0. c.f. minus is better able to survive
higher temperatures and desiccation than 0. c.f. clavipectinata,
either directly or because it can move away from these extremes
and, for example, penetrate the deeper layers of soil. There was
no decrease in population size in relation to treatments.
Changes in numbers of Collembola are summarized in Figs.
37 to 44. The Onychkridae (Fig. 37) were influenced most by the effects of heating without adding water probably because these
springtails were susceptible to desiccation. The onychiurids consisted of several species, the most common ones being
Gnychiurus armatus gp. and Tullbergia krausbaueri, but other species within these two genera were also frequent.
No differences in numbers in response to the treatments
occurred for the Hypogastruridae (Fig. 38) nor the Isotomidae
(Fig. 39), but there were many species in these groups. No single species of Hypogastruridae occurred consistently in sufficient numbers to allow a statistical analysis of the data, but the
Isotomidae were abundant and in this family both Isotoma spp.
(Fig. 40) and Isotomodes productus (Fig. 41) were identified and counted.
Isotoma spp. (Fig. 40) increased initially in numbers in all the heated plots and this increase seemed independent of decreases in soil moisture content. Towards the end of the treatment time, the effects of desiccation became noticeable, because numbers in
unwatered heated plots decreased markedly and became significantly less (P = 0.05) than in the controls; but this did not occur in heated plots which were watered.
Isotomodes _productus (Fig. 41) showed no effects of treatments
throughout the experiment, so this species seems to be more
tolerant of changes in physical conditions than other isotomid
Collembola. I. productus is small, so it is also possible that
this species was able to move away from unfavourable conditions by
moving to the deeper layers of soil.
Most of the entomobryid Collembola live at or near the surface
of the soil, but some, such as Heteromurus
nitidus and Pseudosinella alba, occurred (as shown by careful soil sectioning) in deeper layers also. The Zntomobryidae as a
whole differed in their response to the treatments (Fig. 42), but the general trend was for an increase in the population in heated plots during the first part of the experiment and later, possibly due to desiccation, numbers in the unwatered heated plots decreased.
Lepidocyrtus cyaneus occurred in sufficient numbers to consider them separately, and the response of this species to the treatments (Fig. 43) was similar to that described for the entomobryids as a whole. One trend which is most noticeable was the steady increase in the population of L. cyaneus throughout the experiment. The reason for this increase is not known, but because the control plot populations also did this it could possibly be due to the fewer samples being taken as the experiment progressed.
The Sminthuridae (Fig. 44) are mostly surface-living species but Sminthurinus spp. and Sminthurides pumilis also occurred in deeper layers. For the Sminthuridae the peak populations in control plots occurred in June, but in the treated plots these peaks were in March. In June 1972 (after the treatment had ended) there were peak numbers of sminthurids in the heated plots that had been watered. Why this occurred is not clear, but differences in the vegetational composition of the plots still existed at that time; the peak may therefore have been due to the amount of available food within the plots.
The Thysanoptera and Hemiptera occurred in relatively large numbers. Thysanoptera (Fig. 45) populations differed in response to treatment just before the treatment ended, and then the numbers of thrips (mainly Aptinothrips rufus) in the heated plots were leSs than those in controls. This suggests that Thysanoptera were - 1!8 - intolerant of high soil temperatures, regardless of the soil moisture content, although some species may have multiplied and left the soil as winged adults.
Soil-inhabiting Hemiptera responded differently to the treatments (Fig. 46), because in the Spring of 1971 there were significant increases (P = 0.05) in the hemipteran population in all heated plots relative to the controls. These Hemiptera (mainly soil aphids, including Rhopalosiphum sp.) survived relatively high temperatures under moisture conditions which varied by up to 6%, based on the wet weight of soil (Fig. 10).
My conclusions are that soil arthropods differ in their reaction to changing conditions of temperature and moisture in soil. viuch of the fauna could withstand relatively high temperatures when the soil did not become dry and it could be implied that in temperature/moisture interactions, desiccation was the most important factor influencing most soil populations. Certain soil fauna (the Acaridae and Uropodina, for example) were apparently able to survive the drying of soil better, as were Oppia c.f. minus and Isotomodes productus. Clearly the picture is complex, because some of these forms are probably able to penetrate the smaller soil cavities more easily than others, and could thereby escape the more extreme physical conditions to which the non-burrowers or non-tunnellers are exposed.
(iii) Proportional changes in the composition
of the soil fauna in response to treatment; The numbers of various soil arthropods changed in response to the treatment, but there was some indication that other factors also influenced the fauna, making the treatment effects sometimes - 14 9 - difficult to isolate. These other factors can be related to the disturbance due to sampling and cropping, although such disturbances were kept as small as possible; or, some long-term trends in weather conditions may have had some effect. For example, there was a trend for the total annual rainfall at
Rothamsted to decrease from 1970 to 1973 (Table 9). Whatever the factors involved, there were marked decreases in numbers of many soil invertebrates (Fig. 16) from 1970 to 1972, and these occurred independently of treatment.
A possible way to minimise the effect of these large changes in numbers (and thus clarify effects related to treatment) is to consider proportional changes in the composition of the soil fauna. Changes in the proportion of one group, relative to another could possibly give a better indication of the effects of the treatments on factors like natality and mortality.
Results
Figs. 47 to 58 summarise the proportional changes in the composition of the soil fauna, and Table 14 gives a summary of significant differences related to treatments.
Discussion
Changes in the proportions of Acarina, Collembola and of others (total fauna minus 'mites + Collembola') relative to total soil fauna, are summarised in Figs. 47 to 49. Trends shown by the Collembola (Fig. 48) are inversely related to those of the Acarina (Fig. 47) because together, the mites and Collembola made up over 957A of the total fauna in the experiment. The effects of the tre=itments on the composition of the soil fauna, particularly of these major taxonomic groups, was slight, the only well-defined Figs. 47 - 58. Garden Plots Experiment: Proportional changes in the cam•osition of soil arthro•ods in res onse to treatment. In each graph, the abscissa gives the mean percentage composition (angular transformation) and the ordinate, the date. Years are indicated at the bottom of each page only, and the key symbols are given at the top of each page. The bars in each graph give the 1% and 5% LSD's for comparing differences between treatments for any given date; the arrows indicate when the treatments ended. — 151 —
esa
oCT 9trt OCC .evi F91 MR wo MT AIN AL sus sot err NNr orc Jeo FOS NM OPII MY .01 JUL rex an act Nov ow 4111 tat ma
1f) th COL L EMBOL
45: 611
0 §—e 03 ).4 CO 0 10
0 ea Ea N
03
19 OCT NOV OCC its MO SFR 1W! 01 .0. RUC RCP OCT NOR NEC al RN MR MR MY .1114 JUL SRC CCP OCF NOV NEC FEB MO
OCT NOV Ott 401 F03 MR MY AN .01. RUC CCP OCT MY MC ,0 Its MR MR MY .01 At RUC SIP OCT NOV MC .01 c MR
1970 1971 1972 1973 - 15 2 —
PROST I GMATR + HET. HW X H FIG. 50
11111111111111111 OCT Wff WM AW i MR WM WIT ATI .M RUC WP OCT MOT OEC JRN FEN TAR aPR MAY JUN AL WC WP OCT NOT DEC JON KB CM
MESOST I GMAIR
FIG. 51
OCT NOT OEC JNN FEN ORD WS OW AM JUL MC sts OCT NOV WC JAN MR NM RPR MY AN *L RUC $ OCT WV WC JON TO NW
RYPTOS I GMATR FIG. 52
OCT NOT OM JAN R3 WA OM NRY AN JUL Nuc aip OM' NOT DEC AN PER TAR APR MRY JUN AL RUC DO OCT WY OEC JRN FEN NM 1970 1971 1972 1973
— 15'3 — C fr AST I CMATR • HW FIG. 53 X H SD •—
•• CO
I OCT NOV Olt 4114 FIX OW aaa WIY JLIE JUL WC SW ocr IOC JOE NZtaw WRtwv a SIL MX SW acr Nov OM a E5
ONYCH I UR ORE
OCT NDY awc JON MO NW OW WTI JUN JUL WIC WP 1117 NOY WC MN EDI NW NPR WE a JJL WC SW ocr NOW WC a Ra aRR te
(5) g 1-4YPOCRSTRUR I ORE
FIG. 55 etea
S ocr Y DEC 9est WO WO IWY JUN AIL WC CEP OCT WY Wit JON c 101 WI MY JUN JUL 01/C WP OCT NU DEC Jell E IaIR 1970 1971 1972 1973 — 154 — I SOTOM I ORE FIG. 56
OCT irm DC JAN Fie We We YAW XII et AUC UP OCT NAY WC JAN 113 NOR WM NW JUN JUL GP Oct tot KC JAN 113 ea 62 • CO ENTOMOBRY I ME FIG. 57
62 • — CV CV
OCT MX 130 JAN I Ma MI t*T JA. AL MAC OM OLT ILIV al fle tMR Oft ray 4,44 JIL 111.6 UP fa In arc JAN a CO SM I NTHUR I ORE
II FIG. 58
NNW
ea act mow INC ea twa foR 16Y Afti JUL tax I MT JiNJI Ft S twa ITP2 PAY JIM AL Tit UP OCT MY AA! RD twa 1970 1971 1972 1973 Table 14. Comparison of differences between proportions of one group of soil arthropods, relative to another, in relation to treatment. Values in the table are percentages, calculated from un- transformed data. Scores underlined indicate P=0.01, otherwise P=0.05. Treatment compari- son 1, 2 and 3 were control c.f. heated; control c.f. heated + watered, and hePted heated + watered plot populations respectively. The sign of the difference indicates the direction of the difference (for example, a negative difference under treatment comparison 1 indicates that the population in the control plots was smaller than that in the nnwetered heated plots; a positive sign indicates that the control population was lar7er).
SAMPLING DATE / 1 2 3 4 5 6 7 8 9 10 11 12 TREATMENT OCT DEC JAN MAR APR JUN SEP DEC livIl JUN OCT R mmup COMPARISON COMPARISON 70 70 71 71 71 71 71 71 72 72 72 73 ACARINA 1 (C:IT) C:HW) 13 H:HW) -27 COLL7NDOLA 1(C:H) H C:HW) E- I3 TI:ItW) G2, 0 OTHERS T-(A+0) 1(C:H) 2(C:HV) 3(H:HN) P",OSTITG. + HE'17ROSTIG. 1 (C:IT) -24 -20 IC:H1
NA 3 11:1W +17 +25
Ara MESOSTIGMATA 1C:H) 2 C:HW) -12
AC 3 H:1110 CRYPTOSTIGNATA 1 C:ir.) +39 +25 2 C:NW) VE TO 3 IT: ) -40 -24
ATI A STIGMATA 1 C:H) -6 -16 -11 -19_8 -13_ 2 C :TTW -5 REL 3 HW +11 +11 +10
Table 14 continued
SAMPLING DATE 4 1 2 3 4 5 6 ,, 8 9 10 1 1 12 TREATMENT OCT DEC JAN MAR APR JUN SEP DEC F1 ?I; JUN OCT ' -''R CROUP COMPARISON COMPARISON 70 70 71 71 71 71 71 71 72 ' 72 72 73 ON,Yr7TURTDAE 1(C:U) +24 2(C:111 ty 3 (IT:I P, ,r -19 TYPOGA STRUR E 1 C 2 C :MT) 3 11:111,1 ) ISOTOMIDAE 1 C:11 2(C:111 C 3(11:H 1;; N.TOMO YIDAE 1 2 C: ) -16 3 SMINTITURIDAE 1TC40 -2 +10 +21
+9 +21 -2 3 II:11W -3 - 157 - treatment effect being differences in the proportions of Acarina
(see Table 14) in unwatered heated plots and heated plots which were watered. These differences occurred in October 1972, after the treatments had ended, and were related to an increase in the proportion of mites in the heated plots which had been watered
(Fig. 47), possibly caused by differences in the fecundity of the mites in the plots and effected either by the treatments influencing feeding behaviour, or by affecting the availability of food for the mites (Wallwork, 1970).
An overall decrease in the proportion of mites (and corresponding increase in that of Collembola) occurred during the - experiments, irrespective of treatment. This also indicates that other undetermined factors influenced the population of the mesofauna. The other invertebrate fauna (Fig. 49), although their relative proportions fluctuated, did not have this overall trend and remained a fairly constant component of the total fauna.
Relative proportions of Prostigmata Heterostigmata
(Fig. 50), increased in the unwatered heated plots, but this effect was not observed in the population counts (Fig. 16).
Few changes relating to treatments occurred that affected the relative proportions of Mesostigmata, but in March 1971, mesostigmatid mites in the heated plots which were watered comprised a larger proportion than those in controls, which supports the theory that the Mesostigmata (mainly the Gamasina) are able to survive relatively high temperatures, unless exposed to desiccation.
The proportion of Cryptostigmata, in relation to that of all Acarina, decreased markedly in the unwatered heated plots
(Fig. 52) and this confirms previous conclusions that this group - 158 - is very sensitive to desiccation.
The relative proportions of Astigmata increased in the heated
plots and the drying of soil enhanced, rather than inhibited,
this increase (Fig. 53). This agrees with earlier conclusions that the Astigmata can withstand (or perhaps avoid, by migration) some degree of desiccation.
The relative proportion of Onychiuridae, to total Collembola, was also influenced by the treatments (Fig. 54), and desiccation was probably the main influence on population decline (Tables 13 and 14).
No effects of treatments were observed for Hypogastrur-idae
(Fig. 55) or Isotomidae (Fig. 56), although heating (whether water was added or not) seemed to increase the relative proportion
of Entomobryidae (Fig. 57), but this effect was not persistent.
The effect of the treatments on proportions of Sminthuridae
(Fig. 58) closely resembled those observed earlier on numbers of this group.
Analysis of the angular transformation of percentages of one group of soil animals relative to another has showed quantitative changes in the composition of the arthropod fauna in relation to treatments, and most of these data support the conclusions made earlier on the basis of population counts. One exception is in the
Prostigmata and Heterostigmata. Results based on numbers of individuals were difficult to interpret, because factors other •
than the treatments influenced the population, but investigations of
proportional differences in this group provided evidence that
these mites increased in unwatered heated soil, and so were tolerant
of partial desiccation.
In these investigations, I have so far used terms such as - 159 -
"able to survive relatively high temperatures" or "susceptible
to some degree of desiccation", but I have not yet indicated
the magnitude of these differences. This was intentional, because
the only available information on which to assess differences
between physical conditions within the soil is based on the
measurements of microclimate described in Section 6 of Part 1.
These measurements were made in order to provide a relative
assessment of the effects of the treatments on physical
conditions in the soil, but it should be clear that there is no
evidence that conditions measured in this way are necessarily
similar to those microclimatic conditions to which the fauna were actually exposed in the small cavities of soil. Within these
limitations, some tentative indications of the soil conditions in
the plots to which the fauna were exposed can be discussed.
Most soil animals seemed susceptible to the drying of soil,
because their numbers decreased in heated unwatered plots, but
not in heated watered plots. The greatest difference between
the water content of soil in these plots was measured as about
11% on a wet weight of soil basis (Fig. 10). This difference
occurred in December 1971, when the treatment effects were
greatest, and at that time the difference in average soil
temperature (at depth 5 cm.) was about 4°C. Certain soil animals
(e'.g. the Astigmata and, for a time, the Prostigmata Heterostigmata)
increased in numbers in unwatered heated plots, and were little ctelfrq affected by drying conditions. The maximum soil temperatures in
the unwatered heated plots occurred in September 1971 and were
about 38°C and the average soil temperature was about 29C, which
was approximately 14°C warmer than the average soil temperature
in control plots at that time. - 160 -
:host of the soil mesofauna occurred in the upper layers of soil, so it is likely that the majority of the fauna were exposed to (or had to move away from) more extreme conditions than those which were measured at depth 5 cm.
(iv) The results of pitfall trapping: The number of animals other than microarthropods extracted from soil cores was sometimes small, and statistical analysis of data relating to these groups was impossible. One method of obtaining further information on the influence of the treatments on this 'other faunal was to use pitfall traps, so that effects of treatments on the numbers or activity of arthropods at the soil surface might be assessed, and also so that information on the effect of treatments on the emergence of certain arthropods from soil might be obtained.
On 15th February 1971, one pitfall trap was placed near the centre of each plot and catches were recorded regularly during the rest of that year.
Results and Discussion
Table 15 summarises the results and shows that the animals caught in the traps were not numerous, perhaps because the area of soil within the plots was relatively small and could not support a large population of macro-arthropods. This is supported by the results of the .macrofauna counts from soil cores but, as Briggs (1960) reported, the number of arthropods trapped in pitfalls often bears no relationship to the actual population since it is dependent on activity.
There were some indications that treatments affected numbers of macro-fauna trapped, but conclusions are uncertain because of the low numbers of animals (Table 15). Certain Coleoptera were
- 161 -
Table Summary of some aclult art'7r000d :Canna collected in pitfall trans durinr7 1971.
TOTAL NO. 7 DATE OF FIRST OCCURRENCE CAUGHT
GROUP PLOT PLOT
C' H HW C H HW
CAUAnIDE 8 JULY 29 JUNE 21 MAY 5 21 5 STAPITYLINIDE 13 APRIL 26 FEB 30 YARCH 9 4 10 ELATERIDAE - 30 MARCH 16 MARCH 0 5 8
CURCULTONIDAE 30 MARCH 30 MARCH '16 MARCH 3 1 14 OTHER COLEOTTERA 16 MARCH 26 FEB 26 FEB 13 45 19
FOIThE 12 fAY 21 )TAY 29 JUNE 4 53 5 ARANEAE 26 FEB 26 FEB 26 FEB 36 47 19 DIPLOPODA 26 FEB 26 FEB 16 MARCH 8 6 22 — 162 — caught in pitfall traps earlier in the heated plots than in the control plots, and this occurred for Carabidae, Staphylinidae and other Coleoptera, but was not so obvious for Curculionidae. There was also some indication that watering the heated plots affected macroarthropods,becadberb-ardbids, elates ids and curculionids occurred in traps earlier in these plots, and staphylinids later, than in the unwatered plots.
Although the total number of individuals of most groups trapped was small, there was some indication that either the number of ants (Iasius flavus), or their activity, increased in the unwatered heated plots. More than ten times the number of ants were caught in pitfall traps in these plots, than in other plots, and it is unlikely that this difference was related to chance because numbers were nearly equal in each replicate.
(v) The effect of the treatments on the phenology of
some species of mites: Studies of the populations of arthropods have so far been discussed in relation to groups of adults (or both adults and immatures); However, the phonology of two species of oribatid mites, Platynothrus peltifer
(a 'lower oribatid') and Pelops tardus (a 'higher oribatid') and species belonging to a mesostigmatid genus (Pergamasus spp.) were also studied, although these data were not statistically analysed.
filIznaLaia...u111121.1 P. peltifer overwinters as the adult (Hartenstein, 1962a;
Block, 1965b), as the protonymph (Block, 1965b) or as the deutonymph
(Harding, 1973), and adults lay eggs from spring to autumn (Block,
1965b; Hartenstein, 1962a; Harding, 1973). According to
Block (1965b), the larvae and protonymphs reach peak numbers in - 16'3 - spring or autumn, the deutonymphs in May, and the tritonymphs in July. With some exceptions, this agrees with the findings of Harding (1973). P. peltifer is a univoltine species (Block,
1965b; Jalil, 1972).
The phenology of P. peltifer in control plots was similar to that described by Block (1965b), with peak numbers of adults in
December 1970, and possibly in September, 1972; larvae were most numerous in September, protonymphs in December, deutonymphs in May and tritonymphs in June. The larvae have a duration of about
1 month (Block, 1965b), so it is probable that most egg batches were laid in summer.
The average time between peak numbers of successive stages should give some indication of the duration of each stage
(including the quiescent period). There was some indication that
protonymphs and deutonymphs took about 3-4 months to develop, and tritonymphs about 1N months (Fig. 59). The total length of nymphal development was probably just over 8 months, and this agrees with the findings of Block (1965b), except that protonymphs in
Moor House soil took 4-5 months to develop and deutonymphs only
2 months. Phenological trends in the population of PLtsel.ti.lex in the unwatered heated plot were not so obvious because the 1972
population was adversely affected by the treatments. Adults reached
peak numbers in December 1970, and larvae, though scarce, appeared in the following autumn. it seems that protonymphs took about
3 months to develop, deutonymphs 2 months, and tritonymphs 3 months.
