LIFE HISTORY STRATEGIES OF TWO
CHORTHIPPUS SPP. IN RELATION TO
THEIR FIELD ^ECOLOGY
KATHRYN ANNE MONK
B.Sc. (HONS) DUNELM.
A THESIS SUBMITTED FOR THE DEGREE
OF DOCTOR OF PHILOSOPHY OF THE
UNIVERSITY OF LONDON AND FOR THE
DIPLOMA OF IMPERIAL COLLEGE
DEPARTMENT OF ZOOLOGY AND APPLIED ENTOMOLOGY,
IMPERIAL COLLEGE AT SILWOOD PARK,
ASCOT,
BERKS. NOVEMBER 1980 2.
ABSTRACT
Field populations of grasshoppers are known to demonstrate consider- able variability in developmental and reproductive phenomena. The aim of the study was to analyse the intra-specific variation in components of life history strategies in relation to habitat type. Two common British grass- hoppers, Chorthippus brunneus (Thunb.) and Chorthippus parallelus (Zett.)
(Orthoptera: Acrididae) were chosen as test species.
A survey of these species was made throughout South-East England.
The relationships between habitat type, as described by the floristic and structural composition of the vegetation, and the population density of the insects were analysed. Spatial and temporal differences in the morphometries and internal reproductive system of the female grasshoppers were also related to the habitat descriptions.
Three field sites supporting both species, yet displaying different habitat characteristics, were selected for intensive study. The micro- environmental conditions and the vegetational features of each habitat were recorded in conjunction with details of the grasshopper populations.
The total nitrogen content of the predominant grasses was determined and related to the grass species selected as food by the grasshoppers.
Complementary field and laboratory experiments, measuring the effects of density on adult longevity and reproductive capacity, were conducted.
Other laboratory studies were designed to show the extent of phenotypic variation in egg size, egg emergence times, and nymphal developmental periods.
Finally, inter-specific differences in the amount of phenotypic and genotypic variation were compared, and an evolutionary explanation for the differences in the field then examined. 3.
TABLE OF CONTENTS
Page
A6STRACT ••• ••• ••• ••• ••• ••• ••• ••• ••• ••• 2
LIST OF TABLES 8
LIST OF FIGURES 14
LIST OF APPENDICES 18
CHAPTER 1 : GENERAL INTRODUCTION 19
CHAPTER 2 : HABITAT DESCRIPTIONS AND ADAPTATION 24
2.1 Introduction 24
2.2 Methods ...... 29
2.2.1. Habitat Range 29
2.2.2. Grasshopper Populations 30
2.2.3. Morphometrical Analysis 31
2.3 Results ... 38
2.3.1. Habitat Types and Population Densities 38
2.3.2. Morphometrical Analysis 50
2.3.2.1. Spatial variation in morphometries ... 50
Differences between species (Analysis 1) ... 50
Differences in C. parallelus in 1978 and 1979
(Analysis 2) • • • ••• ••• • • • ••• ••• 36
Differences in C. brunneus in 1978 and 1979
(Analysis 3) ••• • • • ••• ••• ••• ••• 39
2.3.2.2. Temporal variation in morphometries within
sites ••• ••• • t • • • • ••• 63
Differences between species, in two years, in
seasonal trends (Analysis 4) ... 63
Temporal variation in C. parallelus in 1978
and 1979 (Analysis 5) ... 67 4.
Page
Temporal variation in C. brunneus in 1978 and
1979 (Analysis 6) 67
2.3.3. Spatial and Temporal Variation in Ovariole
Numbers ...... 73
2.3.3.1. Spatial variation in ovariole numbers ... 73
C. brunneus ... 73 \ C. parallelus 78
2.3.3.2. Temporal variation of ovariole number within
a site ...... 78
C. brunneus 78
C, paralletus 81
2.4 Discussion 81
CHAPTER 3 : OBSERVATIONS AND EXPERIMENTS ON THREE PERMANENT FIELD
SITE S ...... ••• ...... 87
3.1 Introduction 87
Physical Characteristics 87
Vegetational Structure and Composition 88
Nitrogen Content of Available Food and Feeding Prefer- OQ ences ...... «• ...... oo
Insect Population Dynamics ... 89
3.2 Physical Characteristics of the Field Sites 90
3.2.1. Methods 90
Microclimatic conditions 90
Methods of analysis 92
a) Surface and soil temperatures 92
b) Soil moisture 92
3.2.2. Results and Discussion 93 5.
Page
a) Surface temperature. ...
b) Soil moisture
c) Soil temperatures ...
3.3 Vegetational Structure and Composition
3.3.1. Methods of Monitoring Vegetational Change
Methods of analysis
Species composition
(1) 3 ~ diversity ...
(2) a - diversity ...
(3) Structural composition
3.3.2. Results and Discussion .
Summary ......
3.4 Nitrogen Content of Available Food
3.4.1. Methods
3.4.2. Results and Discussion .
Summary ......
3.5 Feeding Preferences ...
3.5.1. Methods
3.5.2. Results and Discussion .
C. parallelus ... .
C. brunneus
Summary ......
3.6 Insect Population Dynamics
3.6.1. Methods
3.6.2. Results and Discussion .
C. parallelus ...
C. brunneus 6.
Page
Summary of demographic variation ......
3.7 Field Experiments ......
3.7.1. Methods ......
a) Developmental periods and survival of nymphs
b) Adult longevity at different densities ...
c) Egg eclosion and fertility of adults ...
d) Fecundity of adult females
3.7.2. Results and Discussion
a) Developmental periods and survival of nymphs
b) Adult longevity at different densities ...
c) Egg eclosion and fertility of adults ...
d) Fecundity of the females
Summary ......
3.8 Discussion ......
CHAPTER 4 : LABORATORY EXPERIMENTS TO DETERMINE THE VARIATION IN
CERTAIN LIFE HISTORY COMPONENTS UNDER CONTROLLED
CONDITIONS
4.1 Introduction ...
4.2 Methods
4.2.1. Culturing Techniques
4.2.2. Experimental Work
1) Adult biology
Parameters from low density cages
Parameters from high density cages
2) Egg eclosion
3) Nymphal development
Effect of site 7.
Page
Effect of density 204
4.3 Results and Discussion 204
4.3.1. Hatching Distribution and Success 204
C. parallelus 204
C. brunneus 205
4.3.2. Nymphal Development 214
C. parallelus 214
C. brunneus 217
4.3.3. Adult Reproductive Biology 219
C. parallelus ... 220
C. brunneus 224
CHAPTER 5 : GENERAL DISCUSSION 233
ACKNOWLEDGEMENTS 239
REFERENCES 240
APPENDICES 264 8.
LIST OF TABLES
Page
TABLE 2.2.1 : Examples of morphometrical characters used in
previous studies on Acrididae 33
TABLE 2.2.2 : Morphometric measurements. 35
TABLE 2.3.1 : Survey sites 1978/1979 39
TABLE 2.3.2 : Sorensen's Coefficient of Similarity for vegetation of sites in 1978 survey ... 42
TABLE 2.3.3 : Sorensen's Coefficient of Similarity for vegetation
of sites in 1979 survey 43
TABLE 2.3.4 : Population densities from survey sites in 1978 and
1979* • • • ••• ••• ••• ••• • • • ••• ••• A 7
TABLE 2.3.5 : Samples taken from survey sites for morphometrical
analysis a) 1978, b) 1979. 51
TABLE 2.3.6 : Analysis of specific and yearly differences of
morphometries in C. brunneus and C. -parallelus. ... 53
TABLE 2.3.7 : Mean values of morphometric characters of C. para-
llelus and C. brunneus in 1978 and 1979...... 55
TABLE 2.3.8 : Analysis of morphometries in C. parallelus survey,
1978/1979 57
TABLE 2.3.9 : Analysis of morphometries in C. brunneus survey,
1978/1979 ...... 60 9.
Page
TABLE 2.3.10 : Samples used in analysis of temporal variation in
morphometries...... 64
TABLE 2.3.11 : Analysis of temporal variation in morphometries
within sites for C. parallelus and C. brunneus
(1978/1979) 65
TABLE 2.3.12 : Analysis of temporal variation in morphometries of
C. parallelus (1978/1979). ... 69
TABLE 2.3.13 : Analysis of temporal variation in morphometries of
C. brunneus (1978/1979) 71
TABLE 2.3.14 : Spatial variation in total ovariole number in C.
S • ••• ••• • • • ••• ••• ••• ••• 75
TABLE 2.3.15 : Spatial variation in total ovariole number in C.
parallelus 79
TABLE 2.3.16 : Temporal variation in total ovariole number in C.
brunneus and C. parallelus. 80
TABLE 3.2.1 : Geographical information on field sites 91
TABLE 3.3.1 : Seasonal variation in the Berger - Parker Dominance
index, using all plant species, 1978/1979 105
TABLE 3.3.2 : Percentage bare ground (1978/1979) 108
TABLE 3.4.1 : Total nitrogen content at each sampling time a) 1978, b) 1979. 112 10.
Page
TABLE 3.4.2 : Total nitrogen content at each sampling time,
1979* ••• ••• ••• • • • ••• ••• »• 115
TABLE 3.5.1 : Accuracy of grass species identification: percent-
age of samples identified as a particular species. . 120
TABLE 3.5.2 : Food selection by C. parallelus on 3 sites. ... 122
TABLE 3.5.3 : Food selection by C. brunneus on 3 sites 128
TABLE 3.5.4 : Summary of seasonal variation in food selection by
C. parallelus and C. brunneus 134
TABLE 3.5.5 : Abundance of grass species at each site and their
average total nitrogen content. 138
TABLE 3.6.1 : Population data for C. parallelus 147
TABLE 3.6.2 : Peak densities for C. parallelus populations and significance tests. 150
TABLE 3.6.3 : Life budgets and nymphal developmental periods of
C. parallelus. 155
TABLE 3.6.4 : Population data for C. brunneus. 158
TABLE 3.6.5 : Peak densities for C. brunneus populations and significance tests. 160
TABLE 3.6.6 : Life budgets and nymphal developmental periods of
C. brunneus 165 11.
Page
TABLE 3.7.1 : Nymphal developmental periods derived from caged
cohorts, 1978. 172
TABLE 3.7.2 : Regression coefficients from nymphal survival
curves...... 174
TABLE 3.7.3 : Two methods of derivation of mean and variance for
longevity in type B cages. 178
TABLE 3.7.4 : Egg eclosion in field cages for a) C. iparaHelus
and b) C. brunneus in 1979. 185
TABLE 3.7.5 : Fertility and fecundity of C. paralletus and C.
brunneus in field cages 187
TABLE 4.3.1 : Percentage hatch of eggs in an outdoor insectary. . 208
TABLE 4.3.2 : Hatchling dry weights from eggs laid under low and
high densities. ... 209
TABLE 4.3.3 : Developmental periods of nymphs hatched in 3 field
sites and reared in the laboratory 215
TABLE 4.3.4 : Developmental periods of nymphs hatched in the lab-
oratory - parents collected from 3 field sites. ... 216
TABLE 4.3.5 : Developmental periods of nymphs hatched in the lab-
oratory and reared under high and low density
conditions...... 218 12.
Page
TABLE 4.3.6 : Preoviposition period, interoviposition period and
postoviposition period of C. parallelus, from 3
field sites, under low density conditions in the
laboratory 221
TABLE 4.3.7 : Fecundity of C. parallelus from 3 field sites,
under low and high density conditions in the lab-
oratory...... 222
TABLE 4.3.8 : Adult longevity of C. parallelus from 3 field sites,
under low and high density conditions in the lab-
oratory. 223
TABLE 4.3.9 : Mean daily fecundity of C. parallelus from 3 field
sites, under low and high density conditions in
the laboratory. 225
TABLE 4.3.10 : Preoviposition period, interoviposition period and
postoviposition period of C. brunneus from 3 field
sites under low density conditions in the lab-
oratory...... 226
TABLE 4.3.11 : Fecundity of C. brunneus from 3 field sites, under
low and high density conditions in the laboratory. . 228
TABLE 4.3.12 : Adult longevity of C. brunneus from 3 field sites,
under low and high density conditions in the lab-
oratory...... 229 13.
Page
TABLE 4.3.13 : Mean daily fecundity of C. brunneus from 3 field
sites, under low and high density conditions in
the laboratory. ... 231 14.
LIST OF FIGURES
Page
FIGURE 2.1.1 : Distribution map of C. brunneus (U.K.) 25
FIGURE 2.1.2 : Distribution map of C. parallelus (U.K.) 26
FIGURE 2.2.1 : Platform used for morphometric measurements. 36
FIGURE 2.3.1 : Relationship between grasshopper density and
habitat, 1978 survey 45
FIGURE 2.3.2 : Relationship between grasshopper density and
habitat, 1979 survey 46
FIGURE 2.3.3 : Discrimination of populations of C. parallelus and
C. brunneus 1978 and 1979. 54
FIGURE 2.3.4 : Discrimination of populations of C. parallelus
from varying habitats in 1978 and 1979 58
FIGURE 2.3.5 : Discrimination of populations of C. brunneus from
varying habitats in 1978 and 1979 61
FIGURE 2.3.6 : Discrimination of temporal variation in 3 pop-
ulations of C. parallelus and C. brunneus.
(Canonical variates I and II) 66
FIGURE 2.3.7 : Discrimination of temporal variation in 3 pop-
ulations of C. pcorallelus and C. brunneus.
(Canonical variates I and III) 68
FIGURE 2.3.8 : Discrimination of temporal variation in 3 pop-
ulations of C. parallelus in 1978 and 1979. 70 15.
Page
FIGURE 2.3.9 : Discrimination of temporal variation in 3 pop-
ulations of C. brunneus in 1978 and 1979 72
FIGURE 2.3.10 : Relationship between femur length and ovariole
number of C. brunneus from different habitats. ... 77
FIGURE 3.2.1 : Exponential mean surface temperatures during
sampling period, 1978 and 1979. 94
FIGURE 3.2.2 : Percentage soil moisture during sampling period,
1978 and 1979 95
FIGURE 3.2.3 : Exponential mean soil temperature during sampling
period, 1979. ... 97
FIGURE 3.3.1 : Similarity between 3 field sites - Sorensen's Co-
efficient of Similarity. 102
FIGURE 3.3.2 : Seasonal changes in diversity of vegetation, using
all plant species. 103
FIGURE 3.3.3 : Seasonal changes in diversity of vegetation, using
grass species only. 104
FIGURE 3.3.4 : Seasonal changes in species height profiles, plus
diversity indices at each height 107
FIGURE 3.3.5 : Summary of floristic and structural composition of
3 field sites. ... 110
FIGURE 3.4.1a : Seasonal changes in total nitrogen content of each
grass species of site 1. 113 16.
Page
FIGURE 3.A.lb : Seasonal changes in total nitrogen content of each
grass species of sites 2 and 3. 114
FIGURE 3.6.1 : Total population curves of C. parallelus 149
FIGURE.3.6.2 : Total population curves of C. parallelus in
relation to day degrees. 151
FIGURE 3.6.3 : Partial population curves of C. parallelus in 1978. 152
FIGURE 3.6.4 : Partial population curves of C. parallelus in 1979. 153
FIGURE 3.6.5 : Total population curves of C. brunneus 159
FIGURE 3.6.6 : Total population curves of C. brunneus in relation to day degrees. ... 161
FIGURE 3.6.7 : Partial population curves of C. brunneus in 1978. . 162
FIGURE 3.6.8 : Partial population curves of C. brunneus in 1979. . 163
FIGURE 3.7.1 : Effect of density on longevity of C. parallelus
3-dul ts • ••• • • • ••• ••• ••• ••• ••• 179
FIGURE 3.7.2 : Effect of density on longevity of C. brunneus
3-d ults • ••• ••• ••• ••• ••• ••• ••• 131
FIGURE 3.7.3 : Effect of a) area and b) volume per individual on
longevity of C. parallelus 182
FIGURE 3.7.4 : Effect of a) area and b) volume per individual on
longevity of C. brunneus. ... 184 17.
Page
FIGURE 3.7.5 : Relationship between adult female longevity and
the no. egg pods laid in low density cages in C.
parallelus and C. brunneus 188
FIGURE 3.7.6 : Seasonal changes in dry weight (mg) of C. parallelus
and C. brunneus 189
FIGURE 3.8.1 : Habitat selection by C. parallelus and C. brunneus. 191
FIGURE 3.8.2 : Summary of C. paralletus field population demo-
graphy...... 192
FIGURE 3.8.3 : Summary of C. brunneus field population demo-
graphy• ••• ••• ••• ••• ••• ••• 193
FIGURE 4.3.1 : Hatching distribution of laboratory laid eggs of
C. parallelus in insectary 206
FIGURE 4.3.2 : Hatching distribution of laboratory laid egg pods
of C. parallelus in insectary. 207
FIGURE 4.3.3 : Hatching distribution of laboratory laid egg pods
of C. brunneus in insectary ... 210
FIGURE 4.3.4a : Hatching distribution of laboratory laid eggs of
C. brunneus in insectary, 1979. 211
FIGURE 4.3.4b : Hatching distribution of laboratory laid eggs of
C. brunneus in insectary, 1980. 212 18.
LIST OF APPENDICES
Page
APPENDIX 2 : Floral species list for sites in surveys 1978 and
1979. ••• ••• «•• • •• ••• i•» • • • ••• 264
APPENDIX 3a : Monthly meteorological data. 277
APPENDIX 3b : Trellis diagram of Sorensen's Coefficient of Similarity for survey sites 1978/1979. 279
APPENDIX 3c : No. touches/100 pins of each plant species at
permanent field sites. 282
APPENDIX 3d : Correlation between two methods of expressing height
profiles. ... •...... 285
APPENDIX 3e : Population sampling data 287
APPENDIX 3f : Change in nymphal cohorts of C. parallelus and C, brunneus in field cages, 1978• ••• ••• ••• •• • 301 19.
CHAPTER 1
GENERAL INTRODUCTION
The aim of the study is to investigate population quality in relation to reproductive status, developmental biology and habitat characteristics in two species of grasshopper.
It has been well documented that insect species display many life cycle types (Bonner, 1965; Alexander, 1968). A strategy, defined by the
Oxford English Dictionary, is a procedure calculated to gain some end, and thus a population biologist is concerned with the strategy whereby "a population manages to persist in the world" (MacArthur, 1965). Emphasis is therefore placed on the juxtaposition of various components or "co- adapted traits" (Stearns, 1976), which bring about the optimal strategy for a population in a particular environment (Wilbur, Tinkle & Collins, 1974;
Demetrius, 1975).
From early work on the evolution of life history strategies (Lack,
1948) the theory progressively highlighted single selective pressures which affect species.. MacArthur & Wilson (1967) emphasised the importance of population density in relation to the resources available, in the r- and K-selection theory; characters displayed by r- or K-strategists being compared by Pianka (1970). Since then, other factors which influence the evolution of a species' strategy have been recognised (Wilbur et al.,
1974). Giesel (1976) and Stearns (1976, 1977) provide extensive reviews of the subject. Recently, work has been particularly concerned with the effects of age-specific predation (Law, 1979a; Michod, 1979), and has shown that a strict application of the r- and K-selection theory does not always explain the observed life-history strategy. Many studies have compared the life-history strategies of different species (e.g. Alexander, 1968; Calow & Woollhead, 1977; Atkinson, 1979), in order "to explain the diversity of observable life history patterns in terms of a minimum number of selective pressures" (Wilbur et al., 1974).
However, it seems reasonable to suppose that a single species may adapt its strategy in accordance with its environment. Habitat type has been suggested as part of the selective pressure determining a species' eco- logical strategy (Southwood et al., 1974). For a species whose range covers several habitat types one might expect differences in each pop- ulations strategy. Stearns (1976) suggested that increased understanding would come from studies at the intra-specific level. A theoretical analysis of the effects of intra-specific variations was presented by
Oster (1976). Although detailed studies of plant populations have been carried out (Jain, 1976; Law, 1979b), little attention has been paid to this subject by animal ecologists. Crovello & Hacker(1972) compared the reproductive strategies of feral and urban subspecies of Aedes aegypti- (L) and found the former devoted less energy to offspring production,and eggs were produced over a longer period than by the urban species. These differences may have been brought about by lower survival to reproductive age in the urban environment. The subspecies were therefore exposed to different selective forces and evolved different strategies in response to demographic traits (Machado, 1971). Halkka et al (1973), Halkka,
Raatikainen & Halkka (1974), and Muller (1979) studied colour polymorphisms in different species of leafhopper, and found that there may be intra- specific variation in the strategies of these insects, based on the colour morphs. A genetic base for the colour morphs was found, and by implication the variation in the strategies may be genetically controlled. Other studies on intraspecific variation in life history strategies have been 21. carried out by Dearn (1977), Begon, Hart & Naylor (1979) and Hornbach, Way
& Burky (1980).
No work has so far combined the approaches of comparing different species' strategies and examining intraspecific variations, in relation to habitat.
Here,both inter- and intra-specific variation in the life-history strategies of two closely related species are investigated. The test species were Chorthippus parallelus (Zett.) and Chorthippus brunneus
(Thunb.) (Orthoptera: Acrididae). These were chosen for the following reasons:
1) Their ranges overlap.
2) They are known to show differences in morphological and reproductive
phenomena.
3) They are found on several sites within Silwood Park and throughout
South-east England.
4) Their general biology is well known.
5) Two closely related species allow comparison of life-history strategies
to be made with some bearing on their evolution.
The life cycles can be illustrated as follows: 22.
MARCH APRIL ' MAY JUNE JULY AUGUST SEPT. OCT
Egg C. brunneus Nymph Adult
C. parallelus -i
Richards & Waloff (1954) published an extensive study on their general biology and ecology; whilst the embryology of both species has been described by Moriarty (1969a, b, c; 1970). Waloff (1950) produced a descriptive paper on the structure and ecology of the egg pods. Choudhuri
(1954) studied the oviposition behaviour of both species in the laboratory.
In addition to these life history studies, energy budgets have been produced for C. parallelus by Qasxawi (1966) and Gyllenberg (1969) on grass meadows in England and Finland respectively. No such studies have been carried out with C, brunneus. The social behaviour of C, brunneus has, however^ been recently described by Young (1979).
The relationship of the various components can be seen in the flow chart: 23.
The approach was to investigate these components in both extensive and intensive .studies by:-
1) A study of the morphological and reproductive adaptations by each
species to habitat type,involving a survey of sites in southern England
2) Observations and experiments on three field sites of the species' pop-
ulation dynamics, and the influence of microclimate and food availabili
3) Laboratory experiments to determine the variation in certain life
history components under controlled conditions. 24.
CHAPTER 2
HABITAT DESCRIPTIONS AND ADAPTATION
2.1 Introduction
The aim of this chapter is to distinguish the various habitats preferred by C. brunneus and C. parallelus, and to investigate the extent of morphological adaptation to these habitats as shown by the adult females.
Both species occur in Europe, where grasshoppers form a small but fairly homogenous ecological and taxonomic group (Claridge & Singhrao,
1978). Their range extends to temperate Asia, and C. brunneus also occurs in North Africa (Ragge, 1965). All Orthoptera in the United Kingdom are near the limit of their natural ranges (Haes, 1973). Figs. 2.1.1 and
2.1.2 illustrate that C. parallelus is a more northerly species than C. brunneus (Marshall, 1974). The former's absence from Ireland is probably due to its relatively late arrival in Britain compared to C. brunneus, after the Irish Sea had risen (Ragge, 1965).
Little detail was known of their distribution in the United Kingdom in the first half of this century (Burr, 1936; Kevan, 1952), although
Diver & Diver (1933) described the overlap of their local distribution in an intensive study of Studland Heath, Dorset. Other area studies (e.g.
Brown & Searle, 1974) confirmed that the range of C. parallelus, our most common and "least discriminating" grasshopper (Ragge, 1965) extends to wetter areas, whilst C. brunneus prefers generally drier sites. These differences in local preferences mimic the extent of their geographical ranges, with C. brunneus occurring further south than C. parallelus. The habitat overlap is, however, extensive. 25.
FIGURE 2.1.1 : Distribution map of brunneus (U.K.). (After Stelton.1978) 26.
FIGURE 2.1.2 : Distribution map of C. parallelus (U.K.). (After Skelton, 1978) Tetaperature and humidity are the two most important limiting factors for the distribution of European species (Dreux, 1972) and North American species (Gage & Mukerji, 1977). These factors also correlate with pop- ulation density. Within their geographical ranges, most European species display variation in their preferred habitats (Bey-Bienko, 1965). Much emphasis has been placed on the occurrence of grasshoppers in different habitats, and, in 1913, Vestal linked local variations in grasshopper abundance to vegetational type. Later, Clark (1948) suggested a correlation between habitat structure and population density. Habitat structure and diversity are known to influence various aspects of population biology e.g. bird territories (James & Shugart, 1970) and, oh a community level, faunal
species diversity (Southwood, Brown & Reader, 1979). However, Kaufman
(1965) recognised that moisture also influenced grasshopper distribution between habitats. Most grasshopper species are mesophilic, their ranges
lying within dry to moist areas. A more generalised theory has been proposed by Sanger (1977), who showed that both community type, reflecting
temperature and moisture, and habitat structure contributed to the
habitat ranges of different species. Hence, to some extent local
distribution mimics geographical distribution, and can be described in the
same way. This is given credence by recent work showing that some grass-
hoppers display physiological and behavioural adaptation to thermal and
hydric stress (Anderson, Tracey & Abramsky, 1979).
The ecological plasticity of a species is known to increase with its
habitat range, and this may be reflected in its morphology (Pasquier,
1938) . Variation as found in local and clinal differentiation within a
species is considered to be primarily adaptive (Hubbell, 1956), and the aim
of morphometrical analyses of geographic variation is to elucidate this
adaptation (Bryant & Turner, 1978). Comparing closely related species may 28.
indicate their overall ecological relationships, the amount of character displacement between them indicating the lower limit of similarity for competing species (Maiorana, 1978) .
Morphological differences in populations of solitary grasshoppers were first described by Rubztov (1935) . He suggested that Chorthippus albomarginatus (DeGeer) showed phase differentiation similar to locusts in populationsof high and low densities. Since then,these qualitative changes have not been confirmed, although quantitative measurements on solitary grasshoppers and locusts have been similar (Uvarov, 1961).
Slight geographic variation in morphology was recorded in C, brunneus by Perdeck (1958), whilst stable colour patterns of several British grass- hoppers were shown to be associated with distinct morphological types
(Blackith, 1960). Recently, coloration in C. brunneus has been related to habitat type (Gill, 1979). Considered in conjunction with this, the work of Blackith (1960) suggests that morphometrical adaptation to habitat may occur.
The relationship between size and fecundity in insects (Southwood,
1976) suggests that a variation in fecundity between habitats, related to the morphometrical adaptation, may occur (Labeyrie, 1978). The fecundity potential of an insect has two major controlling factors, the number of ovarioles per female, and the number of eggs per ovariole (Kambysellis &
Heed, 1971).
Waloff (1954), using several species of Acridids from different geographical areas, found a highly significant relationship between mean body length and ovariole number. She suggested that climate influenced a species1 ovariole number. Within a narrower range, Morabine grasshoppers 29.
were investigated by Blackith & Blackith (1969b). Some species maintained a constant ovariole number, whilst others displayed variation along geographical clines. Waloff (1954) recorded that C. parallelus rarely deviated from the 5+5 arrangement of ovarioles (left and right ovaries)5 even in different geographical regions. C. brunneus, on the other hand, showed more frequent variations with an apparent seasonal increase, although no explanation for these differences was given. Coleoptera also show a wide range of ovariole numbers in some species, whilst others are highly stabilised, even between closely related species, (Robertson, 1961).
In Pseudodera xanthospila (Baly) intraspecific variation in ovariole number was related to body size (Suzuki, 1975). Virkki (1979) found that specific differences in ovariole number of flea beetles reflected genetic adaptation to different ecological niches, and Blackith & Blackith (1969b) found that variation along a geographical cline was also under genetic control. The clinal variation of ovariole number within another three species of Australian grasshopper was investigated by Dearn (1977) who related this variation to other life-history characteristics. Thus, the variation in ovariole number in a variety of insects appears to be of importance when considering the life history strategies both inter- and intra-specifically.
2.2 Methods
2.2.1. Habi ta_t Range
Over a period of two years twenty-five sites supporting either or both species of Chorthippus were surveyed. These were visited during
August and early September, when grasshopper populations consist mostly of adults. A range of habitats was covered, both locally and in the New
Forest area. At each site a floral species list was made. 30.
To quantify the vegetational differences between the sites, Sorensen's
Coefficient of Similarity, C , was employed:
where a = species present in Site A
b = those present in Site B
j = number of species occurring in both habitats A and B.
This was calculated for all samples for both years, and trellis diagrams and dendrograms constructed as described by Southwood (1978). Although a dendrogram masks much information, it provides a visual linear relationship between the sites, along which the densities of the grasshopper populations may be plotted.
A more intensive vegetation survey was made at a few selected sites, using fifty point quadrats to collect data for the calculation of Williams
Index of Diversity (a) . (For a full explanation of this method see chapter 3, section 3.3).
2.2.2. Grasshopper^ populations
Various methods for collecting grasshopper population data have been employed by previous workers. For example, specially adapted suction traps
(Qasrawi, 1966) mark and recapture methods or sweep samples (Richards &
Waloff, 1954; Blackith & Blackith, 1969a; Dyck, 1971; Robinson, 1973;
Chapman et at., 1979 ) visual counts (Claridge & Singhrao, 1978) and drop tents (Gabbutt, 1959 (for woodcrickets); Gandar, 1977) have been used.
Onslager (1977) presents a comparison of five methods used for estimating grasshopper population densities (night cages, cage samples, net samples, visual estimation and pointers). Onslager & Henry (1977) developed a modified method of the drop tent, using a metal ring placed on the ground some time before sampling. The bias and inaccuracy could be
estimated, but although only one worker was needed, the time delay inherent
in the method rendered it unsuitable for sites away from the Field Station,
especially those in the New Forest 1
An absolute method of sampling was considered most suitable as the
sites varied widely in structure, which would affect sampling efficiency.
A high-sided quadrat, 0.5 m by 0.5 m, was placed quietly on the ground at
random throughout the site, and all the grasshoppers within it identified.
One hundred samples were taken at each site.
2.2.3. Mo^phometrica_l_Analysis.
Between ten and twenty adult females were collected by sweep-net
from most of the populations. At sites 1, 2 and 3 (Silwood Park) specimens
were collected two or three times throughout the season, for an examination
of the temporal variation in the morphometries of the populations.
To preserve the specimens in a suitable condition for measurement and
dissection, it was found that freezing the insects individually, in
labelled tubes, gave the most satisfactory results. The exoskeleton does
not alter its dimensions or colour, and the internal organs remain in
perfect condition. When preserved in alcohol, with or without glycerine,
specimens are not easily dissected.
Only independent quantitative characters were chosen, as described
by Blackith (1965), to include lengths and breadths of parts as widely
spread over the organism as possible. Ten skeletal characters were
selected as recoirmended by Blackith & Reyment (1971) for a preliminary
experiment where little is known about the discriminatory powers of the
various characters. Ratios were not employed. Table 2.2.1 lists various characters employed by previous authors.
For example, in a study of Mbrabine grasshoppers, Blackith & Blackith
(1969b) used ten characters, whereas Blackith (1971) refers to many studies on locusts using only a few characters. He cites Dirsh (1953), as being one of the few workers who attempted to use more characters, although this work was too early for the application of multivariate analyses. Dirsh is also one of the few people to illustrate the skeletal parts measured. The ten measurements used here are all described by Dirsh, and reference may be made to his drawings. The characters are listed in Table 2.2.2.
Measurement of each character was made by a micrometer eye-piece on a bino^cular microscope, combined with a movable platform placed on the stage. This platform was an adaptation of one produced by Dr. N. Jago
(Centre for Overseas Pest Research). It avoids the use of a scale factor when altering the magnification, and is more suitable for measuring large insects than a micrometer (Fig. 2.2.1.).
As these data were a priori in definable groups, a canonical variate analysis was employed, whereby the within-group variation is minimised, and the between-group variation is maximised. If k samples are collected, each from different populations, and plotted on Cartesian co-ordinates, they will form ellipsoid swarms if the variables are multivariate normally distributed. Canonical analysis transforms the original axes or vectors, resulting in a reduction of the within-sample ellipsoid to a sphere. The first transformed axis is inclined in the direction of greatest variability, the second perpendicular to the first in the direction of the next largest variability and so on. These latent vectors are not generally orthogonal to each other. A set of discriminant functions or latent vectors are therefore produced which correspond to the latent roots or eigenvalues of the determinants! equation of this analysis. The coefficients of the TABLE 2.2.1 : Examples of roorphometrical characters used in previous studies on Acrididae.
