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,