The total nymphal development time remained the same as in controls, although there was some indication that the time for development
(or the quiescent period) of deutonymphs was reduced, but increased for tritonymphs. - 164 - 100— o C • fiW xH
50- ADULTS 11111111 4‘,
50
LARVAE
150
otcl 100- u PROTONYMPHS (I)0 50- u. Ui 118
O
DEUTONYMPHS 50-
0 40
TRITONYMPHS
0 - 0F AJ AOOF AJ AODF 1970 1973
Fig. 59. Phenology of Platynothru's peltifer in relation to
treatment. Arrow indicates when treatment ended. - 165 -
The peak adult numbers of P. peltifer in heated soil which
was watered occurred in January 1971 and larvae also reached
peak numbers in winter. There was no information about the
duration of development in protonymphs, but deutonymphs possibly,
lived 2 months and tritonymphs l2 - 2 months. These last two
estimates are very similar to those of Block (1965b), and it is
likely that protonymphal development took 4 - 5 months. These data are difficult to interpret because the development time
for nymphs of P. peltifer in the heated plots which were watered, was similar to that observed at Moor House, and Moor House
experiences a climate resembling that of the sub-arctic (Block,
1965a; 1966b). Possibly, the effect of watering the heated
plots induced rates of drying in the soil similar to those in the
wind-blown moorland soils of Moor House, but this is only
conjecture.
Certain differences between the phenology of P. peltifer in
Garden Plots soil and at Moor House were that the larval and
nymphal peak numbers occurred about two months earlier in Garden
Plots. In all of these estimations the quiescent period was
included with the development time. Jalil (1972) determined the
actual duration of development of stages of P. peltifer at 25°C, and found that the mean duration of egg, larva, proto-, deuto- and tritonymph was 19, 14, 37, 43 and 57 days, respectively.
Jalil (1972) also suggested that Hartenstein (1962a), in his studies of P. peltifer, was mistaken in the identification of
this mite.
Some indication of the effect of the treatments on the
production of eggs in P. peltifer was provided by Dr. David Harding,
who used data from the Garden Plots experiment in a paper on the - 166 -
phenology of this species (Harding, 1973). Adult P. peltifer in
unwatered heated plots contained eggs on the 18th March, 1971;
six weeks earlier than those in control plots.
Pelops tardus
Attempts were also made to assess the phenology of Pelops
tardus, but the results were confusing. Pelops may be a bivoltine
,or multivoltine species so many phases could have overlapped;
there was also some difficulty in distinguishing the nymphal
stages at the relatively low powers of magnification used during
most of the sorting, so changes in numbers of adults, larvae and
total nymphs are given (Fig. 60).
Peaks of adults occurred in January, May and September, 1971
in control plots, but the following year no obvious peak numbers
occurred. Larvae were most abundant in the winter of 1971 and
1974 nymphs occurred in largest numbers in winter and in
autumn.
There was some indication that deutonymphs occurred in peak
numbers in May, September and February, but this observation
cannot be well substantiated.
Fewer peak numbers of adults occurred in heated plots each
year; those peak numbers which did occur usually did so in winter
or springtime, during the treatments. In the unwatered heated
plots, larvae reached maximum numbers in the spring, so it is
possible that partial desiccation increased the duration of one
or more of the stages in this mite. Peak numbers of nymphs, in
relation to treatment, were difficult to assess, but there is some
indication that partial desiccation was the main factor reducing
the numbers in heated plots. - 167- 500- oC *HW xH ADULTS 100-
X 10-
1 500 LARVAE
100-
(r) 10-- 8 cLljjE—i tn :9- 008
ODFAJAODF AJ AODF 1970 1973 Fig. 60. Phenology of Pelops tardus in relation to treatment. Arrow indicates when treatment ended. - 168 -
The numbers of adults, larvae and nymphs were all increased by heating and watering, and after treatment populations of all stages in plots which had been treated were probably larger than those in controls.
Pergamasus spp.
Phenological observations on a group of species of
Pergamasus, rather than on single species were made because no one species occurred in soil cores in sufficient number to enable a single species to be studied adequately. The results for part of the experimental period are given in Fig. 61. Adults reached peak numbers in control plots in winter 1971-72 and were fewest during the previous summer. Immatures were most abundant in,the late spring of 1971 and mid-summer of 1972 and were fewer during the winter.
The total numbers remained relatively constant in control plots throughout the experimental period (possibly because of the overlapping of several generations or cycles; Hartenstein (1962b) considered that P. crassipes had 4-5 generations a year in the field) but in the heated plots (whether water was added or not) the total numbers were markedly less. It seems likely that this effect was caused mainly by a reduction in the population of adults between the summers of 1971 and 1972.
There was some indication of the effect of treatment on
Pergamasus spp. in relation to the proportion of males to females.
The total number of adult males and females in samples from the control, the unwatered heated and the heated plots which were watered was 348, 211 and 389, respectively. In the control and unwatered heated plots nearly twice as many females as males occurred,
but in heated plots which were watered there were three times as • Ca Fq col C.) w 04 ° TOTAL NUMBERFR OM o Fig. 61..PhenologyofPergamasusspp. inrelationtotreatment. 150 100- 0 1970 ODFAJAODFAJAODF Arrow indicateswhen treatmentended.
- 169 ADULTS • oC xH HW 1973 - 170 - many females.
(vi) Some effects of the treatments on the rate
of change of numbers of arthropods: Heating without adding water changed arthropod numbers most, possibly by the effect of partial desiccation on fecundity. Commonly, the pattern of change was related to an initial increase in numbers in the winter of 1970-71, followed by a marked decline until the following winter, when the treatments ended. After the treatments ended, the numbers usually increased and, for many groups, a complete recovery in numbers occurred.
As heating without adding water generally had the greatest effect, in an attempt to quantify the effect of treatments, I have chosen for each group, specific times when the decrease or increase in numbers in these plots showed the most linear trend in the graphs (i.e. when rates of change approached an exponential form).
Comparisons of the rates of change in numbers in other plots were made in relation to these times, whether the best linear trend in the other plots occurred at these times or not. For example, a more or less linear decrease in numbers of all invertebrates in unwatered heated plots was observed between March 1971 and
September 1971 (Fig. 12). The increase afterwards was more or less linear between December 1971 and October 1972, A comparison with fluctuations in number in other plots during these times showed that decrease in numbers in the heated plots which were watered was not linear. Nevertheless, a linear trend was assumed for these times and it is hoped that an adequate indication of average differences in rates of change can be obtained.
In view of the great variaoility of the raw data in the population counts, .1 considered that more sophisticated methods - 171 - of fitting lines to the slopes in the graphs were unjustified.
Rates of chan:e of populations were calculated using the growth equation:-
rt N . N e (see p. 1 ) t o
By inthoducing logarithms, this eauation becomes:-
log Nt - log No + r./flog e and can be used to determine r, the infinitesimal rate of population increase (or decrease), of the fauna in Garden Plots. This parameter estimates the number of individuals added to the population per head per unit time (e.g. per week) and should not be confused with the finite rate of increase, which is the number of times the population multiplies in a unit of time. The finite rate of increase (usually given by X ) is the natural antilogarithm of, the infinitesimal rate of increase (Birch, 1948).
Under non-limiting environmental conditions, and for populations with a stable age distribution (two criteria probably rarely occurring in nature) the value of r becomes a constant for a given species, and is termed the intrinsic rate of natural increase.
This maximum value of r is conventionally defined as rm (Southwood,
1966; Andrewartha and Birch, 1954) and the latter authors suggested that r be reserved to signify the actual rate of increase in a population in nature.
Values of r in relation to treatment for selected groups of mesofauna were compared (Table 26a), and r represents a rate of population increase, or decrease, depending on circumstance.
Values of N and N for the times given in Table 16a may be obtained o t from App. 2.
In the columns under the heading 'population decrease' Table 16a A cora arison 'of rates of increase and decrease in DO ulations of soil mesofauna in relation to treatment POPULATION DECREASE POPULATION INCREASE GROUP DATES (rate/head/w1g) DATES (rate/head/wk) C H HW C H :! TOTAL FAUNA MAR 71 - SEPT 71 -0.030 -0.097 -0.020 DEC 71 - OCT 72 -0.002 +0.048 +0.010 ACARINA MAR 71 - DEC 71 -0.018 -0.071 -0.016 DEC 71 - OCT 72 +0.001 +0.040 +0.011 COLLEMBOLA 'APR 71 - SEPT 71 -0.066 -0.134 -0.069 SEPT 71- MAR 73 +0.021 +0.045 +0.021 OTHERS,11-(A+C) MAR 71 - SEPT 71 -0.032 -0.091 -0.071 SEPT 71- OCT 72 +0.019 1+0.041 +0.026
PROSTIG.4. HETER- -0.051 +0.024 1+0.030 OSTIG. JAN 71 - FEB 72 -0.038 -0.059 FEB 72 - MAR 73 +0.021 PROSTIGMATA APR 71 - FEB 72 -0.029 -0.033 -0.018 FEB 72 - MAR 73 +0.036 +0.032 +0.026 MESOSTIGMATA MAR 71 - SEPT 71 -0.004 -0.078 -0.018 SEPT 71- MAR 73 +0.008 +0.023 +0.000 CRYPTOSTIGMATA MAR 71 - DEC 71 +0.002 -0.045 -0.015 DEC 71 MAR 73 +0.007 1+0.022 +0.002 ASTIGMATA OCT 70 - MAR 73 +0.005 +0.017 +0.014. ONYCHIURIDAE DEC 70 - SEPT 71 -0.050 -0.08L1. -0.057 SEPT 71- MAR 73 +0.021 +0.043 +0.030 HYPOGASTRURIDAE DEC 70 - DEC 71 +0.002 -0.024 -0.017 DEC 71 - OCT 72 -0.010 +0.039 +0.024 ISOTOMIDAE APR 71 - SEPT 71 40.007 -0.090 -0.053 SEPT 71- MAR 73 +0.018 +0.035 +0.021 ENTOMOBRYIDAE JUN 7t - SEPT 71 40.049 -0.118 -0.036 SEPT 71- 0QT 72 +0.015 +0.060 +0.033 SMINTHURIDAE MAR 71 - SEPT 71 '-0.026 -0.059 -0.050 SEPT 71- MAR 73 +0.002 +0.006 +0.003 - 1";'3 -
(Table ]6a) it is seen that the rates of decrease in numbers in all groups were greatest in the unwatered heated plots. The
Collembola showed the most rapid decrease of the major groups; the Mesostigmata of the Acarina, and the Entomobryidae of the
Collembola.
Population changes are related to the sum of the birth rate and the death rate. When a population remains constant, the birth rate equals the death rate and values of r = O. A population increase gives a positive value for r, a decrease a negative value. When populations in heated plots were declining, those in controls either decreased or increased (Table 16a); decreases occurring mainly in the Acarina and increases in the Collembola.
The increase in the number of Collembola was related mainly to the increase in the number of surface-living species which are most abundant in summer.
The columns under "population increase" in Table 16a give
(except for the control plots) the rates at which the various groups recovered after the treatments ended. Possibly, at least for an initial period, the recovery of the soil fauna in the unwatered heated plots was uninhibited by lack of space and food (as has been suggested by Birch (1948) for the initial stages of build up of populations of species of arthropods which infest stored products). If this was so, the values of r in the table give some indication of the intrinsic rate of natural increase of the population (if such a statistic can legitimately be applied to a multispecific group); but this hypothesis is probably untenable, because so many factors affect natural populations of soil animals that it is difficult to imagine a truly unlimiting environment. - 174 -
The numbers of total soil animals in the unwatered heated
plots recovered at an infinitesimal rate of 0.048 per head of population per week, which means that the population doubled in just over 17 weeks. The numbers in control plots decreased slightly during this time, and in the heated plots which were watered, populations increased at a rate which would double their number in 70 weeks. Clearly, there were more factors limiting the total populations in the control and the heated plots which were watered than in the unwatered heated plots at this time and it is possible that in the latter plots there was relatively more space, more food and less predation.
The rates of increase in Acarina, Collembola and other invertebrate fauna in the unwatered heated plots were similar to those of the total fauna, but within these groups, the population growth rate was usually lower. One exception was the
Eritomobryidae, which doubled in numbers in about 12 weeks.
The initial rate of increase in an expanding population
(until density effects show) gives an estimation of the intrinsic rate of natural increase (Andrewartha and Birch, 1954), but such estimations are probably accurate only for laboratory cultures of organisms with relatively simple life cycles. The values in
Table 16a are probably best considered as giving some indication of the temper-rture and moisture conditions in which the animals can survive and multiply. These conditions are defined most precisely where r exceeds zero.
liaximum rates of population increase for some species and genera are given in Table 16b, from calculations based on times of recovery of populations in the unw,tered heated plots. These - 175 -
Table 16b increase during the recover , period in unwatered heated lots
SPECIES/GENUS DATES (rate/head/wk) Acarina Rhodacarus roseus SEPT 71 - MARCH 73 0.010 Rhodacarellus c.f. silesiacus SEPT 71 - JUNE 72 0.020 Digamasellus spp. DEC 71 - MARCH 73 0.031
Punctoribates SEPT 71 - OCT 0.026 punctum 72
Minunthozetes DEC 71 - MARCH 73 0.017 sernirufus
Oppia c.f. 0.039 c lavipectinata DEC 71 - OCT 72 Collembola Isotoma spp. DEC 71 - MARCH 73 0.047
Isotomodes SEPT 71 - MARCH 0.036 productus 73 Lepidocyrtus cyaneus DEC 71 - OCT 73 0.064 - 176 - values are the closest which can be obtained here to actual intrinsic rates of natural increase for these organisms, but they are likely to be gross underestimates, for reasons discussed earlier.
8. The spatial distribution of the fauna in the plots
The treatments could influence the spatial distribution of the soil fauna in several ways. The animals could be induced to move from a less favourable area into a more favourable one; or, if the animals were able to withstand (or unable to escape) the prevailing conditions in soil, the treatments could influence their relative abundance at a given position in the soil, by effects on natality and mortality. Any of these reactions to the treatments would result in changes in the horizontal or vertical distribution of the fauna in the soil.
(i) Horizontal Distribution: Changes in the horizontal distrioution of the soil fauna across the plots could indicate that part of the experimental design (e.g. the barriers), or the treatments had an uneven effect on the fauna within the plots. The sampling of the fauna was not random (on each sampling occasion, a series of soil cores was taken from the centre of each plot to its perimeter), but was designed so that differential effects across the plots would be detected in the analysis.
The initial horizontal distribution of the major groups of soil fauna across the plots (centre to barrier) was assessed at the start of the experiment (Table 17). There were no Table 17 The relationship between sample core position and the number of animals recovered from soil. Initial distribution within the plots on 7. x.70. GROUP MEAN NUMBER LOG (n+1) PER CORE S.E.D. 1 3 8 4 5 7 2 6 TOTAL FAUNA 2.608 245.22 25.§.(3.22.2.5225.3.1.1252.623_4 0.119 3 4 1 8 5 7 2 6 ACARINA 2.506 2 .52.4.2_,LigL?A66222....42Laz3.2.5.2 .272 0.136 1 8 3 4 2 7 5 6 COLLEMBOLA 1.771 1.767 1.66 1.664 1.643 1.598 1.588 1.393 0.132
1 2 8 6 4 7 5 3 OTHERS T(A+C)- 1.271 j tja11lkL:L21321t121L_._.126 1 .03L32422 0.156
Means are shown ranked in descending order, and the core position is indicated above each mean. Means underscored by the same line do not differ significantly (solid line P=0.05; broken line P=0.01). - 178 - significant differences between the number of animals for the total fauna, Acarina and 'other fauna' recovered from cores along the radii, but for the Collembola there were differences. It is possible that certain surface forms of Collembola could have entered the plots from outside. For instance, the barriers of the plots could have intercepted wind currents and caused the deposition of certain arthropods, including Collembola, which are carried by wind (Glick, 1939; Buahin, 1965). However, counts from sample cores indicated that differences in the horizontal distribution of both surface-living and deeper living species of Collembola occurred, although these data were not analysed statistically at this taxonomic level.
The horizontal distribution of the major groups of fauna was averaged over the whole of the experimental period (Fig. 62).
There is no indication of any consistently large bias in the distribution of the fauna across the plots, a possible exception being in relation to the distribution of 'other fauna' in the unwatered heated plots.
Some differences in the horizontal distribution of the fauna were indicated in the analysis of the data, (Table 18). Plots not represented in the table showed no differences in the distribution of the fauna within them. Although differences were detected, there were no obvious trends in the distributions.
This is difficult to interpret biologically, because if the differences were related to natural aggregations of the fnunal they should have evened out in the bulked results presented here.
The horizontal distribution of smaller groups within the
Acarina and Collembola was also analysed (Table 19) and although Fig. 62.Thehorizontal distributionofthefaunain the plots,averaged centre ofplot,position .8nearbarrier. over thewholeof the experiment.Coreposition1is near
MEAN NUMBER LOG (n + 0.8 0.9 1.0 1.1 1.2 0.7 1.6 1.5 1.9 1.7 1.8 2.0 2.0 2.1 2.5 2.6 2.2 2.2 2.3 2.5 2.3 2.4 2.4 1
2 x
CORE POSITION 3
4 - x
179 5
- ie , 6 x
7
,/x 8 COLLEMBOLA TOTAL FAUNA T- (AC) ACARINA 0 C • XH H W Table 18 Effect of core •osition on the number of arthro•ods extracted from soil - data bulked over the whole of the ex •e r2ment. 0 to ti c CD O a H CD CD 0 Cr) Cl G7 GROUP PLOT MEAN NUMBER LOG (n+1) PER CORE S.E.D.
•0 CD ,t H. "'S H. CD 1 3 4 8 7 5 2 6 O CD c+ CD 0, H. C.0 0.060 0 0" TOTAL FAUNA EW 2....._251j11.1152.1.518 2.16 2.493 2.481 2.433 2.425 I'd C3' 0 9 11 O a c+- 1 3 4 8 5 7 2 6 C) ..1 t32024.36.22t15.52.41402.1.3.03. 2.265 2.264 0.068 try 0 H. c.,) ACARINA HW 2 11.32 • tr) C3'0 ±--2• CD 1 6 8 2 1-$ 0 Qs 7 3 5 4 O 0 PO COLLEMBOLA C 1488131.2316_,..1.8ciij87121611211 1.693 0.066 CD 0 O H., Cl • 0, cp 0 H. d CD • 0 0 0 0 4;1 0 1 8 6 2 7 5 4 3 0 0 COLLEMBOLA H 1.806 1.688 1.685 1.665 1.663 1.592 0.066 11 0 (1) 1.22L4_11.215 c'D 0CITI .0 CI, 0" Fd■ 0 1-b • rte 0 Cl CD 0) CD 4 7 1 3 8 5 2 6 • .• COLLEMBOLA Hid 1.919 1.906 1.904,2.887 1.81.4_1.1.2 1.811 1.707 0.066
8 6 7 5 2 1 4 3 OTHERS T -(A C) H 1216.:L1„..252.2.z.8.1 .L..23.2. 0.896 0.849 0.847 0.795 0.078 - 181 -
Table 19 Table of significances, indicating in which plots differences in the horizontal distribution of certain soil fauna occurred. (* indicates P=0.05; ** indicates P=0.01)
PLOT C H HIM TOTAL FAUNA ACARINA C OLLEMBOLA ** ** ** OTHERS, T-(A-1-C) **
PROSTIGMATA HETEROSTIGMATA ** MESOSTIGMATA ** ** CRYPTOSTIGMATA ** AST IGMATA
ONYCHIURIDAE * ** HYPOGASTRURIDAE ** ISOTOMIDAE * ** ENT OM OBRY IDAE ** SM INTHURIDAE ** - 182 - some differences occurred, there was still no obvious trend in relation to sample core position.