* * _ to u o w 1969 b oc a c. t> 2 f CT> 3 to 196 6 s. .-I -tl rj C a o ou •RI ra • 0. •W -u 196 0 o C. Cen. gregaria E ^ s o e spp . <3 * m ai. , Q W c Blackith , 0
196 0 •a c r-i al ., S £ a* -t-i 195 7 iJ to spp . c t & fl 0 - EE 3 3 6 >. o «fc-
195 3 ra s. S S 193 0 e t a. 03 O S O> -Cl9 tn -S •o o o U £ ? c .C <9 W O Bhanota r S 5 Stove r 5 . Morabin c 5 . Blackith , Blackith , Sahistoaevca Chorthippus Dirsh , Spett , Bi CJ s a e-. ^ CJ C. j L. HIND FEMUR / / / / / / / / / . J / J HEAD WIDTH AT GENAE / • / / / / / / L. TEGMEN / • / • / / / • /' / / L. ANTENNA / L. HIND WING / RATIOS / / / W. EYE • / / / L. PRONOTUM / / / • / W. PRONOTUM / • / / / W. VERTEX / / / / L. BODY / / H. PRONOTUM V • W. MESOSTERNUM / • L. ANTERIOR FEMUR / L. MID FEMUR J J L. EYE / J L. PROZONA / • TABLE 2.2.1 : Continued. O to 1969 b 3 CO •2 * o ~ VO £, o iciie 2 a rvi 196 6 * c spp . gregaria Ov t; * 196 0 1e3 -O Ul C. sanquinipea al. , Blackith , ^ £ ra * C- 196 0 C 195 7 JJ to Cl D. K al. , et spp . 4 migrator n in 193 5 3 3 ts c 194 1 196 8 c migratcria CL, ^ o 195 3 193 0 et •0 ft Ci, <3 t, — at; * § ^ t) a -or: « o .c — 0 « E c. 4 0 gregaria grcgaria parallelus albomarginatus 3 •H <3 tr Ul Bhanota r Blackit h A Stowe r Putnam , E « Blackith , S. Blackith , Chorthipp-is 5 . Morabin e Schistocerca Melanopluc Locusta Dirsh , Spett , Thomas , C. Rubtzov , C. CL, s; u fc k I L. METAZONA / / W. METASTERNUM / / W. HIND FEMUR • / / V. ANTERIOR FEMUR / / NO. EYE STRIPES / / L. FRONS / W. HEAD AT OCULLAR LEVEL / W. TEGMEN / W. EPIPROCT / L. EPIPROCT / W. MEDIAL AND CUBITAL AREAS OF / TEGMEN CONTOUR OF VERTEX / * Also used non-aorphometric characters. 35. TABLE 2.2.2 : Morphometric measurements. E = Maximum length of right tegmen F = Maximum length of right hind femur P = Length of prozona M = Length of metazona H = Height of pronotum Ey = Length of right eye (vertical diameter) St = Total length of thoracic sterna W = Width of mesosternum C = Maximum width of head at genae V = Width of vertex FIGURE 2.2.1 : Platform used for morphometric measurements. Dial indicator gauge, direct reading in mm. Cork platform rotates for easy manoeuvrability characters in each discriminant function correspond to the elements of these latent vectors and indicate the relative importance of each character to the discriminatory power of that vector (Blackith, 1960; Seal, 1964; Blackith & Reyment, 1971). A program by R.G. Davies (Dept. Zoology and Applied Entomology, Imperial College of Science and Technology) was used for all the canonical variate analyses. This uses data for any number of cases arranged in groups,each containing a variable number of sets of characters. It calculates the mean and standard deviation for each character in each group, and for the total data set. It then extracts the latent roots and vectors from the dispersion matrix, and computes the percentage discrimination of each latent root and the normalized eigen- vectors. It then calculates the canonical variates for both the stipulated groups and all the individuals. In all the analyses carried out here, only the group values (group centroids) are plotted for clarity. Canonical variate analysis depends on the assumption that the characters are multivariate normally distributed, and that the sample dispersion matrices are homogenous. Tests to see if the latter assumption is true depend on the correctness of the first, and the testing of the characters for multivariate normality is a laborious task. If the hetero- geneity is not great then there is little effect on the analysis, and the data here appeared suitable (R.G. Davies, pers. comm.). After each specimen had been measured, it was dissected and the number of ovarioles on each ovary was recorded. Waloff (1954) describes the number and development of ovarioles in various Acridids. The mean ovariole number of each species at each site was analysed with respect to habitat type and the morphometrical analyses. 38. 2.3 Results 2.3.1. ftabitat_ Typ_es_ _and_ ]Po£ul_a_tio_n_Dens^it_ie^s The sites surveyed are listed in Table 2.3.1 with National Grid references and general habitat descriptions. Each site was ascribed a code mnemonic, also shown in the table, and these will be referred to in the text from now on. The plant species lists for each site are in appendix 2. The vegetational relationships between the sites are illustrated in Tables 2.3.2 and 2.3.3 as trellis diagrams for each year. In 1978 the sites on which C. paraVleVus and C. brunneus were found formed a continuum, only two sites, DB (extremely wet) and CH2 (very dry) being completely dissimilar from other community types. Three main communities, heathland, grassland, and the motorway central reservations, were distinguished. Within the two former groups a moisture gradient was evident; from DB to CH2 in the heathland, and from dry LNF to the wet meadows of sites 2 and PF in the grassland. The motorway sites were most closely associated with the grasslands, but even here the level was very low, Cg = 0.29. MB was seen as an intermediate site between the grassland and heathland. The relationships are most easily categorised as combinations of the following: either Heathland/Grassland which are 1) Dry/Wet 2) Short/Tall i.e. each category has overlapping areas. In 1979 the survey was extended to twenty-two sites, including two coastal areas. Several sites were intermediate between the heathland and grassland communities. The motorway sites were most closely related to the drier heathland sites in this season's extended analysis. MB and PE TABLE 2.3.1 : Survey sites 1978/1979. YEAR SPECIES PRESENT SITE HABITAT LOCATION GRID REF. SITE " CODE DESCRIPTION VISITED C. parallelus C. brunneus CANFORD HEATH, DORSET SZ 022941 CH 1 / - GRASSY HEATH CHOBHAM COMMON, SURREY SU 972642 CH2 1 / / OPEN GRASSY ACID HEATH POND FIELD, SILWOOD SU 945691 PF 1 / - WET MEADOW DENNY BOG, NEW FOREST SU 361060 DB 1 / - BOG NORTH GRAVEL, SILWOOD SU 947688 NG B / / DISTURBED GRASS- LAND SOUTH GRAVEL, SILWOOD SU 948686 SG B / / OPEN GRASSLAND M4.1 TQ 088786 M4 B - / DRY OPEN MAIDENHEAD MOTORWAY SU 891790 MM B - / DRY OPEN ELM SLOPE, SILWOOD SU 944686 1 B / / DRY GRASSLAND RUSH MEADOW, SILWOOD SU 938692 2 B / / WET MEADOW PENNY HILL, CROWN ESTATES, SU 871664 3 B / / OPEN ACID HEATH BERKS. BISLEY NRA RANGES, SURREY SU 939583 B B / / OPEN ACID HEATH TABLE 2.3.1 : Continued. YEAR SPECIES PRESENT SITE HABITAT LOCATION GRID REF. SITE CODE DESCRIPTION VISITED C. parallelus C. brunneus MATLEY BOG, NEW FOREST SU 336076 MB B / - WET HEATH GARRISON RIDGE, SILWOOD SU 947688 GR B / - THICK GRASSLAND SANDHURST, RMA, BERKS. SU 873637 S B / / ACID HEATH RIDE RHS NASH'S FIELD, SILWOOD SU 945689 RNF B / PRESENT ONLY MEADOW IN 78 LHS NASH'S FIELD, SILWOOD SU 944689 LNF B / / MEADOW BALMER LAWN, NEW FOREST SU 305035 NFB 2 - • HEAVILY GRAZED GRASSLAND GRAVEL PIT, SILWOOD SU 939694 GP 2 - / OPEN DRY GRASS- LAND PIGNALL ENCLOSURE, NEW SU 316039 PE 2 / - GRASSY RIDE FOREST PAGHAM HARBOUR SZ 878976 PH 2 / - SALT MARSH EDGE LONGSLADE BOTTOM, NEW SU 261005 LB 2 — GRASSY HEATH FOREST / TABLE 2.3.1 : Continued. YEAR SPECIES PRESENT SITE HABITAT LOCATION GRID REF. SITE CODE DESCRIPTION VISITED C. parallelus C. • brunneus LEPE, HAMPSHIRE SZ 453986 L 2 - / SALT MARSH GRACIOUS POND, SURREY SU 994636 GPD 2 - / GRASSY HEATH OPEN SILWOOD BOTTOM, SILWOOD SU 944686 SB 2 / / DISTURBED GRASS- LAND M42 TQ 148786 M42 2 - / DRY OPEN CENTRAL RESERVATION Year site visited: 1 = 1978 only; 2 = 1979 only; B = 1978 and 1979. TABLE 2.3.2 : Sorensen's Coefficient of Similarity for vegetation of sites in 1978 survey. DB S 3 B Ch2 CH MB 1 LNF RNF SG NG GR 2 PF MA MM .09 HEATH .17 .64 .26 .50 .56 .21 .40 .48 .50 .18 .43 .42 .43 .42 Grassy Damp .11 .20 .29 .30 .21 0 .15 .07 .07 .23 .35 Open dry 0 .07 .07 0 .22 .25 .55 0 .08 .07 0 .16 .18 .41 .88 GRASSLAND 0 .08 .07 .08 .16 .27 .48 .67 .64 0 .07 .07 .07 .22 .17 .39 .63 .67 .60 0 .10 .09 .06 .15 .11 .36 .57 .55 .41 .57 0 .17 .22 .06 .23 .19 .51 .45 .37 .42 .35 .52 WET MEADOW 0 .23 .22 0 .16 .27 .48 .40 .36 .50 .40 .36 .53 0 0 .10 .24 .13 .15 .10 .19 .21 .21 .29 .14 MOTORWA/ dry open 0 0 0 .12 .13 0 .10 .19 .21 .21 .29 .14 .40 TABLE 2.3.3 : Sorensens Coefficient of Similarity for vegetation of sites in 1979 survey. 3 S B GPD LB MB PE MM M42 M4 NFB SB 1 GP SG RNF LNF NG GR 2 PH L .62 .50 .50 HEATH .40 .50 .44 .32 .32 .47 .62 Grassy Damp .19 .19 .32 .23 .43 .29 .29 .21 .27 .14 0 .11 .15 0 0 0 0 0 Dry Open 0 .10 .11 .14 0 0 0 .62 MOTORWAY 0 .11 .25 .17 . 18 .15 0 .36 .50 .36 .40 .25 .40 .35 .27 .13 ..13 .29 .18 Open 06 .06 0 .07 .07 .14 .07 .07 .07 0 .13 Dry 08 .08 .08 .10 .21 .38 .10 .11 .10 .22 .27 .18 07 .15 .08 .10 .10 .27 .09 .20 .19 .21 .43 .46 .52 GRASSLAND 07 .07 .08 .10 .20 .27 .09 .20 .19 .21 .26 .40 .44 .50 08 .08 .08 .10 .21 .19 .19 .21 .20 .22 .27 .41 .39 .59 .74 08 .08 .08 .10 .21 .29 .19 .21 .20 .22 .27 .29 .39 .52 .74 .69 .08 .15 '.08 .20 .21 .19 .10 .32 .30 .33 .18 .18 .46 .44 .59 .62 .69 WET MEADOW .11 .06 0 .07 .07 .13 .13 .14 .13 .07 .18 .45 .39 .49 .38 .56 .44 .44 .11 .17 .06 .07 .14 . 13 .19 .14 .13 .14 .19 .23 .33 .43 .39 .33 .39 .33 .43 0 0 .13 0 .20 .17 0 0 0 .22 .24 .07 .12 .11 .12 .12 .07 .11 .12 SALT 0 0 .08 0 .11 .10 0 0 0 .11 .09 0 .08 .07 .07 .08 .08 .06 .47 MARSH were also intermediaries, but completely dissimilar to the motorway sites. Of the other communities, the salt marsh sites showed the highest, albeit quite low, similarity to the drier grasslands. The dendrograms produced from these trellis diagrams therefore give a simplified picture of the interrelationships. If the intermediary sites are visualised at right angles to the plane of the paper (Southwood, 1978) the relationships between habitat range and population density of the grasshopper species (Figs. 2.3.1 and 2.3.2) become clearer. In 1978, C. brunneus was scarcer than in preliminary searches in 1977 and in some areas populations had disappeared. C. paralZetus was also depressed in 1978, but to a lesser extent. The following year the pop- ulations of both had increased in some sites (Table 2.3.4). As 1976 was extremely hot and dry^ this pattern reflects that of the population cycles for these grasshopper species at Silwood Park in 1947-1951 (Richards & Waloff, 1954). Both species peaked in 1949, the summer of which was extremely hot. The populations decreased considerably in 1950 and 1951. Other studies have revealed density ranges for these species which are equable considering the yearly fluctuations possible; for example, Qasrawi (1966) found peak densities for populations of C. parallelus of 2.10 m~2 in 1964 and 1.35 m~2 in 1965, whilst Gyllenberg (1969) in Finland found 5-8 m~2 in 1966. The highest population densities for both species were found in the grassland sites, whilst the numbers of C. brunneus decreased more rapidly than C. parallelus in the wet sites. Conversely, on dry heathland C. brunneus seemed to be better adapted than C. parallelus, in that relative to the numbers in grassland they were not so diminished. The motorway central reservations were a particularly interesting case. They were very dry and supported the highest population densities of C. . 45. No.r*f? 2.2 1 J6 ID « 3.1 3.6 OA WET -— HEATHS DRy DRy GRASSLAND WET DRY M-WAY db s 3 b ch2 ch mb l Inf rnf sg ng gr 2 pf rtu mm JQQ 80 60 40 20 FIGURE 2.3.1 Relationship between grasshopper density and habitat, 1978 survey. • = C. brunneus, A = C. parallelus, a = Williams index of diversity. C = Sorensen's Coefficient of Similarity. FIGURE 2.3.2 : Relationship between grasshopper density and habitat, 1979 survey. • = C." brunneus, A = C. parallelus, a = Williams index of diversity. Cs = Sorensen's Coefficient of Similarity. 10.0 6JD 2.0 1.0 No.m*2 0.6 -P- CN 0.2 DRY HEATHS WET 3 s b gpd lb mb pe mm m*2 rru nfb sb i gp sg rnf Inf ng gr 2 ph 100 80 60 40 20 47. TABLE 2.3.4 : Population densities from survey sites in 1978 and 1979 ( x ± S.E., n = 100, m"2 ) 1978 SITE C. PARALLELUS C. BRUNNEUS CODE GR 0. 78 ± 0.1 1 0 RNF 1. 72 + 0. 25 0 04 + 0.0 2 LNF 0. 87 + 0. 16 0. 32 + 0.0 6 PF 0. 31 + 0. 06 0 NG 0. 71 + 0. 11 0. 38 + 0.0 7 SG 0. 03 + 0. 01 0. 16 + 0.0 3 1 0. 69 + 0. 24 0, 64 + 0. 02 2 0. 80 + 0. 15 0. 24 + 0. 06 B 0. 15 + 0. 04 0 09 + 0. 03 S 0. 04 + 0. 02 0. 15 + 0. 03 CH2 0. 11 + 0. 03 0. 05 + 0.0 3 M4 0 2. 16 + 0. 27 MM 0 0.8 6 + 0. 13 3 0. 15 + 0. 04 0. 03 + 0. 02 MB 0. 14 + 0. 03 0 CH 0. 10 + 0. 03 0 DB 0. 09 + 0. 02 0 48. TABLE 2.3.4 : Continued. 1979 SITE C. PARALLELUS C. BRUNNEUS CODE GP 0 0. 17 + 0.0 6 LNF 0. 62 + 0 27 0. 43 + 0. 14 RNF 0. 87 + 0. 17 0 NG 0. 86 + 0. 16 0. 60 + 0. 17 SG 0. 65 + 0. 13 0. 29 + 0. 06 GR 0. 87 + 0. 19 0 SB 0. 70 + 0. 17 0. 80 + 0. 16 1 0. 75 + 0. 18 0. 39 + 0. 06 2 0 .49 + 0,.0 7 0. 20 + 0. 07 GPD 0 0. 17 + 0.0 5 3 0, 05 + 0. 02 0 .19 + 0. 04 S 0. 10 + 0. 03 0. 29 + 0. 05 B 0. 11 + 0. 03 0. 23 + 0. 06 M4 0 6. 79 + 0. 74 M42 0 9. 40 + 0. 93 MM 0 2. 00 ± 0. 18 NFB 0 0. 17 + 0. 05 MB 0. 09 + 0. 03 0 PE 0. 12 + 0. 04 0 PH 0 04 + 0. 02 0 LB 0 0. 20 + 0. 04 L 0 4. 23 + 0. 38 brunneus in both years. These sites were floristically similar to the dry grassland sites of LNF, RNF and NG which also supported relatively high densities. Port & Thompson (1980) have suggested that this apparent motorway anomaly, also seen in other insect groups, may have been due to the relatively high total nitrogen content found in the grasses on the central reservation; a complementary survey of the total nitrogen content was not made here, but this point is dealt with in more detail in chapter 3, sections 3.4 and 3.5. C, paraHelus was not found on any motorway site. This may have been partially due to the extreme drjness of this habitat. Also, this species is less mobile than C. brunneus. An interesting speculation is that C. brunneus may be more salt-tolerant than C. parallelus, and this is given some credence by the fact that the other relatively high density pop- ulation of C. brunneus was found at Lepe, a salt marsh where no C. parallelus occurred. Although very wet, the effective habitat may cause dessication because of the saltier water which the latter species could not stand. However, a very low density population of C. parallelus was found at Pagham Harbour, on the very edge of the salt marsh; there were no C. brunneus present. Without laboratory experiments to ascertain the effect of the salt marsh environment on these species, and further field surveys of these habitat types, little further can be said. When considering a small habitat sample such as this, a species1 absence may be because it has not reached that habitat, rather than a particular limiting factor. The indices of diversity shown on Figs. 2.3.1 and 2.3.2 did not correlate with the population densities in either year. However, the similarity of the indices between sites may well reflect the structure which is most suitable for these grasshoppers. 50. 2.3.2. Mo£phome tri^ca^Analyjsis^ 2.3.2.1. Sj)atial variation in morphometries The sites from which samples for morphometrical analysis were collected are listed in Table 2.3.5. The same site identification codes as in Table 2.3.1 are used throughout this section. All raw data matrices are held at Imperial College at Silwood Park. Differences between species (Analysis 1) Differences between the species in both years were examined by an analysis on four groups, each consisting of all individuals of one species collected in one year. The total variation in the data was explained by the first three latent vectors. These vectors and the coefficients or weights characterising each vector are shown in Table 2.3.6. Fig. 2.3.3 shows the group centroids produced with respect to the first and second canonical variates. The first canonical variate resulted from a contrast in prozonal length relative to the tegmen length and effected complete separation of the species. This vector reflects the differences in wing length between C. parallelus and C. brunneus, the former being brachypterous. The second canonical variate reflected a change in shape in both insects from 1978 to 1979. This resulted from an increase in the eye depth and mesosternum width, relative to the metazonal length and thoracic height. The direction of the change in shape was the same in both species, although the difference was more pronounced in C. parallelus. The distribution of the weights characterising the second vector and the mean values for each character (Table 2.3.7) suggest that both species tended to become shorter and wider in 1979, as lengths and heights decreased, and widths increased. The summer of 1979 was generally TABLE 2.3.5 : Samples taken from survey sites for morphometrical analysis a) 1978, b) 1979. C. parallelus 1978 1979 DATE NO. OF DATE NO. OF OlllOTTTTi oillQTTTTj COLLECTED SPECIMENS COLLECTED SPECIMENS Bisley 24.8.78 20 Bisley 2.8.79 17 Matley Bog 27.8.78 17 South Gravel 28.8.79 20 Garrison Ridge 19.9.78 13 RHS Nash's Field 24.8.79 20 Canford Heath 27.8.78 20 LHS Nash's Field 4.9.79 20 Chobham Common 24.8.78 8 Pignall Enclosure 2.9.79 11 Denny Bog 27.8.78 17 Pagham Harbour 9.9.79 10 LHS Nash's Field 28.8.78 20 Matley Bog 8.8.79 16 North Gravel 15.9.78 19 North Gravel 20.8.79 20 South Gravel 18.9.78 8 Garrison Ridge 14.9.79 20 Pond Field 1.8.78 6 Sandhurst 10.9.79 11 RHS Nash's Field 18.9.78 19 Silwood Bottom 12.9.79 14 Site 1 22.8.78 23 Site 1 20.8.79 20 Site 2 21.8.78 20 Site 2 21.8.79 17 Site 3 23.8.78 22 Site 3 27.8.79 13 TABLE 2.3.5 : Continued. C, brunneus 1978 1979 DATE NO. OF DATE NO. OF SITE SITE COLLECTED SPECIMENS COLLECTED SPECIMENS Chobham Common 24.8.78 9 M4 29.8.79 20 Maidenhead Motorway 31.8.78 20 Maidenhead Motorway 29.8.79 14 LHS Nash's Field 28.8.78 17 LHS Nash's Field 4.9.79 10 Bisley 24.8.78 9 M42 29.8.79 8 North Gravel 15.9.78 21 Balmer Lawn 8.8.79 5 M4 31.8.78 15 South Gravel 28.8.79 20. Site 1 22.8.78 10 North Gravel 28.8.79 20 Site 3 23.8.78 17 Longslade Bottom 2.9.79 11 Gracious Pond 5.9.79 13 Silwood Bottom 12.9.79 20 Lepe 8.8.79 15 Gravel Pit 12.9.79 20 Site 1 30.8.79 20 Site 2 30.8.79 6 Site 3 12.9.79 17 53. TABLE 2.3.6 : Analysis of specific and yearly differences of morphometries in C. brunneus and C. parallelus. VECTOR I II III LATENT ROOTS 48.272 .466 .034 PERCENTAGE 98.975 DISCRIMINATION .955 .070 CHARACTERS E -.212 -.009 .017 F .062 -.155 -.092 P .938 .088 -.316 M .009 -.215 -.234 H -.049 -.255 -.100 Ey .030 .689 -.041 St -.138 .247 .134 W -.104 .552 -.303 c .167 -.122 .846 V .100 -.029 .022 54. "cO Q 0.85 79 O 2.517 h-ttL z u Q_ 3 o &CeZ UJ § 0.75 a; 0J78 >< 0.155 1 U< z o -2.0 -1.0 0 +1.0 FIRST CANONICAL VARIATE O C. brunneus (GROUP CENTROIDS) A C. parallelus FIGURE 2.3.3 : Discrimination of populations of C. parallelus and C. brunneus in 1978 and 1979. (Canonical variates I and II) TABLE 2.3.7 : Mean values of morphometric characters of C. parallelus and C. brunneus in 1978 and 1979 (x ± S.E. mm.) C. PARALLELUS C. BRUNNEUS CHARACTER (code as 1978 1979 1978 1979 in Table 2.2.2) n = 232 n = 229 n = 118 n = 219 E 6.82 ± 0.05 6.70 ± 0.06 16.95 ± 0.09 16.75 ± 0.07 F 11.27 ± 0.04 11.10 ± 0.04 11.83 ± 0.07 11.63 ± 0.05 P 1.87 ± 0.01 1.90 ± 0.01 1.60 ± 0.01 1.61 ± 0.01 M 1.77 ± 0.02 1.72 ± 0.01 2.18 ± 0.02 2.09 ± 0.01 H 3.18 ± 0.02 3.15 ± 0.02 3.45 ± 0.02 3.41 ± 0.02 Ey 1.77 ± 0.01 1.83 ± 0.01 1.76 ± 0.01 1.80 ± 0.01 St 4.30 ± 0.01 4.42 ± 0.02 4.95 ± 0.03 5.05 ± 0.02 W 2.99 ± 0.01 3.10 ± 0.01 3.33 ± 0.02 3.39 ± 0.01 c 3.36 ± 0.01 3.32 ± 0.01 3.23 ± 0.01 3.26 ± 0.01 V 1.11 ± 0.03 1.08 ± 0.01 0.97 ± 0.01 0.97 ± 0.01 hotter and drier than that of 1978, and the change in shape of these species might have been influenced by this. A shorter, wider insect main- taining the same volume as a long, thin insect would have a smaller surface area/volume ratio, and hence decreased water loss. This agrees with the preference of C. parallelus for more mesic habitats than C. brunneus, as it was the former species that showed a greater difference in shape between the two years. Differences in C. parallelus in 1978 and 1979 (Analysis 2) This used samples of C. parallelus from the surveys in 1978 and 1979. The first ten latent vectors explained 99.99% of the total variance, the first three accounting for 81.05% (Table 2.3.8). Fig. 2.3.4 shows the group centroids for each population of C. parallelus for the first two canonical variates. These explained 74.64% of the total variation in the data. The first canonical variate effected partial discrimination between habitat types. This resulted from a contrast between the head width across the genae, relative to the eye depth and sternum width. The second canonical variate represented the change in shape from 1978 and 1979, and resulted from the same contrast of characters as found in the first analysis i.e. a polarity between widths and lengths. There was some overlap along this axis, however, as eye depth and sternum width influenced both axes. The grouping of sites according to habitat type and year was more easily identified by inferred axes drawn at 31° to the original. Comparing the distribution of the sites along the new axes with Figs. 2.3.1 and 2.3.2, it is clear that the sites contained in the heathland community in both years lie on the same side, whilst the grassland sites lie to the left. (It is interesting that the two 'bog* types, DB and MB were associated with the heathland sites). TABLE 2.3.8 : Analysis of morphometries in C, parallelus survey, 1978/1979. VECTOR I II III IV V VI VII VIII IX X LATENT ROOTS 2.099 .553 .228 .220 .141 .104 .079 .059 .037 .033 PERCENTAGE 59.065 15.577 6.411 6.189 3.976 2.921 2.234 DISCRIMINATION 1.671 1.041 .915 CHARACTERS E .003 -.037 .028 .029 -.165 .054 .070 .005 -.050 .035 F .081 -.044 -.084 -.234 .101 -.110 .066 -.111 -.103 .016 P -.174 .088 .022 -.449 -.138 .520 -.889 .560 -.434 .372 M -.025 -.193 -.341 .038 -.024 -.170 .018 .418 .403 .295 H .092 -.253 -.591 .149 -.173 .051 -.098 -.168 -.088 -.295 Ey -.343 .600 .040 .668 .723 -.270 .198 -.477 -.442 .768 St -.233 .194 .270 .062 -.517 -.531 -.081 .178 -.100 -.144 W -.240 .673 -.385 -.196 .242 .550 .352 -.092 .519 -.260 c .851 .192 .550 .478 .000 .160 -.124 -.002 .360 -.010 V .023 .028 -.021 .048 .256 -.004 .073 .451 -.153 -.088 CO g O »— 3.2 Z U J Q_ oCtL SUJ CtZ < 3.0 U Z O CtnO Z< u Q Z uo UJ 2.8 CO 1.4 1.6 1.8 A 1978 FIRST CANONICAL VARIATE (GROUP CENTROIDS) A 1979 FIGURE 2.3.4 : Discrimination of populations of C. parallelus from varying habitats in 1978 and 1979. (Canonical variates I and II) Only in 1979 were two sites (3 and PE) on the.left when expected to be on the right. The wet meadow sites (2 and PF, plus PH in 1979) did not show any consistent pattern,but lay on the periphery of the grassland cluster. The difference in shape of C. parallelus between grasslands and heathlands was therefore generally maintained in the two years. The insects altered in shape from 1978 to 1979 as described in analysis 1. Comparing the positions of the sites included in both years along the newly defined axes, the median grassland sites such as NG and GR varied little, but less suit- able sites such as heathland and very wet sites changed much less uniformly. Differences between grassland sites decreased in 1979, whereas specimens from heathland sites were further differentiated. There was no obvious differentiation between geographical areas, as the sites were organised by habitat type. Differences in C. brunneus in 1978 and 1979 (Analysis 3) All samples of C. brunneus for 1978 and 1979 were analysed together, as in the complementary analysis for C. parallelus. Only 53.31% of the variation in the data was accounted for by the first two canonical variates (Table 2.3.9) as compared to 74.64% for C. parallelus. It was therefore surprising to find that similar patterns to those for C. parallelus could be seen in the relationships between sites as described by the first two canonical variates (Fig. 2.3.5). The first canonical variate partially discriminated samples from the two years. The difference in shape from 1978 to 1979 resulted from a contrast between the width of the head across the genae and the eye depth, relative to the prozonal and metazonal lengths i.e. a marked polarity in widths and lengths. The second canonical variate resulted from an increased vertex width and eye depth, relative to the prozonal length and sternum length in the heathland habitats as compared to the grassland sites. Again, the groupings were separated more distinctly TABLE 2.3.9 : Analysis of morphometries in C. brunneus survey, 1978/1979. VECTOR I II III IV V VI VII VIII IX X LATENT ROOTS .640 .494 .303 .287 .181 .104 .078 .058 .042 .024 PERCENTAGE 28.944 DISCRIMINATION 22.361 13.694 12.990 8.168 4.722 3.528 2.629 1.884 1.080 CHARACTERS E .020 -.028 .020 .011 -.016 -.027 .054 .023 .040 -.143 F .132 .040 -.066 -.014 .059 .123 -.027 -.194 .027 -.022 P .221 .263 .288 .156 -.057 -.642 .722 -.457 -.555 .741 M .375 -.163 .022 -.067 .339 -.296 -.146 .361 .200 .551 H .191 -.035 -.035 .007 -.721 .247 .084 .229 -.120 -.124 Ey -.660 -.354 .246 -.034 .097 -.261 .004 -.573 .733 .298 St -.146 .499 -.133 -.018 -.158 -.205 -.232 .111 .111 -.105 W -.092 -.107 .672 .113 .313 .449 -.054 .250 -.124 -.009 c -.499 -.077 -.529 -.146 .462 .194 .317 .394 -.050 .081 V -.203 -.714 -.317 .967 -.111 -.273 -.538 -.109 -.260 -.071 _ _ FIRST CANONICAL VARIATE (GROUP CENTROIDS) O 10l"/0o • 1979 FIGURE 2.3.5 : Discrimination of populations of C. brunneus from varying habitats in 1978 and 1979. (Canonical variates I and II) 62. by inferred axes. Comparing sites sampled in both years,there appeared to be less variability between sites in 1979. However, this was not conclusive as the number of sites involved was small. The new axes distinguished the heathlands from the grasslands and motorway sites as in Fig. 2.3.1, and the heathlands and motorways from the grasslands as in Fig. 2.3.2 in 1979. The sample from Lepe (L), although a salt marsh area, was associated with the heathlands and motorways, and in fact supported similarly high population densities. C. parallelus displayed distinct site differentiation along the first canonical variate (59.065% of total variance), whilst for C. brunneus this variate differentiated years (22.361%). The second canonical variate distinguished annual variation between sites for C. parallelus (15.577%), whilst the habitat types separated along this axis in the analysis for C. brunneus. Variation between grassland sites decreased slightly for both species in 1979, whilst between heaths variation increased in C. parallelus. Hence, in C. parallelus between-site variation was relatively more important than between-year variation, whereas C. brunneus differed relatively more between years than between sites. C. parallelus therefore appears to be morphologically more adaptable to different habitats than C. brunneus, and within the range of each habitat C. parallelus shows more plasticity between years. Although the morphological separation of the species is complete, they show similar patterns of character correlation with regard to changes in shape relative to habitat type and year. The slight 63. variation in the discriminatory powers of the characters influencing these character patterns may reflect specific differences in patterns of growth. The general increased polarity between widths and lengths seen in 1979 is comparable to that change in populations in heathland habitats, of both species. 2.3.2.2. Temporal variation in morphometries within sites Differences between species, in two years, in seasonal trends (Analysis 4) This analysis used all the samples shown in Table 2.3.10. The first three canonical variates accounted for 98.64% of the variability in the data (Table 2.3.11). This was very similar to the results of analysis 1. The first vector again separated the species (Fig. 2.3.6)? resulting from a contrast in prozonal length, relative to tegmen and sternum length. The second canonical variate resulted from a contrast in the width of the head across the genae, relative to the eye depth and sternum width. This corresponds to the vector discriminating habitat type in analysis 2 for C. parallelus. In this case it picked out samples of C. parallelus from site 3, emphasising the greater site differentiation in C. parallelus compared to C. brunneus. The general seasonal trend in shape at each site appeared to be species specific, as C. brunneus was more consistent between years than C. parallelus. This reflected the survey analysis in that C. brunneus was generally less variable. 64. TABLE 2.3.10 : Samples used in analysis of temporal variation in morpho- metries (3 sites). 1978 1979 DATE SITE NO. OF NO. OF SPECIES SITE COLLECTED CODE SPECIMENS SPECIMENS IN EACH YEAR C. BRUNNEUS ELM SLOPE 14.7.78 1B7 11 12 (1) 24.7.79 22.8.78 1B8 10 20 30.8.79 19.9.78 1B9 20 20 17.9.79 RUSH 20.7.78 2B7 3 6 MEADOW 30.8.79 (2) CROWN 23.8.78 3B8 17 4 ESTATES 19.8.79 (3) 20.9.79 3B9 2 17 12.9.79 C. PARALLELUS ELM SLOPE 19.7.78 1P7 12 15 (1) 24.7.79 22.8.78 1P8 23 20 20.8.79 19.9.78 IP 9 20 19 17.9.79 RUSH 20.7.78 2P7 11 10 MEADOW 25.7.79 (2) 21.8.78 2P8 • 20 17 21.8.79 18.9.78 2P9 20 21 18.9.79 CROWN 21.7.78 3P7 12 16 ESTATES 8.8.79 (3) 23.8.78 3P8 20 13 27.8.79 12.9.79 3P9 0 20 TABLE 2.3.11 : Analysis of temporal variation in morphometries within sites for C. parallelus and C. brunneus (1978/1979). VECTOR I II III IV V VI VII VIII IX X LATENT ROOTS 54.624 .894 .768 .241 .185 .153 .095 .056 .028 .021 PERCENTAGE 95.724 1.566 1.346 .422 .324 .269 .167 .098 .049 .036 DISCRIMINATION CHARACTERS E .280 .008 .006 .021 -.012 -.022 .014 .035 .040 .008 F -.086 .154 -.072 .040 .037 -.061 -.089 .009 -.225 -.094 P -.745 -.150 -.157 .046 .280 -.477 .803 .666 .446 -.298 M .016 .020 -.215 .043 .048 .083 .209 -.355 .289 -.321 H -.014 .130 -.275 -.073 .066 .207 .371 .029 -.175 .380 Ey -.047 -.676 .237 .500 -.678 -.180 .164 -.198 -.411 -.357 St .257 -.197 .109 -.297 -.071 .271 -.062 .175 -.187 -.367 w .063 -.350 .435 .077 .512 -.216 -.128 -.473 -.074 .513 c -.528 .564 .710 -.262 -.363 -.014 .051 -.167 .564 .354 V -.088 -.019 .295 .759 .233 .753 -.341 .328 .328 -.066 FIGURE 2.3.6 : Discrimination of temporal variation in 3 populations of C. parallelus (A = 1978, A = 1979) and C. brunneus (0 = 1978, • = 1979). (Canonical variates I and II - group centroids) A*7 0<1 0.9 2 O< z § 0.85 < 8 u A3P o z o •J ON ON 0.7 0.6 ip9 &3p8 . ft 1- 0.5 2.1 2.3 -1.3 -1.1 ^09 "Y7 1.9 FIRST CANONICAL VARIATE The third canonical variate (Fig. 2.3.7) distinguished yearly differences within bpth species. It was characterised by a similar distribution of weights to that found in previous vectors contrasting yearly variations. It also showed that the seasonal trend on site 3 for both species was different to that on the other sites. Temporal variation in C. parallelus in 1978 and 1979 (Analysis 5) The results of this analysis are shown in Table 2.3.12. Fig. 2.3.8 illustrates the effect of the first and second components. The first differentiated site 3 from sites 1 and 2. The greatest seasonal variation occurred in this site. This vector was similar to the second vector in analysis 4 for both species. The differences between samples was not consistent along either axis, but samples from July and August were closely associated in 1978, whilst in the next year samples from August and September were more similar. The second component differentiated the samples from the two years, and the vector was similar to that in analyses 1 and 2. The third component, explaining 8.478% of the total variance, distinguished site 1 from the others. This resulted from a contrast in the prozonal length, relative to the vertex width and eye depth. This was similar to the vector discriminating habitat type in C. brunneus (analysis 3). Possibly the pattern of growth was more similar between species on grassland sites than in less optimal habitats. Temporal variation in C. brunneus in 1978 and 1979 (Analysis 6) The first three canonical variates accounted for a similar amount of variability as for C. parallelus (Table 2.3.13). Here however, the first component emphasised yearly differences (Fig. 2.3.9a). This supports the earlier suggestion that there was relatively more site FIGURE 2.3.7 : Discrimination of temporal variation in 3 populations of C, parallelus (A = 1978, • = 1979) and C. brunneus (0 = 1978, ••# = 1979). (Canonical variates I and III - group centroids) TABLE 2.3.12 : Analysis of temporal variation in morphometries of C. parallelus (1978/1979). VECTOR I II III IV V VI VII VIII IX X LATENT ROOTS 1.467 .695 .253 .207 .162 .099 .060 .018 .016 .009 PERCENTAGE 49.127 23.283 8.478 6.930 5.435 3.308 2.009 DISCRIMINATION .605 .538 .288 CHARACTERS E -.020 .014 .139 -.034 .058 -.002 -.068 .030 -.021 .021 F .132 -.097 .054 -.003 .073 -.174 .027 -.190 -.022 -.073 P -.106 -.017 .175 -.009 .270 -.058 .635 .674 -.561 -.496 M -.028 -.151 -.071 .068 .182 .253 -.043 .085 .458 -.184 H .047 -.278 -.003 .153 .060 .481 .064 -.053 -.241 .233 Ey -.498 .725 -.621 -.651 .459 .077 -.122 -.469 .023 -.324 St -.185 .087 .122 .154 -.412 .229 -.249 -.163 -.129 . -.353 w -.176 .509 .137 .311 .060 -.231 .424 -.064 .523 .584 C .809 .179 -.095 -.317 -.364 .447 -.054 .447 .168 .299 V -.011 .255 -.717 .571 .605 -.600 -.572 .219 -.313 .017 FIRST CANONICAL VARIATE FIGURE 2.3.8 : Discrimination of temporal variation in 3 populations Of C. parallelUS 111 1978 (A) and 1979 (A) (Canonical variates I and II - group centroids) TABLE 2.3,13 : Analysis of temporal variation in morphometries of C. brunneus (1978/1979) . VECTOR i I II III IV V VI VII VIII IX X LATENT ROOTS 1.320 .477 .357 .209 .125 .077 .043 .038 .013 .005 PERCENTAGE 49.553 17.896 13.417 7.856 DISCRIMINATION 4.699 2.879 1.632 1.409 .477 .182 CHARACTERS E .006 -.009 .006 .051 -.182 .009 -.033 -.087 -.030 .055 F -.185 .029 .065 -.056 .157 -.012 -.033 .100 -.018 .234 P -.101 -.038 .346 -.714 -.086 .140 .605 -.688 -.504 -.286 M -.246 -.089 .145 .178 -.017 .334 .347 .231 .155 -.314 H -.281 -.061 -.221 -.101 -.239 -.335 -.128 .497 -.054 -.398 Ey .452 .162 -.328 .362 .620 .720 -.080 -.208 -.504 -.164 St .320 -.183 -.280 -.031 -.034 -.040 .180 .115 .026 .474 w .438 .051 .647 .213 .155 -.309 -.168 .309 -.123 -.479 c .302 .046 -.180 -.348 -.049 .287 -.400 -.086 .614 -.346 V .475 .960 -.411 .379 -.683 -.243 .518 .224 .266 .056 72. b) 6l Q) 2b 2h7 lbs \3ba b9 1 13 1-5 J FIRST CANONICAL VARIATE Discrimination of temporal variation in 3 populations of C. brunneus in 1978(0) and 1979(f). (a) Canonical var.iates I and II, b) Canonical variates I and IV - group centroids) 73. variation compared to yearly differences in C. parallelus than in C. brunneus. The second component differentiated site 3 from the others, the distribution of the weights in this and the first vector showing that the change in shape in both was similar. Component three was not very useful in interpretating any pattern of growth, but the fourth canonical variate described the seasonal variation at each site (Fig. 2.3.9b). The trend in site 1 was consistent in 1978 and 1979, but the trend in site 3 was reversed. Site 2 was only sampled once in each year. The distribution of weights in this vector (Table 2.3.13) indicated that the same patterns of growth influenced both annual and seasonal variation in shape. These analyses confirmed the findings of section 2.3.2.1, and indicated that the seasonal trend in the growth of females was more consistent in C. brunneus than C. -paralteZus. Also, the populations of both species on site 3 displayed greater modification both seasonally and annually. 