Differences, over the whole of the experiment, were not confined to the treated plots, so_there was some indication that the heating was not a main factor causing these differences.
More differences occurred in the heted plots which were watered than in any other plot, so it may be that the watering had some influence on the horizontal distribution of the fauna, but the evidence is inconclusive. Thus, the results indicate that, although differences in the horizontal distribution of the fauna were detected, these differences were not strongly related to treatment, and no clear pattern was observed.
(ii) Vertical Distribution: In March and
September of 1971 (during the time of treatment) and in July 1972
(after the treatment ended), the vertical distribution of the arthropod fauna in relation to treatment was investigated using soil sectioning techniques. On each of the three sampling occasions, four soil cores (15 cm depth x 5 cm diameter) were taken from each plot and, after clipping the surface vegetation, were carefully sectioned into six layers, 0 - 1 cm, 1 - 3 cm,
3 - 5 cm, 5 - 7 cm, 7 - 9 cm and 9 - 11 cm. The soil from layers
below 11 cm depth was discarded, because too many of the cores
collapsed when further sectioning was attempted. Several samples were bulked for each treatment and depth, and the fauna was extracted from the soil using modified high-gradient Tullgren funnels.
The 0 - 1 cm layer consisted mainly of the vegetation mat and relatively little mineral soil; the deeper layers contained - '1 - maiely mineral soil, but also much plant root material.
Most of the cores held together well during the sectioning procedure (done using a fine-toothed saw with a narrow blade), but occasionally some of the cores from the unwatered heated plot tended to crumble. When this occurred all the soil in each layer was collected, but a certain amount of mixing was unavoidable.
I chose not to freeze the cores prior to sectioning (a procedure which would have made sectioning easier) because I considered that such a procedure would harm the fauna in the soil core.
The vertical distribution of selected groups of soil fauna was assessed from these samples (Fig. 63 (i xiv)).
Values plotted represent the total number of animals extracted from eight cores (i.e. the total number from both replicates of each treatment). The depth of each soil layer is given by the mean depth, for example, the 3 - 5 cm layer given ss 4 cm.
The vertical distribution of total soil fauna (Fig. 63 (i)) in the spring of 1971 was similar in all plots and treatment effects were not Obvious at this time. The general trend was for the number of animals to decrease with increasing depth of soil, at least to a depth of about 5 cm. In September of that year, effects of treatments began to occur because heating, whether water was added or not, displaced the mode of the population distribution in the soil profile from the 0 - 1 cm layer to lower layers. By the summer of 1972 (five months after the treatments ended), the total soil fauna had largely recovered, because similar patterns in their vertical distribution in the soil profile were seen in all of the plots.
Fewer soil invertebrates occurred in the 0 - 1 cm layer in Li246213)-1:1 ER + NUMB OTAL T 0.5 2 4 6 a 10 0.5 2 4 6 8 10 DEPTH (cm) DEPTH (cm) Fig. 63(i) TOTAL FAUNA (ii) ACARINA 0.5 2 4 6 8 10 0.5 2 4 6 8 10 DEPTH (cm) DEPTH (cm) Fig. 63(iii) PROSTIGMATA + (iv) MESOSTIGMATA HETEROSTIGMATA 0.5 2 4 6 8 10 0.5 2 4 8 10 DEPTH (cm) DEPTH (cm) Fig. 63(v) CRYPTOSTIGMATA (vi)' ASTIGMATA - 188 - 0.5 2 4 6 8 10 0.5 2 4 6 8 10 DEPTH (cm) DEPTH (cm) Fig. 63(vii) COLLEMBOLA (viii) ONYCHIURIDAE - 189 - 10 O C •HW •H MARCH 1971 10 10 SEPT 1971 0.5 2 4 6 8 10 0.5 2 4 6 8 10 DEPTH (cm) DEPTH (cm) Fig. 63(ix) HYPOGASTRURIDAE (x) 1SOTOMIDAE - 190 -- 03 0 oC • HW XH MARCH 1971 14 8 10 10 1 1 4 6 8 10 0.5 2 4 6 8 10 0.5 2 DEPTH (cm) DEPTH (cm) Fig. 63(xi) ENTOMOBRYIDAE (xii) SMINTHURIDAE - 191 - 0.5 2 4 6 8 10 0.5 2 4 6 8 10 DEPTH (cm) DEPTH (cm) Fig. 63(xiii) T-(A + C) (xiv) INSECTA 1q2 - the summer after the tre-tments ended than in the spring of 1971, even in controls, so the effect of the treatments on the recovery of the fauna is difficult to assess because of natural differences in the vertical distribution of the fauna in the spring and summer. Changes in the vertical distribution of the Acarina (Fig. 63 (ii)) followed similar patterns to those of the total soil fauna and these trends were also observed in the Prostigmata + Heterostigmata (Fig. 63 (iii)), to a lesser extent in the Mesostigmata (Fig. 63 (iv)), and in the Cryptostigmata (Fig. 63 (v)). In the control plots the Mesostigmata (Fig. 63 (iv)), unlike other mites, did not decrease in numbers in relation to increasing depth in the soil profile. In the spring of 1971, more mesostigmatid mites occurred in the 0 - 1 cm layer in plots which were heated than in control plots and the vertical distribution of these mites in heated plots tended to resemble that of the Prostigmata + Heterostigmata and the Cryptostigmata, in that they all decreased in number with increasing depth. The effect was not persistent because, by the autumn of that year, the population in the surface layers was reduced in heated plots to levels below that in controls. Too few Astigmata were recovered from soil cores to enable proper conclusions to be drawn on the vertical distribution of these mites, but their number in the 0 - 1 cm layer was always grester in treated plots than in control plots. It could be that heating tended to displace the mode of the profile distribution upwards into shallow layers of soil (Fig. 63 (vi)). The Collembola in control plots did not decrease in numbers - 10:3 with increasing 'depth (Fig. 63 (vii)), but the vertical distribution of Collembola is complicated by the occurrence of different life-forms. In the spring of 1971, there were more Collembola in the 0 - 1 cm layer in,treated plots than in control plots, but the long-term effect of the heating (whether water was added,or not) was to decrease the number of springtails in the upper layers of soil, as shown by the distribution in September 1971. Recovery from the effect of the treatments was probably complete by July 1972, because the vertical distribution of populations in soil which had been heated was basically similar to that in control plots. Numbers of Onychiuridae (Fig. 63 (viii)) in. the 0 - 1 cm layer in control and heated plots in the spring of 1971 were similar (unlike in the total Collembola), but in September 1971 there were no onychiurids in the 0 - 1 cm layer in treated plots. In the unwatered heated plots this effect was even more marked because none of these springtails occurred down to a depth of 5 cm. Numbers of hypogastrurid Collembola were generally too few to draw adequate indications of the effect of the treatments on their vertical distribution in soil (Fig. 63 (ix)), but there was some indication that the initial effect of the treatments was to increase their numbers in the upper layers of soil. The Isotomidae (Fig. 63 (x)) were distributed in soil in a pattern similar to that of the total Collembola, except that numbers of isotomids in the lower layers of soil in the treated plots in Spring 1971 were much fewer than those in controls. The longer term effect of the tretments was to decrease the number of isotomids in the upper layers of soil, thereby changing the mode of - 19,1 - the population distribution in the profile from the upper to the lower layers. Changes in the vertical distribution of the Entomobryidae (Fig. 63 (xi)) and the Sminthuridae (Fig. 63 (xii)) were not obvious because many of these species are surface-living forms, and also there were rather low numbers of individuals. For both of these groups, the initial effect of the treatments was to increase the number of individuals, and this resulted in an increase in the number of these springtails in the 0 - 1 cm layer. In the autumn, the population of entomobryids in the 0 - 1 cm layer in heated plots was smaller than that in control plots and no sminthurids were found in any of the cores taken at that time. Trends in the vertical distribution of the total invertebrate fauna (except mites and Collembola) were difficult to discern (Fig. 63 (xiii)) because the organisms comprising this group inhabit various levels in the soil profile. There was a reduction in the number of these organisms in the 0 - 1 cm layer in heated soil in September 1971. The effect of the treatments on the vertical distribution of total Insecta (except Collembola) was to reduce numbers in the 0 - 1 cm layer in tre-ted plot soil in autumn (Fig. 63 (xiv)). The U-shaped distribution in the profile of the insect fauna in the control plots in March 1971 was due to an underground aggregation of ants (Lasius flavus). Discussion In the long-term, the general effect of the treatments was to displace the mode of the population distribution in the soil profile to the lower soil layers. This was probably due more - 195 - to the influence of the treatments on mortality and birth rate, than by inducing vertical migrations, although a combination of these may have occurred. The Astigmata were exceptional in that there was no evidence that a downward displacement of the mode occurred; indeed, there was some indication that the mode was possibly displaced upwards to shallower layers of soil, but the number of mites recovered from the soil was small. If this effect was real, many factors could be involved. It is possible that the decreases in the populations of other fauna in the upper layers left more space and food for the Astigmata, or reduced the degree of predation in these layers. The relationship may be more direct than this, because astigmatid mites were possibly better able to survive the physical conditions prevalent in these layers than most other forms. 9. General summary of Part I 1. Initial investigations on the structure of invertebrate populations in grassland soil at Rothamsted indicated that the experimental area was representative of many grassland areas in Britain in terms of the quality and quantity of the fauna present. 2. The fauna followed an aggregated spatial distribution pattern and this resulted in a large amount of variance in the raw data obtained in sampling procedures. 3. Statistical analysis of population counts was made on transformed data, an the estimate of the error involved was obtained over the whole of the experimental period. This was thought to pruvide the most accurate allowance - 196 - for the variability of the data. 4. The fauna were extracted from soil using e modified high-gradient Tullgren funnel apparatus, and a sub- sampling technique was sometimes used during subsequent counting. 5. Certain physical conditions within the plots were assessed throughout the experiment, and a soil analysis and botanical analysis were done. 6. Changes in the spatial and temporal distribution of populations of arthropods in relation to treatment were investigated at various taxonomic levels. - X97 - ?JUT II. THE SUINEY: A STUDY OF CHANGES IN POPULATION NUMBERS OF CERTAIN FAUNA IN RELATION TO CLIMATE, IN VARIOUS PARTS OF BRITAIN. The results of a controlled field experiment summarised in Part I gave some indication of the ways in which the microarthropod populations in soil reacted to changed environmental conditions, but little information on the effects of such changes was obtained for the larger arthropods, because their number in the plots was low. The survey was initiated so that the influence of climatic changes, particularly temperature, on certain microarthropods in natural conditions could be assessed, and also so that more information on the effects of temperature on certain microarthropods could be obtained. 1. Method: Five sites were chosen, ranging from Scotland to Devon (Fig. 64). The sites were:- Kindrogan Field Centre, Perthshire. Leighton Moss Reserve, Silverdale, Lancs. University of Nottingham School of Agriculture, Sutton Bonington, Leics. Luddington Experimental Horticulture Station, Warwicks. M.A.P.F., A.D.A.S., Starcross, Devon. At each site, a Cambridge thermograph with mercury-in-steel probes was installed, the probes positioned to measure temperatures at the soil surface and at depth 5 cm. Also, a pitfall trap and a Rothamsted light trap were set up to monitor the emergence of adult insects from soil e.g. Swift moths, noctuid moths, crane flies, chafers and click beetles. - 1 98 - SILVERDALE SUTTON " BONINGTON LUDDINGTON STARCROSS Fig. 64. The distribution of the five sites in the survey. - 199 - At two-monthly intervals, 24 soil cores (each 5 cm diameter x 15 cm depth) were taken from each site and the invertebrates were extracted from 16 of these at Rothamsted using the modified Tullgren apparatus described earlier. The remaining 8 cores were used for various soil analyses and other investigations. The five its were chosen (out of a total of 29 sites inspected or discussed in correspondence) on the basis of several criteria:- 1. The site had to offer a reasonable area of relatively undisturbed 'permanent' grassland, which supported an adequate soil fauna. 2. A convenient source of electricity (to operate the light trap) was necessary. 3. An amount of assistance was required of each site operator. Initally, this meant the emptying of the light trap each day (except week-ends), the emptying of the pitfall traps and replacing the thermograph chart each week. It was intended that trap catches should be brought back to Rothamsted for sorting and counting, but some operators offered to- sort the light trap catches. Initially I took soil samples at each site personally, but later, because of economic difficulties, I was unable to visit the sites so regularly and the site operators agreed to take the soil samples for me and to send them to Rothamsted by express post. 2. Descriptions of the sites: Kindrogan Grid reference: NO 055630 - 200 - Height above sea level: 850 ft. Site organisers and operators: Mr. B.S. Brookes (Warden), Mr. A. Wood, Mrs. H. Grant. Description of the site: A general view of the site is shown in Pl. 9. The soil was of the brown earth type. The top layer was well mixed, humus stained and rooty to a depth of 10 cm, and was underlain by about 10 cm of red sandy soil. This was formed upon e considerable depth of fluvio-glacial sand and gravel. The site was flat, but well-drained, and occasionally grazed by geese. Silverdale Grid Reference: SD 476750 Height above sea level: 25 ft. Site organisers and operators: Mr. J. Wilson (Warden), Mr. J. Briggs (identified moth catches)., Description of site (see Pl. 10): The site, a paddock on carboniferous limestone, was under permanent pasture and had probably been so for many years. It was occasionally grazed by a pony. Nearby, reed beds and willow scrub were found and these were on marine clay overlayed with peat - this area was rich arable farmland until 1917, when the drainage was stopped and it was allowed to attain its present state. Sutton Bonington Grid Reference: SK 513263 Height above sea level: 150 ft. Site organisers and operators: Dr. P.W. Murphy, Mr. J.Y. Ritchie, Mrs. I. Garner (identified moth catches). -201 - Plate 9. The site at Kindrogan. Plate 10. The site at Silverdale. - 202 - Description of site (see Pl. 11): The area, known as 'Froghole Farm Paddock', was on sandy loam over Keuper Marl (Astley Hall Complex), and sloped slightly. Most of the field was well-drained, but the area of the paddock which was lowest was often very wet. Soil samples were never taken from this region. The paddock was occasionally grazed by cattle and sheep. Luddington Grid Reference: SP 167528 Height above sea level: 150 ft. Site organisers and operators: Mr. J. Ingram, Mr. E. Dennis, Mr. J.D. Whitwell (Director), Miss B. Letten, Miss M. Kendall and Miss V. Wright. Description of site (see Pl. 12): The soil type was of the Pershore series, a. mixture of coarse sandy drift and Lower Lias clay. From the site, the land sloped northwards to a height of about 180 ft. Soil cores were taken from a broad strip of grassland alongside an orchard. This area of orchard consisted of mature plum trees, grassed down, until November 1971; later, about 75% of the plum trees were replaced by young apple trees, and the area was also grassed down and mown. The paddock to the S. W. of the site was growing spring barley in 1971, and autumn wheat in 1972. Starcross Grid Reference: SX 975822 Height above sea level: 27 ft. Site organisers and operators: Mr. M.H. Davies, Mr. P.L. Mathias, Mr. R.A. Rushton. Plate 11. The site at Sutton Roningtcn. Plate 12. The site at Luddington. Descdotion of site (see Pl. 13): On the western boundary of a 3.66 acre permanent grass field which was flat and free-draining. To west of the site were laboratory buildings. The field contained some deciduous and coniferous trees, and was occasionally grazed by cattle. The layout of the thermograph and the light trap (shown in Pl. 14) was similar at each of these five sites and the pitfall was positioned about 5 yards away from these apparatuses. The light trap was set up at ground level in an attempt to attract emerging adults from the vicinity; it was thought that a trap at a greater height might attract too many insects from more distant areas. This hypothesis may have some valid foundation, but the relationship between the height of the light trap and its catch is complex (L,R. Taylor, pers. comm.). A more detailed comparision of each site, in terms of soil structure, was made during the investigation and this is summarised in Table 20. The methods used in the analyses were similar to those used in the Garden Plots experiment and need not be described again. Included in the table is a comparision of the wet and oven-dry weights of the vegetation mat in the five sites, and the figures give weights for an average mat of diameter 5 cm (representing the vegetation in a typical soil core sample unit). All of the soils were of a loam type (Table 20), but the Luddington site was unlike the others in that a greater proportion of clay was present. Luddington soil was also more compact than the others, in the upper layers (see figures for the bulk density and pore space of the 0.2 cm depth layer) and could influence -205- Plate 13. The site at Starcross. Plate 14. Standard arrangement of light trap and thermograph at each site. - 206 - Table 20 A comparison of the five sites in relation to soil structure. ANALYSIS KIN SIL S.B. LUD. ST Particle size Cr. content coarse sand -17.7 3.2 33.8 35.0 17.6 fine sand 40.6 11.2 23.0 13.6 19.2 coarse silt 6.3 15.0 6.0 1.6 11.0 fine silt 8.4 20.8 11.2 8.0 16.8 clay 12.0 20.7 17.8 31.7 20.2 (difference) 15.0 29.1 8.2 10.1 15.2 SANDY SANDY SANDY Soil class LOAM LOAM LOAM CLAY LOAM LOAM Particle density (gm/cc) 0-2 cm layer 2.13 2.05 2.30 2.30 2.28 2-7 cm layer 2.37 2.11 2.40 2.41 2.42 Bulk density (gm/cc) 0-2 cm layer 0.67 0.80 0.91 1.04 0.97 2-7 cm layer 0.97 0.95 1.34 1.28 1.28 Pore space (%) 0-2 cm layer 66.8 66.1 60.4 55.5 57.5 2-7 cm layer 59.0 55.2 44.2 46.9 47.2 Organic carbon CO 0-2 cm layer 6.6 8.0 5.3 6.1 5.9 2-7 cm layer 5.4 7.4 3.9 4.5 3.8 Soil reaction (pH) average 6.0 7.5 6.75 7.5 6.0 Vegetation mat (per core) Wet wt 11.1 8.5 8.5 8.9 7.1 Oven dry wt 5.5 3.9 4.3 5.3 4.5 the relative abundance and distribution of the soil invertebrate fauna. The upper layers of the Kindrogan soil were less bulky and more porous than those at other sites and this may be related to differences in the botanical composition of