2.3.3. Spatial and Temporal Variation_i_n ^var^ole_Numbers 2.3.3.1. Spatial variation in ovariole numbers C. brunneus Most variation within a site was caused by the asymmetry in the left and right ovariole numbers, although there was usually a difference of only one ovariole, e.g. 7+8,8+7, 7+6. Within a site, ovariole numbers varied from 5 to 9 per ovary, but there was no significant differ- ence between the number per left or right ovary on any site. The relationship between body size and ovariole number was considered by taking one skeletal structure, the femur length, and calculating regression coefficients. Only two regressions of the 74. ovariole number on the femur length at a site were significant (Table 2.3.14). As this was only 8.7% of the total number of relationships tested, they may have occurred by chance. The lack of any significant relationship may reflect the large intra- site variation in morphology shown in the previous section. However, there was a significant inter- site relationship between ovariole number (y) and femur length (x) in both years. The regression lines were 1978 y = 8.60 + 0.398x (tn6 = 2.09 , 0.05 > p > 0.02) 1979 y = 9.80 + 0.344x (t2iy = 3.05, 0.01 > p > 0.002) There was no significant difference in the regression coefficients between years (d =0.243, p > 0.10). Fig . 2.3.10 shows the relationship between the mean ovariole number and mean femur length per site for each year, with the regression lines based on the individual data points. Populations of C. brunneus on heathland and drier grass- land tended to produce lower ovariole numbers than populations on lusher grassland or wetland. An analysis of variance on the average ovariole numbers for sites sampled in 1978 revealed significant differences between the sites (F^ ^^ = 7.21, p < 0.01), whereas the data for 1979 were not significantly different (F-j^ 203 = p > . This could have been caused by annual fluctuations in the average ovariole number per site. However t-tests, between the sites sampled in both years (M41, MM, LNF and NG) showed no significant change. The lack of significance between sites in 1979 was therefore probably due to the presence of more inter- mediate habitat types. TABLE 2.3.14 : Spatial variation in total ovariole number in C. brunneus. 1978 Ovarioles Number Femur length . mm. Regression Site (x ± S.E.) of specimens (x ± S.E.) t-test Chobham Common 12.69 ± .423 9 11.18 ± .251 N.S. MM 14.35 ± .264 20 12.27 ± .147 N.S. LHS Nashs Field 13.18 ± .289 17 11.95 ± .126 t = 2.17, 0.05 > p > 0.02 Bisley 11.67 ± .333 9 11.19 ± .299 N.S. North Gravel 13.86 ± .333 21 11.71 ± .184 N.S. M41 13.00 ± .426 15 12.10 ± .134 N.S. Elm Slope (1) 14.50 ± .402 10 11.99 ± .199 N.S. Crown Estates (3) 12.18 ± .335 17 11.72 ± .169 N.S.. 1979 M41 13.80 + .257 20 11.22 ± .158 N.S. MM 14.86 + .329 14 12.13 + .145 N.S. LHS Nash Field 13.80 + .468 10 11.57 + .225 N.S. M42 13.38 + .324 8 11.03 + .236 N.S. Balmer Lawn 13.40 + .680 5 11.17 + .232 N.S. South Gravel 13.65 + .196 20 12.06 + .176 N.S. North Gravel 13.75 + .347 20 11.66 ± .180 N.S. . Longslade 14.55 + .594 11 11.83 + .300 N.S. Gracious Pond 13.46 + .313 13 11.95 + .134 N.S. Silwood Bottom 13.50 + .286 20 11.37 + .171 N.S. TABLE 2.3.14 : Continued. 1979 : Continued Ovarioles Number Femur length mm. Regression Site (x ± S.E.) of specimens (x ± S.E.) t-test Lepe 13.73 ± .266 15 11.66 ± .113 N.S. Silwood Gravel Pit 13.90 ± .250 20 11.48 ± .136 N.S. Elm Slope (1) 14.15 ± .311 20 11.57 ± .136 t= 3.37, 0.01 > p > 0.002 Rush Meadow (2) 13.83 ± .167 6 11.74 ± .241 N.S. Crown Estates (3) 13.38 ± .257 17 11.75 ± .205 N.S. N.S. = not significant FIGURE 2.3.10 : Relationship between femur length and ovariole number of C. brunneus from different habitats. a) 1978, r = .192, df = 116, 0.05 > p > 0.02 b) 1979, r = .203, df = 217, 0.05 > p > 0.02 78. Although the average ovariole number for a particular site did not show annual fluctuations, body length did (section 2.3.2). As the regression coefficients for the relationship between ovariole number and femur length were not significantly different between years, this supports the suggestion made in section 2.3.2 that the morphometrical differences in C. brunneus between sites were maintained from year to year, even though the magnitude of the characters within a site may vary. This also suggests that ovariole number, unlike shape, was not environmentally influenced, but specifically adapted to habitat type. C. -parallelus In 1978 C. parallelus displayed a slight variation in ovariole number on the more extreme habitats in one or two specimens, whilst the grassland sites were extremely consistent (Table 2.3.15). No relationship with body size was therefore found, and, as the variation in 1979 occurred in different sites, there appeared to be no relationship to habitat type. 2.3.3.2. Temporal variation of ovariole number within a site The mean ovariole number per site, and the relationship with the femur lengths for C. brunneus were tested by regression analyses and are shown in Table 2.3.16. C. brunneus There were no significant relationships between ovariole number and femur length within sites at any time of the season. Also, there were no significant differences between samples taken from one site at different times in the season 79. TABLE 2.3.15 : Spatial variation in total ovariole' number in C. -parallelus. 1978 Ovarioles Site No. x ± S.E. Bisley 9.10 + 0.410 20 Matley Bog 9.95 + 0.054 20 Garrison Ridge 10.00 + 0.113 13 Canford Heath 9.75 + 0.176 20 Chobham Common 9.75 + 0.250 8 Denny Bog 9.71 + 0.106 17 LHS Nashs Field 10.00 ± 0.0 20 North Gravel 10.00 + 0.0 19 RHS Nashs Field .10.00 + 0.0 19 South Gravel 10.00 + 0.204 8 Pond Field 10.00 + 0.0 6 Elm Slope (1) 10.10 + 0.060 23 Rush Meadow (2) 9.95 + 0.050 20 Crown Estates (3) 9.80 + 0.100 22 1979 Bisley 10.00 + 0.0 17 South Gravel 10.00 + 0.0 20 RHS Nashs Field 10.00 + 0.0 20 LHS Nashs Field 10.00 + 0.0 20 Pignall Enclosure 10.00 + 0.0 11 Pagham Harbour 10.00 + 0.0 10 Matley Bog 10.00 + 0.0 16 North Gravel 10.00 + 0.0 20 Garrison Ridge 9.95 + 0.050 20 Sandhurst 9.91 ± 0.091 11 Silwood Bottom 9.93 + 0.071 14 Elm Slope (1) 10.00 + 0.0 20 Rush Meadow (2) 10.00 + 0.0 17 Crown Estates (3) 10.00 + 0.0 13 80. TABLE 2.3.16 : Temporal variation in total ovariole number in C. brunneus and C. parallelus (3 sites). C. brunneus 1978 Femur Length Ovarioles Regression Site No. mm. (x ± S.E.) t-test (x ± S.E.) 1B7 14.47 ± 0.341 11 11.93 ± .198 N.S. 1B8 14.50 ± 0.402 10 11.99 ± .199 N.S. 1B9 13.90 ± 0.347 20 11.60 ± .166 N.S. 2B 13.33 ± 0.664 3 11.94 ± .541 N.S. 3B8 12.18 ± 0.335 17 11.72 ± .169 N.S. 3B9 11.00 ± 0.997 2 — — 1979 1B7 14.09 + 0.416 12 12.07 + .158 N.S. 1B8 14.05 + 0.311 20 11.57 + .136 t= 3.37, 0.01 > p > 0.002 1B9 14.25 + 0.324 20 11.54 + .156 N.S. 2B 13.83 + 0.167 6 11.74 + .241 N.S. 3B8 12.00 + 0.0 4 - - 3B9 13.53 + 0.257 17 11.75 + .205 N.S. C. parallelus 1978 1979 1P7 10.00 + 0.0 12 1P7 10.00 + 0.0 15 1P8 10.00 + 0.0 23 1P8 10.00 + 0.0 20 1P9 10.00 + 0.0 20 1P9 9.95 + 0.050 19 2P7 10.00 + 0.0 11 2P7 10.00 + 0.0 10 2P8 10.00 + 0.0 20 2P8 10.00 ± 0.0 17 2P9 10.00 + 0.0 20 2P9 10.00 + 0.0 21 3P7 10.00 + 0.0 12 3P7 10.00 + 0.0 16 3P8 10.00 + 0.0 22 3P8 10.00 + 0.0 13 3P9 9.95 + 0.050 20 N.S. = not significant 81. (Site 1: 1978 F2 38 = 0.89, p > 0.05; 1979 F2 ^ = 0.06, p > 0.05) (Site 3: 1979 t^ = 1.12 , p > 0.05) The mean ovariole numbers for each site only showed slight seasonal variations, which may have corresponded to those found in the morphometries seen in section 2.3.2.2. This supports the finding of site differences in section 2.3.3.1. If significant differences in ovariole number occurred within a site during the season then samples taken at varying times may have given misleading results. However, all the samples were collected during 3/4 weeks in August/September, which minimises this risk. Significant differences were again found between sites at the same time of the season (1978, 1B8, 2B, 3B8, F2 ^ = 9.70, p < 0.01). The differences between samples from site 3 were not tested as 3B8 had no variation in its small sample. As t-tests between these sites, at the same sampling time, were not significant, it can be assumed that the same relationships between sites and samples held in 1979 as in 1978. C. parallelus C. parallelus showed no significant variation in ovariole number either spatially or temporally. 2.4 Discussion The habitat preferences shown by C. parallelus and C. brunneus in the two surveys reflected the findings of previous authors,described earlier. The results agreed with the description of Sanger (1977) in that the species responded to both the plant community per se and the micro- environmental range within each community. The description by Haes (1976) of their distribution in Sussex,emphasised C. parallelus' avoidance of the very hot and dry areas in which C. brunneus thrives. It is interesting to speculate whether these species are in any way similar to those described by Anderson et al (1979); where Psoloessa delicatula (Scudder) displayed thermoregulatory postures and shade seeking behaviour, and was often found in areas with bare ground, its body temperature being kept at a relatively constant level. Eritettix simplex (Scudder) was more abundant in dense vegetation. Its nymphs lost water rapidly, and were therefore restricted to more mesic environments. Whilst the adults had some apparent physio- logical mechanism for preventing water-loss, their body temperature was usually at the ambient level. The morphological analyses showed several features of interest in both species, the first being a similar change in shape in the two years although there was complete morphological separation. This provided some evidence of adaptation to the environment (Bryant & Turner, 1978). Separate analyses of the species confirmed this, whilst emphasising the specific differences in the magnitude of response. C. parallelus showed greater inter-site differences, which altered in a variable way between years in the more extreme habitats, such as the heathlands and bogs. It is likely that C. parallelus would be more sensitive to the temperature and humidity differences associated with such sites,than the more xerophylic C. brunneus. Changes in the densities of both species between years did not correlate with the morphological changes. C. brunneus therefore appears more adapted within a habitat, and not as affected by environ- mental change. Various authors have performed laboratory experiments on the response of the insect in terms of its morphology to temperature, and have found significant changes in shape (Dudley, 1964) or size (Petersen, 1949; Masaki & Oyama, 1963; Hensleigh & Atchley, 1977; Arai, 1978). Analyses of geographical variation in houseflies (Bryant, 1977) and grasshoppers (Kritskaya, 1972; Litvinova, 1972) also showed alteration in size. However, whilst the grasshoppers increased in size from north to south, and with decreasing altitude, i.e. as the temperature increased, the houseflies displayed the opposite trend. The latter therefore appeared to agree with Bergmann's rule, the basis of which is thermoregulation, and is really applicable only to homeotherms (Calow, 1977). As an organism decreases its size, the surface area/volume ratio increases, and for poikilotherms this would be of more importance in the conservation of water. The grass- hoppers, by decreasing their surface area/volume ratio as they increased in size, would reduce water loss through the cuticle. Popov (1963) presented field and laboratory evidence for a lengthening of iegmina on solitary Russian grasshoppers at higher temperatures, accompanied by lower humidity, which was independent of population density. However, he also records that as the temperature increased they changed habitat type, possibly to decrease moisture loss in a behavioral way. Schoener & Janzen (1968) using several different insect species, found a significant negative correlation between insect size and environ- mental humidity. In this study, it therefore seems plausible that the main influencing factor for the change in shape was humidity. Although the insects did not show an overall difference in size in drier habitats, the variation in shape would have had the same effect on the surface area/ volume ratio. Morphological variation has also been related to niche width (Van Valen, 1965; Hespenheide, 1973) and to variation of behaviour (Wilson, 1969) . Less morphological variation was explainableas , adaptation to habitat in C. brunneus than in C. parallelus. The former may partially .avoid environmental stress in some behavioral manner. Fluct- uations in nutrition between sites would not explain the differences found as these remained consistent between years. Fleming & Scott (1971) found that size differences in cicadas from different plant communities were not related to nutritional differences. It is normally assumed that geographical variation in morphology is produced by natural selection, but whilst inter-population levels may be mainly genetic, intra-population levels are also environmentally influenced (Soliman & Lints, 1977) . This is certainly at least partially the case here. The genetics of morphological characters are often complex, being polygenic and pleiotiophic (Wool & Roach, 1976; Petkov & Yolov, 1979) and are therefore difficult to determine. Atchley & Hensleigh (1974) were, however, able to determine differences in the patterns of morphometric shape of four chromosomal races in two species of Morabine grasshoppers. The inheritance of ovariole number has been more successfully studied, even though the environment can also cause great variation. In Drosophilia spp. possibly 60% of the variation is genetic in origin (Robertson, 1957). Blackith & Blackith (1969b) found that ovariole counts in Morabine grass- hoppers were under genetic control, with high numbers dominant in reciprocal crosses between high and low ovariole count specimens. Here, however, C. parallelus maintained a constant number at all sites in both years, whilst C. brunneus showed significant and consistent differences between sites. There were no seasonal or annual variations. Thus, whilst in both species the ovariole counts must be genetically controlled, C. brunneus shows ecotypic adaptation. Virkki (1979) suggested that the species specific difference in ovariole numbers in fleabeetles was related to the more hazardous environment inhabited by the species with the higher count. This was demonstrated in Cmophoita oyanipennis (F.) which has 12-19 ovarioles, and lives in dry to humid habitats, whilst fflagoasa bicolor (L.) has 8-12 ovarioles and lives in drier conditions. The reverse applies to the grasshoppers, but the difference here may reflect requirements of egg development, and how the species differ in their reproductive strategy. This will be analysed in chapter 4. Comparing the two species1 morphological and "reproductive" adapt- ation to different environments, it appears that populations of C. brunneus are adapted to a particular habitat, and are less influenced by fluctuations in the physical environment than C. parallelus. The latter, whilst not altering its ovariole number, reacts more strongly morphologically to environmental change, indicating greater phenotypic plasticity. C. brunneus may partially cope with environmental stress in a behavioural way as described by Anderson et al (1979). C. paraitelus, whose optimum habitat is more equable i.e. moist with lush vegetation, may be directly affected with no avoidance behaviour. The genetics of these species have not been studied, but their chromosomal variation has. John & Lewis (1966) described this as being at least as important as external variation in natural populations. The chromosomal phenotype is a reflection of genetic variation, and hence geographically or ecologically marginal populations tend to be less poly- morphic than central populations. Da Cuhna (1960) reported that the relationship between chromosomal variation and the environment was not clear for grasshoppers. Chorthippus species have individually identifiable chromosomes (John & Hewitt, 1963) and are therefore easy to study. Hewitt (1964) has shown that C. paralZelus has a significantly higher chiasraa frequency than C. brunneus in mixed populations. There was no difference between the chiasma variation within an individual for each species, but the variation between individuals within a population was larger for C. •parallelus (Hewitt, 1965) . Differences in an individual's variation may be environmentally controlled, although naturally occurring conditions would seem ineffective, as only very high temperatures affect chiasma frequency in C. parallelus (White, 1951). Higher frequencies in chiasma formation cause increases in genetic recombination (Barker, 1960), and hence C. parallelus may have more genetic recombination than C. brunneus in extreme environments. It may therefore have a larger capacity to create new adaptive types (Da Cuhna, 1960). This may be related to the increased morphological variation seen in the extreme habitats. This chapter thus suggests that both species are influenced by the habitat and the physical environment in such a way as to alter their reproductive strategies. The genetical makeup of each species may in part dictate these differences. 87. CHAPTER 3 OBSERVATIONS AND EXPERIMENTS ON THREE PERMANENT FIELD SITES 3.1 Introduction This chapter describes work designed to establish whether observed differences in the structure of grasshopper populations are environmentally influenced. Habitat effects can be classified as physical, vegetational or nutritional. These interrelate, and potentially affect the population dynamics of the insects present. The chapter is constructed as follows:- Physical Characteristics Temperature and moisture (humidity) are the two physical factors most important to animal growth and development (Parker, 1930; Andrewartha & Birch, 1954; Hodson & Rawy, 1956; Ruscoe, 1970; Wigglesworth, 1972; Robin- son, 1973). Temperature is easily measured, but humidity presents practical problems in monitoring a site for some time (Long, 1968). Soil moisture is simpler, and not only affords indirect information on humidity of the habitat, but also on the environment for the eggs (Choudhuri, 1954; Moriarty, 1970; Hunter-Jones, 1970). Vegetational Structure and Composition The vegetational structure and composition, whilst affected by the physical attributes, can also affect the micro-habitat (Waterhouse, 1955) . A correlation between habitat structure and the general distribution of grasshoppers is described in Chapter 2, and detailed habitat descriptions here a) accurately describe the three "type" sites of these species as determined in the preceeding chapter and b) show if the population structure is affected by the habitat structure (Kershaw, 1957; Stebaev, < 1970; Gibson, 1976; Raatikainen et al., 1977; Smith & Whittaker, 1980 ). Nitrogen_Content of Available Food and ^Feeding Preferences The floristic composition provides information on available food. The exact composition of the insects1 diet is identified by faecal analysis based on work by Williams (1954), Brusven & Mulkern (1960), Cavanagh (1963), Uvarov (1966), and Bernays & Chapman (1970a), which showed that the Gramineae is the dominant plant group fed on by Acrididae. Gangwere (1961) provided an extensive review of this subject. Joern (1979) also summarised work on grasshopper diets, and discussed the factors influencing diet specialization in American grasshoppers from arid-grasslands. He suggested that phylogenetic constraints were evident in that Gomophocerinae were primarily grass-feeders, whilst Melanoplinae were forb-feeders. He found that some species shifted the relative proportions of plant species in their diet at different sites, whilst others were more consistent, and again other species showed a complete change in diet. Variations in the feeding preferences of sub- species of Chorthippus maorocerus (F.-W.) were seen within different pop- ulations of a subspecies, and within a population between years, by Kritskaya (1971). Specific work on C. brunneus and C. parallelus by Richards & Waloff (1954), Qasrawi (1966) and Bernays & Chapman (1970a) showed that these species feed exclusively on a range of grass species. Emphasis has been put on the performance of insects on single food plants, and Smith (1960) found that the size and fecundity of a population of grasshoppers could be considerably influenced by changes in its host plant. Pickford (1958), Bernays et al (1975), Bailey & Mukerji (1976) and Chapman et al (1979 ) demonstrated that different plants could determine survival, development and reproductive potential of Acridids. However^the approach by Kaufman (1965) is perhaps more easily related to the field situation. He investigated the effects of mixed diets of naturally preferred food plants on Orthoptera, and found good correlation between the level of preference and the ability of plants to support growth and survival (Otte, 1975). The differences in nutritional quality of the plants preferred by these species is determined by analysis of the total nitrogen content of the leaves. The growth and reproduction of phytophagous insects should be influenced by the quality and quantity of the proteins and amino acids in their foods (McNeill & Southwood, 1978). The total nitrogen levels reflect the protein levels in the leaves which are probably the most important plant structure for mesophyll feeders (Hill, 1976). There are few important studies of nutritional effects on grasshoppers (Bernays & Chapman, 1978), mainly on economically important species e.g. Smith & Northcott (1951). Only one theoretical paper (White, 1976) has considered the effect of nitrogen levels in Acridid populations. Insect Population Dynamics The basic components of population dynamics are variations in the rate 90. of natality, mortality and dispersal, which are "connected inextricably with density responses" in Acridids (Waloff, 1970). It is therefore necessary to establish the effects of density on adult longevity, fertility and fecundity. All the work is field based, and,apart from some field experiments to verify certain population parameters, the methods are basically the collection of relevant data from the field throughout the season from each site. 3.2 Physical Characteristics of the Field Sites 3.2.1. Methods^ Three permanent field sites were established in 1977 in different habitat types, each supporting populations of both C. brunneus and C, -parallelus. Basic geographical information on each site is given in Table 3.2.1. Microclimatic conditions The most suitable technique for measuring surface and soil temperatures was the sucrose-inversion method (Berthet, 1960). The solution tubes were easily transported to the field and inconspicuous in situ. The measurement of temperature within a site was thought to give a better indication of site conditions than the use of local meteorological data. As the solution reaction is proportional to temperature, an exponential mean value is obtained for the period in the field. This has an advantage in invertebrate ecological studies over the arithmetic mean, since less emphasis is placed on the lower end of the specific temperature range where little development occurs (Andrewartha & Birch, 1954). The chemical basis of this method was discussed by Lee (1969). Solution tubes were prepared each month, and frozen before and 91. TABLE 3.2.1 : Geographical information on field sites. DIMENSIONS NO. SITE GRID REF. HABITAT TYPE ASPECT SOIL TYPE m 1 Elm Slope SU944686 40 x 40 Dry grassland SW Acid, sandy Silwood Park facing soils slope derived from Eocene Bracklesham Beds. 2 Rush Meadow SU938692 60 x 20 Wet meadow SSE II * Silwood Park 3 Penny Hill SU871664 1200 x 10 Acid heathland level II Crown Estates * Site 2 gleyed type. 92. after exposure to field conditions. A covering of tin foil avoided radiant heating of the surface tubes, which were changed weekly throughout both seasons. During the summer season a slow reacting solution was used to avoid complete molecular rotation during this period. The soil temperature was also measured in 1979, by tubes buried to a depth of 3 cm (the depth at which egg pods are usually found (Waloff, 1950)). The angle of rotation of the solutions was measured using a model D polarimeter (Bellingham & Stanley Ltd.). Soil moisture was measured every four weeks in 1978, and weekly during the more changeable 1979 season. Four 4 cm deep samples were taken randomly from each site using a 4 cm diameter cover. After transfer, in sealed plastic bags, to the laboratory, samples were weighed and then dried at 80°C before re-weighing. Methods of analysis a) Surface and soil temperatures The exponential mean temperature for the surface and soil microhabitats were calculated using the equations supplied by Berthet (1960), with corrections by the Atomic Energy Research Group. b) Soil moisture The percentage soil moisture was derived from four replicates collected at each sampling time, thus: 4 WDa % SOIL MOISTURE = E (1 - x 25 a=l1 Ww a where W^ = dry weight of replicate and W^ = wet weight of replicate The replication decreased the error involved in sampling from different drainage areas of the site. 93. In order to analyse differences between the microclimates of sites during either season, each set of temperature and soil moisture results was tested by Freidman's two-way analysis of variance, using site type and sampling time as the two treatments. This test was used as it avoided the assumption of normality implicit in the use of the analysis of variance (Siegel, 1956). The samples were taken seasonally, and therefore were not normally distributed. 3.2.2. Results_ and_ Di^cuss_ion a) Surface temperature In 1978 the surface temperatures for each site were significantly different (X2 = 8.13, k = 3, n = 20, p < .019). Although early and late season values were similar, from late June to mid August there was a marked site difference (Fig. 3.2.1.). The range of temperatures experienced at each site was large. In 1979, the surface temperatures showed a different pattern. There was no significant difference between sites, (X2 = .78, k = 3, n = 18, p > .86) and the range was narrower, with less extreme lower temperatures. Within this range, however, the temperatures fluctuated considerably on each site. b) Soil moisture In both years, the soil moisture differed significantly between sites (1978, X2 = 10.33, k = 3, n = 6, p = .0017; 1979, X2 = 38.61, k = 3, n = 23, p < 0.0000006). Site 2 was always the wettest, and site 3 the driest (Fig. 3.2.2.). Although the sampling frequency was increased in 1979 the trend was similar to the monthly measurements of 1978. The soil moisture values were less variable in 1979, which was a generally warmer and drier season. As water has a higher specific heat than air, wet soil could equilibrate the surface temperatures, thereby reducing the wide Y4. j j ~ a) 1978 ::> j < 30 a:: w j Q.. w~ j 1- z j w< j ~ 22 ....J j < j:: j z wz j 0 Cl.. j >< w j -oc 14 j j j j 6 j b) 1979 j 28 j j j j j 24 20 16 ~----~----~----~----~------MAY JUNE JULY AUG SEPT OCT 0 Site 1 • t::. Site 2 A D Site 3 • FIGURE 3.2.1 : Exponential mean surface temperotures during sampling period (3 sites, a) 1978, b) 1979). J 95. 70 a) 1978 >- CO QLU£ 60 3»— oto LU . _ o 40 £ Z uLL I DC 20 50 b) 1979 40 \ 20 0 MAY JUNE JULY AUG SEPT OCT O Site 1 • A Site 2 A • Site 3 • FIGURE 3.2.2 : Percentage soil moisture during sampling period (3 sites, a) 1978, b) 1979). 96. fluctuation usually experienced at the air-soil interface (Macfadyen, 1968). Thus, in 1978, when the soil was waterlogged for much of the season, the surface temperatures would not fluctuate so much as they did in 1979 when the soil was drier. c) Soil temperatures The soil temperatures of each site are shown in Fig. 3.2.3. They were not significantly different (X2 =-19.00, k = 3, n = 19, p = 1.0). However, the early season measurements revealed differences between sites which progressively decreased. Soil temperatures rise through the summer, with increasing air temperature, but are tempered by rainfall. Thus, these relatively simple microclimatic measurements showed that the three sites provided different microhabitats for the grasshoppers. Site 2 was a very wet area, where, in the first year, temperatures remained much lower than the other sites. In 1979, the wide fluctuations in temperatures may have been caused by the large variation in soil moisture content. The local meteorological data for that year showed that the weather was highly variable throughout the season (see Appendix 3a). The driest site in both years was site 3. In 1978 it experienced the widest range of temperatures, whilst in 1979, when all sites were drier, it showed a different pattern of increasing surface temperature with a decreasing soil moisture content. The interrelation between these factors is complex. In addition, some of the variation between sites is due to differences in vegetation type. This component and its effect on the microclimate will be described in the next section. u o 28 r MAY JUNE JULY AUG SEPT OCT • Site 1 A Site 2 • Site 3 FIGURE 3.2.3 : Exponential mean soil temperature during sampling period (3 sites, 1979). 98. 3.3 Vegetational Structure and Composition 3.3.1. Metho_ds_ o_f_Moni_toring^ Ve^eJ^a^iona_l_Chap_ges The three sites, each of approximately 1200 m2 (Table 3.2.1.) were regularly sampled with respect to the floristic and structural composition of the vegetation, over the period from grasshopper egg eclosion to term- ination of the adult phase. Point quadrats provided a quick and efficient method for a sole worker to achieve this (Mueller-Dombois & Ellenberg, 1974) . Goodall (1952) discussed the effect of pin size on percentage cover data. The pin used here was 3 mm in diameter and 100 cm high, with divisions marked every 10 cm, enabling the collection of structural as well as floristic data. For recording seasonal changes, fixed points were marked at each site, decreasing the variance otherwise produced by the heterogeneity of the habitat (Goodall, 1952). Random number tables were used to generate 100 pairs of coordinates, the relative points being marked in the field; canes set along the site boundaries at 10 m intervals marked the axes. On sites 1 and 2 short garden canes marked the points, whilst metal tags embedded in the soil were used on site 3, the latter being accessible to the public and liable to interference. Each cane or tag was numbered from 1 to 100 with indelible pen. The pin was always placed in the same spot immediately in front of the marker, when recording the vegetation. The survey was repeated fortnightly in 1978 and every four weeks in 1979. The extra data collections the previous year in fact added little to the overall inform- ation. In 1978 all plant touches at each height were recorded, but after examining the data, only the presence of a species at each height division was included in 1979, reducing the survey time. Data collection had two 99. parts: (i) recording percentage frequency or cover by each species by presence or absence data and (ii) the stratified contribution to cover by each species by recording either multiple touches or presence/absence within each height division. In 1979 data was recorded directly onto computer coding forms to simplify the data-processing. Methods of Analysis Sgecies composition (1) 3 ~ diversity To quantitatively define the differences between thve three sites, Sorensen's Coefficient of Similarity, Cg,was employed, as in Chapter 2. (2) a - diversity a) Williams index of diversity was chosen to quantify the seasonal changes in diversity of each habitat. It has been used successfully in the past to compare samples from the same habitat (Southwood, 1978; Southwood et al., 1979). The index a was calculated from ST = a In (1 + N/a) where S^ = total number of species in sample and N = total number of individuals. A maximum likelihood method was employed for the computation (program by Rothamsted Experimental Station), for each sampling time. A common ct was also derived for each site over the whole year. These calculations were performed for all species and for the grasses only, as the latter are the food plants of the grasshoppers. 100. b) Although diversity and dominance are directly correlated (Krebs, 1972), the Berger - Parker dominance index d was also calculated. It has been described as a very useful and simple indicator of the habitat structure (May, 1975; Southwood, 1978). It was calculated for each sample, at each height category, using the total number of species and grasses separately. The index is d = Nw.v MAX NT where NWAV = number of individuals of the most abundant species in the MAX category concerned, and N^, = total number of individuals in that category. (3) Structural composition The multiple touch data collected in 1978 allowed the calculation of foliage height profiles for entire sites as in Southwood et al (1979). This was compared to a height profile using presence/absence data from each height from data of the same year. The 1979 data was used to produce the latter height profile only, referred to as a species height profile. The height profiles were derived from the percentage cover values at each height division:- NH. = total touches at height i /N^, total touches at all heights These were plotted as layer diagrams (Mueller-Dombois & Ellenberg, 1974), (with percentage along the abscissa and height categories along the ordinate). The percentage bare ground was expressed as the proportion of pins not touched by any species. 3.3.2. Result_s and^ Discission The three sites studied were qualitatively very different; a dry grassland (site 1), a wet meadow (site 2) and an acid heathland (site 3). The dendrogram in Fig. 3.3.1. shows this demarcation quantitatively, and illustrates the closer association between sites 1 and 2. The trellis diagrams are given in appendix 3b. Within each site there was a high level of similarity throughout the two years. Site 3 had the highest association between samples and site 2 the lowest. This reflected the regimes that maintained these subseres (Tansley, 1939). The dry grassland was intermittently maintained by removal of scrub, whilst the wet meadcw was part of a rapid hydrosere, kept by cutting every three or four years. Site 3 was mown each year as a fire break. The raw data matrices are in appendix 3c. Figs. 3.3.2. and 3.3.3. show the diversity of each site in terms of all plant species and grasses respectively. The seasonal trends were similar in both years within a site, although more equable in 1979. This can be correlated to the initially poor growing conditions of 1979 due to the cold and wet spring (as indicated in Fig. 3.2.3.) which depressed growth for several weeks. The effect of spring conditions on grass growth was discussed by Roy & Peacock (1972). The diversity of each site decreased slightly through the season, but this was mainly due to the forbs, which had a late season regrowth. The average indices of diversity for each season show that the yearly differences in diversity were also due mainly to the forbs. The Berger - Parker Dominance Indices are shown in Table 3.3.1. The table shows that grasses were the dominant species when all the plant species on a site were considered, except for the late samples in 1979 on site 2. There was little change in the dominant species between years. FIGURE 3.3.1 : Similarity between 3 field sites - Sorensen's Coefficient of Similarity (1-6 = sampling times; 8, 9 = 1978 or 1979) Site 1 Site 2 Site3 29 l9 I8 3® 28 39 58 59 68 49 69 48 l8 l9 38 48 58 68 69 59 49 39 29 2® 39 l9 I8 38 28 48 58 68 29 4* 59 69 X T 100 90 O ro 80 Cs 50 25 a) 1978 8r co MEANVALUE ac FOR SEASON (±S.E. £ 6 A ST2 6.6 ±.47 O x LU Q o ST1 4.1 ± .35 Z • ST3 3.8+.38 CO < b)1979 £* a ST2 5.5+.55 • ST1 3.7 ±.45 • ST3 3.0 ±.42 MAY JUNE JULY AUG SEPT OCT FIGURE 3.3.2 : Seasonal changes in diversity of vegetation, using all plant species (3 sites, a) 1978, b) 1979). CO La:U > 4 MEANVALUE FOR SEASON (±S.E.) x QLU Z A ST 2 2.9 ±.30 CO < O ST 1 1.7 ±.21 £ < • ST3 0.6 ±.13 0 b) 1979 a ST 2 2.2 ±.36 • • ST 1 1.9 ±.30 * • "ST 3 0.6 ±.16 * MAY JUNE JULY AUG SEPT OCT FIGURE 3.3.3 : Seasonal changes in diversity of vegetation using grass species only (3 sites, a) 1978, b) 1979). 105. TABLE 3.3.1 : Seasonal variation in the Berger - Parker Dominance'index, using all plant species, 1978/1979 (3 sites). YEAR 1978 1979 SITES SAMPLING TIME 1 2 3 1 2 3 1 F.O. .24 H.L. .47 M.C. .82 A.T. .32 A.T. .24 M.C. .55 2 A.T. .35 H.L. .34 M.C. .88 - - 3 A.T. .26 H.M. .24 M.C. .77 A.T. .34 A.T. .19 M.C. .62 4 A.T. .32 A.T. .33 M.C. .77 - - 5 A.T. .39 A.T. .39 M.C. .84 A.T. .28 A.T. .20 M.C. .63 6 A.T. .48 A.T. .45 M.C. .94 - - 7 A.T. .42 A.T. .41 M.C. .94 A.T. .28 A.T. .11 M.C. .54 8 A.T. .43 A.T. .35 M.C. .88 - 9 A.T. .42 A.T. .36 M.C. .86 A.T. .20 R.R. .15 M.C. .52 10 A.T. .48 H.L. .40 M.C. .84 - 11 A.T. .47 H.L. .39 M.C. .84 H.M. .20 R.R. .17 M.C. .48 F.O. = Festuca ovina; A.T. = Agrostis tenuis; H.L. = Holcus tanatus; H.M. = H. mollis; M.C. = Molinia eaerulea\ R.R. = Ranunculus repens. This index also shows the equability of each site, the larger the index the less equable the species abundance. The height profile values from the multiple touch and presence/absence data were highly correlated at all height categories (Spearman rank correlation coefficient, N = 11, p < 0.01; see appendix 3c). The height profile diagrams in Fig. 3.3.4. therefore represent the biomass stratification of each site as described by Mueller-Dombois & Ellenberg (1974), using presence/absence data rather than multiple touch data. This method is suitable for an overall seasonal index of biomass, but not for individual species. The tallest vegetation, up to 1 m, occurred on site 2, during July and August. The vegetation of site 1 reached a maximum of 0.7 m during the same period. Site 3 supported generally lower growth, the maximum height attained being 0.5 m by flowering heads. Vegetative growth was usually below 0.3 m in height. The structure of each habitat did not alter from 1978 to 1979, reinforcing the conclusion from the diversity data that the sites had changed little between the two years. Fig. 3.3.4. also shows the Williams index of diversity of each height category in June and September. The highest diversity at all sites was found in the lowest and highest height categories, reflecting the fact that all plants would be present at low levels, and that only a few species would make up the cover at the highest levels. The percentage bare ground calculated from the number of untouched pins, varied considerably between site 3 and sites 1 and 2. Site 3 was a very open habitat (Table 3.3.2). a)1978 b) 1979 O 60 Sifel 2.1 3.0 40 20 !l MAY JULY SEPT MAY JULY SEPT FIGURE 3.3.4 Seasonal changes in species height profiles, plus diversity indices at each height (3 sites; a) 1978, b) 1979) a = Williams index of diversity. 108. TABLE 3.3.2 : Percentage bare ground (1978/1979, 3 sites). SAMPLE TIME- SITE 1 2 3 4 5 6 7 8 9 10 11 1) 1978 2 3 0 0 2 2 0 0 0 0 1 1979 3 6 0 1 2 1 2) 1978 5 4 0 0 0 0 0 0 0 0 0 1979 5 0 0 1 1 2 3) 1978 36 29 26 15 11 20 17 13 12 12 19 1979 19 22 7 10 5 20 109. Summary A summary of the habitat descriptions is provided in Fig. 3.3.5, which diagrammatically represents the floristic and structural composition of the three sites. 3.4 Nitrogen Content of Available Food 3.4.1. Methods^ The grass species selected for analysis from site 1 and site 2 included all species present throughout the season in which the mean percentage cover exceeded 5% (from section 3.3). As there were only three grass species on site 3 these were all analysed. Samples were collected from each site from May until October; monthly in 1978, and weekly in 1979, since inspection of the 1978 data suggested certain nitrogen flushes may have been missed. Leaves and sheaths of each species were taken randomly, sealed in polythene bags, and freeze dried immediately on returning to the laboratory. The nitrogen does not break down in the freeze dried plant material when stored in airtight bags. The Kjeldahl method was used to extract the nitrogen (adapted from Hill, 1976). Bradstreet (1965) discussed the chemical processes involved in this analysis. A sub-sample of the material was taken from each bag and ground to a fine powder in a ball mill. This was checked regularly for metal scrapings which would have affected any further chemical analysis. Between 0.03 g and 0.06 g of powder was weighed and transferred to a boiling flask. The powder was then gently refluxed with 2 ml concentrated nitrogen- free sulphuric acid and one selenium catalyst tablet. After three to five hours the colour had changed from dark brown to pale yellow, and, on cooling, the liquid was made up to 100 ml or 200 ml with distilled water. Subsamples were analysed in batches, each batch containing blanks of 110. SITE I Height m Overoll diversity oc Grass diversity CC Dominance d Bare ground 36^ f flnristic and structural composition of 3 field FIGURE 3.3.5 : Summary of floristic ana sites 111. distilled water and nitrogen standards (Autoanalyser system by Technicon Instrument Co. Ltd.). The autoanalyser recorder gave a readout of -the amount of total nitrogen in each sample in ppm. The amount of total nitrogen per gramme of dried material was calculated from:- A x B = mg N g"*1 dry weight W. x 1000 1 where A = parts per million B = number of mis. of refluxed material and distilled water W^ = weight of dried sample 3.4.2. Resul^ts_ and_ Discussion There was little between-year variability in total nitrogen content of leaves and sheaths at each site, except for the increased late spring and summer growth on site 2, in 1979. This was shown by comparing the average nitrogen content for each sampling time (Table 3.4.1.) and the specific levels (Fig. 3.4.1.), between 1978 and 1979. McNeil & Southwood (1978), when describing the between-year variability for Eolcus mollis, also showed that the seasonal trends coincided, although differences in levels did occur. The specific levels of total nitrogen content shown in Fig. 3.4.1. did not have standard errors attached as the collected sample was taken randomly throughout the site and a subsample taken for analysis. There was not sufficient time to carry out replicates of the 312 samples. For purely comparative purposes, a subsample was considered sufficiently representative of the levels present in each species. There was a significant difference between sites in the average amount of total nitrogen available from all the grass species, in both years. Using the data in Tables 3.4.1. (1978) and 3.4.2. (1979), Freidman's twoway analysis of variance by ranks TABLE 3.4.1 : Total nitrogen content at each sampling time a) 1978, b) 1979 (3 sites) x ± S.E.mg N g-1 dry weight SAMPLE t-test SITE 1978 1979 TIME t 1 1 19.08 ± 2 22 14.27 ± 1.73 1.20 (n = 10) 2 12.58 ± 1 85 14.84 ± 1.98 0.83 3 9.06 ± 1 08 12.31 ± 0.52 2.72 * 4 11.50 ± 2 12 11.08 ± 0.52 0.19 5 11.10 ± 0 32 11.01 ± 1.18 0.07 6 12.02 ± 0 87 10.97 ± 1.47 0.16 2 1 13.08 ± 1 80 19.25 ± 2.10 2.55 * (n = 10) 2 11.88 ± 2 69 19.58 ± 1.46 2.37 * 3 9.37 ± 1 32 14.88 ± 1.65 . 2.65 * 4 12.35 ± 2 36 14.64 ± 3.10 0.60 5 10.45 ± 2 21 14.23 ± 1.38 1.38 6 11.1 ± 0 76 12.96 ± 1.75 0.97 3 1 18.50 ± 3 30 19.25 ± 4.32 0.12 (n = 6) 2 13.28 ± 2 75 17.15 ± 1.35 1.39 3 15.17 ± 2 04 11.92 ± 1.88 1.17 4 13.60 ± 1 29 12.80 ± 1.56 0.40 5 14.03 ± 0 19 16.02 ± 1.03 1.90 * Significant t-test for small samples, variances equal, 0.05 > p > 0.02. 113. Holcus 25 mollis 15 Holcus 25 lanatus 15 (• Festuca 25 ovina 15 Festuca 25 r rubra I 15 5 Agrostis 25 r tenuis I 15 mgNM ^^ dry wt. 5 MAY JUNE JULY AUG SEPT OCT Sitel O 1978 • 1979 FIGURE 3.4.1a : Seasonal changes in total nitrogen content of each grass species of site 1 (1978 and 1979). 114. Poa 25 trivialis 15 5 Holcus 25 mollis 15 Holcus 25 lanatus 15 Festuca 25 rubra 15 5 Agrostis 25 tenuis 15 Agrostis 25 canina 15 5 Agrostis 25 tenuis 15 5 Molinia 25 caerulea mgN,/g '5 dry wt. 5 MAY JUNE JULY AUG SEPT OCT Site 2 a 1978 a 1979 Site 3 • 1978 • 1979 FIGURE 3.4.1b : Seasonal changes in total nitrogen content of each grass species of site 2 and 3 (1978 and 1979). TABLE 3.4.2 : Total nitrogen content at each sampling time, 1979 (3 sites full data set) x ± S.E. mg N g"1 dry weight SITE SAMPLING TIME 1 2 3 (n 5) (n = 5) (n 3) 1 22.67 + 0 71 19.74 ± 1 83 26.29 + 3 23 2 20.45 + 0 84 19.80 ± 0 59 25.23 ± 2 28 3 14.27 + 1 73 19.25 ± 2 10 22.13 ± 0 14 4 14.73 + 3 26 23.62 ± 2 50 25.42 ± 3 14 5 14.84 + 1 98 19.58 ± 1 46 19.25 + 4 32 6 15.24 + 2 52 19.67 ± 1 68 19.21 + 2 74 7 18.14 + 1 32 15.95 ± 2 00 17.14 + 2 54 8 15.32 + 1 25 11.04 ± 1 55 14.12 + 1 63 9 12.31 + 0 52 14.88 ± 1 65 17.15 + 1 35 10 13.31 + 0 68 13.78 ± 1 13 14.64 + 0 72 11 12.08 + 1 14 16.34 ± 1 51 . 13.22 + 0 97 12 11.32 + 0 76 14.39 ± 1 71 14.81 + 3 49 13 11.08 + 0 52 14.64 ± 3 10 11.92 + 1 88 14 10.42 + 0 86 11.50 ± 2 48 13.78 + 1 79 15 10.71 + 1 32 13.63 ± 2 18 13.74 + 1 24 16 10.23 + 0 49 13.16 ± 1 77 12.98 + 2 08 17 11.01 + 1 18 14.23 ± 1 38 12.80 + 1 56 18 11.10 + 0 76 14.94 ± 1 89 14.34 + 1 88 19 9.67 + 0 32 13.88 ± 1 64 14.18 + 2 22 20 9.86 + 0 91 14.66 ± 0 51 13.51 + 2 58 21 11.42 + 0 93 14.38 ± 1 64 14.64 + 0 55 22 10.97 + 1 47 12.96 ± 1 75 16.02 + 1 03 23 9.83 + 1 33 11.58 ± 2 06 14.30 + 0 86 24 8.05 + 0 80 13.37 ± 2 39 10.04 + 1 36 116. gave the following values, 1978 X2 » 7.60, n = 5, k = 3, p = 2.4 x 10"2 1979 X2 = 21.58, n = 24, k = 3, p < 6.0 x 10""7 See section 3.2.1. for discussion of reasons why non-parametric tests were used. The grass species on site 3 had the highest average nitrogen levels, and site 1 species had the lowest. Two sources of variation may have contributed to the differences in nutritional quality of each site, environmental conditions and specific composition. The environmental conditions of each site are described in section 3.2. There has been much work on the positive effect of water stress on plant nitrogen levels (Roy & Peacock, 1972). Site 3 experienced such water stress, corresponding to the highest levels of nitrogen seen here. However, sites 1 and 2 did not follow this pattern. Site 1 was drier than site 2, but had lower nitrogen levels. Site 2 had a consistently wet soil, and this might have been expected to leach the soil and decrease the nitrogen levels (Roy & Peacock, 1972). However, the explanation of increased nitrogen levels in plants in wet soil may be that the spring line running across part of site 2 introduced extra salts into the habitat. The grass species composition varied between sites, but when the levels of nitrogen in Agrostis tenuis were compared between sites the same trend as above was seen i.e. Site 3 > Site 2 > Site 1. Sites 1 and 2 supported similar species, and for each, site 2 had a higher nitrogen level. Thus,the difference in average total nitrogen content between sites appears to be caused by a combination of different environmental conditions and different species composition. 117. • Fig. 3.4.1. illustrates the similarity of seasonal patterns in total nitrogen content for each species at each site. All species showed high levels in late May, due to the spring flush of growth (McNeil & South- wood, 1978). The levels remained low during the summer, until the autumn regrowth resulted in another increase. Only some species considered produced this autumn flush. This was probably a result of the sampling technique whereby samples were taken randomly without differentiating new and old growth. Hill (1976) found that there was a massive increase in total nitrogen content of the new autumn growth, but that the old leaves and sheaths maintained low nitrogen levels. Throughout the season, no grass species had a lower total nitrogen level than 6% of dry weight. There have been many studies on the effect of plant species on acridid growth (e.g. Bailey & Mukerji, 1976; Chapman et al., 1979 ), but little on the effect of nitrogen (Bernays & Chapman, 1978). Torrence (1975) collected more Erittetix simplex and Hippisous rugosus (Scudder) from plots of nitrogen-fertilized prairie grasses than from unfertilized control plots. However, Melanoplus femurrubrwn (DeGeer) was more common on the control plots. On nitrogen-fertilized orchard grass, Byers & Jury (1977) found an increase in the numbers of several grasshopper species. These experiments are not conclusive however, as nitrogen fertilization changes architectural features of the habitat as well as increasing the nutritional quality of the food (Prestidge, 1980). Smith & Northcott (1951) appear to be the only workers who have used different nitrogen levels in plants in controlled laboratory experiments to feed acridids. Using Melanoplus mexicanus mexioanus (Sauss.), they found that 6% total nitrogen allowed 48% survival to the adult stage. No comparison to field conditions can really be made with Dadd's work (1961) on artificial diets. 118. From this it seems that the levels of nitrogen would not be detri- mental to survival on any of these sites. However, further comment depends on the grass species eaten by the grasshoppers and this is examined in section 3.5. Summary 1. There was little between-year variability in total nitrogen content of leaves and sheaths at each site. 2. There was a significant difference between sites in both years, in the average amount of total nitrogen available from all the grass species. The grasses on site 3 had a higher average level than site 2. Site 2 had a higher level than site 1. 3. Each grass species at each site showed similar seasonal patterns in the total nitrogen content. 4. No species had levels of nitrogen thought toolow to support growth and development of the grasshoppers. 3.5 Feeding Preferences 3.5.1. Methods_ During the season three samples of live grasshoppers were collected during vegetation surveys from each site. The insects were brought to.the laboratory, and left in individual glass tubes until a faecal sample had been obtained, after which they were returned to their original field site. The tubes, each marked with the date, site number and developmental stage of the insect, were stored in a freezer. Examples of all the grasses present on each site were also stored in the freezer. The method of identifying the plant remains in the faeces was basically 119. that of Mulkern & Anderson (1959) and Bernays & Chapman (1970a). Reference slides of all grass species at each site were produced, as a species might vary morphologically between sites. The sheath, and upper and lower epidermis of the leaves, were coated with clear cellulose lacquer. When dry, this was peeled off displaying all the diagnostic surface features (Bernays, pers. comm.). Metcalfe (1960) described these characters in detail; in most cases only the genus can be identified accurately. All the faecal samples from one individual were mounted in phenol, broken up with a scalpel, and all the grass remains identified. All the pellets were used because they were so small. The observed number of insects having fed on each species was compared,by a X2 test,with the number expected if they fed on the grass species in direct proportion to their relative abundance. This expected number was generated from the abundance values of each grass in the vegetation survey data (section 3.3). When species occurred in very low percentages, they were combined to produce an expected value of 5 or more, as is necessary in X2 tests. The group "other species" therefore referred to all grass species present not specifically named. Accuracy of identification was tested by collecting the faeces of insects fed on known grass species and preparing slides of these. The slides were coded by another person, identified and the results checked, as in Bernays & Chapman (1970a). 3.5.2. Result s_ and_ D.iscussion The accuracy to which the grasses in the faecal pellets could be identified was in most cases 80% or more (Table 3.5.1.), except between the two species of Festuoa, The two Agrost-is species occurring on site 3, were also combined as they were difficult to differentiate. The,scores TABLE 3.5.1 : Accuracy of grass species identification: percentage of samples identified as a particular species. % IDENTIFIED AS SAMPLE SPECIES NUMBER IN SAMPLE FESTUCA FESTUCA HOLCUS HOLCUS POA MOLINIA EXAMINED AGROSTIS OTHER spp. OVINA RUBRA . LANATUS MOLLIS spp. CAERULEA AGROSTIS spp. 30 87 10 3 FESTUCA OVINA 20 10 60 30 FESTUCA RUBRA 20 5 50 45 HOLCUS LANATUS 20 85 10 5 HOLCUS MOLLIS 20 10 90 POA spp. 20 15 80 5 MOLINIA CAERULEA 18 94 6 OTHER 20 5 5 5 85 for these species were therefore added together in the analysis. The • rarer grasses such as Bromis mollis and Glyceria x pedicellata were grouped as "other species" for identification purposes, as they occurred so irregularly. The results of the faecal pellet analyses are shown in Tables 3.5.2. and 3.5.3. with both the observed and expected number of insects per grass. No faecal sample contained more than one species of grass probably because the pellets contained the remains of only one meal. Bernays & Chapman (1970a), however, found more than one species present in the crop in 15% of first instar nymphs and 43% of adult females (C. parallelus). No forbs wer e f ound. C. parallelus Faecal analysis of the samples from site 1 demonstrated that selection of particular grasses occurred in each stage throughout the season, based on three sample times. Most insects sampled had fed on Agrostis tenuis (the most abundant species) but there was more Holcus and "other" grasses eaten than expected from their relative abundances. Festuca was avoided especially by the early instars. This corresponded with the findings of Bernays & Chapman (1970a), who suggested that the preferences observed were not deliberate, but originated from an avoidance of Festuca. In a subsequent paper, Bernays & Chapman (1970b) found that early instars of C. parallelus would not feed on Festuca as their man- dibular gape was too small. However, the adult diet showed an excess of Festuca, This was also noted by Bernays & Chapman (1970a) but dismissed as a sampling error. However, the later instars might be less restricted in their feeding because of their larger size, if avoidance of Festuca was due to a TABLE -3*5.2 : Food selection by C. parallelus on 3 sites. (0 = Observed number, E = Expected number feeding on each grass) SITE 1 SAMPLING NO. INSECTS AGROSTIS FESTUCA HOLCUS OTHERS* 2 INSTAR X TIME COLLECTED TENUIS OVINA + RUBRA LANATUS + MOLLIS P JULY I 87 0 29 1 31 19 41.92 < 0.001 E 37 24 19 7 II 60 0 26 0 16 18 50.49 < 0.001 E 26 16 13 5 III 60 0 36 0 14 10 24.92 < 0.001 E 26 16 13 5 AUGUST I 50 0 17 5 27 1 28.50 < 0.001 E 18 15 12 5 II 50 0 21 3 15 11 18.05 < 0.001 E 18 15 12 5 III 50 0 14 12 11 13 14.37 0.01 > p > 0.001 E 18 15 12 5 IV 50 0 21 14 12 3 1.36 N.S. - E 18 15 12 5 50 0 13 13 21 3 9.21 0.05 > p > 0.02 ? E 18 15 12 5 SITE 1 : Continued. SAMPLING NO. INSECTS AGROSTIS FESTUCA HOLCUS OTHERS* 2 INSTAR X TIME COLLECTED TENUIS OVINA + RUBRA LANATUS + MOLLIS P AUGUST cf 50 0 17 24 2 7 14.59 0.01 > p > 0.001 E 18 15 12 5 SEPTEMBER IV 50 0 2 13 33 2 74.88 p < 0.001• E 19 11 10 10 50 0 3 32 15 1 64.16 p < 0.001 ? E 19 11 10 10 cf 50 0 1 42 4 3 112.90 p < 0.001 E 19 11 10 10 * "Others" = all other grass species present, but in too low a frequency to give an expected value £ 5 as needed in a X2 test. N.S. = not significant TABLE 3,5.2 : Continued SITE 2 SAMPLING NO. INSECTS AGROSTIS HOLCUS HOLCUS POA INSTAR OTHERS X2 TIME COLLECTED TENUIS LANATUS MOLLIS TRIVIALIS + PRATENSIS P JULY I 50 0 32 0 12 6 0 29.60 0.001 E 16 6 12 10 6 < II 50 0 33 0 9 4 4 29.08 0.001 E 16 6 12 10 6 < III 50 0 17 0 22 11 0 20.50 0.001 E 16 6 12 10 6 < AUGUST I 50 0 30 0 . 20 0 0 36.27 0.001 E 17 6 12 9 6 < II 50 0 35 0 15 0 0 40.80 0.001 E 17 6 12 9 6 < III 50 0 28 3 19 0 0 27.70 0.001 E 17 6 12 9 6 < IV 50 0 14 0 28 4 4 31.30 0.001 E 17 6 12 9 6 < 50 0 17 0 33 0 0 57.75 0.001 ? E 17 6 12 9 6 < SITE 1 : Continued. SAMPLING NO. INSECTS AGROSTIS HOLCUS HOLCUS POA 2 INSTAR OTHERS X TIME COLLECTED TENUIS LANATUS MOLLIS TRIVIALIS + PRATENSIS P AUGUST SEPTEMBER IV 50 0 20 3 27 0 0 35.50 < 0.001 E 16 6 12 9 7 50 0 10 6 26 6 2 23.15 < 0.001 ? E 16 6 12 . 9 7 50 0 6 10 27 4 3 & 32.73 < 0.001 E 16 6 12 9 7 TABLE 3.5.2 : Continued. SITE 3 SAMPLING NO. INSECTS MOLINIA AGROSTIS 2 INSTAR X TIME COLLECTED CAERULEA TENUIS + CANINA P JULY I 50 0 19 31 95.70 < 0.001 E 43 7 II 50 0 23 27 66.45 < 0.001 E 43 7 III 50 0 38 12 0.05 > p > 0.02 E 43 7 4.50 IV 50 0 38 12 4.50 0.05 > p > 0.02 . E 43 7 50 0 41 9 3.67 N.S. ? E 43 7 cT 50 0 32 18 20.10 < 0.001 E 43 7 AUGUST IV 55 0 44 11 7.92 0.01 > P > 0.001 E 50 5 55 0 37 18 37.18 p < 0.001 ? E 50 5 . SITE 1 : Continued. SAMPLING NO. INSECTS MOLINIA AGROSTIS 2 INSTAR X TIME COLLECTED CAERULEA TENUIS + CANINA P AUGUST N.S. = not significant TABLE 3.5.3 : Food selection by C. hrunneus on 3 sites. (0 = Observed number, E = Expected number feeding on each grass) SITE 1 SAMPLING NO. INSECTS AGROSTIS FESTUCA HOLCUS INSTAR OTHERS X2 TIME COLLECTED TENUIS .OVINA + RUBRA LANATUS .+ MOLLIS P JULY I 92 0 57 8 26 2 24.45 p < 0.001 E 40 25 20 7 II 50 0 34 3 13 - 13 - 0 15.20 p < 0.001 E 22 14 14 III 44 0 31 0 8 - 10 -- 21 20.27 p < 0.001 E 19 12 13 0 11 0 AUGUST I 50 0 39 44.58 p < 0.001 E 18 15 12 5 II 50 0 25 3 18 4 15.50 0.01 > p > 0.001 E 18 15 12 5 2 20 11 III 50 0 17 23.86 p < 0.001 E 18 15 12 5 22 5 IV 50 0 20 3 18.16 p < 0.001 - E 18 15 12 5 ¥ 0 18 3 20 9 50 18.13 p < 0.001 E 18 15 12 5 SITE 1 : Continued. SAMPLING NO. INSECTS AGROSTIS FESTUCA HOLCUS INSTAR OTHERS X2 TIME COLLECTED TENUIS OVINA + RUBRA LANATUS + MOLLIS P AUGUST cf 50 0 14 11 3 20 53.71 p < 0.001 E 18 15 12 5 SEPTEMBER IV 50 0 6 27 17 0 47.07 p < 0.001 E 19 11 10 10 o + 46 0 5 18 23 0 45.65 p < 0.001 E 17 10 9 9 SITE 2 POA SAMPLING NO. INSECTS AGROSTIS HOLCUS HOLCUS 2 TRIVIALIS OTHERS INSTAR TENUIS LANATUS MOLLIS X P TIME COLLECTED + PRATENSIS 0 6 14 8 0 JULY I 50 22 8.98 0.05 > p > 0.02 E 16 6 12 10 6 0 7 - 15 - 8 5 - 16 - 11 AUGUST IV 35 4 8.36 0.02 > p > 0.01 E 12 12 11 o + 0 6 15 9 30 4.20 N.S. E 10 10 10 0 16 cr 30 3 11 8.60 0.02 > p > 0.01 E 10 10 10 N.S. = not significant TABLE 3.5.2 : Continued. SITE 3 SAMPLING NO. INSECTS MOLINIA AGROSTIS INSTAR X2 TIME COLLECTED CAERULEA TENUIS + CANINA P JULY I 50 0 36 14 8.14 0.01 > p > 0.001 E 43 7 IV 50 0 40 10 1.50 N.S. E 43 7 50 0 28 14 ? 12.23 < 0.001 E 43 7 50 0 24 16 cf 11.57 < 0.001 E 43 7 N.S. = not significant 132. structural inhibition in the early stages. Greater consumption of Festuca by adults on site 1 might have been caused by increased encounters with this species, since it grew close to the oviposition sites and is often the dominant species here. Young (1979), in discussing the areas chosen for aggregation, suggested that these were for socio-sexual activities and would dictate which grasses were eaten in the- vicinity. On site 2 a similar feeding pattern was observed; all instars exhibited selective feeding throughout the season. Festuca was again avoided, particularly by the early stages, which took more Agrostis and Holcus than expected. The difference in amounts taken of these two species were roughly in proportion to their relative abundances. On site 3 most insects fed on Molinia, the dominant plant here, but more Agrostis was taken than expected. Bernays & Chapman (1970a) found that on sites with only Molinia and Agrostis setacea, the grasses were taken in proportion to their availability, whilst Qasrawi (1966) found that C. -parallelus from similar sites actively preferred Molinia in the laboratory. In this study, however,-Agrostis tenuis was more acceptable than Molinia. Instances where all the grasses were taken in direct proportion to their relative abundance were few, but these instances always occurred in later instars e.g. fourth instar nymphs of C. parallelus on site 2. C. brunneus Similar feeding patterns were seen for C. brunneus. On site 1 there was a slight increase in preference for Agrostis, whilst Holcus was taken roughly in proportion to its availability. Festuca was again avoided. Young (1979) mentioned that although feeding was observed on thirty-seven 133. occasions, on only three were C. brunneus seen feeding on the dominant grass Festuca ovina. This could be due to a structural inhibition as demonstrated for C. parallelus by Bernays & Chapman (1970a). The few samples of C. brunneus from site 2 indicated that the same selection occurred in each instar as before, and again more Agrostis was taken than expected. The samples from site 3 specimens also exhibited some feeding preferences. Whilst the highest percentage fed on Molinia3 Agrostis was taken more often than would be expected from random encounters. Table 3.5.4. summarises the trends in feeding preferences in both species. The differences between the grasses preferred by each stage may have been caused by the physiological state of the insect (Chapman, 1957), but it might also be due to differences in behaviour bringing the insect into contact with different species. Simple laboratory studies showed that the later instars became progressively more active and covered larger distances between feeding. They would therefore come into contact more frequently with each grass species than small,relatively immobile stages. This would reduce the apparent selection of a particular species if, once the insects had found a suitable plant, they tended to collect there by orthokinesis (Mulkern, 1970). Only on site 1 were all instars sampled for both species. The difference in the feeding preference of C. parallelus in this study to that described by Bernays & Chapman (1970a) may have been due to the presence of C. brunneus. For example, first instar nymphs of C. parallelus showed preference for Holcus whilst C. brunneus showed preference for Agrostis, whereas from the work, cited above, the former species preferred TABLE 3.5.4 : Summary of seasonal variation in food selection by C. parallelus and C. brunneus (3 sites). SITE 1 C. PARALLELUS C. BRUNUEUS SAMPLING INSTAR TIME Agrostis Festuca Holcus Agrostis Festuca Holcus OTHERS X2 OTHERS X2 tenuis spp. spp. P tenuis spp. spp. P I JULY - - + + + - + - AUGUST 0 - + - 7.49 0.05 > p > 0.01 + - - - 10.99 0.05 > p > 0.01 II JULY 0 - 0 + + - - AUGUST + - + + 4.38 N.S. + - + - 3.68 N.S. III JULY + - + + < + - - - AUGUST - - - + 21.70 < 0.001 - - + + 7.49 0.05 > p > 0.01 IV AUGUST + - 0 - + - + 0 SEPTEMBER - + + - 25.73 < 0.001 - + + 32.51 < 0.001 ? AUGUST - - + - 0 - + + SEPTEMBER - + + - 15.27 0.01 > p > 0.001 - + + - 27.15 < 0.001 (f AUGUST - + - + - - - + SEPTEMBER - + - - 21.40 < 0.001 - + + + 7.53 N.S. TABLE 3.5.4 : Continued. SITE 2 C. PARALLELUS C. BRUNNEUS SAMPLING INSTAR TIME Agrostis H I Holous Poa 2 Agrostis Holcus Holous Poa O QUS OTHERS X OTHERS X2 tenuis lanatus mollis spp. P tenuis lanatus mollis spp. P I JULY + - 0 + - + 0 + - - AUGUST + - + - - 8.06 N.S. II JULY + - - - - AUGUST - - + - - 9.56 0.05 > p > 0.01 III JULY + - + + - AUGUST + - + - 16.91 < 0.001 IV AUGUST - - + - - - + + SEPTEMBER + - + - - 12.08 0.01 > p > 0.001 ¥ AUGUST 0 - + - - - + SEPTEMBER - 0 + - - 16.65 0.01 > p > 0.001 cf AUGUST + - + - + - + + SEPTEMBER - + + - - 26.25 < 0.001 TABLE 3.5.4 : Continued. SITE 3 C. PARALLELUS C. BRUNNEUS SAMPLING INSTAR TIME Molinia Agrostis 2 Molinia Agrostis X X2 caerulea spp. P caerulea spp. P I JULY - + - + II JULY - + III JULY - + IV JULY - + - + AUGUST - + 0.25 N.S. ? JULY - + - + AUGUST - + 2.97 N.S. cf JULY - + - + AUGUST - + 12.98 < 0.001 - = less eaten than expected. 