this site, compared with others (see later). The vegetation mat at Kindrogan was more plentiful than at the other sites, based on wet weight, but the difference between dry weights was smaller than might have been expected. This was possibly related to the occurrence of mosses at the Kindrogan site. The Silverdale site had the greatest organic carbon content, probably because the soils contained some peaty material. The average soil reaction was near neutral in all of the sites, the Kindrogan and Starcross soils being slightly acidic; but too few determinations of pH were made to give an adequate indication of the range of pH at each site. Detailed botanical analyses of each site were not made, because the chief requirement of a "more or less uniform area of permanent grassland" seemed to be satisfied. One exception occurred at kindrogan, where there was a more varied mixture of vegetation types, and the warden, Mr. Brian Brookes, very kindly provided me with an estimate of the relative abundance of plant species in the general area of the light trap, as follows (mosses were riot included):- - 20R Gramineae Comoositae Holcus mollis (a) Taraxacum officinale (c) Dactylis glomerata (a) Cirsium heterophyllum (o) Agrostis spp. (0) C. vulgare (r) Deschampsia caespitosa (f) Achillea millefolium (o) Poa annua (o) Senecio jacobaea (o) Festuca rubra (o) S. vulgaris (o) Agropyron repens (r) Umbelliferae Polygonaceae Aegopodium podagraria (c) Rumex spp. (c) Anthriscus sylvestris (c) Rumex acetosa (o) Conopodium majus (c) Heracleum sphondylium (r) Scrophulariaceae Onagraceae Veronica chamaedrys (o) Chamaenerion angustifolium (r) Papilionaceae Ranunculaceae Trifolium repens (c) Ranunculus acris (o) Caryophyllaceae Urticaceae Cerastium holosteoides (o) Urtica dioica (c) Where:- (a) indicates abundant, (c) common, (f) frequent, (o) occasional, (r) rare. Trees included Acer_pseudoplatanus, Tilia sp. and Quercus app. - 2O9 - 3a) The results of temperature recordings Difficulties were experienced by some site operators in running the Cambridge thermographs, most commonly in re-setting the pen arms whenever fibre-pens needed replacing. Consequently, some of the recordings (on later inspection) were inaccurate and occasionally a few days or weeks were missed when pens dried up or when the mechanical clock was not rewound. Adequate recordings of temperatures in the soil were obtained, but soil surface temperatures were sometimes not acceptable if the surface probe had been inadvertently disturbed or exposed to direct sunlight. The soil temperatures recorded by probes set at depth 5 cm at each site, are summarised as the monthly mean and the monthly range of temperatures (Fig. 65). Monthly mean temperatures were calculated as the mean of the average of daily maxima and minima (as in the Garden Plots Experiment). A comparison of overall temperatures at the five sites is given in Table 21, and in terms of overall mean soil temperatures (at depth 5 cm) for the period October 1971 to October 1972 inclusive, Kindrogan was the coldest site and Starcross the warmest. The order of sites, in terms of increasing overall mean soil temperatures was Kindrogan, Sutton Bonington, Luddington, Silverdale and Starcross. When other temperature data in the table are ranked, the order of sites changes, so comparisons of the effects of weather on populations of animals in the soil at these sites should not be considered in a simple north-south relationship. 31)) Population fluctuations at the sites : results of counts of animals extracted from soil cores Changes in the number of certain species and genera of soil - 2 10 - KINDROGAN SILVERDALE 25 25 15 15 SUTTON BONINGTON LUDDINGTON STARCROSS Fig. 65. Soil temperatures (at depth 5'cm) at the sites from October 1971-72. Abscissae indicate temperatures in °C. - 211 - Table 21. A comparison of overall temperatures at the five sites for the year October 1971-72 TEMPERATURE °0 OVERALL MAX. 1-1"‘Z. SITE t'TEA,N 1"(\NTTTLY "ONITLY MAX. MTN. MEAN T;AN- KIN 5.5 12.0 -0.5 19.0 -2.0 SIL 9.5 17.5 2.0 25.0 -3.0 SB 8.0 13.5 3.0 18.0 -1.0 LUD 9.0 17.5 2.5 23.0 -2.0 ST 10.5 17.5 3.5 22.0 -0.5 - 21? - animals common to the five sites, were recorded throughout the year October 1971-72. Two mesostigmatid mites Rhodacarus roseus and Pergamasus sop. were identified and their population fluctuation assessed (Figs. 66 (i) and (ii) respectively). Mean numbers log (n 1) per core were plotted (so the median counts are represented) with vertical bars which give the standard error of each mean. At Kindrogan, there was a possible trend in which population maxima in R. roseus occurred in autumn (Fig. 66 (0)- but at the 5,/a- level of probability (estimated by doubling the standard error on either side of the mean) few changes in numbers were significant. No differences in mean numbers of R. roseus were detected at Silverdale, but at Sutton Bonington a decrease in numbers in summer was indicated. At Luddington and Starcross populations tended to decrease in summer, although numbers of animals were low. Numbers of Pergamasus spp. (Fig. 66 (ii)) (mainly P. crassipes)remained fairly constant at Kindrogan throughout the year, but at jilverdale a steady decrease in numbers occurred, apparently independent of season. No significant differences (P = 0.05) in numbers occurred at Sutton Bonington, Luddington or Starcross during the observation period. These results indicate that changes in the abundance of these mesostigmatid mites throughout the seasons may be relatively independent of temperature (and possibly of moisture also, because these factors interact), because population trends did not follow noticeable trends in temperature change. It is possible that food became a limiting factor for these mites, but at some sites the number recovered from soil cores was too low to effectively assess populations. - 1 - Fig. 66(1) - (viii) Seasonal fluctuations in II o•ulotions of selected arthropods at the sites in the surve from October 1971-72. In each graph, the abscissa gives the mean number of animals log (n+1) recovered from each core. The standard error of each mean is indicated on each side of the mean. The site order is Kindrogan, Silverdale, Sutton Bonington, Luddington and Starcross from top to bottom in each figure. - 214 - KINDROGAN KIN 2.0- 1. 1- 1 1. 1. SILVERDALE S IL 1.51 1. 1- SB SUTTON BONINGTON 1. LUDDINGTON LUD 1.— I 1- 1- 1. STARCROSS 1- .... ST 11111111mi ODF AJ AO ODFAJ AO Fig. 66 (i) Rhodacarus roseus (ii) Pergamasus spp. - ?15 Z•0 20- KIN KIN 1 1. L 1. — 1- S IL S IL 1- 1- 1- 1- SB SB 1. 1- LUD LUD 1- 1- I 1. 1- ST ST 10- till ODFAJ AO ODF AJ AO 66(iii) Minunthozetes semirufus (iv) Oppia c.f. clavipectinata - 216 - 20- 2.0 KIN KIN 1.0- 1.0 0. 1.0 1. — S IL 0 1.5 1. SB 1.0- 1.0 _ 0 1.5 1. 1.0- LUD 1• H LUD 0 ) 1.5 1. i 1.0- 1. I— ST ST D A A 0 ODF AJ AO 66(v) Schwiebia sp. Onychiurus spp. - 2,17 - 2.0- 20- KIN 1.0- 0 0 1.0 1.0 SIL OM* 0 0 1.5 1.5 SB 1.0- 1.0- 0 1.5 1.5 LUD 1.0- 1.0- 0 0 1.5 1.5 ST 1.0- 1.0- ODF AJ AO 66 (vii) Isotomo spp. Mycetophilidae 2.18 Changes in the number of two species of oribatid mites were observed (Fig. 66 (iii) and (iv)). At Kindrogan, maximum numbers of Minunthozetes semirufus (Fig. 66 (iii)) occurred in December and a steady decrease in numbers occurred throughout the summer and into the autumn. At Silverdale, differences in numbers between sampling dates were not significant (P = 0.05); nor were seasonal trends which could be supported statistically observed at the other three sites. Few significant changes in numbers of Oppia c.f. clavipectinata (Fig. 66 (iv)) occurred et any of the sites, but there was some indication that at Sutton Bonington a decrease in numbers occurred from October 1971 to December of that year. Population changes of an astigmatid mites, Schwiebia sp. (probably S. talpa) throughout the year were also studied (Fig. 66 (v)). Peak numbers occurred at all of the sites between late autumn 1971 and early spring 1972 but this was not statistically significant at the 5% level, although at Sutton Bonington a trend was observed in which numbers gradually declined from the winter of 1971 - 72 to the autumn of 1972. It is interesting that the population of Schwiebia at Sutton Bonington followed an almost inverse trend to the changes in soil temperature at that site; when high soil temperatures were recorded, low numbers of Schwiebia occurred ana vice versa. This is perhaps surprising because the astigmatid mites in Garden Plots soil (which included Schwiebia sp.)survived the high temperatures in heated plots better than most other mites. It is unlikely that temperature, alone was a factor decreasing populations of Schwiehia at Sutton Bonington, and possibly predators may be more important. 219 - Population changes in Onychiurus spp. (Fig. 66 (vi)) (Collembola) resembled those of jchwiebia in that a decrease in numbers usually occurred in late autumn and winter time. Populations of Isotoma spp. (Fig. 66 (vii)) at Kindrogan were greatest during October in 1971 and 1972 and smallest in August 1972. A similar pattern occurred at Silverdale, though fluctuations were less marked. At Sutton Bonington, peak numbers occurred later in the year, because there was a maximum in December 1971; only low numbers occurred in June. Population fluctuations at Luddington were almost the reverse of those seen at Sutton Bonington, with peak numbers in October and in June, and low numbers in February and August, although a critical analysis of the data showed that few of the counts were significantly different (P = 0.05). At Starcross, peak numbers occurred in autumn or winter and minimum numbers in summer. Certain groups (besides Collembola} within the Insecta were also identified and counted, but in some, the numbers recovered from sample cores was small. For example, soil Hemiptera (Aphididae) were counted, and at Kindrogan and Silverdale occurred only during October of each year. At Sutton Bonington and Luddington, soil aphids were found in October and December 1971 and in August and October in 1972. But the occurrence of these insects was not spread over a longer period in the south of Britain because, at Starcross, soil aphids were found only in October of each year. Perhaps these results are not significant because the largest numbers of aphids recovered from 16 soil cores at any one time was 29; even so, the presence or absence of these animals was probably a fairly reliable indication of peak numbers, because these aphids were generally evenly distributed 720 - between the 16 bores of any one sample. Larvae of the dlateridae (click beetles) were also identified and counted because these insects are of economic interest. Population fluctuations are not summarised here because the numbers of larvae recovered from soil from Luddington and Starcross were relcitively small and they were not found at all in sample cores from Sutton Bonington. At Kindrogan and Silverdale there were click beetle larvae in samples throughout the year (October 1971 - 72) and numbers at each site did not change significantly (P = 0.05). At Luddington, elaterid larvae occurred throughout the year, except during February-April, but occurred in very low numbers. At Starcross, these larvae occurred only in February. In view of the low number of elaterid larvae at some of the sites and their absence from one of them, no valid conclusions can be drawn on the effects of soil temperatures on this group. Soil-living thrips were also counted and. Aptinothrips rufus was common to the five sites, though in low numbers in some. At Kindrogan, peak numbers of A. rufus occurred in February and in October of 1972, but none was found in December or in summer. At Silverdale, peak numbers occurred in October 1971 and A. rufus was present in very low numbers from then until June. In August and October 1972 none was found. A maximum population at Sutton Bonington occurred in October and December 1971 and in August 1972, with low numbers from February to June. At Luddington, peak numbers occurred in August and low numbers were found during the rest of the year, except in April, when no A. rufus were recovered from soil cores. Starcross soil contained the largest number of these Thysanoptera and they occurred throughout the year. - 221 - Maximum numbers were observed in October 1971 and there was a significant decrease in the population (P = 0.05) in December of that year. The population remained at the December level throughout 1972 and began to increase around October 1972, but the number in October 1972 was less than that of the previous October. Population fluctuations of larvae of Mycetophilidae (Diptera), which were relatively abundant in all of the sites, also-occurred (Fig. 66 (viii)). At Kindrogan, mycetophilid larvae occurred throughout the year, except in June, and no maximum or minimum numbers were observed (F = 0.05). A similar pattern was observed at Silverdale and Sutton Bonington, but larvae also occurred in June at these sites. At Luddington, mycetophilid larvae were not found in October (in either year) or in August, but otherwise their numbers remained fairly constant. These larvae did not occur in December at Starcross, but were present in low numbers throughout the rest of the year. There is thus some evidence that mycetophilid larvae do not have seasonal peaks of numbers, and it is probable that the overlapping of several generation, cycles, or species, in the year caused these results. 3c) Laglllap112hfla An attempt was made to study populations of leatherjackets (larvae of Tipulidae) at the five sites. In April and October 1972, samples for leatherjackets were taken by two methods:- 1. St. Ives leatherjacket extraction solution (based on orthodichlorobenzone) was used at a dosage of 2 pints/s% ft of double-strength solution (Milne et al., 1958); four 1 ft sq, random quadrats were sampled at each site. 000 2. Six 10: cm diam. x 15 cm deep soil cores were taken at random from each site. These cores were brought back to Rothamsted and tipulids were extracted using a washing technique (Ladell, 1936; Salt and Hollick, 1944). Very few leatherjackets were recovered from soil using the St. Ives method. In April, no tipulid larvae were found at Sutton Bonington, Luddington or Starcross, and only one larva was recovered from the Kindrogan and Silverdale sites. Mr. Maurice _Davies at Starcross had sampled the site for tipulid larvae in December 1971 (he took 24 5 cm diam. soil cores) and had found no larvae. He believed the absence of these dipterous larvae to be due to the exceptionally dry September of 1971, when eggs and young larvae may have desiccated. In October 1972, no tipulid larvae were recovered by the St. Ives method at any of the sites. There is therefore good indication that leatherjackets were very few at all of the sites during these investigations, because at the times of the year when the St. Ives method was used there should have been an 85A recovery of tipulid larvae (Milne et al., 1958). Counts from washed soil cores were no better. From the Kindrogan samples taken in April, two leatherjackets were recovered, and at Silverdale only one. None was found in soil from the other sites. The cores taken in October also contained too few leatherjackets to enable site comparisons to be made. All of the leatherjackets found in October (four from the total five sites) were early instar larvae, as might be expected (Laughlin, 1967). The low number of tipulid larvae extracted from soil in the Tuligren apparatus gave supporting evidence that populations of these larvae at the sites were small (although the Tullgren - 223 - apparatus is not the most efficient method of obtaining leatherjackets from soil). From a total of 112 soil cores (diam. 5 cm x 15 cm deep) taken from each site, only one tipulid larva was found (in soil from Kindrogan). 3d) The results of pitfall trapping The pitfall traps did not give good indication of the times of first occurrence of species of ground-crawling adult arthropods because the number of individuals caught were too few to give reliable estimates. More valuable results would have been obtained if more pitfalls had been set up, and it was intended that the survey should later be expanded, but travelling restrictions eventually precluded this. Hence the results of pitfall trapping were inadequate, at least for the Silverdale and Luddington sites. At Kindrogan, the carabid beetle Feronia madida first occurred as adults in the trap in May 1972, whereas at Starcross this species was caught in March of that year. At Sutton Bonington, however, F. madida did not occur until July. A related speciesIF. melanarivas caught as the adult at all three sites in July, although one adult specimen of F. melanaria occurred in the trap at dtarcross in January. However, few individuals of these beetles were trapped, so the dates given may not relate closely to their times of first activity as adults. Because of the small numbers of any one species trapped, the only meaningful results are obtained by considering groups of animals instead of individual species. Maximum numbers of adult Carabidae (Fig. 67 (i)) occurred between June and September at Kindrogan and in June at Sutton Bonington. aeveral peak catches occurred at Starcross (in January (i) CARABIDAE (ii) STAPHYLINIDAE BER + OTHER COLEOPTERA (iv) COLEOPTERA LARVAE 100-z AL NUM OT T J MMJ S N J M M S N Fig. 67 (i-iv). Fluctuations in numbers of Coleoptera caught in pitfall traps at three of the sites .