0 = same as expected. + = more than expected N.S. = not significant Agrostis. As their oviposition sites are relatively similar (Waloff, 1950) there may have been some competition between the species. Where C. brunneus occurred in much smaller numbers than C. -parallelus on sites 2 and 3 there were no differences between the species1 feeding behaviour. The apparent segregation was absent in the later stages on site 1. This may have been because adults are possibly less sensitive to physical interference from other individuals. There were also seasonal differences in the feeding behaviour of a particular stage (shown in Table 3.5.4.). Whilst differences between stages have been shown before, seasonal differences within a stage have not. The samples used here, although they gave significant results, were small, and they may have emphasised different areas within the hetero- geneous sites. This is supported by the results from site 3 where the vegetation was the least diverse. Here, the only seasonal differences found were in the mobile adult males, which were therefore the stage with the highest probability of being collected from a different area in the site. There were no obvious relationships between preferences for a grass and its nitrogen content (Table 3.5.5.). The observed feeding preferences of the nymphs were probably caused by the deliberate avoidance of Festuca spp. and Holcus lanatus, rather than deliberate selection. This is confirmed by the fact that the species apparently preferred were taken approximately in proportion to their availability, excluding the two species mentioned. Only in some cases did the preferred species have the highest nitrogen content. In site 3, Molinia had the highest nitrogen content, but Agrostis was still preferred. Both species could feed on a wide range of grasses, the expression 138. TABLE 3.5.5 : Abundance of grass species at each site and their average total nitrogen content (3 sites). SITE 1 SAMPLING AGROSTIS FESTUCA HOLCUS OTHER TIME TENUIS spp. spp. spp. JULY % Abundance 43.0 27.2 22.2 7.6 N/mg/g dry wt 14 12-14 16-25 - AUGUST % Abundance 36.0 29.6 24.2 10.1 N/mg/g dry wt 12 9-12 11-14 - SEPTEMBER % Abundance 36.9 22.2 20.5 20.5 N/mg/g dry wt 11 9-13 9-10 SITE 2 SAMPLING AGROSTIS HOLCUS HOLCUS POA OTHER TIME TENUIS LANATUS MOLLIS spp. spp. JULY % Abundance 31.2 11.5 24.8 19.1 13.4 N/mg/g dry wt 17 16 15 12 10 AUGUST % Abundance 34.9 11.4 23.4 17.7 12.7 N/mg/g dry wt 16 19 18 11 12 SEPTEMBER % Abundance 31.1 12.1 23.8 19.0 14.2 N/mg/g dry wt 11 21 13 9 10 SITE 3 SAMPLING MOLINIA AGROSTIS AGROSTIS TIME CAERULEA TENUIS CANINA JULY % Abundance 86.6 4.5 - 13.5 - 9.0 N/mg/g dry wt 20 13-14 AUGUST % Abundance 91.6 3.6 - 8.4 - 4.8 N/mg/g dry wt 15 11-14 139. of their selectivity being dependent on the habitat and the grasses available, confirming the findings of Williams (1954). Mulkern (1970) suggested that although most grasshoppers showed preference for certain grasses they did not actively search for them. However, once the grasses were being eaten the insects may ingest them at a faster rate. If the nutritional level was too low, a faster ingestion rate would compensate for this (McNeil & Southwood, 1978), suggesting that the nutritional requirements of the insects would be satisfied in each habitat. Summary a) This study supported past work on C. parallelus that the expression of feeding selectivity was dependent on the nature of the habitat, and demonstrated that this applied to C. brunneus also. b) Overall, the grass species taken were eaten in proportion to their relative abundance. The apparent increased selection of other grasses can be explained by deliberate avoidance of Festuca spp. and Holcus spp. because of their structural inhibition to feeding. c) Differences in the degree of selectivity were seen in each stage of both species, due partially to structural inhibition to feeding and to mobility. d) The difference in nitrogen levels between species was very small and nutritional differences in diet could not be shown in this study. 3.6 Insect Population Dynamics 3.6.1. Method^ a) The methods used in previous population studies of grasshoppers are described in chapter 2, section 2.2. The most efficient method mentioned (Onslager & Henry, 1977) was again unsuitable as it did not allow the examination of the insects, and the early instars were not counted. The present study required both density values and stage-frequency data, which necessitated frequent collection of large samples of each species through- out the season. The absolute method used in the survey in chapter 2 was considered too cumbersome for a sole worker sampling six populations at least once a week. Consequently sweeping, combined with direct counts as a calibration method, was chosen as the most time effective technique. The factors affecting this method, reviewed by Carpenter & Ford (1936), Dyck (1971) and Southwood (1978), were borne in mind. The time of day for sampling was kept as consistent as possible; if the vegetation was wet however, the sampling was delayed until it had dried. Calibration of the sweeping data by direct counts cancelled the effect of differing capture efficiencies of each instar in varying habitats. Each site was frequently checked during early May for the first emergence of nymphs. The nymphs were then sampled weekly in 1978 and twice weekly in 1979. The sampling procedures were altered in 1979 because certain population changes had occurred quite suddenly during the previous year. A nylon sweepnet, 0.33 m wide, covered an average of 0.5 m per sweep, thereby collecting insects over 1.5 m2 every nine sweeps. This was confirmed by sweeping superficially across damp sand and measuring the scour marks. One hundred samples of nine sweeps were collected at each sampling time, the total area sampled being 150 m2 (i.e. 9.4 - 12.5% of the total site area). On a number of occasions direct counts were made on the same visit. A 0.5 x 0.5 m high-sided quadrat was placed carefully onto the ground and the area enclosed thoroughly examined for grasshoppers. 141. This was repeated eighty times, covering 20 m2 (i.e. 1.3-1.7% of the total area). Whilst only a small percentage of the site was therefore sampled, this was the largest area manageable in the time available. The species and stage of all grasshoppers collected were recorded. Early instar nymphs of each species were identified in the field using a x 10 hand lens (Richards & Waloff, 1954). b) The analysis of the stage-frequency data. From sampling data, the average number of individuals per square metre for each species, nymphal instar, and the adults of both sexes were calculated. The calibration indices were obtained from the ratio of the average direct count value (of a particular stage) to the average sweeping value. In 1979 this method produced similar results to 1978, and so the same calibration indices were used in both years. It was intended to regress the sweeping data on the direct count values , as per Southwood (1978)^ where y = bx + a y = number in sweep x = number in direct count The slope b would then be the calibration index, but the density values in 1978 were so low that in some cases direct counts did not show the presence of any insects, and so there were insufficient points for a regression. The direct count values, the calibration indices and the corrected stage-frequency data are given in appendix 3e. The population changes were expressed in terms of days and day degrees. It is more useful to employ day degrees when examining the duration of populations or instars, since temperature affects development as discussed in section 3.2.1. and by Bodenheimer & Swirski (1957). In this study habitat differences in the population dynamics of each species may have been partially due to the temperature differences. Therefore, thermal summation would serve to reduce the variability seen in the population parameters in the field. Graphs of developmental rate against temperature for these acridid species or any closely related species were not available, and so the developmental threshold could not be calculated. However, the use of this parameter does not influence the size of the difference between,for example, two developmental periods. As this study was concerned with differences between certain parameters within a species, the use of develop- mental periods calculated from a base line of 0°C was satisfactory. The period during which a population persisted at any given site was calculated in days and day degrees. It was referred to as the "population persistence" (Smith & Whittaker, 1980 ). An index for the length of the emergence period at each site was obtained by dividing the total period during which first instar nymphs were present by the first instar develop- mental period. There are many models available for analysing stage-frequency data for the preparation of a life-budget. Southwood (1978) provides the latest summary and discussion of methods, pointing out the disadvantages and assumptions made in each case. Most methods were rejected because additional information was needed to that available in this work, or the assumptions made were inappropriate. The method of Kiritani & Nakasuji (1967) as modified by Manly (1976) was chosen in favour of more complex methods because it required little mathematical transformation of the data, all calculations were based on the areas under the frequency curves, and 143. hence was probably also quicker for the analysis of twelve sets of pop- ulation data. Southwood describes this method as "relatively simple and reliable". Apart from the numbers entering a stage and the stage-specific survival rate, nymphal developmental periods were also required for this study. Very few models calculate these, except for Manly (1976) and Manly (1974), a more mathematically complex method. Manly (1976) employed a graphical technique to estimate the nymphal developmental periods, by calculating the median stage at each sampling time. This median stage was plotted against time (along the abscissa) and the time between stage 1.0 and 2.0 etc. was read off the abscissa. These estimations were used to calculate a constant daily survival rate, and hence values of each instar developmental period. The initial estimation of this period had an inherent error pointed out by Manly, when using median stage values during stage 1 when not all the eggs have hatched. Whilst this was probably a fairly accurate estimation, an independent method was devised, using the areas under the curves, which did not involve this error. The area under the frequency trend curve for the ith stage is equal to the number of insects entering that stage multiplied by the average time spent in the stage. The time at which the 50% area value occurs is indicative of the time at which 50% of the individuals in that stage have been present. This point can be calculated for the curve for each instar and by subtraction the average duration of each instar is obtained. This value is influenced by the distribution of mortality within the stage; if a proportion of individuals in the ith stage do not survive to the (i + l)th stage then the developmental period of the ith stage will be falsely shortened. The area A. under the frequency trend curve for the ith stage is 144. found by the trapezoidal rule, where eq, 1 A. = 1 (x1-x) (y^+y) + (x^) fy+yj + ..... (x -x i) (y +y ,) n n-1 n n-1 -1 which can also be expressed as n eq. 2 A. = j ^ (x^-x-.p y. This value is halved ( /2) and the process in eq. 1 repeated until two pairs of coordinates (x-^y^) and are obtained between which the value of /2 lies. A^ = area produced from known co-ordinates A£ = area > /2 using next pair coordinates. 2 (x-Xl) 72 - Ax = yx (X-Xl) + J x2-x1 # ^l'7!* This simplifies to a quadratic equation such that only one root lies with- in the specified range x^ and xNo error is obtainable for this value, and it is merely an indication of the differences between the development of different populations. It is at least as reliable as the only other method available, (Manly, 1976) and avoids the error involved in using the median stage values during stage 1 when not all the eggs have hatched as described before. 145. The survival rate J0\ of the ith stage as described by Manly (1976) is: q 0. = 1 - A./ I A. l l . . j J=i J where q = last stage (adults). The daily survival rate is calculated from the relationship a. = J0T, 1 SS.l d where a^ = duration of ith stage, which in this study is calculated separately. Hence log£Td = l°g0./a_ 1 which,if calculated over the total nymphal developmental period,gives a more accurate estimate of 0^. A constant daily survival rate for all stages was the only assumption made in this method. The population frequency trend curves indicated a logarithmic survival curve and specific field experiments, described in section 3.7, confirmed that the assumption was valid. Finally, the numbers entering each stage No^ could be found from q No. = - log SS, l e d I A. i-i J This parameter is sensitive to differences in the distribution of sampling times, and minor inconsistencies in the results may occur. These parameters provided data for partial life-budgets i.e. for individual developmental stages,and indicated the significance of mortality 146. found in these stages. Data for eggs are available from field cages, (section 3.7, and chapter 4). 3.6.2. ResuIts^ and_ D^iscjjss_ion C. parallelus Distinct site differences between the dates of first emergence occurred in both years (Table 3.6.1.). The earliest was site 1, where hatching occurred nine days before site 3 (the last site) in 1978, and twenty-six days earlier in 1979. The trend in population persistence was consistent in the two years, whether expressed as a function of days or day degrees. The eggs hatched first of all on site 1, and emergence continued for the longest period. The shortest emergence period occurred on site 3, where hatching started after sites 1 and 2. The population persistence was generally shorter in 1979. The index of the emergence period differed between sites in both years, and the trend was inconsistent. In 1978, site 2 had the longest emergence, then site 3 and site 1. In 1979 the longest emergence period occurred on site 1 followed by site 2, with site 3 the shortest. The errors involved in the first two parameters were very small. The date of first emergence was identified to within a day, as each site was thoroughly examined in the days preceeding the first collection of nymphs. The period of population persistence was less accurately known; when the population reached too low a level, sampling 12% of the area would produce an underestimation of the survivors. However, these individuals would contribute little to the next generation as they were in poor condition; they moved slowly, were very thin and sometimes mouldy. 147. TABLE 3.6.1 : Population data for C, parallelus. Population persistance Date of first Index of SITE emergence emergence days day degree period 1978 1 29.5 165 2871.5 • 5.80 2 31.5 162 2609.9 14.05 3 7.6 110 2354.9 8.14 1979 1 22.5 148 2788.2 7.30 2 5.6 119 2124.5 4.81 3 17.6 95 1682.0 2.76 148. The error attached to the index of emergence period was relatively large, in that the average first instar developmental period was used as a denominator. The variance of this value was probably large, due to the effect on the nymphs of the microclimatic conditions. Hence this index can only be used with caution. The total population curves for each year, (Fig. 3.6.1) graphically display the site differences in emergence time, population persistence and the population density. Within a year, the site profiles were similar, but with varying population levels, whilst between years the profiles were different. The site differences in peak densities were tested for significance, (Table 3.6.2.). The raw sampling data indicated that although many individuals were sampled, the chance of their occurrence in a particular sweep sample was low, and many samples were zero i.e. the sampling distribution approx- imates to a Poisson distribution. Although the data was not tested for this, the assumption was thought valid as Onslager & Henry (1977) also found that their grasshopper data followed a Poisson distribution. The Poisson parameter m was estimated from the sample average. The peak densities on sites 1 and 2 were not significantly different in 1978, but both differed significantly from site 3. In 1979, all the sites were significantly different. The site differences seen in Fig. 3.6.1 were altered when the population changes were in day degrees (Fig. 3.6.2), although the rates of recruitment and mortality appeared similar. The partial population curves for each site (Figs. 3.6.3 and 3.6.4) clearly illustrate the differences between populations. In 1978, 149. FIGURE 3.6.1 : Total population curves of C. parallelus (3 sites, a) 1978, b) 1979) . 150. TABLE 3.6.2 : Peak densities for C. parallelus populations and signific tests (3 sites). a) Peak densities m"2 SITE YEAR 1 2 3 1978 .9667 1.0533 .3833 1979 1.1866 1.2400 .4333 b) Significance tests for two samples (Poisson distribution) 1978 1979 d. 1 2 3 1 2 3 1 1978 2 .60* 8.64 3 5.02 5.59 9.99 6.24 (Bailey, 1959) * = p > 0.10 Other tests were all significant at p < 0.001. 151. FIGURE 3.6.2 : Total population curves of C. parallelus in relation to day degrees (3 sites, a) 1978, b) 1979). 152. MAX JUNE JULy AUG SEPT OCT NOV FIGURE 3.6.3 : Partial population curves of C. parallelus in 1978 (3 sites) — = I instar, II instar, III instar, IV iristar, adult. 153. site 3 site 2 MAX JUNE JULy AUG SEPT OCT FIGURE 3.6.4 : Partial population curves of C. parallelus in 1979 (3 sites) — = I instar, --- =11 instar, = III instar, = IV adult. extensive overlap of the instars occured in sites 1 and 2, causing an accumulation of adults. Similar partial population curves were produced by Richards, Waloff & Spradbery (1960) using a model of Nomadacris septem- fasioata (Serv.) populations, when the emergence period was extended from one to fifteen days. Sites 1 and 2 had large indices of emergence compared to site 3, where no such adult build-up occurred. In 1979, the structure of the populations was very different, caused by an apparent increase in the number of first instar nymphs. No obvious adult accumulation occurred, probably because the emergence periods were shorter in that year. The population differences were quantified by the use of the analysis of Manly (1976), and simple life budgets prepared (Table 3.6.3.). The numbers entering the first stage i.e. the numbers hatched per square metre reflected the differences in peak densities of the total population curves. The populations at each site were larger in 1979 than 1978; the numbers hatched per square metre increased in 1979 at all sites and, although the daily survival rates were less, there were still more adults present in that year. The variability in the stage-specific survival rates between years was due to the annual differences in daily survival rates and the duration of the instars. The individual instar developmental periods for each population of C. parallelus are also shown in Table 3.6.3. Although variation between years occurred in the individual instar developmental periods, the total nymphal developmental period at each site was consistant, and showed significant site differences in both years. Thus, there would seem to be a fixed period for development to maturity, although the individual instar TABLE 3.6.3 : Life budgets and nymphal developmental periods of C. "parallelus (3 sites, 2 years), a) Life budget 1978 1979 1 2 3 1 2 3 No. 8. No. No. No. No. No. 0. I 0I . i I 1.13 .7889 1.69 .7652 .50 .9073 3.42 .6192 2.19 .6697 .45 .7965 II .89 .7988 1.30 .7973 .45 .7686 1.93 .6324 1.47 .7870 .36 .7511 III .71 .7994 1.04 .7772 .32 .6103 1.22 .7002 1.16 .7284 .27 .7390 IV .57 .7564 .80 .7372 .22 .5220 .86 .7386 .85 .6327 .20 .5816 Ad. .43 .59 .11 .63 .53 .12 Survival rate per .9993 .9989 .9988 .9988 .9985 .9988 day degree No. = no. entering stage m 2 0. - stage specific survival rate. TABLE 3.5.4 : Continued. b) Nymphal developmental periods (day degrees) 1978 1979 1 2 3 1 2 3 I 288.01 116.93 118.24 289.36 460.85 205.55 II 466.43 336.81 338.91 210.98 156.05 220.01 III 123.77 126.45 205.73 276.47 97.83 227.42 IV 472.02 397.00 614.00 566.43 253.29 457.44 TOTAL* 1350.23 977.19 1276.88 1343.24 968.02 1110.42 * Analysis of variance on the total developmental periods between sites. F2,3= 15.25, 0.05 > p > 0.01 Bartletts test X2 = 5.84, p > 0.05. 157. durations were flexible. The latter enables insects to take advantage of of the immediate conditions. C. brunneus C. brunneus displayed distinct site differences in each of the parameters recorded in Table 3.6.4. In 1978 there were fourteen days between the first emergence at site 1 and at site 3. The following year this increased to twenty days. The population persistence followed a similar trend in both years and was longest at site 1, than site 2 and site 3. However, expressed in day- degrees, sites 2 and 3 were very similar in 1979. The index of emergence period for each site decreased from site 2 to site 1 and site 3 in both years. However, the magnitude of this index showed considerable within-site variation, site 2 having an index of 19.93 in 1978, and 9.83 in 1979. The total population curves (Fig. 3.6.5) showed that the high- est population densities occured on site 1 in both years, then site 2 and site 3, although there was no significant difference between these peaks on sites 1 and 2 in 1978 (Table 3.6.5). The site profiles were similar within years, but, as for C. paratletus, they changed between years. In 1979 the peaks were higher and sharper. Differences between populations may have been due in part tp site variations in temperature, and so the population changes were expressed in day-degrees (Fig. 3.6.6). The site profiles remained diagnostic, although the initial rate of increase within the first four hundred day-degrees and the mortality rates appeared to be very similar between sites. The partial population curves, (Figs. 3.6.7 and 3.6.8) illustrate 158. TABLE 3.6.4 : Population data for C. brunneus. Population persistance Index of Date of first SITE emergence emergence days day degree period 1978 1 31.5 156 2788.19 5.65 2 4.6 123 2124.46 19.93 3 14.6 72 1681.95 1.47 1979 1 28.5 143 3095.96 6.33 2 15.6 93 1981.58 9.83 3 17.6 84 1992.09 3.64 159. ^ 1-0 r d 0# Site 1 A A Site 2 • • Site 3 FIGURE 3.6.5 : Total population curves of C. brunneus (3 sites, a) 1978, b) 1979). 160. TABLE 3.6.5 : Peak densities for C. brunneus populations and significance tests (3 sites) a) Peak densities m~2 SITE YEAR 1 2 3 1978 .8533 .6933 .3066 1979 1.5467 1.0267 .3467 b) Significance tests for two samples (Poisson distribution) 1978 1979 cL 1 2 3 1 2 3 1 1978 2 1.29* 3.23 3 5.08 3.87 8.79 5.80 * = 0.10 > p > 0.05 Other tests were all significant at p < 0.001 161 . DAY DEGREES xlOO FIGURE 3.6.6 : Total population curves of C. brunneus in relation to day degrees (3 sites, a) 1978, b) 1979). 162. FIGURE 3.6.7 : Partial population curves of C. brunneus in 1978 (3 sites). — = I instar, =11 instar, III instar, IV instar, = adult. 163. site 3 site 2 site 1 MAX JUNE JULY AUG SEPT FIGURE 3.6.8 : Partial population curves of C. brunneus in 1979 (3 sites) — = I instar, II instar, III instar, IV instar, adult. the between-site differences in population structure for both 1978 and 1979. Whilst the emergence period varies between sites in both years (Table 3.6.4) and each population had a very complex composition at any one time, only site 1 in 1978 displayed an obvious build-up in adult numbers. This indicated that there was generally high nymphal mortalityi particularly of the first instars, in each case. In 1979, there was an increased density of first instar nymphs, but a decrease in adult numbers on site 1 compared to the previous year, suggesting an overall decrease in the nymphal survival rate. The partial life budgets show that this was the case (Table 3.6.6). The numbers hatching on site one increased in 1979 whilst the survival rate of the site decreased, and therefore fewer adults occurred. On sites 2 and 3 however, mortality was less severe and more adults occurred than in 1978. The between-year differences of the stage-specific survival rate for each instar appears to be due to a combination of the variation of the daily (day degree) survival rate and the instar duration period. The populations on site 1 showed the least variation in individual nymphal stage developmental periods, (Table 3.6.6), whereas sites 2 and 3 had considerable between-year fluctuations. The total nymphal developmental periods conversely varied little between years, whilst the differences between sites were significant. This was similar to the situation seen for C. paraltelus, where fluctuations in the period of an individual stage were compensated for in other stages, so that the total developmental period was consistent between years. The same relationship between length of nymphal period and site was also seen. Sites 1 and 3 were not signi- ficantly different but sites 1 and 2 were. TABLE 3.6.6 : Life budgets and nymphal developmental periods of C. brunneus (3 sites, 1978/1979). a) Life budget 1978 1979 1 2 3 1 2 3 No. No. No. No. No. No. 0.l 0.l 0.l 0.l 0.I 0.i I 1.80 .6735 2.12 .3106 .32 .5623 3.29 .3248 1.49 .3513 .69 .5699 II 1.21 .7658 .66 .5287 .18 .5537 1.07 .6174 .52 .7605 .39 .7427 III .93 .6879 .34 .6008 .10 .6795 .66 .6715 .40 .7981 .29 .6151 IV .64 .5082 .21 .4108 .07 .3548 .44 .5611 .32 .0105 .18 .6037 . Ad. .32 .09 .02 .25 .19 .11 Survival rate per .9986 .9965 .9977 .9980 .9975 .9981 day degree No. - no. entering stage m"2 0. = stage specific survival rate. TABLE 3.5.2 : Continued. b) Nymphal developmental periods (day degrees) 1978 1979 1 2 3 1 2 3 I 340.29 76.25 185.54 326.77 133.48 262.83 II 315.40 125.47 246.50 335.29 48.52 543.57 III 196.59 399.60 442.48 162.60 159.50 27.42 IV 599.04 278.69 250.13 482.73 482.45 114.46 TOTAL* 1251.32 911.01 1124.65 1307.39 823.95 948.28 * Analysis of variance on the total developmental periods between sites. F2 3 = 12.30, 0.05 > p > 0.01 Bartletts test X2 = .845, p > 0.05. 167. Summary_of demographic variation' 1. C, parallelus showed a consistent pattern of response to habitat type in the date of the first emergence, the total nymphal developmental period and the population persistence. The trend in the site emergence period and the peak population density varied between years. This suggests that certain population parameters such as the nymphal develop- mental period, may be definitive for each population,whereas factors such as the emergence period may be more susceptible to fluctuations in the immediate environment. 2. C. brunneus showed a more consistent response pattern. Each of the five parameters maintained the same trend in 1978 and 1979. 3. In both species the direction of the between-year variation was similar. The population dynamics of both species will be discussed further in relation to habitat type in section 3.8. 3.7 Field Experiments 3.7.1. Methods_ The experiments described in this section fell into four parts, each designed to extend and confirm observations described in the previous section. They are illustrated in the following flow chart:- 168. ON EACH SITE ADULT LONGEVITY AT DIFFERENT DENSITIES 1978/79 DEVELOPMENTAL PERIODS EGGS LAID IN CAGES AND SURVIVAL OF NYMPHS ECLOSION 1978 EGG 1979 FERTILITY OF ADULTS 1979 SOIL COLLECTION FROM CAGES FECUNDITY (NO. OF EGG PODS PER FEMALE) 1979 DRY WEIGHT OF ADULTS 1979 a) Developmental periods and survival of nymphs The effect of habitat on the development and survival of the immature stages was studied by following cohorts of newly emerged first instar nymphs in field cages on each site. Two types of cages were used, large (0.7 m wide x 0.7 m deep x 1.5 m high) and small (1.0 m x 0.5 m x 0.5 m). The area under each was 0.5 m2, whilst the volume was 0.7. m3 and 0. 3 m3 in the large and small cages respectively. The cages were dug into the ground, and secured with stakes and guys. Temperature records showed that there was an average increase of 1-2°C within the cages per day, compared to external conditions. This would not affect the develop- mental rates of the grasshoppers to any great extent (Southwood & Siddorn, 169. 1965). Three cages per species were randomly placed on each site, and thirty newly emerged nymphs introduced to each. The numbers surviving in each instar were recorded weekly. Missing data were due to a) technical problems with cage installation on site 3, and b) vandals damaging cages on site 2. The latter cages were later moved to a similar, but safer site on Silwood Park (Pond Field, see chapter 2, section 2.3). b) Adult longevity at different densities A three factorial experiment was set up to investigate the effect of density, habitat, and sex on adult longevity. For each species and site 10 small cages (A) each containing 1 pair of adults (1 1 d) and 3 large cages (B) each containing eight pairs per cage (8 8 d) were set up. The low density cages (A) were made of wire cloche frames covered with a terylene netting bag (0.18 m radius at base, 0.39 m high); the top being fastened with wire garden ties. This cage type had an area of 0.10 m2 (TCr2) and a volume equalling 0.04 m3 (TCr2h) . The high density cages (B) were those described in 3.7.1a, with new ones on site 3. All the cages were randomly placed throughout the site. Originally, it was intended to use the cohorts from the previous section for these experiments, but so few reached the adult stage that fourth instar nymphs from the field population were used. As the population was very low on site 3, additional specimens were collected from other nearby rides where similar conditions prevailed. The cages were inspected on each population sampling day, (section 3.6) for recruitment to the adult stage and mortality, until all the adults had died. In 1979 the data recording was facilitated by marking all individuals with non-toxic paint on the prothorax. The 170. marking scheme was simple and allowed up to eighty-one combinations. One or two dots were put on the thorax in various combinations in a three by three design. c) Egg eclosion and fertility of adults By recording the hatching of the eggs laid during the density experiment, two parameters could be determined i) the hatching distribution of the two species under various conditions, ii) the fertility of females from the previous year (where fertility = number of eggs hatched, not the number of viable eggs laid). In 1979 therefore, the cages were checked daily from the time of the first emergence in the field. The number of nymphs found in each cage was recorded. The individuals were transferred to a stock cage on the same site so that the number hatching each day would be known. d) Fecundity of adult females Once all hatching in the cages had finished, having checked the cages each day, the cages were relocated on the same site. The top 4 cm of soil from the cages* original position was carefully removed with a turfing iron and turf cutter. The samples were dried on trays in a glass- house, and then stored in plastic bags in the 10 C controlled temperature room. The soil was later hand sifted and the number of egg pods found recorded for each cage. To complement this combined measurement of fecundity and egg survival,three samples of female adults of each species were collected throughout the season, and their dry weights found. Richards & Waloff .(1954) found that the weight of adult females correlated with their fecundity. 171. 