- Kindrogan (full circles), Sutton Bonington (open circles), Starcross (crosses). - 225 - May, July and in autumn) but because the number of carabids trapped was small, indications of times of maximum activity and numbers were possibly unreliable. Staphylinids were caught in maximum numbers from June to September at all three sites (Fig. 67 (ii)), Maximum numbers of "other Coleoptera" (mainly Chrysomelidae and Curculionidae) were trapped from August to late autumn at Kindrogan and Sutton Bonington. At Starcross the peak number was in April and October (Fig. 67 (iii)). Peaks of beetle larvae (mainly of Carabidae and Staphylinidae (Fig. 67 (iv)) were observed at Kindrogan in February and in October. Minimum numbers were trapped in August, a time when relatively large numbers of the adults were trapped at this site. A similar pattern did not occur at Sutton Bonington, because maximum numbers of larvae were found in June; smallest numbers were trapped from March to May and in October. It is possible that cycles of activity and/or numbers at Kindrogan and at Sutton Bonington were out of phase with each other; those at the latter site occurring in advance of those at Kindrogan. Cycles of maximum trap catches of larvae at Starcross were probably intermediate between those at Kindrogan and Sutton Bonington. The overall results of pitfall trapping indicated that there were possibly differences between times of maximum and minimum activity and numbers of certain insects at the three sites, and this was most marked in larvae of staphylinid and carabid beetles. However, these differences did not readily relate to differences in soil temperatures recorded at the sites. p 3e) The vertical distribution of the soil fauna The vertical distributions of the fauna at the survey sites were investigated in October 1971 and in December 1971. Soil cores taken in October and December were sectioned in exactly the same way as the cores in the Garden Plots Experiment. In the October samples, the whole of the fauna was sorted into various taxa and counted so that a preliminary comparison of the sites could be made. In December, only certain genera and species of arthropods common to all sites were counted, in an attempt to make a more detailed comparison of specific differences in vertical distributions in soil. Initial comparisons of the sites In October the total invertebrate fauna (Fig. 68 (1)) was most abundant in the 0 - 1 cm layer at each site, and there was a tendency for numbers to decrease with increasing depth in the soil profile for most sites. Kindrogan and Starcross soils contained the largest number of animals, with a geometric decrease in numbers with increasing depth; the remaining sites contained fewer animals but their distribution in the soil profile was basically similar. The Acarina (Fig. 68 (ii)) were distributed vertically in soil in a way similar to that of the total soil fauna. The Collembola were not similarly distributed in the soil profile (Fig. 68 (iii)) at all sites. At Luddington and Starcross there was a geometric decrease in numbers with increasing depth in the soil, but at Kindrogan, Silverdale and Sutton Bonington, the mode of the population distriouticn was not in the uppermost layer. At ,3ilverdale the general trend was for numbers to increase with increasing depth, even though the same dominant groups of Collembola - 227 - Fig. 68 (i_x). The vertical distribution in soil of certain groins of soil fauna at the sites in October 1971. In each graph, the abscissa gives the total number of animals recovered from eight soil cores (diam. 5cm), and the depth layer is represented by the mean depth of that layer. - 228 - 1000 KINDROGAN 1000 KIN 500 0 500 500 S IL 0 0 500-i SUTTON BONINGTON 500 SB S E OR 0 0 SOIL C 8 LUD 500 LUDDINGTON 500 OM FR R BE 0 0 NUM AL STARCROSS 1000 ST OT 1000 T 500 500 0 0 0.5 2 4 6 8 --10' 052 4 6 10 DEPTH (cm) DEPTH (cm) Fig. 68 (i) TOTAL FAUNA (ii) ACARINA — 229 — 150 150 KIN 100 100 50 50 0 0 150 150 100 100 SIL 50 50 0 0 100 SB 100 SB V) 50 50 ce 0 0 0 2 250 250 co 0 200 200 ce 150 150 100 100 50 50 0 0 0 150 150 100 ST 100 ST 50 50 0 0 0.5 2 4 6 8 10 a5 2 4 5 8 10 Depth (cm) Depth (cm) 68 (iii) COLLEMBOLA (iv) T-(A + C) — 2 3 0 — 150 150- 10 100- S IL S IL 50- 0 1 t (r) 100 100 00 - 5 SB 0 so SB 0 0 03 2 100 LUD 100] I I La: z- 50 i0 50 0 0 1 I 1 150 150- 100 100- ST ST 50 50- 0 Oil I I I I 08 2 4 6 10 05 2 4 6 8 10 Depth (cm) Depth (cm) 68 (v) PROSTIGMATA + (vi) MESOSTIGMATA HETEROSTIGMATA' TOTALNUM BERF ROM 8SO IL CORES 68 (vii) CRYPTOSTIGMATA 400 600 200 200 200 0 0 0 0 05 246810 Depth (cm) KIN S IL ST — 231 100 40 40 60 80 20 40 40 60 20 0 0 0 0 0.5 246810 (viii) ASTIGMATA Depth (cm) S IL SB LUD ST TOTAL NUMBERF ROM 8S OIL CORES 68 (ix)ONYCHIURIDAE 50 0 52 46 Depth (cm) ST — 232 10 50 (x) ISOTOHIDAE 0.5 24 Depth (cm) ST 6 810 (the unychiuridae snd isotomidae) ,Aich occurred at the other sites also occurred here. This difference in the vertical distribution may have been related to the relative abundance of organic matter in the deeper layers of soil at Silverdale (Table 20), on which the Collembola may feed. At all sites, except Sutton Bonington, there was a decrease in numbers of all invertebrates (other than mites and Collembola) with increasing depth in soil (Fig. 68 (iv)), but at Sutton Bonington a similar pattern did not occur because relatively large numbers of nematodes occurred in the deeper layers of soil. Of the mites, the Prostigmata # Heterostigmata (Fig. 68 (v)) did not markedly decrease in number with depth in the soil at any of the sites. The Nesostigmata (Fig. 68 (vi)) decreased in number with increasing depth at most sites, but at Sutton Bonington the mode of the distribution was at a depth of 4 cm. This difference in the vertical distrioution pattern was possibly related -to the greatest numbers of nematodes (on which the Mesostigmata may feed) at this depth (Fig. 68 (iv)). The Cryptostigmata decreased in number with increasing depth at all sites, (Fig. 68 (vii)) but very few of these mites were recovered from soil cores from Silverdale. The Silverdale results are surprising, because it is unusual for the Cryptostigmata to be poorely represented in most grassland soils which have been studied, and no indication of low numbers of oribatid mites at Silverdale could be forecast from the counts of hinunthozetes ssmirufus and Oppia c.f. clavipectinata in October 1971, described earlier. Astigmata were distributed in the soil profile of each site in a similar way to the Acarina as a whole (Fig. 68 (viii)). - 23h - Of the Collembola, the jnychiuridae did not decrease in number with increasing depth in soil.(Fig. 68 (ix)) and their distribution in the soil profile differed with the site. Possibly the distribution offood_was an important factor governing the vertical distribution of these springtails, and the occurrence of relatively large numbers of onychiurids at a depth of 4 cm in soil at Sutton Bonington might be related to the abundance of nematodes at that depth. Isotomid Collembola at Kindrogan, Luddington and Starcross decreased in abundance proportionally with depth in the soil (Fig. 68 (x)). At Silverdale and. 3utton Bonington, however, their distribution was more or less uniform throughout the 10 cm depth of soil and this was probably related to the low numbers of Isotoma sensibilis and 1. notabilis in the upper layers of soil at these sites. Changes in the vertical distribution of certain soil arthropods in autumn and winter The vertical distribution of certain genera and species of mites and Collembola were investigated in October and December 1971, (Fig. 69 (i vii). Changes in the distribution of Rhodacarus roseus (Mesostigmata:Rhodacaridae) occurred in the soil profile (Fig. 69 (i)). At Kindrogan, the mode of the population distribution was in the 1 - 3 cm layer in autumn, but in winter the mode occurred in the 3 - 5 cm layer, although differences between numbers in different soil layers in winter were small. Probably this change was rel-ited to the low temperature in the surface layers of soil in December, which could have influenced the population size through effects on fecundity, mortality or - 235 - Fig. 69 (i - vii) C1259m2siELLtheyertical. distribution of selected species and genera of soil arthropods at the sites in autumn and winter. In each graph, the abscissa gives the total number of animals recovered from eight soil cores (diem 5 Cm), and the depth layer is represented by the mean depth of that layer. — 236 — 60 SUTTON BONINGTON to 40 0 0 —3 i•-1 C) U) 20 CO 0 LL Lei ca LUDDINGTON —3 0 Depth (cm) Depth (cm) Fig. 69 (i) RHODACARUS (ii) RHODACARELLUS ROSEUS SILESIACUS - 237 - 20 KIN 150 100 0 50 0 S IL 15 SIL S E 100 OR 50 0 L C SOI 0 50 8 SB OM 100 4 FR SB 3 BER UM N 20 AL 100 10 TOT LUD 0 0 20 LUD 20 ST 0 Depth (cm) Depth (cm) 69 (iii) MINUNTHOZETES (iv) OPPIA c.f. SEMIRUFUS CLAVIPECTINATA - 238 - S IL 0 450 SB u.) 40 s-4 300 00 200 LU X7. 100 100 ST 0 05 2 6 8 10 Depth (cm) 69 (v) SCHWIEBIA sp. — 239 — 75 75 KIN KIN 50 50 25 25 0 0 75 75 SIL 50 50 25 2 0 0 SB 50 SB ES 50 OR C IL SO 8 FROM ER B UM AL N TOT ST 50 ST 0.5 2 4 6 8 10 0.52 4 6 8 10 Depth (cm) Depth (cm) 69 (vi) ONYCHIURUS spp. (vii) ISOTOMA spp. - 240 - migration. Silverdale, a similar relationship did not occur, but numbers of t. roseus were small throughout the profile. Little seasonal infuence on vertical distribution of these mites at Sutton Bonington was observed, although the mode of the population distribution in the soil profile was at a greater depth in autumn than in winter (in the 1 - 3 cm layer in winter, but in the 3 - 5 cm layer in autumn). At Luddington there were no differences in the vertical distribution of R. roseus in relation to season, and numbers generally increased with increasing depth in the soil. At Stareross, R. roseus occurred only in the 7 - 9 cm layer in autumn, but there were more mites in December and then they were evenly distributed in the profile, from a depth of 1 cm to about 9 cm. The vertical distribution of another rhodacarid mite, hhodacarellus silesiacus, was studied at each site (Fig. 69 (ii)). At Kindrogan the number of individuals recovered from soil cores was too small to give good indication of the distribution of R. silesiacus in the profile, although the mode of the population distribution was probably at a greater depth than 3 cm in both autumn and winter. Maximum numbers of R. silesiacus were found at 10 cm depth in autumn at Silverdale, but in winter the mode was at depth of 4 cm. R. silesiacus was more abundant in autumn than in winter at Sutton Bonington and at Luddington, and winter populations at both sites were fairly evenly distributed throughout the soil profiles. In autumn, at Sutton Bonington, most of these rhodacarids occurred at a depth of 4 cm; at Luddington, peak numbers were noted from several depths, but the overall trend was for numbers to increase proportionally with depth. The population of R. silesiacus at Starcross and its distribution pattern in the soil profile was similar in both autumn and winter, and there - 241 W2S an obvious trend in which numbers increased with depth, down to the 7 - 9 cm layer. At hindrogan, few individuals of Minunthozetes semirufus occurred in winter in the upper layers of soil (Fig. 69 (iii)); most were found in the 1 - 3 cm layer. More individuals of M. semirufus were found in autumn when the mode of the population distribution in the profile was in the 0 - 1 cm layer. This provides further evidence that the relatively cold winter at Kindroan restricted increases in numbers of certain soil fauna in the upper layers of soil, because at Silverdale, where soil temper-Itured were less extreme in winter (Fig. 65), an abundance of M. semirufus occurred in the upper layers. The very small population in autumn was perhaps unexpected, but may have been due to moisture conditions. At Sutton Bonington maximum numbers of M. semirufus occurred in autumn and minimum numbers in winter. This difference cannot be related to differences in temperature at the sites, because the mean soil temperature in October was about 800 and in December about 50C (Fig. 65) at both sites. Possibly the phenology of M. semirufus was out of phase at the two sites, and local moisture conditions in soil may have been of major influence. The numbers of M. semirufus at Luddington were too few in autumn and winter to enable many conclusions on the distribution of these mites in the soil profile to be made, but M. semirufus. occurred only in the 0 - 1 cm layer. Possibly, peak numbers occurred in April at Luddington, and the vertical distribution of these mites was investigated at times of minimum numbers. At Starcross, numbers of M. semirufus decreased with increasing depth, both in autumn and winter, and very few individuals were found at depths greater than about 3 cm. -242 - At Kindrogan, Silverdale, Sutton Bonington and Luddington, a distribution basically similar to that of M. semirufus was observed for Onpia c.f. clavipectinata at each site (Fig. 69 (iv)), although populations were very different. At Sutton Bonington, ■•■ large numbers of 0. c.f. clavipectinata occurred in the 0 - 1 cm layer of soil in autumn, but few occurred in that layer in winter. There was some indication that numbers of 0. c.f. clavipectinata in winter increased with increasing depth in the soil at Sutton Bonington (though numbers of individuals were small) and if this was real, the vertical distribution pattern in the soil profile in winter was the reverse of that observed in autumn. The reason for this difference is obscure, because similar trends were not seen at Silverdale, where the mean soil temperatures were similar to those at Sutton Bonington. Possibly, the water status of these soils influenced numbers more. Few individuals of 0. c.f. clavipectinata occurred at Starcross, so there is no information on their vertical distribution. Probably, maximum numbers of 0. c.f. clavipectinata, like those of M. semirufus, occurred in April at Starcross. Few individuals of Schwiebia sp. (Astigmata) (Fig. 69 (v)) were found in autumn or in winter at Kindrogan, but in autumn most of them were found in the 0 - 1 cm layer of soil. A similar pattern occurred in autumn at Silverdale and there was some evidence that in winter the mode of the population distribution was displaced to the deeper layers of soil. At Sutton Bonington, however, the distribution patterns in soil were similar in autumn and winter, although the winter population of Schwiebia sp. was much larger than that in autumn. Very few individuals were recovered from Luddington and Starcross soils in autumn and winter, but there was - 2 4 3 - some indication that at Luddington, the maximum population in the upper layers in autumn was displaced to deeper layers in winter. It was not possible to study the vertical distribution of individual species of Collembola in soil, because no one species occurred in sufficient number at all of the sites to enable comparisons to be made. Instead, changes in numbers of two genera, Onychiurus spp. and Isotoma spp. were investigated. Many of the onychiurid Collembola belonged to the O. armatus group and some were O. fimetarius; the isotomids were mainly 1. notabilis and I. sensibilis but probably some I . olivacea-violacea, especially immatures, were also included in the counts. The distribution at I%-indrogan of Onychiurus spp. (Fig. 69 (vi)) was similar in both seasons and most onychiurids probably occurred between 1 and 5 cm depth. At Silverdale, numbers of onychiurids remained fairly constant throughout the soil profile in winter, but in autumn there was a tendency for numbers to increase with increasing depth in soil. At Sutton BOnington, most onychiurids occurred at a depth of about 4 cm in autumn, but in winter the mode was at a depth of 10 cm, although the number recovered from the Sutton Bonington soil was low. Maximum numbers of Onychiurus spp. occurred at Luddington in the 1 - 3 em depth Dyer in autumn and in winter. At Starcross, most onychiurids occurred in the 0 - 1 cm layer in autumn and in the 1 - 3 cm layer in winter. According to Cisin (1943), Isotomn spp. probably occur in greatest numbers in the upper layers of soil, and this trend was observed in the sites of the survey (Fig. 69 (vii)). At Kindrogan, most Isotoma spp. occurred in the top 3 cm of soil in autumn and in winter_, but the v,inter population Nils smell. At Silverdale and Sutton Bonington, fewer isotomids occurred and their vertical distribution in soil was less distinct, but there was some indication that individuals were found in the upper layers of soil. Isotoma spp. were most abundant at Luddington in the 0 - 1 cm layer of soil in autumn, but in winter the mode of the population distribution in the profile was displaced to the 1 - 3 cm layer. Similar patterns were observed at Stareross, though the numbers of individuals were less. It seems from these studies that the distribution pattern of certain species and genera of mites and Collembola change in relation to season. At Kindrogan, and possibly at other sites, low winter temperatures probably induced a downward displacement of the mode of the population distribution in the soil profile; but temperature alone was unlikely to be the cause of some of the changes in the distribution pattern, because changes at one site were often not confirmed at another site which had similar temperature conditions. Kindrogan was the only site at which a mean temperature (in soil at depth 5 cm) of 2,5°C was found in winter (Fig. 65), and the other sites had mean temperatures of 5°C or more at that time. It is possible that differences in the water status of soil at the various sites was of major importance in determining vertical distribu-cion patterns, but changes in the distribution of food and pred,Dtors may also be important. 3f) The results of li:,7ht trapping A lare number of animals were caught in the light traps, but most of the species bore little relptionship to the soil fauna. Only the Lepidoptera were identified and counted. - 245 - Of .the Lepidoptera, some species can be considered as transient members of the soil fauna. t'hese include ,‘th larval and pupal stages which overwinter in a more or less passive, state. tither lepidopterous larvae can be more active in soil, and feed on plant roots, (Wallwork, 1970). Such active forms include cutworms (larvae of certain Noctuidee) and the larvae of swift moths (Hepialidae) and may be considered as temporary members of the soil community. It was intended that the light trap at each site should provide evidence of the relative times of adult emergence of certain Lepidoptera which pass their larval and pupal stages in soil, and there is good evidence that many species of moths caught in light traps are caught as young adults i.e. before they are sexually mature (Johnson, 1960, 1963; Macaulay, 1972). Before the results of the light trapping are discussed, a comparison of the sites in terms of factors which may have influenced the catches is necessary. One way of relating a Lepidoptera population to environmental charues is provided by the index of diversity, a , derived from the log-series by Fisher, Corbet and Williams (1943), but generally attributed to Williams in the context of a diversity discriminant. Williams' a is independent of sample size and of the attraction factor which affects the size of light trap samples from different sites (See Taylor, 1973). Taylor stated that 20=A of the variance of a between sites is related to the site latitude, and a further 20=A from land-use immediately adjacent to the trap (Taylor, 1973). The area around the trap showing the closest relationship to diversity was 1.34 ha (i.e. a circle of radius 64.4 metres, centred on the trap), - 246 - which indicates the small area sampled by a light trap. The five sites in terms of land-use were compared (Fig. 70) (figures in brackets for each site give the land-use index). The scoring system making up this index is based on that of Taylor (1973), in which different categories of land-use were given weightings, as follows:- Category We Buildings, roads, water 0 Arable, grassland 2 Gardens, waste 3 Woodland, orchards 6 Hedgerows 29 The land-use index was obtained for each site by determining the relative size (percentage occurrence) of each of the above categories within the light trap area (a circle of radius 1 in drawn on a map of scale 25 in to the mile) and these percentages were multiplied by the appropriate weightings and summed to give the total land-use index. Percentage occurrence of each category was determined by weighing cut-out portions of the mapjcopied onto high-quality paper) using an Oertling balance. Williams' index of diversity, a , was here used to describe the relationship between the number of species and the number of individuals of Macrolepidoptera caught in each light trap. Moth catches at the sites for 1972, indices of diversity and their standard errors for the Macrolepidoptera, and also the land-use index for each site were compared (Table 22) and a was determined using the computer programme presently in use by the Hothamsted Insect Survey. - 247 - KINDROGAN SILVERDALE (198)- (279) SUTTON BONINGTON LUDDINGTON (285) (395) KEY BUILDINGS & ROADS ARABLE PERMANENT PASTURE ORCHARDS & WOODLAND GARDENS & WASTE HEDGEROWS LIGHT TRAP STARCROSS (189) Fig. 70. A comparison of the Survey sites in relation to land use within a 64.4 m radius of the light trap. - 248 - Table 22. A comnrison of moth catches at the sites for the year 1972. (11ie la.nd-use index is given in brackets under each site-name). NU',IBER OF NUMBER SITE GROUP INDIVIDUALS OF SPECIES 4-— SE KIN mAcRoLEPID. 2473 135 30.7 + 3.0 (1 98 ) MICROLEPTD. 582 6 (IN PART) SIL MACROLEPID. 1371 149 142.5 + 4.1 (279) MICROLEPID. 1071 10 (IN PART) SD MACROLEPID. 2353 104 22.3 + 2.5 (285) MICROLEPID. 3723 6 (IN PART) LUD MACROLEPID. 2475 131 29.5 + 2.9 (395) MICROL7PID. 4743 10 (IN PART) ST MACROLEPID. 1301 121 32.6 4. 3.5 (189) - MICROLEPID. 2154 13 (IN PART) - 21[9 - Indices of diversaty and the land-use indices are given here as a means of comparing the nature of the environment of the light trap at each site. When many sites are considered, a increases with increasing land-use index (Taylor, 1973), but this trend was not observed because the five sites in the survey were too few. Luddington had the highest land-use index and Starcross the lowest, but at Silverdale there was the greatest diversity of Macrolepidoptera and at Sutton Bonington the least. In terms of both Williams' a and the land-use index, Kindrogan and Starcross were closely related sites, but there were very few Crambinae (Microlepidoptera) at iindrogan, compared with other sites. Of the many species of Macrolepidoptera identified from each site, only twenty-seven were common to all. Fifteen of the species belonged to the Noctuidae, ten to the Geometridae, one to the Arctiidae and one to the Notodontidae (Table 23). Most of the moths (especially the noctuids) occur in soil as eggs, larvae or pupae, although some (mainly the geometrids) occur as immatures only at the soil surface or on vegetation (South, 1961). Of the Microlepidoptera which were identified, three species were common to all sites, Agriphila culmellus, A. tristellum and Crambus hortuellus and all of these moths belong to the Pyralidae. The times of first appearance in traps of adult Noctuidae and Geometridae common to all sites was summarised (Fig. 71 (i) and (ii)). The cumulative appearance of the moths is plotted in each graph so the order of species from left to right in each graph is not necessarily the same for each site. The cumulative appearance of the noctuids followed a similar pattern (which may he represented by an S-shaped curve) at each - 250 - Table 23 Mccrolepidoptera common to the five sites in the curve . The probable overwintering stage is indicated in brackets next to each species name, E = egg, L = larvae, P = pupae. SPECIES SPECIES NOCTUIDAE GEOMETRIDAE Agrotis exclamationis (L) Colotois pennaria (E) Allophyes oxyacanthae (E) Crocallis elinguaria (E) Amathes xanthographa (L) Dysstroma truncata (L) Amphipyra tragopoginis (E) Epirrhoe alternata (p) Apamea monoglypha (L) Lygris pyraliata (E) A. secalis (L) Operophtera brumata (E) Diarsia mendica (L) Opisthograptis luteolata (L or P) D. rubi (L) Selenia bilunaria (p) Gortyna micacea (E) Xanthorhoe fluctuata (p) Hypena proboscidalis (E) X. montanata (L) Leucania impura (L) Noctua pronuba (L) ARCTIIDAE Ochropleura plecta (L) Spilosoma lubricipeda (p) Orthosia gothica (P) Procus fasciuncula NOTODONTIDAE Lophopteryx capucina (P) - 251 - 15 10 5 0 15 S ILVERDALE 10 10 5 5 a cl 0 0 • • 15 C LII Li'.4 10 SUTTON CD 5 BONINGTON g 0 Lr (.3,t- 15 >I I 10 LUDDINGTON 15 10 STARCROSS 0 - 0 M J S N MMJS MONTH MONTH Fig. 71. The times of first appearance in light traps of species of (i) Noctuidae and (ii) Geometridae, common to all sites. - 252 - site and the dotted line is meant to represent the slope of the straight part of the curve and relate to that period during which the appearance of the new species of moths in traps was most rapid. The slope of each line may indicate the relative rate of emergence of species of noctuids at each site (although the size of the population may also influence the time of first appearance of a given species in a trap), and if so, it is meaningful to compare these slopes with environmental factors, such as temperature, at each site. During the time which each slope covers, the mean soil temperature (at depth 5 cm) at each site, estimated from Fig. 65, was as follows:- o Kindrogan 120C Luddington 15 C o Silverdate 15 C Starcross 15.75 C Sutton Bonington 12.5°C. Banking the sites in order of increasing mean temperature gives:- Kindrogan < Sutton Bonington < Silverdale = Luddington-< Starcross. when the sites are ranked in order of decreasing rates of appearance of noctuid moths (indicated by the slopes in Fig. 71 (1)), the order of sites is similar to that in terms of increasing temperature, except that Luddington is placed before Silverdale. This is circumstantial evidence that soil temperatures influenced the date of emergence of these noctuids from soil. The onset of emergence at Kindrogan was in late June, and o the mean soil temperature was about 10 C (see Fig. 65). At other sites, the rapid emergence began earlier (sometimes in May), — 25'3 0, but also when the mean soil temperatures were about 10 C. Therefore, it is likely that an.earlier emergence of noctuids at Kindrogan was inhibited by the relatively low temperature in soil (about 7°C) in May. The cumulative appearance of geometrid moths in relation to time followed a similar curve (Fig. 71 (ii)) but was somewhat flattened, and it was difficult to detect times when rates of appearance were maximal. This may, in part, be related to the few species common to all sites, but it is also possible that the weaker association with the soil that is shown by the Geometridae (compared with the Fioctuidae) meant that the immature geometrids were possibly influenced_ more by soil surface or air temperatures than by those in soil. Surface or air temperatures fluctuate more than those in soil, and also the environment outside soil is generally more heterogeneous than in soil, so it is not surprising that the emergence of adult geometrids seemed to be less synchronised than that of the noctuid moths. Even so, at Kindrogan, most of the geometrids appeared in July, whereas at other sites an earlier emergence, or an emergence over a longer period occurred. The Lepidoptera of economic importance are the cutworms, and the number of individuals of certain species caught, their times of first appearance and of median occurrence in light traps at the sites were compared (Table 24). The times of median occurrence of moths in light traps were used in preference to the times when maximum numbers were caught, because it was considered that the former gave a more stable indication of the average times of seasonal flight activiy than the latter. Agrotis exclamationis was trapped at Starcross earlier in the year than at the other sites and this species was caught later in the season at kindrogan. The difference between times of first Tnble 0,1 A comparison of catches of moths of possible economic interest at the sites in the survey SPECIES YINDROGAN SILVERDALE SUTTON 110NINGTON LUDDINGTON STARCPOSS 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 ; Agrotis exclamationis 30/6 30/6 1 18/6 15/7 9 25/6 21/7 86 13/6 22/7 211 6/6 16/7 21 A. sr,7etum 7/7 13/7 4 25/6 15/7 23 Apamea secnlis 15/10 15/10 1 16/7 17/7 7 25/7 19/8 66 31/7 13/8 11 4/8 17/8 A. sordens 2/6 11/7 4 4/7 6/7 2 21/6 29/6 2 Cerapteryx ,7raminis 28/7 8/8 13 7/8 7/8 1 23/8 23/8 1 Dinteraxin olerncea 111/7 18/7 25 5/6 19/7 7 Pucl.-esis comes 22/8 31/8 16/9 16/c) 1 Gortynn micncea 12/8 1/10 188 8/2. 12/9 23 7/9 28/9 12 6/8 1/10 9 1/9 30/9 26 Lurerina testncen 12/8 22/8 12 3/8 3/9 43 31/7 31/8 96 14/8 6/9 23 Melanchra persicari ae 4/8 4/8 1 17/7 26/7 4 16/7 18/7 11 Procus stri7jlis 30/6 14/7 6 14/7 23/7 25 21/6 15/7 13 Hepialus lunulina 26/5. 29/5 4 29/5 15/6 407 21/5 10/6 291 27/5 22/6 190 A7riphiln culmellus 19/7 28/7 24 13/7 20/7 376 15/7 7/8 1519 16/7 5/8 1265 16/7 5/8 402 A. tristellus 19/7 6/8 59 7/7 8/8 90 26/7 19/8 70 23/7 12/8 261 28/7 9/8 110 Crambus bortuellus 14/7 15/7 4 11/6 18/7 408 25/6 21/7 1082 21/6 21/7 1821 20/6 24/7 1235 C. perlellus 22/7 29/7 2 3/7 29/7 1028 2/7 25/7 1134 12/7 28/7 249 Kev: 1= time of first appearance Of moth in light trap (day/month) 2= time of median occurrence: (day/month) 3= total number if individuals trapped - 755 - cetcees at z3tarcross and c-incrocan was juFt three; weeks, but comoarisons of these catches as indications of times of emerence are not really valid, because only one individual was caught at /4ndrogan. idfferences between times of appearance may eually relate to differences in the populations (and thereby the relative chance of an individual being trapped) at the two sites. A. segetum was caught in light traps only at Sutton Bonington and Luddington in 1972, so comparison of catches between these sites cannot be made. Apamea secalis was trapped at all sites, but only one individual was caught at kindrogan. Southwards from Silverdale, the times of first appearance of A. secalis became progressively later in the year, but this trend was not reflected in the times of median occurrence of these moths, and a reduction in the length of the total flight period of moths in northerly latitudes was indicated. The noctuid Gortyna micacea was also found at all sites, and in relatively large numbers at kindrogan (Table 24). However, no consistent trend in times of first occurrence was detected in relation to site position, or in terms of temperatures recorded there. Crambus hortuellus and C. perlellus were first caught in traps in June and July, respectively, at most sites; one exception being at Kindrogan where very small numbers of C. hortuellus were trapped in July. The time of median occurrence was in July for both species, but that of C. perlellus was somewhat later than that of C. hortuellus, and approximately in proportion to the later times of first occurrence of C. pr,rlellus. Moths differed in their times of appearance and median occurrence in light traps. These differences were difficult to relate to environmental factors, because the interpretation of the 7r. trap catches was confused by the low n;mbers of individuals of some species at certain sites. Nevertheless, there seems little doubt that, at least for the noctuids (Fig. 71 (i)), the lower temperatures at Kindrogan could have delayed the emergence of adult moths at this site; and ttere was also some indic tion that the rate of emergence of the majority of the noctuids (common to all sites) at .Lindrogan was greater than that of noctlids at more southerly sites. This latter point would seem to indicate that environmental conditions under which the emergence of adult noctuids occurs were limited to a shorter period at Kindrogan than at more southerly sites, probably due to the more extreme conditions in soil at Kindrogan. General summary of Part II. 1. The survey was an investigation of the influence of soil temperature on populations of certain macro- and microarthropods in nature. 2. Five sites were chosen for study, ranging from Scotland to Devon, 3. At each site, fluctuations in numbers of certain soil arthropods were investigated, and a comparison was made of their vertical distributions in the soil profile, using soil samples. 4. Pitfall traps and light traps were used at each site, in an attempt to relate temperature conditions in soil to the times of emergence of adult arthropods from soil. 73:=7'"? GENERAL DISCUSSION- AND CONCLUSIONS The aim of these experiments was to determine how populations of arthropods in soil reacted to changes in certain environmental factors. The emphasis of the research was on investigating the effects of these factors on field populations under conditions that were as natural as possible. Although the soil temperature and moisture conditions in the Garden Plots experiment were created artificially in some plots, the methods used to produce these conditions were such that their effects were as natural as possible, and the soil environments that they produced were intended to be the extremes of those which could possibly influence populations in natural grassland soils in temperate regions. In attempting a synthesis of the significance of the work in this thesis, I shall first recapitulate briefly the more important or outstanding responses of the animals to the various treatments described in Part I, and, wherever possible, relate these findings to results obtained in Part The interpretation of the population changes which occurred in response to treatments in the Garden Plots experiment is complex and involves not only the direct effects of the treatments on soil animals, but also indirect influences on the availability of food and space and on the numbers of predators that occurred as a result of the treatments. None of the treatments totally eradicated any species of arthropod from the soil, but large changes in the relative abundance of various groups occurred. Presumably, weather conditions such as those simulated in the experiment would not limit the geographical range of the species of soil arthropods which were studied, but, more probably, would influence - 25 their abundance, and hence their relative importance in soil ecosystems. This happened, for example, in species belonging to the Acaridae (Tyrophagus sp.), the Uropodina (Olodiscus minima), the Oribatidae (Oppia c.f. minus) and isotomid, Oollembola (Isotomodes productus) when_ populations of these species probably became much more important because, unlike those of the majority of the other soil microarthropods, numbers did not markedly decrease in heated but unwatered soil. When soil was heated and also regularly watered, scme species of Uropodina increased greatly in numbers; so it is likely that uropodids would be more numerous and probably more, important in warm, moist habitats. By contrast, the Acaridae increased in numbers in heated plots, irrespective of whether extra water was added or not; so in warm, moist or in warm, dry habitats the Acaridae would tend to be more important than in colder environments. This may explain why the acarid mites sometimes reach pest proportions in stored products, where temperatures are often relatively high and conditions usually dry. The effect of the treatments on numbers of soil animals differed markedly with species, but there was a common pattern of change for most other mites and sprint, ails and also other arthropods, which is best summarized by the fluctuations in the total numbers of soil invertebrates in the different plots. The treatments had little effect on overall numbers of animals during the winter of 1970-7l or the following spring, but in the summer of 1971, heating the soil without adding extra water tended to decrease populations of most species or groups of soil animals. Probably, this was due mostly to desiccation, because arthropod populations in the heated plots which were also watered - 259 - did not decrease. The average temneratures in the soil at this time (August) were about 23-25°C but in the control soil only 16-17°C. Many soil arthropods can tolerate temperatures as high as those in the rested plots. Moisture contents ranged from 15-30/0 (based on wet weight of soil) in the heated and watered plots, and 10-3070 in the heated unwatered plots. Most soil animals require relative humidities of about 100A for survival, and these humidities are normally maintained in soil. Moisture contents as low as In in soil in the heated but unwatered plots possibly reduced the relative humidity, and in this way may have produced limiting conditions for the survival of soil arthropods. In an earlier unreplicated experiment, in which populations of soil animals in the field were compared in soil exposed to normal weather conditions and in soil which was heated (but not watered), Edwards and Lofty (1971) reported that numbers of most soil animals decreased markedly when soil temperatures exceeded b 20°C ut they did not distinguish between the effects of high temperatures and desiccation, although they assumed that desiccation was the major factor. Treating soil as described in the Garden Plots experiment influenced numbers of other animals besides the microarthropods, and gave some indication of the relative importance of temperature and moisture on population size. For instance, in the paper by Edwards and Lofty (1971), in which considerable increases in the numbers of root-aphids in heated plots occurred, Professor Ghilarov, in the discussion, offered an explanation in terms of the drying of soil. He stated that in localities where root-aphids were of importance, they were most abundant in dry years, and be - 2 60 - 'ftonght the ho connected with improvements in conditions for Suckin sac when a water-vapour pressure deficiency oceerred. However, in the Carden. Plots experiment, root-aphids increFzed in spring 1971, not only in heated but unwatered plots, but also in those whieh_mere heated_and watered; so it seems unlikely that the drying of soil was of major importance in this instance. The numbers of soil aphids recovered from the sites in the survey were too few to give much further evidence of major effects of temperature on this group of arthropods. The numbers of thrips (Thysanoptera) in the Garden Plots experiment decreased in December 1971 in the heated plots, whether extra water was added or not and this decrease could have been due to the prevention of hibernation in winter in heated plots. An increase in numbers of thrips in summer in response to heating did riot occur in the Garden Plots experiment, but has been reported in other experiments (Edwards and Lofty, 1971). Data on temperatures in heated soil in the experiment by Edwards and Lofty are not available, but probably resemble those recorded in the unwatered heated plots at Garden Plots, because the,heat sources used were similar. Also, the minimum soil moisture levels reached in their heated plot and in my unwatered heated plots were similar, being about 10A (based on dry weight of soil). The separate and combined influences of temperature and moisture on populations of arthropods in soil were assessed carefully, because different groups and species of arthropods which live in soil react differently to changed environmental conditions. Most workers have studied the effects of temperature and moisture on numbers and distribution of soil arthropods separately. My acprocch was to consider the combined effect of - 261 - these faCtors, because there are problems in differentiating b-,:tw,,en the relative importance of the two factors when they interact. One way of attempting this approach might be as follows:- The numbers of soil invrtebrates in the Carden Plots ,,:xperiment were smallest in the unwatered heated plots in September 1971. At that time, the mean soil temperature in these plots was 29.5°C and the moisture content was Wo. The product of these two values, which I have tentatively termed "moisture- degrees", and which seems to be a possible way of expressing the desiccating power of the soil environment, was 236. By contrast, the products of moisture and temperature values in September 1971 for the control plots and heated watered plots were 293 and 322 respectively, and in September 1971, the populations in these plots were not decreasing. In December 1971, populations in the heated plots which were not watered began to increase again, and then the product of tne moisture and temperature values was 289. So it is possible that "moisture-degree" values of below about 240 or 250 indicate a limiting environment for soil invertebrates considered as a whole. This indicates that the use of "moisture-degrees" is possible and may give a quantitative value for the overall effect of moisture/temperature interactions. One difficulty in interpreting the data in these experiments is that interactions between predators and their prey greatly complicate the results. For instance, when the effect of the treatments on the relative proportions of certain soil animals was investigated, an increase in the relative numbers of mesostigmatid mites in unwatered heated soil was associated with a decrease in tie relative numbers of cryptostigmatid mites on which the predatory species may feed, wren though the overall numbers of both 262 - mesas ii;±:atid- and crsptostitid- mites were decreasej by this tretmen. 