3.7.2. Result s_ and_ D^i scu s si on a) Developmental periods and survival of nymphs The developmental period for each instar was not calculated in the same manner as in section 3.6. Because cohorts had been used, the time between the occurrence of peak numbers in each instar indicated the nymphal developmental periods. These were expressed in day-degrees as before, using temperature data from section 3.2. (The raw data are shown in appendix 31). The individual instar and the total nymphal developmental periods (Table 3.7.1) show the same order of magnitude and site differences as found from the field population data (Tables 3.6.3 and 3.6.6). Thus, on site 2 both C. -parallelus and C. brunneus showed significantly shorter total nymphal developmental periods than on site 1. Moreover, the variance between cages in one year was greater than the difference between field populations on the same site in the two years. This suggests that had variances been found for the field population data they would have been large, although the average period required for nymphal development on a site was stable. The model used in section 3.6 to derive data for the life- budgets made only one assumption, that survival per unit time was constant for all stages. The cohorts of nymphs provided data for a regression of the equation = l°g yt 1°8 + t log 0 where y = population at time unit t = peak numbers (numbers hatched) and 0 = fraction of population surviving per unit time. (Richards & Waloff, 1954). Hence, the antilog of the slope gives the survival per unit time. The value N was known because cohorts had been 172. TABLE 3.7.1 : Nymphal developmental periods derived from caged cohorts, 1978 (day-degrees). CAGE C. PARALLELUS C. BRUNNEUS INSTAR\. 1 2 3 1 2 3 SITE 1 I 394.87 302.75 153.42 394.87 302.75 394.87 II 310.56 310.56 489.34 438.47 438.47 310.56 III 447.67 447.67 268.89 438.87 438.87 566.78 IV 416.87 416.87 208.44 297.76 297.76 333.53 TOTAL 1569.97 1477.85 1120.08 1569.97 1477.85 1605.74 SITE 2 I 166.63 231.92 - 231.92 — — II 249.60 244.11 244.11 III 119.60 259.41 448.48 IV 233.19 290.87 101.80 TOTAL 769.02 1026.31 1026.31 Mean total nymphal developmental period (± S.E.) C. -parallelus SITE 1 x = 1389.30 ± 137.21 SITE 2 x = 897.67 ± 128.65 (F2 ^ = 1.71 p > 0.05 : variances assumed normal) 1 Tailed t = 2.44, df = 3, 0.05 > p > 0.02 C. brunneus SITE 1 x = 1551.18 ± 38.09 SITE 2 x = 1026.31 (comparison of 1 sample with mean) Hailed t = 13.72, df = 2, 0.01 > p > 0.002 173. used. Richards & Waloff (1954) used this technique for each instar. Here, the instars were combined as there was insufficient data available to treat them separately. However, the significance of the regression coefficient could be used to indicate similarity between the individual instar regressions. The regression on all the individuals was really an amalgamation of four separate regressions on each stage. Thus, the more significant the slope the less variance there is between each stage's survival per unit time, and the more confident one can be in assuming a constant daily survival rate for all stages. The regressions were repeated using the number of days and day- degrees as the abscissa, the latter to determine if temperature had any effect on survival rates. The regression coefficients were all highly significant, and hence each species at each site showed constant survival per unit time (Table 3.7.2). Taking the daily survival rate first, t~tests between regression coefficients for cages on the same site showed that there were no signi- ficant cage differences for C. paraZZeZus. Hence, in this species it can be suggested that the daily survival rate was not significantly affected by any microclimatic variations which may have occurred between the cages. Conversely, significant differences were found between cages of C. brunneus, implying that the survival of this species was perhaps more affected by its microclimatic conditions. These suggestions were confirmed by the use of day-degrees in describing the survival rate per unit time. The log "day-degree" survival rates were also highly significant, (i.e. the slope b was significantly TABLE 3.7.2 : Regression coefficients from nymphal survival curves, log Y. = log N + t log 0> DAILY - COEFFICIENT SURVIVAL DIFFERENCE BETWEEN TWO SPECIES SITE CAGE t * df b ± S.E. RATE REGRESSION COEFFICIENTS 0t c. parallelus 1 1 - 0.0230 ± 0.0019 12.32 8 .9484 CAGE 1/2 t =S 0.59, p > 0.05 2 - 0.0108 ± 0.0018 5.96 7 .9754 2/3 t = 3.82, 0.01 > p > 0.02 3 - 0.0250 ± 0.0035 7.24 6 .9441 1/3 t SS 0.70, p > 0.05 2 1 - 0.0250 ± 0.0035 7.20 6 .9441 CAGE 1/2 t = 2.14, p > 0.05 2 - 0.0180 ± 0.0010 19.25 8 .9594 c. brunneus 1 1 - 0.0189 ± 0.0017 11.48 8 .9574 CAGE 1/2 t SS 2.44, 0.05 > p > 0.02 2 - 0.0261 ± 0.0025 10.32 7 .9417 2/3 t SS 7.05, p < 0.001 3 - 0.0076 ± 0.0008 9.17 9 .9827 1/3 t = 6.28, p < 0.001 2 1 - 0.0184 ± 0.0030 6.11 8 .9585 - TABLE 3.7.2 : Continued. DAY-DEGREE COEFFICIENT DIFFERENCE BETWEEN TWO SPECIES SITE CAGE t * df SURVIVAL b ± S.E. REGRESSION COEFFICIENTS RATE C. parallelus 1 1 - 0.001037 ± 0.000097 10.70 8 .9976 CAGE 1/2 t = 0.119 , p > 0.05 2 - 0.000475 ± 0.000082 5.79 7 .9989 2/3 t = 0.109 , p > 0.05 3 - 0.001109 ± 0.000165 6.73 6 .9974 1/3 t = 0.015 , p > 0.05 2 1 - 0.001469 ± 0.000201 7.31 6 .9966 CAGE 1/2 t = 0.108 , p > 0.05 2 - 0.001101 ± 0.000059 18.38 8 .9975 C. brunneus 1 1 - 0.000855 ± 0.000081 10.50 8 .9980 CAGE 1/2 t = 0.199 , p > 0.05 ' 2 - 0.001161 ± 0.000109 10.66 7 .9973 2/3 t = 6.990 , p < 0.001 3 - 0.000346 ± 0.000042 8.22 9 .9992 1/3 t = 0.150 , p > 0.05 2 1 - 0.001129 ± 0.000175 6.45 8 .9974 - * All t-tests on b were significant at p < 0.001. 176. different from zero), and therefore a constant day degree survival rate occurred throughout the nymphal developmental period. The higher value of the rate itself compared to the daily rate was because the unit day- degree was smaller than the unit day. The smaller range of values was also caused by this difference. However, the difference between the rates was decreased as there was only one significant difference found between the • regression coefficients for C. brunneus. By expressing the survival rate in day degrees most of the species and cage differences were lost. Temperature therefore had a significant effect on the survival of these species, especially C. brunneus. The values derived here were similar to the day degree survival rates shown by the population data (Tables 3.6.3 and 3.6.6), and showed comparable site differences. Thus, the assumption of a constant survival per unit time was a valid one, and the experiments described here confirmed the life budget results of the previous section. b) Adult longevity at different densities The effect of each factor was identified by an analysis of variance for a three factorial arrangement. The GLIM statistical package (Royal Statistical Society, London) fits generalized linear models, and hence overcomes the difficulties presented by a mixed factorial design and unequal numbers of observations per cell. The two years data sets were analysed separately as the longevity values for the high density cages were derived differently in each year. The individual longevities were unknown since specimens were unmarked. There were two possible methods of obtaining a variance for each cage: 1) to assume that the first individual to become adult was the first to 177. die, i.e. that the dates of adult emergence and death were correlated. Correlations of time of death on emergence date using known individual longevities from low density cages were not significant. 2) an average entry time could be calculated and then individual longevity values found by subtracting the average entry time from individual dates of death. The resulting mean and variance were not significantly different from the mean and variance from the actual individual values (Table 3.7.3). Consequently the second method was used in the analysis. Significant effects of site and density on longevity of C. parallelus were seen in both years (Fig. 3.7.1). In 1978, two significant interactions were found. The effect of density differed with site, and also with sex. No absolute difference between the longevity of the sexes existed as their responses to density were in the same direction. The site differences in longevity were more marked in the B cages (Fig. 3.7.1a), sites 1 and 2 showing decreases in longevity. The following year the same experimental design produced independent effects of site and density, but there were no interactions. However, the main site differences again occurred in B cages. There was therefore a contradictory effect in B cages between years, when compared to A cages. The latter provided uniform conditions for the insects, whilst the large B cages provided more opportunity for variation, especially in terms of density by a) the difference in size of cages in 1978, and b) large differences in mortality affecting total numbers present. These two altered the numbers per unit area and volume. Before pursuing this further, the data for C. brunneus should be examined. If this idea is correct then similar responses would be expected in this species. 178. TABLE 3.7.3 : Two methods of derivation of mean and variance for longevity in type B cages (see text for explanation). METHOD 1 METHOD 2 SPECIES AND SITE r ESTIMATED ACTUAL X ± S.E. (n) C. parallelus SITE 1 ? .29 ? 729.19 ±87.58 729.19 + 87.39(ioJ cf .40 cf 599.12 ± 57.58 599.06 + 86.20(io) SITE 2 .48 ? 616.65 ± 48.95 594.82 + 38.7119) d* .39 c? 453.64 ± 96.95 442.80 + 85.52(8) C. brunneus SITE 1 ? .24 ¥ 606.31 ± 75.45 606.31 + 81.55*0) d* .22 cf 600.13 ± 84.51 600.12 + 86.06(io) SITE 2 ? .32 ? 478.94 ± 84.76 478.93 + 61.01(10) d* .67 cr 615.30 ± 47.80 615.28 + 39.47(io) 179. b)l979 700 550 400l 1 H 'L H L H FIGURE 3.7.1 Effect of density on longevity of C. parallelus adults (3 sites, L = LOVJ density, H = High density, x ± S.E., ? cf = x of each sex). a) 1978 site = 9.76, p < 0.001 density F1 = 6.13, p < 0.05 site.density F2 133 = 5.98, p < 0.01 sex.density F^ = 6.78, p < 0.01 b) 1979 site F0 .,. = 4.67, p < 0.01 2,144 density F. = 19.69, p < 0.01 1,144 In 1978, C. brunneus had a significant response only to density (Fig. 3.7.2). The following year a significant increase in longevity occurred in B cages. There were also significant differences in longevity between sites, and sexes. Although this was the only data set to show significant sex differences, all showed some decrease in the difference between the sexes at high densities. This indicated that the presence of several individuals of both sexes may synchronize their longevities. Both species, therefore, showed significant differences in the effect of density, with the most striking site differences occuring in the high density cages, and both displayed a reversal in reaction between years. To determine the cause of this reversal, the densities in the TBf cages were examined closely. The area and volume per individual was calculated for each site and species, and each factor plotted against the average longevities. Fig. 3.7.3 shows that in C. yaralZeZus there was the same general response to both factors. Area per individual explained the overall difference in response more effectively. Due to high mortality in 1978 the area per individual, was much greater than in the "low density" cages, whilst in 1979, the area per individual was less. Such an increase in density of C. paraltetus seemed to have affected these insects so that their longevities increased. There appeared to be an optimum point for "group stimulation" after which crowding decreased longevity. It might be expected that C. paraVLelus would be more sensitive to the area available to an individual rather than volume, as this insect is restricted to ground level movement, having reduced wings. When undisturbed, C. parallelus tends to walk through its habitat. C. brunneus, conversely, showed a strong response to the volume per individual, possibly because it is a far more mobile insect (Fig. 181. SITE 2 b) 1979 65O\ 50C4- .cf •cf 350*- L H L H L H FIGURE 3.7.2 Effect of density on longevity of C. brunneus adults (3 sites, L = Low density, H = High density, x ± S.E., ? cf x of each sex) a) 1978 density ^ = 5.75, p < 0.05 b) 1979 site F = 5.98, p < 0.01 sex F1 = 14.20, p < 0.01 density F 12 = 9.05, p < 0.01 site.density F2 12Q = 3.17, p < 0.05 sex.density F1 12Q = 5.10, p < 0.01 AREA M2 PER INDIVIDUAL VOLUME M3 PER INDIVIDUAL FIGURE 3.7.3 : Effect of a) area and b) volume per individual on longevity of C. paraltetus (x ± S.E.). 3.7.4). The volume per individual in 1978 was much greater than in 1979, and again there was an increase in longevity with decrease in volume. This trend occurred to an optimum point. This "group stimulation" was also suggested by the uniformity in longevity that the sexes seemed to display when in larger numbers. The site differences at low density were not consistent in either species, and no site characteristics emerged. c) Egg eclosion and fertility of adults The initial emergence of nymphs in the field cages occurred within a few days on each site (Table 3.7.4). Although C. parallelus hatched earlier in the field populations (Ragge, 1965), C. brunneus hatched first m the cages. This may have been the result of drier soil inside the cages, as the netting restricted the formation of dew on sites 1 and 3. On site 2 the soil was perpetually wet. C. paraHelus requires damper conditions for hatching than C. brunneus and hatching may therefore have been inhibited (Moriarty, 1970). Watering the cages artificially caused a marked increase in the hatching of C. "parallelus. No hatching occurred Co rtJpi-noruS on site 2, probably due to waterlogging, causing either anaerobic A or fungal infection (Robinson, 1973). Overall, very few eggs hatched, and there was no initial "pulse" as suggested by Richards & Waloff (1954). In heterogeneous habitats, the synchronization of development of all eggs achieved by diapause (Moriarty, 1969b) may be weakened by environmentally-induced variability in post- diapause development. This could explain the difference in length of emergence in the field populations (Tables 3.6.1&4). Site 1 was the most heterogeneous habitat providing considerable variation in oviposition sites. Site 2 was more consistent and the soil cold and wet, whilst site 3 being sparse, provided oviposition sites which were consistent in 184. AREA AA2 PER INDIVIDUAL FIGURE 3.7.4 : Effect of a) area and b) volume per individual on longevity of C. brunneus (x ± S.E.). 185. TABLE 3.7.4 : Egg eclosion in field cages for a) C. parallelus and b) C. brunneus in 1979 (3 sites). (All cage data combined for one site). a) C. parallelus SITE 1 SITE 2 SITE 3 NO. NO. DATE DATE HATCHED HATCHED JULY 6 NONE HATCHED JULY 10 10 13 12 (cages 13 watered) 20 (cages 21 18 watered) 22 19 13 24 23 22 25 24 6 26 26 9 30 3 AUGUST 6 2 11 5 b) C. brunneus JULY 3 3 NONE HATCHED JULY 1 3 5 6 2 5 13 3 3 3 16 21 4 27 (cages 6 7 watered) 18 7 3 19 19 11 21 23 12 15 14 24 6 18 11 30 6 (cages 20 - watered) AUGUST 22 2 186. temperature and moisture. The results for female fertility were not very conclusive, the poor hatching rate probably being influenced by the cage conditions as described above. Females of both species from site 1 produced more viable eggs than those on site 3. d) Fecundity of the females The number of egg pods found in each cage is a function of female fecundity and the survival of the egg pods in winter. Fecundity per se could only be found by laboratory experimentation. Table 3.7.5 shows that there were more egg pods per female on site 2 than site 1 for C. parallelus and less on site 3. For C. brunneus there was a decreasing number of egg pods per female from site 1, to site 2, to site 3. Although these data show that the number of egg pods surviving the winter varies between sites, this may indicate differential predation rather than variation in fecundity. Only data from low density cages were used to compare the number of egg pods per individual because, as Fig. 3.7.5. shows, some individuals died during the pceoviposition period. Also, high density cage data would have assumed all females behaved similarly. The high density cage data would therefore have been subject to large errors. These data were very sparse and unfortunately contribute little to the section. The dry weight of female adults was used as an indication of fecundity. Weight has been shown by many authors to be directly pro- portional to an insect's fecundity (Bleuweiss et al., 1978; Southwood, 1978) and this was also demonstrated for C. parallelus and C. brunneus by Richards & Waloff (1954). The seasonal variation in weight (Fig. 3.7.6.) of C. parallelus showed a general increase, although site 1 females showed 187. TABLE 3.7.5 : Fertility and fecundity of C. parallelus and C. brunneus in field cages (3 sites) (x ± S.E.(nj) FERTILITY FECUNDITY SITE NO. NYMPHS/FEMALE NO. EGG PODS/FEMALE C. parallelus C. brunneus C. parallelus C. brunneus 1 8.14 ± 1.29(ioj 9.33 ± 1.28(io) 2.29 ± O.42(io) 3.17 ± 0.40(M 2 - - 3.83 ± 0.79 (9) 2.60 ± 0.40(io) 3 1.80 ± 0.37(io) 2.00 ± 0.41(io) 1.17 ± 0.2lOo) 1.33 ± 0.2l(icj 1 KH. a) Site 1 O AO O O A A Q O Q. OO A A o UJ 1 A A ^ A ^A 100 300 500 700 900 1100 b) Site 2 A A A OA A O OO O A A A loo 300 500 700 900 C) Site 3 O O A O A CA A A nn, A -6- .A. 100 300 500 700 900 LONGEVITY (DAY DEGREES) OF ADULT FEMALE FIGURE 3.7.5 : Relationship between adult female longevity and the no. egg pods laid in low density cages (3 sites) in C. paralLplus (.'.) and C. brumous (0). FIGURE 3.7.6 : Seasonal changes in dry weight (mg) of C. parallelus and C. brunneus (3 sites,x±s.E.) 190. a slight decrease at the end of the season. C. brunneus also displayed this pattern, although there were only a few samples from site 2. Through- out the season there were differences between sites 1 and 3. For both species, females at site 3 were much heavier at the end of the season than the other sites. Relating the number of egg pods per female (Table 3.7.5) to the weights found, the low number in site 3 was probably due to differential survival rates in both species. Summary 1) For both species nymphal developmental periods were significantly shorter on site 2 than on site 1. 2) Constant daily and day-degree survival rates were found for sites 1 and 2. Temperature affected the survival rate of both species, but part- icularly C. brunneus. 3) C. parallelus showed an increase in longevity with increasing density (area per individual) to an optimum and then a decrease. C. brunneus displayed a similar trend, the best fit occurring with density measured as volume per individual. No consistent site differences in longevity of either sex was found. 4) Emergence distributions were probably affected by the heterogeneity of the habitat, causing a greater spread. Moisture was an important stimulus to hatching. 5) Fertility was markedly different between sites. However, this is in- conclusive due to the unsuitable cage conditions. 6) The number of egg pods per female differed between sites. The low value 19 1. on site 3 was probably due to differential predation rather than differences in fecundity. Individual dry weights support this. 3.8 Discussion One way of describing the relationships between the three sites and their effects on the grasshopper populations, is to think of the position of these habitats within a continuum. Chapter 2 established the habitat ranges of these species as dry heathland (site 3) through grassland (site 1) to wet meadow (site 2) and bog. The position of the habitats and the distribution of grasshopper species is illustrated below:- Habitat type FIGURE 3.8.1 : Habitat selection by C. -parallelus and C. brunneus. From this,one might expect the best performance of both species at site 1, with varying responses on sites 2 and 3. Their performance in terms of various criteria is shown in Figs. 3.8.2 and 3.8.3 which provide summary figures for the chapter. A comparison of these also indicates that the species react in like manner to each of the sites, but that the level of response is different. This would be expected as C. brunneus is more xerophilic than C. parallelus. 192. FIGURE 3.8.2 : Summary of C. parallelus field population demography (3 sites, 1978 and 1979). 193. 1978 1979 Site 2 at 10/6 31/5 I0)s - d) x X 15 i o | tt) c FIGURE 3.8.3 : Summary of C. brunneus field population demography (3 sites, 1978 and 1979). C. brunneus never occurs in boggy areas and is often found on very dry heathland with Myrmeleotettix maaulatus (Thunb.) (Ragge, 1965; Marshall, 1974). The coexistence of such closely related species raises the question of competition for available resources. Competition for food is unlikely as British grasshoppers are not generally limited by food supply (Richards & Waloff, 1954), and there seems to be some avoidance present in the feeding preferences of nymphs. No physical interaction between species was observed in the field, although adults would congregate in the same areas since both species oviposit in bare soil (Waloff, 1950). Seasonal partitioning in hatching occurs, but generally only a few days separate the two species. Although the site differences in each parameter were maintained in both years, the overall levels altered. Climate was probably responsible for this (Richards, 1961); as the climate in Britain is unpredictable, long-term studies are needed to assess the importance of climatic factors. It is therefore more relevant to examine the relative responses at each site within one year. In this study, soil temperature was found to affect hatching as first suggested by Shotwell (1941), site 1 having the earliest emergence and being warmer than the other sites during the period of hatching. Surface temperature, however, did not directly relate to hatching. Previous authors have also found differences between sites in the date of first emergence both in British grasshoppers (Richards & Waloff, 1954; Robinson, 1973) and others (Chapman et al. 9 1979). Richards & Waloff (1954) and Qasrawi (1966) pointed out the combined effect of temperature and solar radiation in accelerating hatching dates. Rainfall also affected hatching since it was noted repeatedly that a shower triggered a fresh pulse of hatching as in Shotwell (1941), Richards & Waloff (1954) and Pickford (1966). Watering the cages had a similar effect. Robinson (1973) found significant differences between hatching dates on three sites, and suggested it was an adaptation to the different conditions. Nymphal survival rates were shown by Richards & Waloff (1954) to be affected by temperature, rainfall and humidity. In this study, temperature expressed as day-degrees explained much of the difference between survival rates on each site. However, Robinson (1973), using M. maculatus and assuming constant daily survival rates, found no large differences in mortality between sites. It is often stated that the highest mortality occurs during the early nymphal stages (Waloff, 1970), and that this may be due to their increased susceptibility. It may, however, be a function of their high numbers, length of developmental period and the daily survival rate. This rate does appear to be constant throughout nymphal development. The slight site differences in survival per unit time did not correlate with nutritional quality as suggested by Bailey & Mukerji (1976) and Chapman et at (1979 ). There was no evidence to suggest predation was of importance, as the caged cohorts showed similar survival rates to the field populations. Predation and parasitism have been shown to have a negligible effect on populations of these species by several authors, e.g. Richards & Waloff (1954), Dempster (1963), Greathead (1963), Gyllenberg (1974). In all the samples of female adults dissected for the work described in chapter 2, none were parasitised in 1978 (352 C. paraHetus and 154 C. brunneus). In 1979 the percentage found parasitised was 1.3% for C. parallelus (4/312) and 0.4% for C. brunneus (1/255). In all cases the parasite was Blaesoxipha laticomis (Meiger) (Diptera: Sarcophaginae). 196. These percentages were lower than those found by Richards & Waloff (1954). The similarity between field and cage survival rates also indicated that dispersal was negligible in the nymphal stages. Chapman (1952), Dempster (1955), Gyllenberg (1969) and Chapman (1970) showed that no major dispersal of adults was likely to have occurred, since the vegetation of a site altered little between years. Chapman (1952) showed that most individuals remain permanently within the main habitat, whilst a few individuals may wander. Some studies by Richards & Waloff (1954) also demonstrated that the main movement by grasshoppers was between areas within their hetero- geneous habitats and that directed migration was not likely to occur. Differentiating between trivial and deliberate movement, Gyllenberg (1974) found that migration of C. parallelus only occurred through macropterous individuals, whose occurrence was density-dependent. The differences in overall developmental time for each species at each site did not correlate with the nutritional levels. The fluctuations between years in individual instars may have been caused by variations in the physical and vegetational environment. However, the overall develop- mental times remained constant for each site. Chapman et al (1979 ) found that the nymphal developmental period for Zonocerus variegatus (L.) was shorter where more acceptable plants were available, but remained constant from year to year at a site. The shortest developmental time occurred on site 2 where the most diverse supply of grasses was available. Site 3 had only three species of grass available, and although nitrogen levels were higher, the developmental time was longer. The nymphal survival rate at each site follows the same trend as the numbers hatching. The adult longevity did not show any inherent differ- ences between sites; insects under similar density conditions at each site 197. lived for similar periods. Increasing the density produced a restricted increase in longevity. The population densities observed were in the order of 1 m""2 or less, providing little chance of encounter. There was, however, obvious clumping of both species, caused by the vegetational heterogeneity and the varying behaviour of each stage of the life cycle. The adult groups could also serve as socio-sexual groupingsallowing the stimulatory effects of voluntary crowding to produce the maximum longevity possible for maximum fecundity. Young suggested this grouping might cause increases in longevity (1979) . The factors contributing to mortality of the nymphs were physical, but,as overall they were constant throughout nymphal periods,the pop- ulation numbers depend on: a) The number entering the first stage. There were large site differences in the number of eggs hatching, which is a function of egg survival and adult fecundity. b) Survival rate of the nymphs due to the environment, for which there was little site difference. The main cause therefore of the difference in population size at each site appears to be the number entering the first stage. The number of egg pods per female surviving to the next year was different between sites, and is a function of the number of egg pods and egg survival rate. The physical conditions of each site presented a decrease in optimal conditions e.g. the soil being too dry for the eggs to survive, from site 3 through site 2 to site 1, whilst the nutritional quality of the sites may 198. have increased from 1 to 2 to 3. There were corresponding increases in adult weights from site 1 to 2 to 3, suggesting that there may be differ- ential fecundity. A preliminary study by Mill (1979) showed that pods from one site may be larger and hold more eggs than other sites. Thus^the reproductive parameters of the adult females need to be investigated in more detail, and this is described in the following chapter. 199. CHAPTER 4 LABORATORY EXPERIMENTS TO DETERMINE THE VARIATION IN CERTAIN LIFE HISTORY COMPONENTS UNDER CONTROLLED CONDITIONS 4.1 Introduction The aim of the work in this chapter was to determine distinct site differences in various developmental and reproductive parameters, which were maintained under standard laboratory conditions and not therefore immediate effects of the environment. The effect of density on these parameters was also investigated. The population density fluctuations seen in some species of British grasshoppers have been previously discussed (Chapters 2 and 3). Apart from the work of Rubtzov (1935) there has been very little study on the effect of density on solitary grasshoppers, but both Chapman (1952) and Young (1979) have described C. brunneus as gregarious in Great Britain. One might therefore predict a stimulation of reproductive behaviour by crowding these species. Crowding in locusts however results in a variety of effects on ovarian maturation and repro- ductive activity (Labeyrie, 1978) . Waloff (1970) pointed out the need for more observations on field populations. It is well known that some life history parameters in grasshoppers vary between years (Richards & Waloff, 1954), and generally accepted that they are ecologically very plastic. However, this has rarely been quantified. This study concentrates on key aspects of developmental and. reproductive biology which would be part- icularly sensitive to changes in the environment. Many others have defined these components (Wilbur et aZ., 1974; Stearns, 1976, 1977; Calow, 1977), and have discussed their effects on the reproductive strategy of a species. The work was organised as follows:- 200. Experiments to determine the effect of site and density on: Adult longevity Egg eclosion -»• Nymphal development Female reproductive parameters Hatchling weight The scope of this investigation was necessarily restricted as these are univoltine species. It was thought that accelerating egg development in the laboratory to decrease the generation time m^y have affected sub- sequent experiments. 4.2 Methods 4.2.1. CujL^tur^ng^ Techniques Egg pods which were laid under experimental conditions by both species in the laboratory, were stored between dampened germination discs in 9 cm diameter butter dishes, in an outdoor insectary. Each dish was coded to identify the parents, the field site from which the parents were collected (i.e. 1, 2 or 3) and the date of laying. The eggs are referred to as site 1, 2 or 3 eggs. During the winter the dishes were surrounded by vermiculite to prevent the eggs freezing. The germination discs were changed regularly to restrict fungal attack; fungicides were not used as they may have had unknown side effects on hatching dates. Hatching success was 60-100% per pod by this method. All experiments using nymphs or adults were carried out in a controlled temperature room (20 ± 1 C) with a 16/8 hr. light/dark regime. Radiant heat was provided for 12 hours per day using 60 watt bulbs held on retort stands placed 15 cm from the cages. Humidity was uncontrolled. Nymphs were kept in Watkins and Doncaster breeding cages (23 cm high x 12 cm diameter), with a netting top in place of the metal lid. This produced a humidity gradient within the cage suitable for each nymphal stage (Ruscoe, 1970). Adults were kept either in similar cages or in the large Watkins and Doncaster cages (35 cm high x 20 cm diameter), using the original lids in each case. Damp sand in small plastic pots was provided as oviposition sites, and food suitable for the nymphs and adults was provided by growing a mixture of Agrostis tenuis and Festuca rubra in 3 cm diameter plant pots. This grass survived far longer than cut grass, and provided not only a more manageable technique, but a more natural feeding area. In designing the cage, reference was made to the designs of Moriarty (1969c) and Kelly- Stebbings & Hewitt (1972). Fourth instar nymphs collected from each site for experimental purposes subsequently provided the eggs and nymphs for experiments on egg eclosion and nymphal development the following year. 4.2.2. Experimenta.1 Work 1) Adult_biolog2 Fourth instar nymphs were collected from each site and placed either in pairs (1 ? 