6imilr a IneractIonst erew reported cy :dwurds (1968, 1969b), who compared the numbers of inv,:.rtebrates in irradiated soil with those in 1,,oreated soils, and others treated with different pesticides werc compared with those in control soils. Edwards showed clearly that the abundance of the mesostigmatid mites in soil usually influenced markedly the numbers of oribatid mites, and other prey organisms. The rates of change of size of populations of certain groups and species of soil animals in response to the treatments were calculated, based on the data collected both during and after the treatment period. Commonly, a decrease in numbers was observed for most of the soil fauna in heated but unwatered soil during treatment and a comparison between the rates of decrease in populations of the various invertebrates may give some indication of the relative susceptibility of these animals to the direct or indirect influences of desiccation. Of all the major groups of invertebrates, the numbers of Collembola decreased the most rapidly, which implies that the springtails as a whole were relatively intolerant of heating and drying conditions in soil. The rates of increase of populations during the recovery period were also calculated for certain invertebrates, and I suggested that, for animals in heated but unwatered plots, if the populations were then under non-limiting conditions, the rate of increase would approximate to 'r', the 'intrinsic rate of natural increase'. However, it is unlikely that non-limiting conditions ever occurred in the plots. No other 'r' values are available for soil microarthropods, so it is difficult to conclude how realistic are my calculations of 'r' for certain species and genera. - 263 Values of around 0.04 (rate per head per week) were calculated for certain species-of Ptinidae (Andrewartha and Birch, 195A), whereas the values I obtained for species of soil arthropods in my field experiment were of the order of 0.01 - 0.06, so possibly my figures are acceptable estimates of the true values. However, values of 'r' for various strains of the grain beetle, Calandra oryzae, were between 0.44 and 0.77 (Andrewartha and Birch, 1954), so comparisons of 'r' values for different organisms probably give little indication of expected values for other species. Possibly, when the life-tables of some of the soil arthropods kv,ve been constructed, changes in populations of these animals can be predicted much better, especially if accurate values for 'r' can be obtained. It should then be possible to actually measure the controlling influence of the environment on invertebrate populations. Seasonal differences between the numbers of microarthropods and of other groups in the soils of the survey sites were difficult to relate to temperature, because the soil and air temperatures at many of the sites were much too similar. I had hoped that there would be much greater differences between soil temperatures at the different sites over such a wide range in latitude, so that the influence of temperature on population numbers and rates of change could be investigated. In studies on the effects of the treatments in the Garden Plots experiment on the phenology of some species of mites, there was some indication that the partial desiccation of soil during heating influenced the duration of development of larvae and nymphs. Increases or decreases in development times (which included the quiescent periods) depended on species, but the effects of the treatments were difficult to assess, because numbers of individuals were sometimes low and peak populations were difficult to define. There was also some indication that e:,,c-s of some species such as Platynothrus peltifer (Cryptostigmata) were produced earlier in -eated plots than in control ones, and that heating soil and adding extra water increased the relative proportion of females to males of Pergamasus spp. (Mesostigmata). Phenological trends in various species of microarthropods, common to all sites in the survey, could not be determined because the changes in numbers of individuals recovered from soil cores taken periodically throughout the year were generally small, and statistical analyses indicated that few of the differences recorded were significant. Soil sectioning was used in Parts 1 and 2 to determine the vertical distribution of animals in the soil profile. Marked changes in the vertical distribution of most animals occurred in response to the treatments in the Garden Plots experiment. Using the total numbers of invertebrates in soil samples as an indication of the overall response of animals to the treatments, it seems that heating greatly decreased populations in the upper layers of soil, particularly when the soil was not watered to . counteract the accompanying desiccation. Probably, these changes were mostly due to mortality or decreased fecundity in animals which live in the surface layers of soil; though vertical migrations of animals in soil may also have occurred, and a combination of these factors may have been involved. It is also possible that metamornhnsina species completed their development earlier, and left the surface soil as winged adults earlier in heated soil than those in unheated soil. In the soils of the survey sites, differences between the - 265 - vertical distribution of certain microarthropods in the profile were noticed in ,October and i)ecember 1971. The most marked and consistent effect was a decrease in the numbers of individuals the upper layers of soil at M.ndrogan during winter, as this was probably related to the lower temperatures in soil at Kindrogan at this time, compared with soil temperatures at the other sites. In more southerly sites this effect was not obvious,- and certain species of arthropods, such as Minunthozetes semirufus, occurred in greatest numbers in the surface layers of soil in the winter, instead of the autumn. Possibly, the moisture content of the soil was a limiting influence on the size of populations in autumn in this instance. Studies on the factors influencing the movements of animals in soil or litter placed in extraction funnels can also provide some evidence on how changes in vertical distributions of animals in the soil profile may be achieved. Nef (1970), dried litter samples in such funnels and found that it was possible to collect mites, even before he could record a humidity gradient through his samples. Block (1966c), using a Macfadyen high gradient extractor, collected 50% of the total Mesostigmata, 20% of the Cryptostigmata and 18% of the Collembola from the soil samples before there was any weight loss of the soil which would have accompanied desiccation. Such results indicate how variable are the effects of environmental factors and how difficult is the task of assessing the influence of the "effective" environment of organisms (Allee et al., 1949) on their populations and distributions. I did not attempt to assess the influence of temperature on populations of soil arthropods in terms of heat summation, due to — 266 — the lack of data on thresholds of development of soil arthropods. Yany soil animals can remain active and even develop at temperatures below 0°C; also closely related species often differ markedly in their response to temperature. I decided against using some arbitrary developmental threshold for the various groups, especially because those assessed by other workers (Andrewartha and Birch, 1954; Sarvas, 1970; Hardwick, 1971) for arthropods above ground are likely to be inappropriate to soil organisms. Furthermore, values of "day-degrees" calculated for development of various arthropods in the experiment could not take into account the differences in moisture content of the soil in the different plots, and moisture seemed to be an extremely important factor in determining rates of population increases or decreases. The implications of my research are to verify that changes in the moisture or temperature conditions in soil can lead to considerable changes in the number and spatial distribution of much of the arthropod fauna, although there is not usually much change in species composition. However, the dominant species may change and some of the new dominant species could conceivably become pests. These conclusions could be relevant to soil under glass, or in other situations where soil temperature and moisture conditions are artificially controlled. Even if the extreme conditions do not influence any arthropods to the level of pest proportions, there could still be changes in the overall dynamics of the soil fauna and flora. For example, a decrease in numbers of most microarthropods due to heating with insufficient watering could possibly influence the rate at which organic matter is re-cycled through the soil, and affect soil fertility, although this is unlikely under normal greenhouse management. There was some indication that the treatments caused considerable differences in the botanical composition of the.plots. Probably, these differences were related to t?ie direct influence of the treatments, but it is also possible t*at different numbers of soil animals caused by the treatments had some effect on the flora. Fox (1957) reported that certain insects could alter the floristic composition of grassland, and he suggested that the role of insects as a factor in grassland succession deserved more attention. Edwards (in litt.) suggested that heavy pesticide treatments sometimes encourage growth of weeds. It is clear that the ecology of grassland has been very much neglected. Little is known of the beneficial effects or the importance as pests of the diverse organisms which live there, or of the importance of factors influencing their number. Possibly, some relatively unimportant organism could become economically important, if conditions occurred which destroyed its natural enemies but did not reduce its own numbers. It would be useful to know some of the factors which limit population size of any organisms in a given community, so that control methods could be used to create as inhospitable an environment as possible for the new pest. Further, biological control often depends on the maintenance of many varied organisms (Wigglesworth, 1965), so knowledge of how environmental factors influence natural populations of soil animals is fundamental to the understanding of the dynamics of the soil and has obvious potential use in the economics of soil management. SUMMI,RY 1. The relative' abundance of arthropods in Garden i'lots soil was typical of many grassland. areas. 2. Quantitative differences in the botanical composition of the plots were related to treatment, but qualitative differences were probably not. Effects of the treatments on the flora in the plots were relatively long-lasting. 3. The growth of fungi in soil was enhanced by heating; this may have increased the amount of food available for certain soil animals, and influenced their abundance. 4. Watering probably caused a decrease in the porosity of the surface layers of soil in heated watered plots, and this may have influenced the vertical distribution of the animals in the soil profile. 5. In counting soil animals, a sub-sampling method was sometimes used which gave a good estimate of actual numbers, especially when many animals were present. 6. Heating soil without adding extra water decreased total numbers of animals. This did not occur -when soil was heated and watered, so the major influence on numbers was desiccation. 7. Groups within the total fauna were affected differently by the treatments:- Acarid mites, especially Tyrophagus sp., always increased in number in heated soil, regardless of watering. (ii) Uropodid mites (mainly Olodiscus minima and Dinychus sp.) increased in number only in heated sr-d1 which was watered. (iii) Numbers of total ?rostigmata, total hypog strurid and isotomid Collembola and EsotoRlodes productus were unaffected by the treatillnts. (iv) Onpiidae as a whole decreased in number in heated soil, whether extra water was added or not. (v) Numbers of Oppia c.f. minus and of sminthurid and entomobryid Oollembola, increased or decreased in response to treatments, depending on the period of exposure. 8. Heating soil decreased numbers of most invertebrates in the upper layers, thus changing the relative abundance of animals in the soil profile. Often numbers in the upper layers decreased by an order of magnitude, especially in heated but unwatered soil. 9. Changes in the vertical distribution of invertebrates in soil in response to treatment were possibly due more to differences in birth rate or mortality between the various layers than to vertical migrations, though a combination of these factors probably occurred. 10. Rates of population change during and after treatment were determined for certain groups of soil animals, and crude estimates of intrinsic rates of natural increase of some species of microarthropods were made. 'dates (per head per week) were between 0.01 and 0.06. 11. Effects of treatments on the phenology of Platyhothrus ultifer, Pelops tardus and Pergamasus spry. were investigated, but results were difficult to interpret because times of peak numbers of adults and immatures in treated soil were ill-defined. Gravid adults of i'. peltifer were observed six weeks earlier in heated soil W- ich was not watered, than in controls. Some — 2,70 — evidence suggested that heating and watering increased the proportion of females to males in Pevgamasus sop, 12. Pitfall traps indicated that the number or activity of Lasias flavus increased in heated plots which were not watered; carabid, staphylinid and other beetles were caught earlier in traps in heated plots, whether the plots were watered or not, 13, Temperatures in soils of the sites in the survey were much too similar to allow a good assessment of their influence on populations of animals in soil, 14. An attempt was made to define the limiting influence of temperature/moisture interactions on soil arthropods as a whole. It was suggested, in terms of "moisture-degrees", that values below about 240 or 250 might indicate conditions which were unfavourable for their s.nrvival. - 271 - ACKNOWLEDGEMENTS I wish to express my sincere thanks and gratitude to Dr. C.A. Edwards, who supervised this work and made valuable comments on the presentation of the thesis, and to Professor T.R.E. Southwood, my Director of Studies. I also thank Drs. C.G. Johnson (previous Head of the Department of Entomology) and C.G. Butler (present Head) for allowing this work to be done at Rothamsted. Many thanks are due to R.H. Turner and F.D. Cowland for their help in producing the plates, and again to H.H. Turner for other assistance,including the use of the computer graph-plotter. I thank many of the members of the Department of Entomology for giving helpful advice and assistance whenever it was sought, and in particular to Dr. L.R. Taylor, I.P. Woiwod, C.J. Stafford and E.D.M. Macaulay. I am very grateful to all the site organisers and operators mentioned in the thesis, especially to those who identified light trap catches, and in particular to B.J. Withers. R. Kempton gave invaluable help with the analysis of the data, for which I am extremely grateful. The help of D. Macfarlane, who identified many of the mites, and of P.N. Lawrence, who identified much of the Collembola, is gratefully acknowledged. I thank my wife, who drew many of the figures and gave much other assistance. The work was done whilst on an A.R.C. Research Assistantship. - 272 - REFERENCES AGRELL, I. (1941) Zur ZIkologie der Collembolen. Untersuchungen im Schwedischen Lappland. Opuscula Ent., Suppi. III, 1-236 ALLEE, W.C. et al. (1949) Principles of Animal Ecology. Saunders, Philadelphia and London, 837 pp AN DER LAN, H. (1961) Zur Winter - Ukologie des Gletscherflohes. Die Pyramide, 1, 33-34 AN DER LAN, H. (1963) Tiere im Ewigschneegebiet. Umschau Wiss. Technik, 2, 49-52 ANDERSON, J.M. 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(1934) An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil Sci., 1/, 29 - 38 WALLWORK, J.A. (1959) The distribution and dynamics of some forest soil mites. EgalEa, 557 - 563 WALLWORK, J.A. (1960) Observations on the behaviour of some oribatid mites in experimentally - controlled temperature gradients. Proc. zool. Soc. Lond., 135, 619 - 629 WALLWORK, J.A. (1967) Acari. In Soil Biology ed. A. Burges and F. Raw. Academic Press, London and New York, 532 pp WALLWORK, J.A. (1970) Ecology of Soil Animals. McGraw Hill : London and New York, 283 pp WALLWORK, J.A. and RODRIGUEZ,.J.G. (1961) Ecological studies on oribatid mites with particular reference to their role as intermediate hosts of anoplocephalid cestodes. J. Econ. IL, 701 - 705 WETS-POOH, T. (1948) Ecological investigations on mites and Collemboles in the soil. Natura Jutlandica, 1, 135 - 270 WELLINGTON, W.G. (1957) The synoptic approach to studies of insects and climate. Ann. Rev. Ent., 2, 143 - 162 WHEELER, W.M. (1910) Ants their Structure Develosment and Behaviour. Columbia Univ. Press ; New York, 663 pp WIGGLESWORTH, V.B. (1965) [Introductory remarks from the Proc. Assocn. Apple Biol.]. 