1 6) in ten small cages per site, or in groups in two large cages per site (8 + 4 <$& per cage, 1978; 8 + 8 The pods from high density cages were collected when all the individuals were dead. It was not possible to identify which individuals had ovi- 202. posited in these cages, except by continuous observation or by weighing each female daily. Both methods were impractical. No high density cages from site 2 were set up for C. brunneus in either year, as the numbers were too low, and removal of individuals from the field populations may have been detrimental to other parts of the work. Mortality was high in the high density cages in the fourth instar nymphs and newly moulted adults, and further nymphs had to be collected to maintain the numbers. Parameters from low density cages Dates of oviposition for each female enabled the following mean values to be calculated for each site:- a) preoviposition period b) interoviposition period c) number of egg pods/female In addition, values of individual female longevity yielded site means for d) postoviposition period Egg eclosion data obtained in the insectary the following year allowed e) number of eggs/pod f) total number of eggs/female to be calculated (as averages) for each site. Parameters c and f above, taken for each individual together with that individual's longevity enabled mean values at each site to be calculated for g) number of pods/female/day h) number of eggs/female/day Parameters from high density cages These parameters were calculated in a different manner to those for the low density cages, as individual female data were not 203. available, for the reasons discussed on page 201 . No variances could be attached to.the mean values. For each site, the parameters calculated were:- a) number of egg pods/female Total number of pods Total number of females b) number of eggs/pod Total number of eggs Total number of pods c) total number of eggs/female Total number of eggs Total number of females d) number of pods/female/day Total number of pods Total number of adult female days e) number of eggs/female/day Total number of eggs Total number of adult female days Whilst site differences between low density cages were analysed by one- and two-way factorial ANOVAS, the effect of density on these parameters was tested by t-test comparisons of a sample mean with a single sample (Bailey, 1959). All data were assumed to be normally distributed. The number of eggs hatching per pod in the insectary was recorded every day during the late spring and early summer of 1979 and 1980. In 1980, samples of hatchlings from each site were freeze dried immediately after eclosion to find their weight. When hatching had finished, all pods were dissected to determine the number of unhatched eggs. From these counts, the fertility of eggs from parents originating from different sites was found. 204. 3) Nymphal development Effect of site Newly emerged nymphs from the field were collected from each site, and pairs put into small cages (15 cages per site per species). The cages were checked daily and moulting dates recorded. Newly emerged nymphs in the insectary (from eggs laid in the laboratory under low density conditions) were also used to test the effect of site on development. Five cages, each containing two nymphs, were set up for each site and species. The data were collected as above. Effect of density Samples of newly emerged nymphs from the insectary were collected and put into small cages, either singly or in groups of ten (thirteen replicates of each per species). By checking the cages daily, dates of moults were recorded. In the high density cages, each insect was marked, and so individual moulting dates were found and individual nymphal developmental periods calculated. A control group of nymphs without markings showed no difference in mortality rate or overall development period. To an extent, numbers in each cage were maintained by combining cages which had suffered high mortality. Only nymphs which reached the adult stage were included in the analyses. 4.3 Results and Discussion 4.3.1. Hajtching_D^st^r^buti_on and_ Success^ C. paratlelus The hatching distributions of the eggs laid by females from the three field sites are shown in Fig. 4.3.1. For each site, the distribution of egg eclosion was very similar between eggs laid under high and low density conditions. In neither year was the hatching distribution of a distinct type, in part because the number of eggs was small. Fig. 4.3.2. shows that on most days only single pods hatched in each group. Data on egg pods laid under high density conditions were not included here as it was not known from which pod each nymph had emerged. The first eggs to hatch in each year were laid by females from site 3, then those from site 2 and then site 1. Although only a few days separated each site,the trend was consistent in both years for eggs laid under both high and low density conditions. The most successful hatch occurred in pods from site 3, then site 2 and site 1 (Table 4.3.1). The only inconsistency in this was in the eggs from females from sites 2 and 3 in 1980 under low density conditions. The percentage hatch was 0.71X - higher in site 2 batch. The dry weights of hatchlings from each group are shown in Table 4.3.2. A two-way factorial ANOVA revealed a significant difference between the weights of nymphs from each site (F2 ^^ = 26.72, p < 0.01). A significant interaction between the effects of site and density was also found (F2 = 4.53, p < 0.05). C. brunneus The hatching distribution of eggpods laid by females collected from each site (Fig. 4.3.3) reflected the distribution of egg eclosion as shown in Fig. 4.3.4, in both years. The distributions of eclosion of eggs laid under high and low density conditions were similar in each site. Each site displayed a more unimodal distribution than did C. parallelus partly because more pods had been laid, but secondary peaks were present. 206. a) 1979 30 b) 1980 JULY FIGURE 4.3.1 Hatching distribution of laboratory laid eggs of C. -pavdllelus in insectary. a) 1979, site 1 = t, 2 = A, 3 = • ; b) 1980, site 1 = 0, 2 = A, 3" = • . (- = low and high density) 207. a) 1979 o z X ..A. u< X CQO O a. O O b)l980 A A A A 2 14 20 26 • O SITE 1 JULY AA SITE 2 • • SITE 3 FIGURE 4.3.2 : Hatching distribution of laboratory laid egg pods of C. parallelus in insectary (3 sites, low density only). 208. TABLE 4.3.1 : Percentage hatch of eggs in an outdoor insectary (parents collected from 3 sites). X^ SITES 1 2 3 DENSITY YEAR LOW HIGH LOW HIGH LOW HIGH C. parallelus 1979 68.38 69.72 69.09 69.92 69.13 70.13 1980 59.35 62.61 61.95 65.12 61.24 66.85 C. brunneus 1979 53.10 57.02 73.91 - 75.66 78.50 1980 59.60 60.07 60.89 - 63.70 64.50 209. TABLE 4.3.2 : Hatchling dry weights from eggs laid under low and high densities (x ± S.E. (n) mg). DENSITY SITES LOW HIGH C. parallelus 1 0.784 ± 0.013 (20) 0.884 ± 0.018 (20) 2 1.022 ± 0.055 (20) 1.049 ± 0.045 (20) 3 1.313 ± 0.091 (20) 1.114 ± 0.049 (20) C, brunneus 1 0.666 ± 0.010 (66) 0.626 ± 0.010 (27) 2 0.762 ± 0.012 (84) - 3 0.779 ± 0.011 (117) 0.692 ± 0.013 (55) 210. AA SITE 2 • • SITE 3 FIGURE A.3.3 : Hatching distribution of laboratory laid egg pods of C. brunneus in insectary (3 sites, low density only). 211. FIGURE A.3.4a : Hatching distribution of laboratory laid eggs of C. jbrunneus in insectary, 1979. Site 1 = i, 2= A, 3 = • (— low and high density) 212. a SITE 3 FIGURE 4.3.4b : Hatching distribution of laboratory laid eggs of C. brunneus in insectary, 1980. (— low and high density) The peaks coincided between sites, suggesting that the factor influencing the hatching distribution may be the daily temperature conditions. The starting date for hatching of eggs from each site showed a consistent pattern between years. Eggs from site 3 hatched first, then from site 2 and finally site 1, irrespective of the density in which they were laid. The hatching success of each batch of eggs also maintained a consistent pattern (Table 4.3.1). Site 1 had the lowest percentage hatch at both densities, followed by site 2 with site 3 having the highest hatching success. Table 4.3.2 shows that the hatchling dry weights increased from site 1 to site 2 and site 3 at low densities (F_ = 30.45, p < 0.01), z, Zoq whilst at high densities sites 1 and 3 were significantly different (variances equal, t = 2.08, df = 80, p = 0.042). There were significant decreases in the dry weight of hatchlings from sites 1 and 3 under high density conditions (site 3, variances different, t = 4.78, df = 121, p < 0.01; site 1, variances equal, t = 2.27, df = 91, p = 0.026). Hence, under uniform conditions, females of both species produced hatchlings whose weights increased from site 1 to site 2 to site 3. C. brunneus females who laid eggs under high density conditions produced hatchlings whose weights were significantly less than those from low density conditions. The opposite effect was noted for C. paratlelus. It is reasonable to suppose that the heavier hatchlings emerged from heavier, and therefore probably larger, eggs, i.e. that females from different sites or under varying density conditions produced different sized eggs. There was no difference in the hatching distribution of eggs 214. from different densities within a site even though the weights of the hatchlings were significantly different, but the heavier hatchlings from site 3 emerged earlier than those from sites 2 and 1. They also showed a higher hatching success than the other sites. The increased percentage hatch of both species from high density conditions is not explained by weight differences because, although C. parallelus tended to produce heavier hatchlings under high density conditions, C. brunneus did not. There might have been a stimulatory effect where several egg pods were kept in one dish. However, this was unavoidable since the number of pods laid under high density was large. The pods from the females at low density were stored singly. 4.3.2. Nymphal_ l>evelopment_ C. parallelus The total nymphal developmental periods of specimens collected as newly emerged nymphs from the three field sites, were subjected to a two-way factorial ANOVA (Table 4.3.3). The variation in developmental periods between nymphs from different sites was significant (F2 ^ = 17.09, p < 0.01). There was also a significant difference between the sexes of each group (F^ ^ = 4.96, 0.05 > p > 0.01), males taking longer to complete development than females. Each sex showed the same shortening in nymphal developmental period from site 1, to site 2 and then site 3. There was not a significant interaction between the two factors, (p > 0.05). Nymphs from eggs laid in the laboratory, from females collected from the three field sites, showed the same significant differences in the total nymphal developmental periods between sites (F2 = 10,52, p < 0.01) and between males and females (F^ = 18.48, p < 0.01) (Table 4.3.4). In both experiments the fourth instar tended to be longer than the others. TABLE 4.3.3 : Developmental periods of nymphs hatched in 3 field sites and reared in the laboratory (x ± S.E., days). SITE 1 2 3 STAGE ? $ ? I 7.08 ± 0.88 8.11 ± 0.59 6.89 ± 0.31 6.80 ± 0.33 6.40 ± 0.34 6.36 ± 0.20 II . 6.62 ± 0.68 6.55 ± 0.96 7.33 ± 0.73 6.90 ± 0.55 7.10 ± 0.23 7.18 ± 0.33 III 7.23 ± 0.47 6.56 ± 0.78 5.78 ± 0.32 6.70 ± 0.50 5.70 ± 0.37 6.45 ± 0.41 IV 11.08 ± 0.91 11.33 ± 1.14 8.11 ± 0.51 9.70 + 0.42 7.40 ± 0.43 8.45 ± 0.25 TOTAL 32.00 ± 0.94 32.56 ± 1.31 28.11 ± 0.65 30.30 ± 0.82 26.60 ± 0.43 28.45 ± 0.45 C. brunneus n = 8 n = 7 n = 10 n = 10 n = 10 n = 10 I 7.38 ± 0.42 10.14 + 0.63 6.90 + 0.31 7.70 ± 0.60 6.50 ± 0.27 7.30 ± 0.37 II 10.13 ± 1.47 7.43 ± 0.72 9.30 + 0.52 8.10 ± 0.31 8.30 ± 0.26 7.80 ± 0.25 III 7.75 ± 0.65 6.86 + 0.59 7.70 ± 0.30 6.70 ± 0.33 7.80 ± 0.25 7.30 ± 0.37 IV 8.88 ± 0.81 7.86 ± 0.55 8.90 ± 0.43 7.40 ± 0.40 8.80 ± 0.36 7.00 ± 0.30 TOTAL 34.13 ± 1.76 32.29 ±0.68 32.30+0.80 29.40 ± 0.58 31.20 ± 0.61 29.60 ± 0.62 TABLE 4.3.4 : Developmental periods of nymphs hatched in the laboratory - parents collected from 3 field sites (x ± S.E., days). SITE 1 . 2 3 0 STAGE + d" S E ? I 7.40 ± 0.51 8.40+0.51 6.50+0.65 7.80 ± 0.20 6.86 ± 0.34 7.33 ± 0.33 N3 II 7.03 ± 0.32 6.80 + 0.37 6.75 ± 0.85 7.20 ± 0.37 7.00 ± 0.38 7.33 ± 0.33 IV 10.00 ± 0.71 10.40 ± 0.51 9.50 ± 0.50 10.00 ± 0.32 7.43 ± 0.37 8.67 ± 0.33 TOTAL 31.40 ± 1.21 34.20 + 0.92 28.25 + 0.85 32.00 ± 1.30 27.14 ± 0.59 31.33 ± 0.67 C, brunneus n = 6 n = 4 n = 5 n = 5 n = 4 n = 6 I 8.17 ± 0.40 8.50 + 0.96 . 7.60 ± 0.40 9.00 ± 0.89 6.50 ± 0.29 6.83 ± 0.31 II 12.83 ± 0.65 9.25 ± 1.49 12.00 ± 0.55 8.40 ± 0.60 8.50 ± 0.29 7.00 ± 0.26 III 9.17 ± 1.24 9.50 ± 0.96 7.80 ± 0.37 7.20 ± 0.73 7.00 + 0.41 6.50 ± 0.22 IV 11.67 ± 1.65 10.75+0.75 10.20 + 0.80 9.00 ± 0.84 7.75 ± 0.48 7.17 ± 0.31 TOTAL 41.83 ± 2.09 38.00 ± 0.71 37.60 ± 0.81 33.60 + 1.33 29.75 ± 0.85 27.50 ± 0.43 217. Another experiment, again using nymphs hatched in the insectary from the three sites, showed that there were significant increases in the total nymphal developmental period under high density conditions (two-way factorial ANOVA F1 ^ = 24.48, p < 0.01), (Table 4.3.5). Also, individual instars were rather more variable; although the males required a longer developmental period as in the previous experiment, the difference was not significant. C. brunneus The total nymphal developmental periods of C. brunneus (Table 4.3.3) were analysed by a two-way factorial ANOVA, and showed significant differences between sites (F2 ^ = 5.42, p < 0.01) and between the sexes at each site (F^ ^ = 8.51, p < 0.01). As in C. parallelus, the total developmental periods were shortest in nymphs from site 3, then site 2 and site 1. However, females had a longer developmental period than males in this species. The developmental periods of individual instars did not follow any particular pattern between sites or sexes. The data from the complementary experiment using nymphs from the insectary (Table 4.3.4) confirmed the above findings. A significant decrease in the total nymphal developmental period from site 1 to sites 2 = and 3 was found (F2 24 43.21, p < 0.01). Again, males developed more quickly than females (F^ ^ ~ 9.98, p < 0.01). The total nymphal develop- mental periods of nymphs (hatched in the insectary) under high and low density conditions, were also analysed by a two-way factorial ANOVA (Table 4.3.5). There was a significant increase in the length of the develop- mental periods in high density cages (F. 77 = 32.96, p < 0.01), and males 1, / / developed more rapidly than females (F^ ^ = 9.86, p < 0.01). For both species therefore, the shortest developmental times 218. TABLE 4.3.5 : Developmental periods of nymphs hatched in the laboratory and reared under high and low density conditions (x ± S.E., days). ^VTJENSITY LOW HIGH STAGE ? cT ? d C. parallelus n = 13 n = 10 n = 25 n = 25 I 8.38 ± 0.31 8.30 ± 0.33 9.00 ± 0.37 9.44 ± 0.52 II 6.23 ± 0.30 6.60 ± 0.16 6.88 ± 0.44 7.32 ± 0.52 III 6.15 ± 0.32 7.40 ± 0.31 8.84 ± 0.46 7.68 ± 0.34 IV 8.31 ± 0.54 8.60 ± 0.37 11.24 ± 1.00 12.68 ± 0.89 TOTAL 29.08 ± 0.60 30.90 ± 0.83 35.96 ± 1.19 37.12 ± 1.25 C. brunneus n = 10 n = 12 n = 34 n = 25 I 13.70 ± 0.52 11.00 ± 0.37 14.69 ± 0.31 14.40 ± 0.42 II 10.30 ± 0.45 11.08 ± 0.50 10.26 ± 0.49 10.88 ± 0.60 III 10.20 ± 0.39 9.75 ± 0.45 12.94 ± 0.48 11.99 ± 0.60 IV 12.00 ± 0.71 10.75 ± 0.45 13.52 ± 0.53 12.64 ± 0.67 TOTAL 46.40 ± 0.64 42.25 ± 0.70 51.41 ± 0.97 49.68 ± 0.70 219. were displayed by nymphs either collected from site 3, then 2 and 1, or hatched from eggs laid by females from these sites. The latter correlates with the occurance of the heaviest hatchlings from site 3 eggs. The large eggs laid by some locust species when crowded are more advanced when they hatch than their smaller counterparts, and therefore develop more rapidly (Albrecht, 1970). The overall developmental periods of nymphs from each site kept at low density were very similar to those found by Richards & Waloff (1954). They found that both species took slightly longer to develop in the laboratory (greenhouse) than in the field. This may well be due to the more fluctuating temperatures experienced under field conditions. Other Acridids, for example Loousta migratoria migratorioides (R. & F.), Sohistooeroa gregaria (Forsk), Nomadaeris septemfasciata and Melanoplus fermurrubrum also develop more slowly in the laboratory under constant conditions (Hamilton, 1936; Dyck, 1971). Increasing the density of nymphs lengthened the developmental period in each species. However, whilst C. parallelus males developed more slowly than females, C. brunneus showed the reverse trend. These latter results agree with those of Moriarty (1969c). Since the hatchling weights were unknown, the sexual differences in developmental times cannot be related directly, although it is intuitively obvious that a smaller insect (i.e. the males) may well develop faster. This is the case in many insect groups (Southwood, 1976) and has obvious advantages for reproductive purposes. The results for C. parallelus are somewhat anomalous. 4.3.3. Adul_t Re£rodjucJ^ive_Bio2Logy The following parameters have been considered (i) longevity (ii) fecundity C. parallelus The low density cages provided values for the preoviposition period, the interoviposition period and the postoviposition period of females from different sites (Table 4.3.6). Under uniform conditions there were no significant site differences in any of these parameters, in either year. Also, no significant differences were found in the number of pods/female or the total number of eggs/female in either year (Table 4.3.7), nor was there any significant effect of density on these parameters However, the number of eggs/pod significantly decreased from site 1, to site 2 and site 3 in 1979 (Y^ ^ = 3.73, 0.05 > p > 0.01), under low density conditions. The same trend was seen in 1978. High density conditions generally caused significant increases in this parameter. The reverse trend seen in the other parameters might be explained by a compensatory increase in the, number of pods/female. However, these differences were not significant. The decreases in the number of eggs/pod from site 1 to sites 2 and 3 at low density corresponded to a significant increase found in the weight of hatchlings. Under high density conditions however, although the number of eggs/pod increased per site, the change in hatchling weight varied between sites. Table 4.3.8 shows the effect of site and density on adult long- evity in experiments corresponding to those in the field (Chapter 3, section 3.7). The data for each year were analysed by a three-way factorial ANOVA; site, sex and density being the three factors. In 1978, females lived significantly longer than males (F^ ^^ = 13.35, p < 0.01). There was also a significant increase in adult longevity under high density conditions (F^ = 8.61, p < 0.01). However, specimens collected the following year showed no significant changes in adult longevity related TABLE 4.3.6 : Preoviposition period, interoviposition period and postoviposition period of C, parallelus, from 3 field sites, under low density conditions in the laboratory (x ± S.E. (n) days). YEAR 1978 1979 SITE 1 2 3 1 2 3 PREOVIPOSITION 10.50 ± 1.06 (10) 14.09 ± 1.26 (11) 12.60 ± 0.90 (10) 13.88 ± 2.26 (8) 17.00 ± 2.34 (7) 18.00 ± 2.55 (9) PERIOD INTERPOD 6.33 ± 1.18 (6) 5.36 ± 1.55 (14) 5.64 ± 1.08 (14) 6.00 ± 0.85 (8) PERIOD 9.63 ± 2.22 (8) 7.74 ± 1.92 (19) POSTOVIPOSITION 5.73 ± 1.34 (10) 4.00 ± 0.91 (11) 6.00 ± 2.37 (10) 7.00 ± 2.27 (8) 6.14 ± 1.26 (7) 7.33 ± 2.21 (9) PERIOD TABLE 4.3.7 : Fecundity of C. parallelus from 3 field sites, under low and high density conditions in the.laboratory (x ± S.E. (n)). YEAR 1978 1979 SITE DENSITY 1 2 3 1 2 3 NO. PODS/ LOW 1.60 ± 0.31(10) 2.27 ± 0.45(11) 2.40 ± 0.43(10) 2.00 ± 0.50(8) 2.14 ± 0.51(7) 3.11 ± 0.75(9) ? HIGH 1.27 2.20 4.87 2.27 1.92 2.67 * P N.S. N.S. p < 0.001 N.S. N.S. N.S. TOTAL NO. LOW 11.70 ± 2.23(10) 15.00 ± 2.90(11) 16.20 ± 2.10(10) 15.38 ± 4.28(8) 16.14 ± 4.76(7) 19.78 ±5.44(9) EGGS/ ? HIGH 9.47 17.73 25.00 20.18 16.54 23.48 P N.S. N.S. 0.02 > p > 0.001 N.S. N.S. N.S. NO. EGGS/ LOW 7.31 ± 0.40(16) 6.60 ± 0.35(25) 6.75 ± 0.44(24) 7.69 ± 0.54(16) 7.53 ± 0.38(15) 6.36 ± 0.32(28) POD HIGH 7.47 8.06 8.72 8.88 8.60 9.50 P N.S. p < 0.001 p < 0.001 0.05 > p >. 0.02 0.02 > p > 0.01 p < 0.001 * = Significance of difference between high and low density values tested by a t-test comparison of a sample mean with a single sample (variance unknown). N.S. = not significant TABLE 4.3,8 : Adult longevity of C. parallelus from 3 field sites, under low and high density conditions in the lab- oratory (x ± S.E. (n) days). 1978 DENSITY LOW HIGH SITE ? & ? cT 1 22.30 ± 3.23 (10) 20.30 ± 2.46 (10) 27.63 ± 4.11 (15) 27.38 ± 4.79 (8) 2 25.45 ± 2.02 (11) 20.18 ± 1.58 (11) 32.75 ± 3.99 (15) 20.38 ± 3.28 (8) 3 24.80 ± 1.76 (10) 20.60 ± 1.49 (10) 34.69 ± 2.95 (15) 22.50 ± 3.00 (8) 1 30.50 ± 2.32 (8) 31.00 ± 2.22 (8) 27.64 ± 1.83 (11) 34.58 ± 2.20 (12) 2 38.29 ± 4.85 (7) 32.43 ± 4.64 (7) 33.92 ± 2.19 (13) 34.00 ± 2.33 (9) 3 44.00 ± 6.38 (9) 29.56 ± 1.85 (9) 37.20 ± 4.14 (15) 34.60 ± 4.12 (10) to any of the factors. In general, males seemed little affected by site and density changes, although in 1979 they lived longer. The females however appeared far more sensitive to the effects of site and density. This would be expected, since female longevity would affect reproductive output. The results under high density conditions were similar in both years, but longevities at low densities were increased considerably in 1979. The mean daily fecundity of C, parallelus females (Table 4.3.9) showed no significant site differences (p > 0.05) or effects of density, although site 1 and 3 females increased their reproductive rate in one instance. The parameters measured in this section were all subject to large variances, partially due to the small samples, and this caused some difficulty in elucidating the relationships. In general, it seems that the total reproductive output of C. parallelus was not affected by site or density. The "packaging" of the eggs varied between sites, however. The insects from the extreme habitat, site 3, tended to produce many pods containing fewer, larger eggs. C. brunneus There were no significant differences at low density in the preoviposition period of females taken from the field sites in either 1978 or 1979 (Table 4.3.10). The interoviposition period,however, varied significantly between sites in both years (1978, F^ ^2 = 9.42, p < 0.01; 1979, F2 gg = 5.38, p < 0.01), with site 3 having the shortest inter- oviposition period, and site 2 the longest. This is interesting since site 1 may be considered as the "usual" site and therefore one might have expected the shortest period to be seen here. It may be that sites 2 and 3, as extreme habitats, are acting in opposite directions in this parameter. TABLE 4.3.9 : Mean daily fecundity of C. iparallelus from 3 field sites, under low and high density conditions in the laboratory (x ± S.E. (n)). YEAR 1978 1979 SITE DENSITY 1 2 3 1 2 3 NO. PODS/ LOW 0.08 ± 0.02(10) 0.08 ± 0.02(11) 0.10 ± 0.03(10) 0.06 ± 0.01(8) 0.06 ± 0.11(7) 0.07 ± 0.01(9) DAY/ ? HIGH 0.05 0.07 0.08 0.08 0.06 0.07 * P 0.05 > p > 0.02 . N.S. N.S. N.S. N.S. N.S. NO. EGGS/ LOW 0.57 ± 0.10(10) 0.58 ± 0.01(11) 0.61 ± 0.07(10) 0.50 ± 0.12(8) 0.43 ± 0.09(7) 0.41 ± 0.08(9) DAY/ $ HIGH 0.34 0.54 0.72 0.79 0.49 0.65 P N.S. N.S. N.S. N.S. N.S. 0.02 > p > 0.01 * = Significance of difference between high and low density values tested by a t-test comparison as in Table 4.3.6. N.S. = not significant TABLE 4.3.10 : Preoviposition period, interoviposition period and postoviposition period of C. brunneus, from 3 field sites, under low density conditions in the laboratory (x ± S.E. (n) days). YEAR 1978 1979 SITE 1 2 3 1 2 3 PREOVIPOSITION 14.00 ± 1.53 (10) 11.89 ± 0.63 (9) 11.70 ± 0.75 (10) 17.30 ± 1.46 (10) 15.00 ± 1.52 (10) 13.11 ± 1.23 (9) PERIOD INTERPOD 3.83 ± 0.21 (35) 4.46 ± 0.41 (20) 3.09 ±0.14 (64) 6.33 ± 0.46 (27) 7.50 ± 0.79 (34) 4.98 ± 0.29 (40) PERIOD POSTOVIPOSITION 3.20 ± 0.29 (10) 5.00 ± 0.94 (9) 5.10 ± 1.34 (10) 11.70 ±.2.48 (10) 5.20 ± 1.40 (10) 5.56 ± 1.52 (9) PERIOD The only significant difference in postoviposition period between sites was in 1979 (F2 26 = 3.82, 0.05 > p > 0.01). The values for sites 2 and 3 were consistent between years, but the females from site 1 showed a considerable increase in this period in 1979. Table 4.3.11 shows the effects of site and density on the fecundity of C. brunneus in the laboratory. The number of pods/female did not vary significantly between the sites in either year, nor was there a significant response to density. The total number of eggs/female however, increased significantly from sites 1 to 3 in 1979 (F« 0/- = 3.79, ZyZO 0.05 > p > 0.01), but was not affected by density. The mean number of eggs/pod increased from site 1 females to sites 2 and 3 in both years, although as in the previous parameter only the data for 1979 showed significant differences (F2 = 4.37, 0.05 > p > 0.01). Increasing the density also caused the females to significantly increase the number of eggs/pod in both years. Continuing the suggestion on page 224 , one might have expected a decrease in the number of eggs/pod from different sites to correlate with the increase in weight of the hatchlings (section 4.3.1). In fact, in this species both the number of eggs/pod and the weight of the hatchlings increased from site 1 to sites 2 and 3. However, at high densities, although the number of eggs/pod increased, the weight of the hatchlings decreased. The effects on adult longevity of site and density are shown in Table 4.3.12. Since there were insufficient data for the site 2 high density cages, a three-way factorial ANOVA was carried out only on the data for site 1 and 3 specimens, and a two-way factorial ANOVA performed on the complete data set from the low density cages. Firstly, the three- way ANOVA on sites 1 and 3 only, showed that in 1978 there were insufficient TABLE 4.3,11 : Fecundity of C. brunneus from 3 field sites, under low and high density conditions in the laboratory (x ± S.E. (n)). YEAR 1978 1979 SITE DENSITY 1 2 3 1 2 3 NO. PODS/ LOW 4.50 ± 0.81(10) 3.89 + .0.89(9) .7.40 ± 1.31(10) 3.80 ± 0.68(10) 4.40 ± 0.62(10) 5.56 ± 0.82(9) ? HIGH 3.93 _ 11.13 . . 3.70 - 6.00 * P N.S. 0.02 > p > 0.01 N.S. N.S. TOTAL NO. LOW 40.30 ± 7.43(10) 38.23 ± 9.67(9) 68.20 ±11.54(10) 28.10 ± 5.82(10) 35.80 ± 4.90(10) 51.12 ± 6.82(9) EGGS/ ? HIGH 40.21 - 118.07 35.60 - 60.57 P N.S. 0.002 > p >0.001 N.S. N.S. NO. EGGS/ LOW 8.96 ± 0.29(45) 9.86 + 0.39(35) 9.22 ± 0.25(73) 7.40 ± 0.40(38) 8.04 ± 0.31(45) 9.20 ± 0.32(50) POD HIGH 10.24 10.60 9.62 - 10.09 P p < 0.001 p < 0.001 . p < 0.001 0.01 > p > 0.002 * = Significance of difference between high and low density values tested by a t-test comparison of a sample mean with a single sample (variance unknown). N.S. = not significant TABLE 4.3.12 : Adult longevity of C. brunneus from 3 field sites, under low and high density conditions in the lab- oratory (x ± S.E. (n) days). 1978 DENSITY LOW HIGH SITE 9 c? ? c? 1 30.70 ± 3.10 (10) 25.40 ± 2.42 (10) 30.05 ± 6.08 (14) 16.73 ± 1.38 (8) 2 28.78 ± 4.03 (9) 27.78 ± 3.59 (9) - - 3 36.50 ± 3.82 (10) 36.90 ± 3.23 (10) 54.20 ± 4.48 (15) 37.75 ± 7.86 (8) 1979 1 43.40 ± 4.05 (10) 39.90 ± 2.34 (10) 54.00 ± 3.90 (10) 40.14 ± 5.22 (8) 2 46.10 ± 4.46 (10) 39.20 ± 3.18 (10) - : - 3 42.00 ± 4.73 (9) 36.78 ± 3.09 (9) 44.93 ± 3.88 (14) 38.50 ± 2.14 (8) differences between sites (F^ ^ = 24.17, p < 0.01), for sex (F^ ^ = 7.58, p < 0.01), and a significant interaction between site and density (F^ ^ = 4.67, 0.05 > p > 0.01). There was a strong response to increased density by females from site 3, whereas those from site 1 were little affected. The males displayed the reverse trend. In 1979 however, the only signi- ficant effect on longevity was that of sex (F^ ^g = 7.32, p < 0.01), males having shorter lives than females. A two-way factorial ANOVA on the low density data only for 1978 showed significant differences between the sites (F^ ^ = 4.33, 0.05 > p > 0.01), but not between the sexes. In 1979 there were no significant differences either between the sites or the sexes at low densities. As in 1978, high density conditions had exagerated the sexual differences. Females lived longer than males in all cases and were more sensitive to each factor. The effect of habitat on adult longevity of C. brunneus appears subject to some factor which varies between years. The mean daily fecundity of C. brunneus from different sites, and under varying density conditions, is shown in Table 4.3.13. In 1979, there was a significant difference between the sites in the number of = egg pods/day/female (F2 2g 4.53, 0.05 > p > 0.01). Females from site 3 produced most pods/day, in both years. There was no significant difference between site 1 and 2 in either year. There were therefore at least two factors which contributed to increased total reproduction of C. brunneus from site 3. Not only were more eggs/pod produced by these females, but more pods/day were produced together with greater longevity. In some cases high density conditions increased the females longevity, and this caused an increase in the number of pods/female, and hence total egg production. However, there was no increase in daily production. Fecundity measured TABLE 4,3.13 : Mean daily fecundity of C. brunneus from 3 field sites, under low and high density conditions in the laboratory (x ± S.E. (n)). YEAR 1978 1979 SITE DENSITY 1 2 3 1 2 3 NO. PODS/ LOW 0.14 ± 0.02(10) 0.12 ± 0.02(9) 0.19 ± 0.02(10) 0.09 ± 0.01(10) 0.10 ± 0.01(10) 0.13 ± 0.01(9) DAY/ ? HIGH 0.13 0.21 0.07 - - 0.13 P N.S. N.S. • N.S. N.S. NO. EGGS/ LOW 1.24 ± 0.16(10) 1.23 ± 0.25(9) . 1.79 ±0.53(10) 0.67 ± 0.11(10) 0.75 ± 0.11(10) 1.23 ± 0.15(9) DAY/ ? HIGH 1.34 2.18 0.66 - 1.35 P N.S. N.S. N.S. N.S. N.S. = not significant 232. in terms of the number of eggs/day/female was also significantly different between sites in 1979 (F^ 26 = 5.71, p < 0.01). This correlated with increases in both the number of eggs/pod, and the rate of pod production by females from site 3. Increased density conditions did not affect the daily production of eggs. The effects of site on the egg eclosion and nymphal development of both species seems to act in some way through the hatchling weight, possibly reflecting egg weight and size differences. Hatchling weight increased in extreme sites in each species. The effect of density on this parameter seems to vary according to species. The effect of site per se on the fecundity of C, paratlelus appears to be one of how to package a relatively stable number of offspring, whereas C, brunneus displays signi- ficantly increased fecundity in extreme sites. It is difficult to describe a specific effect of density on these reproductive parameters as there appears to be an historic influence on the response by both species to this factor. However, in neither species did increased density stimulate increased daily production of eggs or pods, although total fecundity may be increased as a result of increased longevity. 