1.1,222 22212_2121.1 315 - 317 WIGGLES WORTH,V.B. (1972) The Pr inc i le s of Insect Physiology (7th editn). Chapman and Hall : London, 827 pp - 287 - WILLIAMS, E.C. (1941) An ecological study of the floor fauna of the Panama rain forest. Bull. Chicago Acad. Sol-, 6, 63 - 124 WILLIAMS, R.J.B. (1970) Relationship between the composition of soils and physical measurements made on them. Rep. Rothamsted exp. Stn. for 1970, Part 2, 5 - 35 WILLIAMS, T.D. and WINSLOW, R.D. (1955) synopsis of some laboratory techniques used in the quantitative recovery of cyst-forming and other nematodes from soil,In 221112212EL ed. Kevan, D.K. Mc.E.,Butterworths ; London, 512 pp WILLMANN, C. (1931) Moosmilben oder Oribatiden (Oribatei). Tierwelt Dtschr., 22, 79 - 200 WILLSUN, M. (1960) The effect of temperature and light upon the phenotypes of some Collembola. Proc. Iowa Acad. Sci., 62, 598 - 601 WILSON, E.O. (1971) The Insect Societies. Belknap Press of Harvard Univ. Press, Cambridge, Mass., 548 pp WOOD, T.G. (1966) The fauna of grassland soils with special reference to Acari and Collembola. Proc. N.Z. ecol. Soc., No. 13, 79 - 85 WOOD, T.G. (1967a) Acari and Collembola of moorland soils from Yorkshire,,England. I. Description of the sites and their populations. Oikos, 18, 102 - 117 WOOD, T.G. (1967b) Acari and -Collembola W- Moorland soils from Yorkshire, England. II. Vertical distribution in four grassland soils. Oikos, 18, 137 - 140 WOODFORD, E.K. (1971) (Presidential Address) J. Br, Grassld Soc., 26, 1 - 7 WOODFORD, E.K. and MORRISON, J. (1971) National use of grassland. Ann. appl. Biol., 62, 278 - 285 WOODRING, J.P. and COOK, E.F. (1962) The biology of Ceratozetes cisalpinus Berlese, Scheloribates laevip-atus Koch, and 02planeerlandica Oudemans (Oribatei), with a description of all stages. Acarolop'ia, L, 101 - 137 — 288 — APPENDIX 1 List of plant Species identified at Garden Plots SPECIES SPECIES GRAMINEAE CONVOLVULACEAE Agropyron repens Convolvulus arvensis Agrostis gigantea A. stolonifera CRUCIFERAE A. tenuis Capsella bursa-pastoris Arrhenatherum elatius Cynosurus cristatus LABIATEAE Dactylis glomerata Prunella vulgaris Festuca ovina PAPILIONACEAE F. rubra Holcus lanatus Lotus corniculatus Lolium perenne Trifolium pratense Phleum bertolonii T. repens Poa trivialis T. striatum Trisetum flavescens PLANTAGINACEAE CARYOPHYLLACEAE Plantago lanceolate Cerastium glomeratum P. media Stellaria media POLYGONACEAE COMPOSITAE Rumex acetosa Achillea millefolium R. obtusifolius Bellis perennis RANUNCULACEAE Centaurea nigra Ranunculus repens Hieracium sp. ROSACEAE Hypochoeris radicata Leontodon hispidus Potentilla reptans L. taraxacoides Picris hieracoides Senecio vulgaris Sonchus asper Taraxacum officinale APPENDIX 2 - GARPT'N PLOTS PXPERIMr\TT S.E. OF DIFFERENCr9 TABLE OF L0 10(N+1) TRANSFORMED MEANS (use (1) for compnrin treat- ments for the same date, use (2) for comparing dates for the same treatment) TOTAL FAUNA C 2,64 2.65 2.64 2.57 2.71 2.42 2.23 2,39 2.38 2,29 2.36 2,53 (1) 0.179 H 2,43 2.71 2.73 2,73 2.61 2,24 1,64 1.66 1.97 2.19 2,53 2,63 (2) 0.128 NW 2.54 2.72 2.77 2,56 2.65 2.27 2,33 2.31 2,34 2.38 2.49 2.60 ACARINA C 2.54 2.50 2.54 2,48 2.58 2,22 2.11 2.19 2.14 2.05 2.21 2.25 (1) 0.187 H 2.32 2.59 2.62 2.65 2.47 2.03 1.59 1,48 1,73 1,85 2.23 2.26 (2) 0.129 NW 2.42 2.60 2.61 2.43 2.43 2.04 2.23 2.17 2.16 2.13 2.38 2,35 1 ra Co COLLE',OLA C 1,75 1.91 1.61 1,58 2.01 1.87 1.44 1,82 1,87 1.83 1.71 2.16 (1) 0.281 H 1,45 1.98 1.90 1.73 1.92 1.73 0.76 1,08 1,49 1.86 2.14 2,34 (2) 0.217 HW 1.71 2.04 2.14 1.77 2.05 1.74 1.45 1.62 1.68 1.93 1.96 2,18 0THEPs T-(M+C) C 1.12 0.92 1.07 1,03 1.08 1.24 0.67 1.03 1,03 1.06 1.13 1,08 (1) 0.22 H 1.17 0.93 1.18 1.22 1.18 0.95 0,19 0,44 0.74 0.86 1.14 1.10 (2) 0.203 NW 1,0,3 0.8? 1.05 1,30 1.27 1.14 0,50 0.81 0.93 0,99 1.12 1.20 PRT3Tir;c4TA HETEROSTIG"ATA C 1,93 1.9:1 1.94 1.86 1.81 1.34 1.12 1.18 1.06 1.34 1.47 1.68 (1 0.182 H 2.0') 2.11 1,76 1.53 0.99 0.91 0.93 0,79 1.30 1.53 1.57 (2) 0.176 lw 1.47 1.95 2.13 1,63 1,61 0.87 1.15 0.97 0,94 1,32 1,64 1,47 ran Ined IE.50,5r1GATA 1,72 1,56 1.32 1,40 1.50 1.60 1.59 1,61 (1) 0.16 C 1,79 1.52 1.50 1.36 (2) 0.161 H 1.27 1,50 1,52 1,72 1.61 1,36 0.84 0.98 1,15 1.22 1,42 1.63 Hw 1,54 1.78 1.71 1,72 1.80 1,40 1,52 1,48 1,49 1.47 1,66 1,53 CRYPTOSTIGmATA 2.26 2.23 2.41 2,02 1,95 1,99 1,96 1,64 1.94 1.91 (I) 0.261 C 2,26 2,23 (2) 0.133 H 2,09 2.33 2.26 2,47 2,31 1,80 1,35 0,92 1.29 1,37 1.74 1.74 Hw 2,27 2.36 2.26 2,21 2,28 1,88 2,04 2.00 1,97 1,87 2,08 2.16 ASTICOATA 0,38 (1) C 0,11 0.25 0,23 0,34 0,05 0.19 0,19 0,14 0,18 0,24 0,29 0.255 ( 2') 0.235 H 0,36 0,46 0,17 0,34 0,39 0.43 0,54 0.42 0.91 0,86 1.45 1,31 dw 0,13 0.27 0.34 0,30 0,14 0,29 0.43 0,72 0,85 0,72 1,21 0,92 oNyolumnAE 0.234 C 1,48 1.66 1.34 1,22 1,68 1,25 0,79 1.35 1.46 1,01 1.29 1.53 (1) (2) 0.217 H 1.24 1.61 1,36 1,25 1,27 1.21 0,15 0,36 1,03 0,98 1.33 1,65 11W 1,47 1.60 1.79 1.34 1.64 1,26 0.61 1,09 1.13 1.14 1,44 1.66 HYPOGASTRELRIDAE (1) 0.356 0.56 0.58 0,45 0.59 0,59 0,23 0.61 0,64 0,51 0,43 0,61 C 0,43 (2) 0.270 H 0,25 0.59 0.53 0,29 1.30 0,41 0,08 0,04 0.30 0.35 0,77 0,71 HW 0,68 0,73 0.71 0,61 0.78 0,83 0.51 0,35 0.44 0.34 0.80 0,44 ISOTom/DAE C 1,12 1.25 1.11 1.13 1.30 1,33 1.12 1.36 1.42 1,58 1,14 1,97 (1) 0.462 H 0,81 1.63 1.64 1,41 1.73 1,44 0,72 0,95 1,04 1,70 1,81 2,18 (2) 0.291 Hw 1,20 1,69 1,80 1.39 1,66 1,36 1,17 1,20 1.30 1.72 1.60 1.93 App" -)TX 2 continued INTOPORYIDAE 0.61 0.74 0.98 0,97 (1 0.139 C ().18 0.10 0.04 0.10 0,12 0.32 0,62 0,74 (2 0.143 H 0,21 0.20 0.44 0.35 0.59 0.74 0,02 0,30 0,65 0.98 1.43 0,96 11,4 0,18 0,38 0.51 0.14 0.66 0.49 0.27 0,92 1,01 1,00 1 005 1,04 Sr.INTWJRinAE 0,02 0,07 0,15 0,00 0,15 (1)0.107 C 0.13 0,07 0.00 0.38 0,91 , 1,14 0,09 (2)0.107 H 0.15 0.12 0,18 0,67 0,23 0,11 0,00 0,02 0,04 0.07 0.06 0,22 HW 0.11 0.32 0,19 0,60 0.51 0.08 0,03 0,03 0,12 0.43 0.03 0,13 PYFvOTIDAF: 0,54 0,31 0,41 0,57 0.80 0.31 (1)0.206 C 1.49 1.56 1.25 1.38 1.25 0,72 (2)0.176 0 1.32 1.62 1,69 1.23 0.59 0,43 0,43 0.21 0,34 0,46 0.91 0,78 Hw 1.02 1.18 1.42 1.07 0,96 0.29 0.68 0.34 0,35 0.52 0.9? 0,57 ScUTACARIDAr, 1,37 0,93 0.63 0,42 0.69 0,88 0,92 0.85 (1)0.233 C 1.57 1.64 1.69 1,52 (2)0.233 H 1,23 1.75 1.78 1.45 1,08 0,50 0,13 0.15 0.22 0.48 0.68 0,68 d 1,09 1.68 1.94 1.38 1.24 0,47 0.70 0,34 0,31 0,42 1.02 0,40 ' PV;STIGvATA 0.190 C 1,8 0.87 0,82 0,61 1.1 7 0,82 0,74 1.01 0,66 0,98 1.05 1,59 (1) H 0,53 1.96 0,96 0.74 1.13 0.65 0,61 0,83 0.54 1.13 1,24 1,37 (2)0.171 HW ,66 1.20 0.93 0.67 1.00 0.53 0.58 0,74 0,68 1,16 1.25 1.35 ft!tcDCARI')At: C 1.54 1.14 1.07 1,12 1.56 1.23 1.00 1.12 1.19 1.31 1,39 1016 (1)0.5 H 14 0.93 1.09 1,60 1,43 1.07 0,69 0,92 0.98 1.07 0.93 1.20 (2)0.195 OW 1.24 1.37 1.79 1,44 1.65 1.01 1.35 1,29 1,27 1,19 1,38 1.16 APPT7NnTX 2 continued RHODACARUS ROSEUS C 0.00 0.95 0,44 0.79 0,85 0,70 0.63 0.73 0,73 0,79 0,84 ,0.86 (1 0.252 H 0,00 0,66 0.13 0.29 0,44 0.33 0,24 0.39 0,34 0,30 0,48 0.60 (2 0.199 HW 0,00 1,19 0,99 0.72 0,63 0,77 0.89 0.81 0,80 0,85 1.12 0,97 RHODACARELLWS SP. C 0,00 0.88 0.59 0,90 1,45 1.18 0,81 0,93 0,97 1.15 1,25 0,82 (11 0.222 H 0,00 1.04 1,04 1.60 1.39 1.02 0.64 0,81 0,88 1.00 0.80 1,08 (2 0.187 HW 0.:).; 0,78 0,89 1.34 1.57 0,69 1,20 1.09 1,05 0,94 1,02 0,60 D1GAmASELLIDAF C 1.09 1.07 0.94 0,50 0,91 0.68 0.15 0,61 0,72 0,85 0.73 1,06 (7) 0.08 H 0.55 0.62 0,66 0,30 0,23 0,21 0047 0,06 0.17 0.35 0,71 0,95 (2) 0.`MF dlif 1.01 1.10 1.23 0.98 0.58 0.33 0.20 0.28 0,42 0,45 0.66 0,57 WROPOOINA C 0,13 0.09 0.15 0.12 0,24 0,21 0.10 0.06 0.26 0.02 0.18 0,31 (1) 0.156 H 0.11 0.16 0,18 0,11 0.02 0.04 0,00 0.02 0.15 0.02 0.07 0.13 (2) 0.1:37 HI.j. 0,30 0.56 0,47 0,40 0,37 0,45 0,05 0,57 0,47 0.44 0.36 0.52 AnuLT CIRCUH,MINUS OPPIIQAE 0.380 C 1.83 1.72 1.36 1,75 2.00 1.61 1.62 1.64 1.54 1.36 1.65 1.54 (1) H 1,85 1.88 1,85 1.78 1.72 1,54 0,92 0.64 1.04 0,96 1.35 1.35 (2) 0.155 W,4 1.8; 1.92 1.69 1.64 1.73 1.68 1.60 1.69 1,66 1.60 1.73 1.72 YycoRTIAE C n.3C 1.43 1.59 1.65 1.93 1.56 1.56 1.52 1,43 1.27 1.58 1.41 (1) 0.30 H 0.00; 1.96 1.66 1.74 1.11 1.51 0.87 0.60 0.97 0.77 1.26 1,23 (2) 0.132 Hui 30 1,95 1.90 1,52 1.65 1,57 1.46 1.35 1.37 1.28 1.56 1.35 mTx 2 co itinued INT110.7_ETES SEMI RUFUS C Q,00 1.32 1.40 1.53 1,85 1.51 1.53 1.38 1.32 1.19 1,50 1,34 (1 0.401 0.Cfl 1.84 1.48 0,84 1.55 1,65 1.63 0,55 0,93 0.65 0.92 1.05 (2 0. 163 ,^ 0(.) 1.79 1,1 1,39 1,53 1,49 1,38 1.25 1.26 1,18 1.43 1,14 p,iNcloPIBATES PwicTV C , „Cc 0.76 1,02 0,91 1.07 0,62 0.48 0,86 0,75 0,54 0.82 0.64 0.269 r,.00 1.39 1„:")7 0,97 0..82 0.57 0,16 0,17 0.28 0.36 0.82 0,73 2) 0.223 11 ,1, 1.3,) 1,04 0,80 0,81 0.78 0.65 0.56 0,97 0.62 0.76 0,67 SC!-iELGRIRATIDAE C 1.7 0,89 (1,.99 0,47 0.52 0.69 0,81 J3 1.13 0,4c 0.87 0.84 (1) 0.392 H C00 0.64 ),64 3,54 0,40 0.58 0,15 0,09 0.30 0.40 0.54 0,5/ (,2) 0.192 Hy ,),.r( ,:) 1.1c 1.27 0.94 0,83 0.86 0,80 1.22 1.11 1,10 0.96 1,20 OPPIU)AL C 1,9 1.24 1.71 1.7 2,07 1.64 0.87 1.26 1.39 0.88 1,28 1.26 ) 0.220 0 1,50 1.91 2.02 2.30 1,99 1.17 0,84 0,56 0.62 0.93 1,11 1.04 ,)p2 0.186 1,2,! 1.95 1.86 2.04 1.11 1,29 0,Q1 0.90 1.11 1.1? 0,82 OPPJA c.r. cLAv1PECTINATA C 1.72 1.72 1.57 1.65 1.65 0.99 0,72 1.23 1.24 0.76 1.18 1.21 p) 0.266 H 1.3 1.!,6 1,59 1,24 1,06 0.92 0.45 0,27 0.48 0,69 1.00 0,91 \ 2) 0.233 00 1,7c 1.7 -2, 1,43 1.25 1,19 0.80 0.83 0.83 0.77 0.82 1 ,1 0 0,79 c*:;.,rdn C.F. 'rJS C 1.3 1.1R 1,00 1.33 1,66 1„4 0,37 0,20 0.54 0.46 0.48 0.24 (1) 0.229 H 1.41 1.76 2.22 1,93 0.71 0,64 0.41 0,31 0.51 037 0,56 (2) 0.212 90 1,35 1.32 1.60 1,70 1,95 0.83 1,04 0,26 0.25 0.62 0.48 0,15 A:PPM:1)TX 2 continued IYYATuRE CIRCW4 DEHISC, C 1.23 1.22 1,22 0,90 1,00 0.80 0,F9 1.04 1.16 0.86 1.20 :1,10 (1) 0.319 H 0.96 0.90 0.71 1.05 0.57 0.53 0.27 0,57 0.40 0.98 0,82 (2) 0.220 1„0 1,06 1.32 0.93 1.07 0.73 1,44 1.36 1.03 0.86 1.40 1.32 ISOTIWODES C 1.C8 0,91 1,04 1.12 0.80 0,91 1.03 0.95 0.83 0.71 1.24 0.628 H :),73 1.49 1.16 0.75 1.24 1,07 0.70 0.94 0.92 1.27 1.61 1,96 2, 0,325 1.14 0.0° C.5 0.40 0,93 0.64 1.08 1,17 0,96 0,92 1.12 1,32 f5C-r,vA$PP. C 0.41 0.46 0.29 0,43 1.05 0.67 0.85 1,11 1,33 0.89 1,84 (1) 0.270 H t.25 1.01 1.4 1.18 1.21 1.10 0,10 0.13 0.61 1.26 1,34 1,50 (2) 0.206 ":, ,34 1.23 1.65 1,37 1.35 1.02 0,25 0.45 0,98 1,57 1.36 1,80 r'etYPTUS C 0.1() 0.1)14 0.07 0,12 0.25 0.61 0,68 0,54 0,68 0.91 0.60 (1) 0.1(3 H 0,21 0.20 0.44 0.25 0,47 0.60 0.02 0,13 0.37 0,85 1,30 0,83 (2) 0.155 ,').12 1.37 0.50 0,14 0.60 0,46 0,29 0.69 0,90 0.90 0.95 1.00 HE'1rTFA C ,)0 0,00 0.',0 0.13 0.14 0.00 0,05 0.00 0.02 0,04 0.02 0.04 0.275 0.02 0.22 0,63 0.75 0,08 0.09 0,00 0.13 0.07 0,53 0,23 2) 0.2'38 i),(1 4 0.02 0,11 0,71 0.60 0.02 0.13 0.07 0.35 0.11 0.11 0.14 Ti'f5A', P,'TERa C 0.28 0.38 0.30 0.23 0.15 0.33 0.57 0.48 0.39 0.44 0.25 (1) 0.210 H 0.5q 0.46 0.60 0.58 0,36 0.38 0,04 0,09 0,46 0,20 0,46 0,30 (2) 0.195 36 0.53 0,67 0.48 0,21 0.10 0.14 0.36 0.35 0,73 0,43 - 295 - p "Try Svstematjcs of certain microarnronod fauna iAertifie rre— qnrien Plots. - 1-'vemotirlae: ,N7mepborus rnesernbri.nae Can. Pyr,mephorns snn. Sciitacaridae: Sciitacarus crassisetus plumosus Paoli S. montanus (7aoli) S. quadran7ularis (Paoli) Scutacarus spp. Tarsonemidae: Steneotarsonemus spirifex (Marchal) PROSTIGMATA Alicorhagiidae: AlicorhaPja sp. Bdellidae Calyptostomatidae: Abrolophus sp. C}ieyletidae Cunaxidae Ereynetidae Eriophyidae: Abacarus sp. Erythraeidae Eupodidae: Eupodes sp. Linopocles sp. Nanorchestidae: Speleorchestes sp. Nanorchestes sp. Pachyg.nathidae Rhaqidiidae: Rhagidia sp. Stigmaeidae: Stigrnaeus sp. Tetranychidae Trombiculidae Trombidiidae: Allothrombium sp. Tydeidae: Tydeus so. Unidentified spp. MESOSTIMTATA: Gamasina Ameroseiidae: Ameroseius ecl-linatus (C.L.K.) Epicriopsis sp. ?1,scidae: Cheiroseiiis borealis (Berl.) Gamasellodes sp. Tphidozercon c.f. corticalis Leioseius sn. Neojordensia levi s (Oucis. P VoiTts) — 296— PP77-1T1' '3 .sc,*(Ine cniltuod: Proctolooinns 'ercononsjs Sr. Unjdontirjed spp. Dormanvssidne: Gneolaelaas Sr. Hvnoasnis acul ei fer clavi.rrer H. -(AllonarasitnS) oblon7us Halb. Pseudolaelans sp. Digamasellidae: Dip.amasellus sp. Evipbididae: .Aliiphis balleri Eviphis ostrinus (C.L.K.) nalolaelapidae: Saarolaelaps sp. Machrochelidao: Coholasnis sp. Pachylaclapidae: Onchodellus sp. Pachvlaelaps sp. Parasitidae: Parasitus sp. Pergamasus crassipes (L.) P. lon7icornis Berl. Pergamasus spp. Phytoseiidae: Iyphlodromus sp. Unidentified spp. Rhodacaridae: Rhodacarus roseus Oudms. Rhodacarellus silesiacus Willm. Veigaiidae: Gamasolaelaps (?) sp. Zerconidae: Zercon (?) sp. Unidentified spp, MESOSTIGNATA: Uropodina Uropodidae: Dinychus sn. Olodiscus minima (Tsramer) ------Uropoda sp. Unidentified son. CRY7TOSTIn-NATA Bracychthoniidae: BrachycThthonins spp. Camisiiaae: Piatynothrus peltifer C.L.K. Carabodidae: Carabodes sp. (c.f. /nbvrinthicus) Ceratozetidae: Corato7otes_,Traci1is (Mich.) Eromneidae: Eremaons sp. 7unbt7-liracaridne: rZlivsotritin dunlicatn (rrrandjoan T7uzeti.Onc: 7nzotcs -lob-11ns (1\Tic.) 207 - .\r )F7\Trcfl: Protorl te:7 rf-voct-onjino: rnCnins Mvcobatidao: Tinnntfrozotoc qn-tirnPn (C T ) ''unctorib- tcs nunctum Onaidae: Onnin c.f. clavinoctinata Onnia c.f. minus (Paoli) Oppia nova? (Oudms.) Oppia spp. Oribatulidae: Oribatula tibialis (Nic.) Pelopidae: Pelops tardus C.L.N. Phthiracaridae: Phthiracarus sp. Ste7anacarus ma(mils? (Nic.) Scheloribatidae: Liebstadia simili s (?`rich.) Scheloribates laevigatus (C:L.N. Tectocephiidae: Tectocepheus velatus Mich. Unidentified Circumdehiscentiae Others ASTIGMATA Acaridae: Rhizoglvphus sp. Schwiebia talna? (Oudms.) Iyrophagus spp. Anoetidae: hypopi Glycyphagidae: Gl1cvpbagus sp. Unidentified spp. COLLEMBOLA ONYCUIURIDAE Onvchiurus armatus gp. (Tulib.) Gisin O. fimetarius Denis Onvehiurus spp. ru11hfi 1liPYE2s Born T. krausbaueri (Porn.) Unidentified spp. 'HYPOGSTRURIflAP Brae7vstomella parvula (Sellafr.) Friesea mirabilis (Tullb.) Tlvnoastrnra rTonticulata (11a7n11) Pseudacborutes sp. asigillatus" Born. Xenvlia n-risea Axelson Unidentified spp. - 298 - -X 3 TSOT(rlInA Polsomia ouadr3ocul2ta Tsotoma notribiljs I. olivacea viol cea (Tullb.) T. sensibilis (TulTb.) I. viridis Isotoma spo. Isotomiella sp. minor? (Schaff.) Tsotomodes nroductus (Axelsou) Tsotomurus nalustris (Muller) Unidentified spp. ENTLMBRYIT'AE Entomobrya albocincta (Templeton) E. nivalis (L.) Heteromurus nitidus (Templeton) Lepidocyrtus cyaneus Tullb. L. lanuginosis? (Gmelin) Orchesella cincta (L.) Pseudosinella alba (Packard) Tomocerus sp. SMINTUURIDAE Arrliopalites (?) Dicvrtoma sp. Sminthurides pumilis (Krausbauer) Sminthurinus spp. Sminthurus viridis (L.) - 299 - Apr.P.7DTN- 4 list of io7idontera crulr-ht in lifrht tra7.--,s at the sites in the survey SITE T"T SIL SE LET) Abraxas grossulariatn 0 8 8 Acasia viretata 1 Aids jubata 1 A. renandata 3 2 4-2 1 Alsonhila aescularia 19 3 3 2 Anaitis plagiatn 1 Anticlea derivata 4 Apeira svrinaria 1 Anocheima hisoidaria 1 Banta temerata 1 Piston strataria 2 Calotbysanis amata 7 8 14 Campaea margaritata 25 13 4 Chesias legate] a 44 Chinsmia clathrata 1 3 1 Chloroclysta miata 26 2 5 C. siterata 11 Chloroclystis coronata 1 C. rectangulata 1 5 5 , Cidaria fulvata 1 16 1 Cleora rhomboidaria 2 3 1 Coenocalpe lapidata 2 Colostygia diclyrnata 10 15 12 C. multistrigarin 86 C. pectiriataria 13 6 9 9 C. salicata 4 1 Colotois pennaria 7 11 10 4 1 Cosymbia porata 2 Crocallis elincmnria 3 7 9 3 5 Deilinia exnntl-emata 12 3 .1,_ P. pusprin 80 5 1 Pcutoronoos ninif-rin 2 3 ,) 1 P. orosaria 1 D. fuscantaria 1 - 300 - r--":°-1-Tr)T."7 oontinned YTN ::-4TI, SP LUD ,_=1(.7.'^ D'c.2 '1 r fr --.,' 1- U 1 Dvs F, tro-li- citratn 270 •-,2 1 P. trTinc=lta 22 11 21 6 12 Enrophila haJl_nta 4 2 ,)2 ,,, Eclintol)cra silaconta 1 4 Ectronis biunduloria 1 Ellopia fasciaria 1 Ennomos quercinaria 2 Entephria caesinta 26 Epione rcpandaria 1 Erirrhoe alternata 1 '3 3 2 4 E. rivata 2 Prrnnis Purim±iorin r,-,)=-. 1 1. E. dePoliaria 9 22 2 -1 E. marosinarin 17 1 LI. Eunitbecia contnureata 1 7. icterata 13 10 1 E. indigata 2 E. linariata 1 '. nanata ,)4. E. phoeniciata 2 E. sobrinata 3 E. succenturinta 1 ,,, 1 E. vni.7ata 1 1 E. spp. 15 7 16 17 3 Geornotra papilionaria 4 Gonodontis bidentata 4 2 Hemitbea aestivaria 10 11 7 7ydriomena fureata 71 24 1 ruberata 1 Lampropteryx sufrunatn 3 Lnrenti:- clavnrin 6 clilorcs:-;tn 1 Lonspi1 ismar7inatn 1 Lvcin hi rtaria 9 1 8 7e113_nota - 301 - contino,!. 1-1---; ST1, ST1 LITT) ST v s - 0 Ty 55 1-__ 1,1p ta 1 L. nv-rnliata 35 53 49 14 8 L. tc7,tnta 40 1 Lyncomntra ocellnta 20 6 16 Mysticoptera sexalata 1 Odezia atrata 2 Operophtera brumata 103 21 30 10 7 0.-faata 19 17 Opisthograpfis lutcolata 1 12 16 7 4 Oporina dilutata 75 111 O. fiii.;rammaria 1 0. spp. 474 12 2 Ortholitha chenopodiata 4 5 14 O. mucronata 3 Orthonama lignata 1 14 Ourapteryx sambucaria 4 1 1 Perizoma albulata 3 P. alcbemillata 5 4 P. flavofasciata 1 Phigalia pilosaria 10 1 Plemyria rubipinata 1 Pseudoterpna pruinata 1 Scopula imitaria 39 7 14 S. ternata 1 Selenia bilunaria 1 12 39 6 12 S. tetralunarin 1 Sterra aversata 28 11 19 64 S. bisolata 10 1 3 11 S. dimidiata 55 63 4 26 S. emar7inata 2 2 S. interjectaria 1 S. scriatn 1 S. straminota 1 S. snbsericeatn 1 7 - 302 - G.-20MT7ZTFI contrwed KTN STL SI-1 T,UD ST 11,11ne.,'rtn 1 T, oboli ,cato 1 2 0 Thoria rupicrlprPria 5 J Trichoptery crroin, XantThor'loc desi7nz,ta 1 0 4 X. ferrurrata 15 31 2 18 X. fluctuata 2 17 4 6 23 N. montanata 55 66 49 10 19 X. munitata 46 X. spaclicoaria 1 2 3 NOCTUTW,E Agrochola circellaris 2 1 .A.„ iota 2 2 1 2 A. lychnidis 67 188 16 A. macilenta 12 10 Agrotis exclamationis 1 9 86 211 21 A. puta 1 1 A. segetum 4 23 AUophyes oxyacanthae 2 35 59 5 2 Amathes baja 66 9 A. c-nio:rum 33 360 12 A. depuncta 20 A. clitrapezium 5 A. sexstrigata 25 1 3 A. trian7u1u,n 2 A. xanthographa 4 2 28 15 18 Amnhipvra tragonoginis 1 6 6 1 1 Anpnlectoides prasina 3 Ancoscelis litura ,)2 1 4 3 Antitype chi 18 1 A. flnvicincta 1 Apamea crenata 5 1 A. epomidion 1 A. infesta 9 A. lithoxylaea 3 1 1 A. monoglypha 25 4 18 15 6 A. remissa 2 1 A. secalis 1 ry, 66 11 7 A. screens 4 ,_.2 2 - 303 - NOCTFITX.E covtinued KTN STL 511 LUT? ST 11lneberr701is 1 A. lunula 1 Arenestola .;) A. pymina 7 Atet!Imin xerampelina Axylia putris 7 17 1 1 3 Bombvcia viminalis 2 10 Brachionycha sphinx 3 Caradrina alsines 2 12 13 8 C. ambip:ua ,1 C. blanda 7 10 7 C. morphous 55 6o 9 Catocala nupta 2 Ceramica pisi 1 6 Cerapteryx graminis 13 1 1 Cerastis rubricosa 15 Cirrhia gilvago 1 2 Citria lutea 10 4 Colobochyla salicalis 2 Colocasia coryli 1 Conistra ligula 2 C. vaccinii 13 8 2 4 Cosmia trapezina 1 Cryphia perla 6 Cucullia verbssci 1 Dasypolia ten,111 4 Di arsia brunnea 37 3 D. dahlii 65 D. mendicl: 64 9 13 2 4 D. rubi 142 40 292 344 143 Diataraxin olerac,?r, 25 7 7--nisema caoruleocepala 27 Enmi e'itis ndustn. licenea 22 1 4 13urois occulta 1 Euschesis conies - 304 - conti.nved KIN STL SD LUO ST Euschesis interjeta 1 a 4 Duxaa ni7rdcans 1 tritici 1 c,ortyna flavapo 9 3 G. micacea 188 23 12 9 26 Graphiphora augur 3 1 13 Griposia aprilina 2 Hada nana 1 1 9 Hadena bicrurls 1 1 H. rivularis 1 1 N. suasa 1 Yydraecia spp. 6 2 Hypena proboscidalis 83 5 59 4 4 Laspeyrie flexula Leucania comma L. conip:ora 1 8 L. impura 4 2 76 11 3 L. lytharP;yria 2 4 2 2 L. pallens 69 44 4 Luperina testacea 12 113 96 23 Lycophotia varia 25 Mamestra brassicae 2 Melancbra persicariae 1 4 4 Meristis trip;rammica 2 Naenia typica 1 Noctua pronuba 6 6 3 2 1 Nonar,ria typbPe 1 Ochropieura plecta 14 13 4 13 33 Omphaloscelis lunosa 17 51 28 Orthosia crudes 13 7 0. gothica )33 30 113 18 33 0. 7raciTis 1 1 0. incerta 12 2 3 - 305 - NOCTUTAE continued LI SIL S T LUD ST Ortosia 1 1 -tabilis 4 Para,linrsia F-lareosr 17 Petilamna mini7la 11 47 6 PliloonLora leticulosa 9 2 ,3J 0 Plusia bractea 1 P. chrysitis 2 4 P. gamma 1 P. interro7atiois 1 P. jota 1 P. pulchrina 9 Polio nitens 3 Procus fasciuncula 13 6 8 10 25 P. furuncula 1 1 P. literosa 1 1 P. strigilis 6 25 13 Rbizedra lutosa 1 Rivula sericealis 21 111 Rusina ferruginea 33 5 52 8 Spaelotis ravida 1 Stilbia anomala 1 Thalpophila matura 3 17 Tholera cespitis 1 T. popularis 4 5 16 2 Tiliacea citrago 1 T. aurar.;.o 1 Unca tripartita 3 1 U. triplasia 1 Xylena vetusta 1 Xylocamna areola 1 Zanclognatha nemoralis 13 7. tarsiponnalis 3 2 7 5 - 306 ARCTT1r)NE YIN SIT, SP MID (")T Arctia caja 3 1 3 Calli-:orPlia jacobaeae 1 14 Cybosia '-iesomella 1 Cvcnia mondica 1 4 2 13 Eilemc, p;riseola 1 15 E. lurideola 110 2 135 46 Miltoclirista miniat6:- 2 Nudaria mundana 98 Spilosoma lubricipeda 2 47 12 15 20 S. lutea 8 26 18 27 D EPANTDAE Cilix rrlaucata 6 21 2 Drepana falcataria 1 HEPTALTDAE Hepialus fusconebulosa 11 1 H. lupulina 4 407 291 190 H. sylvina 3 12 2 LASIOCAMPIDAE Gastropacha quercifolia 1 Macrothylacia rubi 1 Malacosoma neustria 5 Philudoria potatoria 1 3 Poecilocampa populi 20 13 2 9 Trichiura crataegi 1 1 LYMANTRIDAE Dasychira fascelina 1 D. pudibunda 1 Euproctis similis 9 12 12 1 Leucoma salic±s 1 NOLIDAE Nola cucullatella 1 NOTODONTIDAE Cerura vinula 1 Lophopteryx capucina 2 1 2 2 1 Notodonta dromedarius 1 N. trepida N. ziczac 1 1 7reosia 7noma 3 Pterostoma painina 3 — 307 — PUTTM,LT.w.2 • YIN STE, SB TD ST rincilliT)enris 226 is Pr:Z:1,TflAP, A7riphila eulmellus 24 376 1519 1265 402 . f. enieule,)s 2 127 A. inquinatellus 2 tristellus 5o) 90 70 261 110 Catoptria pinellus 1 Craibus falsellus 167 5 2 C. hortuellus 4 408 1082 1821 1235 C. pascuelius 1 1 C. perlellus 2 1028 1134 249 C. protellus 1 C. sp. (?mar7aritellus) 2 8 21 SPITTNC;TflAE Laothoe populi 8 2 1 1 THYATIRIDAE Achiya flavicornis 2 1 Habrosyne pvritoides 1 3 2 2 Tethea dupiaris 3 Thyatira batis 2 1 Unidentified 16