233. ' • CHAPTER 5 GENERAL DISCUSSION This study has shown that the life history characteristics of both C. parallelus and C. brunneus can vary considerably in populations occurring in different habitat types, on a microgeographic scale. The habitats range from moist grassland (site 2) to dry grassland (site 1) and heath- land (site 3). Three areas of possible variation have been considered; morphology, demography and various aspects of reproduction. In Chapter 2 morpho- metrical analyses of C. parallelus and C. brunneus were described. Both species show similar character patterns, which indicate a change in shape between years within each habitat type, and both show some morphological adaptation to habitat. Although the same characters are not effective in discrimination in the two species, the general change in shape is similar. The work described in Chapter 3 quantified the environmental factors that potentially affect life history strategies in grasshoppers, such as temperature, moisture and food availability, in three field sites. Each site supported sympatric populations of C. parallelus and C. brunneus. Various demographic components (i.e. population densities, duration and survival of each stage) measured on each site showed significant intra- specif ic differences in both species. Chapter 4 discussed laboratory work, which showed that the demographic variations mentioned above were maintained under standard conditions, and also quantified various life-history components not measured in the field. Although a full discussion on Chapter 2 has been given, the work in Chapters 3 and 4 complement each other, and will be considered further here. Most aspects of reproduction showed some differences between the pop- ulations in both species. Considering first the field and laboratory data on egg eclosion, populations on site 1 consistently hatched earlier than those on sites 2 and 3. Site 1 is a typical grassland habitat for grass- hoppers, whereas sites 2 and 3 are more extreme (discussion of Chapter 3) . Site 3 appeared especially unsuitable for egg development, as the soil was cold and wet until late spring or early summer, by which time most grass- hopper populations have usually appeared. However, eggs laid in the lab- oratory by females collected from each site, and kept in an outdoor insectary, hatched in the reverse order. This suggested that the intrinsic developmental period at any given temperature was shorter in eggs from site 3, than those from sites 2 hnd 1. Thus, directional selection may have occurred because of the extreme conditions. This type of adaptation has been found in other insects; for example Masaki (1965) described a physiological cline in the egg developmental period of TeleogryHus ernma (Orthoptera: Gryllidae). A preliminary transfer experiment indicated that eggs from site 3 females hatched earlier on site 1 than eggs from site 1 females. However, the number of eggs hatching was very small in each case. On site 3, only a few eggs from site 3 females hatched, and none from site 1 females. Capinera (1979) suggests that time of eclosion is related to egg size. In this study, the dry weight of hatchlings was used as an indicator of egg size. Hatchlings from site 3 were heavier than those from sites 2 and 1, for both species. Causes of mortality of grasshopper eggs have not been studied in depth; however, it is reasonable to suppose that a large proportion of egg mortality is caused by abiotic factors. The pods are laid only 2 cm below the soil surface and thus exposed to wide fluctuations in temperature and moisture. It is possible therefore that the extreme conditions experienced on site 3, especially as the soil 235. is exposed, light and sandy, have produced pressure for selection of larger or heavier eggs. Large,yolky eggs would be better protected from changes in their physical environment. The role of egg size in insect biology has only been studied by Wellington (1960), Barbosa & Capinera (1977, 1978) and Capinera (1979). On extreme sites therefore, there appears to be a significant selective pressure for heavier eggs which have a lower developmental threshold or a faster developmental rate. Even so, the growing season on the extreme sites is shorter than on usual grasshopper habitats, and adult survival may be variable. Semelparous or annual species have an optimum strategy based on the age of first reproduction, and the growth rate is selected according to mortality schedules. Hence selection pressure for early maturation should occur. Both the field and laboratory experiments have shown that the total nymphal developmental period for both species is significantly shorter on the extreme sites 2 and 3, compared to site 1. Although there were no significant differences in the pre-oviposition period of females from each site, the shorter nymphal developmental periods had the effect of decreasing the age of first reproduction. Nymphal mortality was generally very high in all populations, but annual fluctuations within sites indicated that the between-site differ- ences were insignificant. Whilst high nymphal mortality is a character- istic of each species' overall strategy (r-selection types) it does not seem to be an important factor in the intra-specific variations. Females from site 3 were more fecund in the laboratory than those from sites 2 and 1. C. brunneus showed significant site differences both in clutch size (eggs/pod) and in fecundity. C. paraVLeVus also showed differences in clutch size?but other reproductive parameters only reflected the trends shown more clearly by C. brunneus. The adult females from site 3 tended also to be heavier than those from the other sites, which may reflect the higher fecundity. The suggestion made earlier that egg mortality was high on site 3, and the variable adult mortality, might indicate that the harsher environ- ment of site 3 requires greater fecundity for maintaining the populations. However, it has already been shown that selection for larger eggs may have occurred on extreme sites. If there was also selection pressure for higher fecundity then either the insect must become more efficient at assimilating its source of energy, and increase its reproductive effort, or it must find a food supply of greater nutritional value. Grasses on site 3 had a significantly higher mean total nitrogen content, although the grasshoppers' diet was less diverse than, on other sites. The present knowledge on the effect of nitrogen levels on grasshoppers has already been discussed and is not very conclusive, but the insects are known to do better on a mixed diet. Although fecundity may be increased on the extreme sites due to the higher nitrogen levels in the grasses, the numbers of C. brunneus are very low on both sites as a result of the high mortality imposed by the extreme conditions. The trend in decreasing ovariole number in C. brunneus with extreme habitat type, as described in chapter 2, was inversely correlated with fecundity. There does not appear to be any selective pressure for this. Past authors have used ovariole number as an index of fecundity, but in C. brunneus this would be somewhat misleading. It is possible that the decrease in ovariole numbers is related to the decrease in body length in heathland habitats. Not all the ovarioles are active at any one time, and the decreased number of eggs/pod on site 1 may be due to higher resorption rates on grassland sites, where the mean nitrogen levels are lower. How- ever, if it is a nutritional effect, then it must influence the fecundity of the females through the early nymphal stages, as the females in the laboratory were fed on the same food source. Although the responses of the eggs and nymphs of C. brunneus and C. parallelus to selection pressures would appear equally marked, it is interesting that females of C. parallelus show less distinct population differences in various reproductive parameters. Comparing the two species, it might be said that C. brunneus is relatively more r-selected than C. parallelus. Most insects can be generally classified as r-strategists since the predictability and permanence of their habitat determines the strategy selected. Their populations live at a wide range of densities, and because of their high natality and mortality, the potential for selection in new environments is high. C. parallelus is usually found at higher densities within each of its habitats than is C. brunneus, whose, population levels fluctuate far more. Increased density in both species have been found to decrease hatchling weight, increase the total nymphal developmental period, and increase longevity. The data were insufficient to show whether total egg production was affected. However, in the field these density effects are more likely to occur in C. parallelus. C. brunneus is more fecund, more mobile, and occurs more frequently in marginal habitats, thereby experiencing more intensive selection pressure. As discussed in chapter 2, neither species regularly migrates, but the nature of C. brunneus is more likely to produce colonising behaviour than C. parallelus. The occurrence of the macropterous form of the latter is apparently density dependent (Gyllenberg, 1974), and is not frequently found. C. parallelus is a larger, heavier insect producing fewer, heavier eggs. Although brachyptery itself might lead to isolation, possible in- 238. breeding, and hence population differences, Hewitt (1964) has suggested that the higher chiasma frequency seen in C. paraHelus compared to C. brunneus may counteract this. Also, C. -parallelus tends to frequent more diverse habitats, and possibly disruptive selection may maintain the level of genetic diversity within each population. Lewontin (1965) stated that species with a history of colonisation would show little variation in developmental time, but large variances in fecundity. Thus, whilst neither species is a true coloniser, the differences in their reproductive strategies, and their susceptibility to selection pressures may reflect their degree of colonising ability. Here the process of adaptation was studied through the variation in continuous characteristics. The proximal factors influencing these have been taken into account to some extent, but careful experimental manipulation is required to determine the genetic component in these ecologically important life history features. 239. ACKNOWLEDGEMENTS I would like to thank my supervisor, Dr. V.K. Brown, for all her encouragement and advice throughout this project. I am grateful to Professor T.R.E. Southwood, F.R.S., as Director of the Field Station, for the facilities provided. Other people who have aided the completion of this study and to whom I extend my thanks are Dr. S. Walker, for programming help, Dr. T. Bellows, Mr. R.G. Davies and Dr. A. Ludlow for statistical advice, and the technicians at Silwood Park, especially Miss G. Tyler and Mr. L. Warner. I gratefully acknowledge the provision of permits by the Crown Estate Office, the Royal Military Academy, Sandhurst, and the National Rifle Association at Bisley, allowing me access to their land. * Special thanks are due to Miss C.M. Collins for typing the manuscript so quickly. Finally, heartfelt thanks go to my husband, Christopher, who has given unstintingly of his time and help. 240. REFERENCES ALBRECHT, F.O. (1970). The regulation of numbers in locust populations: laboratory studies on reproduction and survival. Proc.Int. Study Conf.Current and Future Problems of Aoridology3London, pp.103-110. ALEXANDER, R.D. (1968). Life cycle origins, speciation and related phenomena in crickets. Q. Rev. 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Studies of the ecology and behaviour of the grass- hopper Chorthippus brunneus (Thun.). Ph.D Thesis, University of Wales, Cardiff. 264. APPENDIX 2 : Floral species list for sites in surveys 1978 and 1979 (names as in Clapham, Tutin & Warburg, 1962; Hubbard, 1968; Smith, 1978). 1978 1. Garrison Ridge Agrostis tenuis Sibth. Anthoxanthum odoratum L. Arrhenatherum elatius (L.) J. & C. Presl. Dactylis glomerata L. Festuca rubra L. Holcus lanatus L. Phleum bertolonii D.C. Poa pratensis L. Poa trivialis L. Car ex spicata Huds. Juncus effusus L. Luzula campestris (L.) D.C. Achillea millefolium L. Cerastium vulgatum L. Cirsium arvense (L.) Scop. Glechoma hederacea L. Hypericum pulchrum L. Lotus comiculatus L. Medicago lupulina L. Plantago lanceolata L. Ranunculus repens L. Rumex acetosa L. Senecio jacobaea L. Stellxzria graminea L. Trifolium dubium Sibth. Trifolium pratense L. Tri folium repens L. Veronica chamaedrys L. Vicia hirsuta (L.) S.F. Gray Vicia sativa L. 2. RHS Nashs Field Agrostis tenuis Anthoxanthum odoratum Festuca rubra Holcus lanatus Poa pratensis Achillea millefolium Bellis perennis L. Crepis capillaris (L.) Wallr. Lotus corniculatus Plantago lanceolata 265. APPENDIX 3e : Continued. Stellaria graminea Tri folium pratense Tri folium repens Veronica chamaedrys 3. LHS Nashs Field as site 2, + Rumex acetosa Rumex acetosella L. 4. Pond Field Agrostis tenuis Deschampsia caespitosa (L.) Beauv. Festuca ovina L. Holcus lanatus Holcus mollis L. Poa pratensis Juncus effusus Luzula campestris .. ... Cardamine flexuosa With. Cirsium arvense Galium saxatile L. Lotus corniculatus Rumex acetosella Stellaria graminea 5. North Gravel Agrostis tenuis Anthoxanthum odoratum Festuca rubra Holcus lanatus Holcus mollis Poa pratensis Luzula campestris Achillea nrillefolium Medicago lupulina Onopordum acanthium L. Plantago lanceolata Stellaria graminea Taraxacum officinale agg. Weber Tri folium pratense Trifolium repens Vicia hirsuta 266. APPENDIX 3e : Continued. 6. South Gravel Agrostis tenuis Festuoa rubra Holous lanatus Holous mollis Poa pratensis Achillea millefolium Crepis capillaris Lotus comiculatus Plantago lanceolata Rumex acetosella Rumex obtusifolius L. Stellaria graminea Tri folium repens Hypnum cupressiforme Hedw. 7. Elm Slope Agrostis tenuis Aira caryophyllea L. Arrhenatherum elatius Festuca ovina Festuca rubra Holcus lanatus Holcus mollis Achillea millefolium Galium saxatile Rubus fruticosus agg. Rumex acetosa Rumex acetosella Stellaria graminea Veronica chamaedrys Hypnum cupressiforme 8. Rush Meadow Agrostis tenuis Bromis mollis L. Dactylis glomerata Festuca gigantea (L.) Vill. Festuca ovina Festuca rubra Glyceria x pedicellata Towns. Holcus lanatus Holcus mollis Poa pratensis Poa trivialis Juncus articulatus L. 267. APPENDIX 3e : Continued. Juncus effusus Achillea millefolium Cirsium arvense Epilobium obscurum Schreb. Galium saxatile Gleohoma hederacea Lotus oornioulatus Ranunculus repens Rumex acetosa Stellaria graminea Urtica diotca L. Veronica chamaedrys 9. Bisley NRA Ranges Agrostis canina L. Festuca rubra Molinia caerulea (L.) Moench. Nardus stricta L. Juncus bulbosus L. Calluna vulgaris (L.) Hull Erica cinerea L. Erica tetralix L. Myrica gale L. Potentilla erecta (L.) Rausch Taraxacum officinale agg. Ulex minor Roth. 10. Sandhurst RMA Agrostis canina Agrostis tenuis Festuca ovina Molinia caerculea Juncus bulbosus Juncus effusus Car ex nigra (L.) Reichard Betula sp. L. Calluna vulgaris Erica cinerea Hypochaeris radicata L. Fotentilla erecta 11. Chobham Common Agrostis setacea Curt. Molinia caerulea 268. APPENDIX 3e : Continued. Betulea sp. Calluna vulgaris Erica cinerea Erica tetralix Ulex minor Polytrichum sp. Hedw. 12. M4 Agropyron repens (L.) Beauv. Festuca rubra Poa pratensis Cirsium vulgar e (Savi) Ten. Taraxacum officinale agg. 13. Maidenhead Motorway A308(M) Helictotrichon pubescens (Huds.) Pilger. Holcus lanatus Poa pratensis Cerastium glomeratum Thuill. Taraxacum officinale agg. 14. Penny Hill Crown Estates Agrostis canina Agrostis tenuis Molinia caerulea Juncus articulatus Juncus bulbosus Juncus effusus Calluna vulgaris Erica cinerea Erica tetralix Galium saxatile Polentilla erecta Carex nigra Polytrichum sp. 15. Matley Bog Agrostis tenuis Festuca rubra Calluna vulgaris Galium saxatile 269. APPENDIX 3e : Continued. Hydrocotyle vulgaris L, Myrica gale Rumex aoetosella Vicia sativa 16. Canford Heath Agrostis tenuis Agrostis setacea Molinia caerulea Calluna vulgaris Erica tetralix Epilobium angustifolium L. Hypochaeris radicata Potentilla erecta Rumex acetosa Stellaria graminea Taraxacum officinale agg. 17. Denny Bog Molinia caerulea Juncus acutiflorus Hoffm. Erica tetralix . Epilobium palustre L. Hypericum elodes L. Myrica gale. Narthecium ossifragum (L.) Huds. Potamogeton polygonifolius Pourr. Potentilla palustris Sphagnum magellaricum Br id. Sphagnum papilosum Lindb. 270. APPENDIX 3e : Continued. 1979 1. Gravel Pit Agrostis tenuis Festuca ovina Festuca rubra Holcus lanatus Poa pratensis Achillea millefolium Galium saxatile Lotus comiculatus Medicago lupulina Plantago lanceolata Rumex acetosa Veronica chamaedrys Vicia hirsuta Vicia sepium L. 2. LHS Nashs Field Agrostis tenuis Anthoxanthum odoratvtm Festuca rubra Holcus lanatus Holcus mollis Poa pratensis Achillea millefolium Cirsium vulgare Lotus comiculatus Plantago lanceolata Rumex acetosella Stellaria graminea Hypnum cupressi forme 3. RHS Nashs Field Agrostis tenuis Anthoxanthum odoratum Festuca rubra Holcus lanatus Poa pratensis Achillea millefolium Crepis capillaris Lotus corniculatus Plantago lanceolata Stellaria graminea Trifolium pratense Tri folium repens Veronica chamaedrys 271. APPENDIX 3e : Continued. 4. North Gravel Agrostis tenuis Anthoxanthum odoratvun Festuoa rubra Holcus lanatus Holcus mollis Poa pratensis Luzula campestris Achillea millefolium Medicago lupulina Onopordum acanthium Plantago lanceolata Stellaria graminea Taraxacum officinale agg. 5. South Gravel Agrostis tenuis Festuca rubra Holcus lanatus Holcus mollis Poa pratensis Achillea millefolium Crepis capillaris Lotus corniculatus Plantago lanceolata Rumex acetosella Rumex obtusifolius Stellaria graminea Tri folium repens Hypnum cupressiforme 6. Garrison Ridge Agrostis tenuis Anthoxanthum odoratum Arrhenatherum elatius Dactylis glomerata Holcus lanatus Phleum bertolonii Poa pratensis Juncus effusus Car ex spicata Luzula campestris Achillea millefolium Cirsium arvense Lotus corniculatus Plantago lanceolata 272. APPENDIX 3e : Continued. Ranunculus repens Rumex acetosa Senecio jacobaea Stellaria graminea Tri folium dubium Tri folium repens Veronica chamaedrys Vicia hirsuta Vicia sativa 7. Silwood Bottom Agrostis tenuis Agrostis stotonifera L. Holcus lanatus Cirsium arvense Crepis capillcoris Hypochaeris radicata Lotus corniculatus Medicago lupulina Plantago lanceolata Plantago major Ranunculus repens Rumex acetosa Rumex acetosella Rumex obtusifolius Senecio jacobaea Silene alba (Mill.) Krausse. Trifolium dubium Trifolium pratense Tri folium repens Vicia hirsuta Vicia sepium L. 8. Elm Slope Agrostis tenuis Aira caryophyllea Anthoxanthum odoratum Arrhenatherum elatius Festuca ovina Festuca rubra Holcus mollis Poa pratensis Achillea millefolium Galium saxatile Rubus fruticosus agg. Rumex acetosa Rumex acetosella 273. APPENDIX 3e : Continued. 9. Rush Meadow Agrostis tenuis Dactylis glomerata Deschampsia oaespitosa Festuca gigantea Festuca ovina Festuca rubra Holcus lanatus Holcus mollis Poa pratensis Poa trivialis Juncus articulatus Juncus effusus Cirsium palustre (L.) Scop. Epilobium obscurum Glechoma hederacea Lotus corniculatus Ranunculus acris L. Ranunculus repens Rumex acetosa Stellaria graminea Urtica dioica Veronica chamaedrys Veronica montana L. 10. Gracious Pond Agrostis setacea Agrostis tenuis Molinia caerulea Betula sp. Calluna vulgaris Erica tetralix Taraxacum officinale agg. 11. Penny Hill, Crown Estates Agrostis canina Agrostis tenuis Molinia caerulea Car ex nigra Juncus articulatus Juncus bulbosus Juncus effusus Calluna vulgaris Erica cinerea Erica tetralrix Pedicularis sylvatica L. 274 APPENDIX 2 : Continued. Potentilla erecta Polytrichum sp. 12. Sandhurst RMA Agrostis canina Agrostis tenuis Festuca ovina Molinia caerulea Juncus bulbosus Juncus effusus Car ex nigra Betula sp. Calluna vulgaris Erica cinerea Hypochaeris radicata Potentilla erecta Taraxacum officinale agg. 13. Bisley NRA Festuca rubra Molinia caerulea Nadus stricta Juncus hulbosus Calluna vulgaris Erica cinerea Erica tetralix Myrica gale Potentilla erecta Taraxacum officinale agg. Viex minor 14. M4 Agropyron repens Festuca rubra Poa pratensis Cirsium vulgare Taraxacum officinale agg. 15. M42 Agropyron repens Eelictotrichon pubescens 275. APPENDIX 3e : Continued. Holous lanatus Poa pratensis Urtica dioica Taraxacum officinale agg. 16. A308 (M) Helictotrichon pubescens Holcus lanatus Poa pratensis Cerastium glomeratum Thuill. Taraxacum officinale agg. Lamium album L. 17. Balmer Lawn Agrostis tenuis Festuca ovina Festuca rubra Bellis perennis Galium saxatile Lotus corniculatus Potentilla erecta Taraxacum officinale agg. Ulex minor 18. Matley Bog Agrostis tenuis Festuca rubra Calluna vulgaris Galium saxatile Hydrocotyle vulgaris Myrica gale Rumex acetosella Vicia sativa 19. Pignall Enclosure Anthoxanthum odoratum Deschampsia caespitosa Molinia caerulea Juncus effusus Pteridium aquilinum (L.) Kuhn Betula sp. 276. APPENDIX 3e : Continued. Lotus corniculatus Potentilla erecta 20. Pagham Harbour Festuca rubra Halimione portulacoides (L.) Aell Puccinellia maritima (Huds.) Pari. Spartina sp. Schreb. 21. Longslade Bottom Agrostis tenuis Agrostis setacea Festuca rubra Molinia caerulea Calluna vulgaris Ulex minor 22. Lepe Festuca rubra Puccinellia maritima Spartina sp. Juncus conglomerates L. Juncus gerardii Lois. Aster tripolium L. Atriplex hastata L. Glaux maritima L. Halimione portulacoides Limonium vulgare Mill. Plantago maritima L. Salicornia stricta Dum. Suaeda maritima (L.) Dum. 277. APPENDIX 3a : Monthly meteorological data. (Silwood Park site, latitude 51° 28fN, height above M.S.L. 67 m) 1978 1 TEMPERATURE (°C) RAINFALL mm. MONTH Max. Min. Mean Total Hrs. TOTAL 304 .8 87.0 190.8 60.2 52.7 APRIL MEAN 10.1 2.9 6.3 2.0 1.8 TOTAL 519.8 187.3 351.6 76.4 56.4 MAY MEAN 16.7 6.0 11.3 2.5 1.8 TOTAL 567.0 261.5 413.8 48.2 30.0 JUNE MEAN 18.9 8.7 13.8 1.6 1.0 TOTAL 604.0 335.7 469.2 51.6 37.0 JULY MEAN 19.5 10.8 15.1 1.7 1.2 TOTAL 605.0 315.8 455.9 68.1 29.2 AUG. MEAN 19.5 10.1 14.7 2.1 0.9 TOTAL 560.3 273.3 419.8 19.7 16.6 SEPT. MEAN 18.7 9.1 14.8 0.6 0.5 278. APPENDIX 3e : Continued. 1979 TEMPERATURE (°C) RAINFALL mm. MONTH Max. Min. Mean Total Hrs. TOTAL 361.0 102.0 223.0 80.3 53.9 APRIL MEAN 12.0 3.4 7.4 2.7 1.8 TOTAL 471.0 177.0 317.0 94.0 67.3 MAY MEAN 15.2 5.7 10.2 3.0 2.2 TOTAL 554.0 288.0 603.0 34.1 31.8 JUNE MEAN 18.4 9.6 14.1 1.1 1.1 TOTAL 669.0 351.0 521.0 15.0 11.8 JULY MEAN 21.5 11.3 16.8 0.5 0.4 TOTAL 613.0 308.0 460.0 47.1 35.7 AUG. MEAN 19.7 9.9 14.8 1.5 1.2 TOTAL 553.0 230.0 394.7 12.3 13.4 SEPT. MEAN 18.4 7.7 13.1 0.4 0.4 APPEKDIX 3b : Trellis diagram of Sorensen's Coefficient of Similarity for survey sites 1978/1979. SITE 1 SAMPLE SITE YEAR 1978 NO. 1979 1 2 3 A 5 6 | 1 2 3 4 5 6 1 1978 1 - 2 .9A - 3 1.00 .95 - 4 .88 .82 .88 - 5 • 9A .89 .9A .87 - 6 .88 .82 .88 .93 .93 - 1979 1 .9A .9A ,9A .80 .88 .80 - 2 .88 .83 .88 .73 .81 .80 .94 - 3 .88 .89 .88 .73 .88 .80 .89 .89 - 4" .71 .85 .77 .67 .83 • 7A .76 .76 .90 _ 5 .68 .89 .88 .80 . 94 .87 .81 .81 .94 .90 - 6 .81 .82 .81 .71 .87 .79 .80 .80 .87 .89 .93 - 2 1978 1 .AO .A8 • AO. .39 • A2 .39 .42 .37 .42 .40 .42 .44 2 .AO .A9 • AO .39 .42 .39 .42 .37 .42 .35 .42 .39 3 • AA . A7 • AA .AA . A7 .AA . A7 .42 .47 .40 .47 .44 4 .43 .Al • A3 . A7 . A5 . A7 . A5 .40 .40 .32 .40 .37 5 . A3 . A5 . A3 . A2 .45 . A2 .45 .40 .45 .38 .45 .42 6 .37 .AO .37 .Al • .39 .40 .39 .33 .39 .30 .39 .35 1979 1 . A2 . A5 . A2 .Al .44 .41 .44 .39 .44 .36 .44 .41 2 .AO .A3 • AO .39 .42 .39 .42 .42 .42 .34 .42 .39 3 .AO . A3 .AO .39 .A2 .39 .42 .50 .42 .34 .37 .39 A .39 . A2 .39 .38 .Al .38 .41 .48 .41 .33 .41 .38 5 .39 . A2 .39 .38 .Al .38 .41 .48 .41 .33 .41 .38 6 .36 .39 .36 . 3A .38 .34 .38 .32 .39 .27 .32 .34 3 1978 1 .13 .12 .13 • 1A .13 .14 .13 .13 .13 .15 .13 .14 2 .07 .07 .07 .08 .07 .08 .07 .07 .07 .08 .07 .08 3 .13 .12 .13 • 1A .13 .14 .13 .13 .13 .15 .13 .14 A .07 .06 .07 .08 .07 .08 .07 .07 .07 .08 .07 .08 5 .13 .12 .13 .15 .1A .15 .14 .1A .14 .15 .14 .15 6 .13 .13 .13 .15 .1A .15 .14 .14 .14 .16 .14 .15 1979 1 .07 .07 .07 .08 .08 .08 .08 .08 .08 .09 .08 .08 2 .13 .13 .13 .08 .14 .08 .14 .14- .14 .16 .14 .15 3 .07 .07 .07 .08 .08 .08 .08 .08 .08 .09 .08 .08 A .07 .06 .07 .08 .07 .08 .07 .07 .07 .08 .07 .08 5 .13 .13 .13 .08 • 1A .08 .14 .14 .14 .16 .14 .15 6 .07 .07 .07 .08 .08 .08 .08 .08 .08 .09 .15 .08 APPENDIX 3b : Continued. SITE 2 SAMPLE SITE YEAR NO. 1978 1979 3456123 4 56 1978 1979 1978 .82 NJ .78 00 .74 86 - O .83 90 .92 - .76 81 .86 .91 - 1979 .81 81 .73 .86 .85 _ .77 82 .78 .87 .81 .76 - .82 78 .78 .87 .86 .86 .91 - .80 80 .85 .89 .84 .79 .89 .89 .80 80 .85 .89 .84 .79 .89 .89 00 - .74 79 .84 .89 .83 .78 .88 .84 91 .91 - 1978 .22 20 .21 .21 .18 .24 .17 .17 16 .16 .17 .18 15 .17 .17 .13 .19 .12 .12 11 .11 .12 .22 20 .21 .21 .18 .24 .17 .17 16 .16 .17 .06 11 .11 .11 .06 .13 .06 .06 06 .06 .06 .23 20 .22 .16 .18 .24 .17 .17 17 .17 .18 .24 21 .22 .22 .19 .25 .18 .18 17 .17 .18 1979 .13 11 .12 .12 .13 .13 .13 .13 12 .12 .13 .18 15 .17 .17 .13 .25 .18 .18 17 .17 .18 .13 11 .12 .12 .13 .13 .13 .13 12 .12 .13 .18 15 .17 .17 .19 .25 .18 .18 17 .17 .18 .18 15 .17 .17 .13 .25 .18 .18 17 .17 .18 .06 05 .06 .06 .07 .13 .13 .13 12 .12 .13 APPENDIX 3b : Continued. SITE 3 SAMPLE SITE YEAR 1978 NO. 1979 3 4 5 612 3 4 5 6 1978 1979 1978 fO 00 1979 1978 88 _ 96 .92 - 92 .87 .96 - 1979 83 .76 .87 .82 - 92 .87 .96 .92 .91 - 83 .76 . .87 .82 1.00 .91 - 92 .78 .88 .83 .91 .92 .91 - 92 .78 .88 .83 .91 .92 .91 .90 _ 83 .76 .78 .73 .90 .82 .82 .91 .91 APPENDIX 3c : No. touches/100 pins of each plant species at permanent field sites. SITE 1 PLANT SPECIES 1 25 SAMPLE M ' u ft w •c cI.i. TOTAL DATE s £ oi H K f'n x •>) to 01 r O H ci a0 1 01 5) -i r> -i 0 ) 01 01 £ — J-3 £ Cq H S M >-j G H i: :' I'; '•1 M ' 1 * p S Cj ft;^ Ct; 11o ^ K H 0a); ^ I i -1 (-to1 •: ft: Q 3 ^ a '4 • M H a: • 23/ 5/78 23 1 12 1 31 11 25 25 0 4 2 0 1 17 1 3 2 5 2 2 168 6/ 6/78 48 2 11 0 29 8 16 24 1 2 1 0 2 20 1 2 6 7 2 1 183 20/ 6/78 45 1 12 3 38 24 16 34 3 7 4 0 2 29 1 4 5 10 2 1 241 4/ 7/78 54 1 6 2 24 34 4 45 0 2 3 0 1 25 I 3 6 12 2 3 228 18/ 7/78 65 3 1 8 38 7 40 0 2 5 0 2 29 1 4 4 9 2 1 223 1/ 8/78 77 1 1 2 6 30 8 36 0 3 5 0 1 32 3 2 4 8 2 2 223 15/ 8/78 71 1 0 0 7 39 8 43 0 0 9 0 1 37 2 0 7 9 5 3 242 29/ 8/78 76 1 0 2 12 37 11 36 0 0 5 0 0 32 4 3 2 2 2 2 227 12/ 9/78 73 1 1 2 8 41 11 36 0 0 6 0 0 37 I 3 4 5 3 1 233 3/10/73 79 1 0 1 9 38 13 22 0 0 5 0 0 34 1 1 2 1 2 0 209 17/10/78 66 1 0 1 6 41 8 16 0 0 3 0 0 33 3 0 1 3 2 1 185 28/ 5/79 53 1 6 1 10 30 13 17 0 1 2 0 1 20 0 7 3 1 1 0 167 2/ 7/79 68 1 1 10 13 30 3 32 0 1 1 1 1 31 0 3 4 . 0 1 0 201 23/ 7/79 67 1 6 9 16 39 3 42 3 1 0 0 35 2 7 8 0 1 0 244 20/ 8/79 65 1 4 5 7 32 0 36 26 0 5 0 0 42 1 2 7 0 0 0 233 17/ 9/79 47 1 11 5 17 29 6 38 30 0 I 0 0 37 1 2 5 0 1 2 233 15/10/79 43 I 5 3 14 33 6 45 34 0 I 0 1) :9 0 1 0 0 2 221 24 / 16 / 29 / 11 / 31 / 17 / 23 / 28 / 14 / 25 / 3 / a- 7 / 2/10/7 8 7 / cn 8/7 9 5/7 9 7/7 9 9/7 9 9/7 8 7/7 8 6/7 8 5/7 8 8/7 8 7/7 8 8/7 8 6/7 8 7/7 8 3 > H> s: vO 30 N> CT* CT* £> Ln CT* CT* ro ui 5 o o Ul o o AGROSTIS TI.VJIS c c = o o NJ - - U> - - - - •c- UJ c o mclzis ro ro o Ln .c- Ui ro o ro ro lac:-lis i "" ------A- - - o NO UJ - ro t- CT* ro - :ZS:LA::;J:A :A-SPITOSA r- - - o NJ - NJ - O - - ,o o c O o NJ u> ro t- NJ UJ u> *o *o CYl'.A ------ui - ro - NJ "Vj vO UJ •C- Ul c- Ul ro CLS7L:A RUBRA - = 3 o o C ------O o O GLILLRIA *i EDICELIJt TA ro LO CT* CT* Ul NJ UJ UJ •ts £ ui O 00 O ro U> UJ CT* Ul 00 UJ KLC-JS LA:;AT'JS UJ NJ UJ CT* CT* Ul NJ f. vO -O Ul CO CO o ro Ul m ^ CT* HCL'jvs a CT* - Oi CO UJ - - NJ o O - CT* CT* UJ tca uj ro ro a 3 O £ £ Ul Ul - - O *o O VO UJ *o 10A TRIVIAL IS NJ ro UJ •c- ro J ULCUS AR TICULA^'US ix u> CT* O O •e- UJ Ul Ul £ u> *o ro •c- f> Ul j'j::cjS effusus o CT* O 00 - UJ £ Ul t- 00 CT* o ro 0 C O O - o o o O - - NJ - - - - o ACHILLEA MILLEFOLIUM o o O O o o o O o o o o o o ro CARDAMINE HIRCUTA -a - - r H o o O o O o o O o o o - o o UJ ro CERASTIUrl CLCMERATUM *0 CT* UJ £> Ul VJ CO VO 00 00 00 CIRC IUM FA LUSTRE m & - o ro •t- ro - O - o o Ul CT* ON Ul UJ UJ UJ EPILC3IUM. 0BCCURUM cn o O O o o - o ro o - - GALIUM SAXATILE o o O o o - o O o O O O - - O O GERANIUM DICSECTUM ro NJ NJ ro ro ro o - Ul ro t- ro f £ ON H UJ Ul cr* NJ VO O GLECHCi-lA HEDERACEA CT* vj CT* LC/WS CCRNICULATUS u ui vi - t> vo Ul - Ul o O o o O O O o O o o o O O o O O - O o LYCHNIS FL0C-CUCULI o O o ho o o o o o o O o O O - O ro MYOSOTIS DISCOLOR o - - O o o o o o o O o o O o O O RANUNCULUS ACRIS Ul ro N> UJ ro ro ro ro vI-l CO ro K vO o UJ £ UJ UJ O 00 £ - RANUNCULUS REPENS o O O O o o o o O O O O - - - o o RUbUS FRUTICOSUS UJ - W1 CT* o o £> - o - - CT* ro HUMEX ACETOSA D o o i- VI - o o o o o O o o O o o U'JMEX OBT'JSIFQL [US CD vO ro STELLAR [A G: AMU. EA - o Ul CT* CO O UJ rj CD i- 'H-TICA LTCrCA - JO t- - ro u, - » - t* - - vO - - CT* - Ln UJ - - - ro UJ u> t- ro ,o O .-lama.-: - O o o O o o ro O O ro O - a ni-A r uj NJ ro ro ro ro H 3 O vi a ro ;") uo 3i* - 3 CT* SITE 3 PLANT SPECIES SAMPLE TOTAL DATE CANINA VULGARIS sp . AGROSTIS AGROSTIS TENUIS MOLINIA CAERULEA NIGRA JUNCUS ARTICULATUS JUNCUS BULBOSUS JUNCUS EFFUSUS CALLUNA ERICA CINEREA ERICA TETRALIX GALIUM SAXATILE PEDICULARIS SYLVATICA POTENTILLA ERECTA POLYTRICHUM 27/ 5/78 6 2 37 5 2 1 3 8 2 2 3 1 2 1 75 7/ 6/78 6 1 53 3 4 2 3 16 4 1 3 1 2 1 100 21/ 6/78 15 0 50 8 4 1 6 10 2 3 4 1 2 10 107 5/ 7/78 15 3 61 5 3 3 7 13 3 2 4 1 2 1 123 19/ 7/78 13 1 71 6 2 4 6 16 2 4 3 1 2 1 132 2/ 8/78 2 2 65 4 0 3 5 13 2 3 3 0 1 105 16/ 8/78 4 0 67 5 0 3 5 13 1 2 4 0 1 1 106 30/ 8/78 4 7 80 5 3 3 3 12 3 3 3 0 1 125 13/ 9/78 2 8 61 5 5 1 2 13 2 4 2 0 2 1 110 1/10/78 2 12 71 5 5 2 2 15 1 3 2 0 0 1 121 15/10/78 1 10 59 5 2 2 2 14 1 3 1 0 0 1 101 3/ 6/79 6 4 56 8 3 2 0 12 2 5 0 0 4 0 102 23/ 6/79 6 3 58 4 1 3 1 12 1 2 1 0 1 0 93 23/ 7/79 4 3 76 6 3 3 0 20 1 3 0 0 1 0 120 19/ 8/79 8 6 68 6 2 2 1 17 2 9 0 1 5 0 127 16/ 9/79 8 10 71 7 1 3 0 22 4 7 1 1 2 0 137 14/10/79 5 18 63 5 0 2 0 22 2 12 0 1 2 0 132 285. APPENDIX 3d : Correlation between two methods of expressing height profiles. Spearmans rank correlation coefficient using data from multiple touches and pressure/absence values for each height category (n = 11). HEIGHT CATEGORY SITE 1 2 3 4 r r r r s P s P s P s P 1 0.867 < 0.01 0.966 < 0.01 0.877 < 0.01 0.982 < 0.01 2 0.827 < 0.01 0.835 < 0.01 0.961 < 0.01 0.891 < 0.01 3 0.879 < 0.01 0.866 < 0.01 0.947 < 0.01 286. APPENDIX 3e : Continued. Height profiles using multiple touches, 1978* SAMPLING TIME 1 2 3 4 5 6 7 8 9 10 11 SITE 1 1 55.2 45.2 39.0 33.9 34.0 37.2 33.2 36.3 38.3 44.4 51.9 2 33.0 29.8 20.9 19.5 25.6 23.4 25.6 26.3 30.9 35.7 35.4 3 10.3 15.4 15.4 16.8 18.2 18.2 17.8 15.6 18.1 14.1 10.0 4 1.5 7.3 9.7 11.9 11.6 10.9 10.4 9.0 5.2 4.4 1.8 5 1.4 10.0 9.0 9.0 7.2 9.0 9.0 5.4 1.2 .9 6 .7 3.2 4.9 2.5 2.7 3.9 3.0 2.2 7 .9 .1 .3 1.9 .8 8 .9 .2 9 .5 .1 10 .2 SITE 2 1 . 57.5 45.5 36.5 27.6 30.7 25.2 25.3 23.3 27.4 29.5 31.1 2 31.5 26.1 23.7 21.1 20.8 23.7 25.1 22.1 25.1 27.5 31.1 3 9.4 14.5 15.9 19.3 20.2 21.5 19.8 17.3 20.2 23.4 24.7 4 1.7 8.2 12.9 11.1 11.2 16.5 13.0 10.3 12.8 13.2 9.1 5 5.2 9.3 8.6 9.6 11.0 9.9 8.1 7.2 5.6 3.9 6 .6 2.7 6.9 4.6 4.5 6.4 3.5 1.9 1.6 7 - 3.1 1.4 .4 1.8 1.6 .3 .3 8 2.6 1.2 .5 .9 1.3 .3 .1 9 1.1 1.1 .3 .3 .2 .2 .2 10 4.0 .2 .1 .1 .2 .1 .2 SITE 3 1 83.0 73.1 72.5 61.6 54.1 74.8 69.4 72.3 80.7 72.2 74.9 2 13.4 18.8 17.0 .23.2 27.0 22.5 24.1 24.2 15.8 20.6 18.3 3 1.8 4.8 6.4 9.9 9.7 1.8 3.7 3.4 2.2 6.4 6.4 4 1.8 .5 3.2 3.9 6.6 .9 1.6 .9 .4 .5 5 .5 .9 1.4 5.0 1.2 .4 .4 6 287. APPENDIX 3e : Population sampling data. 1. Mean densities (m"~2) from direct counts and sweeping methods (Direct c ount/Sweep ing) a) 1978 INSTAR I II Ill IV ADULT SITE C. parallelus. 1 0.2250 0.2000 0.1000 0.0750 0.2250 0.1070 0.1700 0.0900 0.0633 0.2500 2 0.4333 0.2250 0.1833 0.1333 0.2250 0.1822 0.1630 0.1777 0.1356 0.1900 3 - 0.0400 0.1600 0.0400 - 0.0600 0.1933 0.0667 C. brunneus 1 0.3500 0.1833 0.1500 0.1000 0.2000 0.1555 0.1311 0.1533 0.1133 0.2067 2 0.3833 0.1000 - 0.0500 0.0500 0.1089 0.0433 0.0333 0.0267 3 - - 0.0400 - - 0.0200 288. APPENDIX 3e : Continued. 1. Continued, b) 1979 ^^^ INSTAR I II III IV ADULT SITE C. parallelus 1 0.4959 0.3878 0.2771 0.1449 0.0974 0.2244 0.3286 0.2133 0.1233 0.1067 2 0.2691 0.0983 0.1601 0.2013 0.1009 0.1233 0.1080 0.1689 0.1533 0.0911 3 0.1500 0.1009 0.0788 0.1051 0.0486 0.0600 0.0920 0.0720 0.0800 0.0533 C. brunneus 1 0.5332 0.1360 0.0889 0.1018 0.0309 0.2489 0.1209 0.0800 0.0833 0.0356 2 0.2633 0.0809 0.0518 0.0563 0.0167 0.0633 0.0350 0.0233 0.0267 0.0089 3 0.1431 0.0538 0.0515 0.0286 0.0657 0.0344 0.0222 0.0233 0.0133 0.0311 289. APPENDIX 3e : Continued. 2. Calibration indices used in both years. STAGE I II III IV ADULT SITE C. "parallelus 1 2 1 1 1 1 2 2 1 1 1 1 3 2 1 1 1 1 C. brunneus 1 2 1 1 1 1 2 4 2 2 2 2 3 4 2 2 2 2 APPENDIX 3c : Continued. 3. Population sampling data of C. parallelus and C, brunneus on three sites in 1978 and 1979. (Mean number per m2) C. parallelus - SITE 1, 1978 DATE DAY DEGREES I II III IV ADULTS MAY 2 0.00 0.0 0.0 0.0 0.0 0.0 29 32.60 0.1600 0.0 0.0 0.0 0.0 31 83.20 0.1067 0.0267 0.0 0.0 0.0 JUNE 4 184.45 0.6000 0.1000 0.0 0.0 0.0 6 235.10 0.2000 0.1333 0.0167 0.0 0.0 13 356.61 0.2667 0.1133 0.0 0.0067 0.0 20 477.50 0.2133 0.1133 0.0067 0.0200 0.0 27 569.62 0.2400 0.1467 0.0733 0.0333 0.0067 JULY 4 719.55 0.4533 0.2800 0.0800 0.0533 0.0133 10 872.97 0.3467 0.2667 0.1267 0.0867 0.0533 18 1026.41 0.1867 0.2867 0.1067 0.0867 0.0667 24 1157.99 0.0400 0.1533 0.1667 0.1400 0.1800 AUGUST . 1 1362.31 0.0933 0.0733 0.2733 0.1733 0.2400 15 1669.61 0.0133 0.0400 0.0933 0.1933 0.3333 22 1817.59 0.0 0.0667 0.1067 0.1133 0.6800 SEPTEMBER 2 2005.69 0.0 0.0133 0.0333 0.1000 0.6667 8 2088.55 0.0 0.0067 0.0267 0.0533 0.6333 12 2171.03 0.0 0.0 0.0200 0.0400 0.4333 19 2243.97 0.0 0.0 0.0 0.0267 0.3733 OCTOBER 3 2386.35 0.0 0.0 0.0 0.0 0.3533 10 2459.04 0.0 0.0 0.0 . 0.0 0.2133 17 2578.95 0.0 0.0 0.0 0.0067 0.0600 24 2677.56 0.0 0.0 0.0 0.0 0.0533 31 2766.12 0.0 0.0 0.0 0.0 0.0400 NOVEMBER 7 2871.54 0.0 0.0 0.0 0.0 0.0 APPENDIX 3e : Continued. 3. Continued. C. parallelus - SITE 2, 1978 DATE DAY DEGREES I. II III IV ADULTS MAY 29 0.0 0.0 0.0 0.0 0.0 0.0 31 39.60 0.0533 0.0 0.0 0.0 0.0 JUNE 4 121.66 0.2000 0.0500 0.0 0.0 0.0 9 222.66 0.0333 0.0333 0.0 0.0 0.0 19 375.66 0.3467 0.1333 0.0200 0.0067 0.0 26 490.29 0.1867 0.1200 0.0667 0.0067 0.0 JULY 3 605.37 0.2267 0.1267 0.0467 0.0200 0.0 10 840.71 0.4533 0.2333 0.1133 0.1200 0.0067 17 971.28 0.3600 0.3400 0.1600 0.0867 0.0667 25 1139.27 0.2933 0.1867 0.1733 0.1400 0.0933 AUGUST 3 1303.72 0.2000 0.1600 0.2200 0.1800 0.2267 14 1441.69 0.0267 0.1000 0.2467 0.1467 0.2867 21 1559.22 0.0933 0.0867 0.2000 0.2800 0.3933 28 1643.04 0.0133 0.0400 0.1400 0,1533 0.5400 SEPTEMBER 4 1749.30 0.0 0.0267 0.0667 0.1667 0.7267 11 1838.82 0.0 0.0 0.0800 0.1333 0.7933 18 1969.86 0.0 0.0 0.0333 0.0467 0.4800 OCTOBER 2 2082.00 0.0 0.0 0.0 0.0267 0.5400 9 2225.22 0.0 0.0 0.0 0.0 0.1467 16 2330.08 0.0 0.0 0.0 0.0 0.2267 23 2439.44 0.0 0.0 0.0 0.0 0.1333 30 2546.19 0.0 0.0 0.0 0.0 0.0467 NOVEMBER 6 2609.89 0.0 0.0 0.0 0.0 0.0 292. APPENDIX 3e : Continued. 3. Continued. C. parallelus - SITE 3, 1978 DATE DAY DEGREES I II III IV ADULTS JUNE 3 0.0 0.0 0.0 0.0 0.0 0.0 7 80.71 0.0533 0.0 0.0 0.0 0.0 14 228.02 0.0800 0.0067 0.0067 0.0 0.0 21 365.85 0.0400 0.1067 0.0467 0.0067 0.0 28 474.14 0.0667 0.2000 0.0533 0.0067 0.0 JULY 5 637.17 0.0333 0.1833 0.1333 0.0333 0.0 10 753.30 0.0300 0.0867 0.1333 0.0400 0.0 13 822.98 0.0267 0.0600 0.1933 0.0667 0.0067 19 962.34 0.0133 0.0600 0.1133 0.1533 0.0133 26 1105.42 0.0 0.0067 0.0133 0.1400 0.0133 AUGUST 4 1387.27 0.0 0.0067 0.0933 0.0467 0.0800 16 1743.79 0.0 0.0 0.0 0.0067 . 0.1400 23 1882.77 0.0 0.0 0.0 0.0 0.0667 30 2014.30 0.0 0.0 0.0 0.0 0.0800 SEPTEMBER 6 2105.51 0.0 0.0 0.0 0.0 0.0333 13 2225.00 0.0 0.0 0.0 0.0 0.0133 20 2354.85 0.0 0.0 0.0 0.0 0.0 APPENDIX 3e : Continued. 3. Continued. C. brunneus - SITE 1, 1978 DATE DAY DEGREES I II III IV ADULTS MAY 29 0.0 0.0 0.0 0.0 0.0 0.0 31 50.60 0.1067 0.0 0.0 0.0 0.0 JUNE 4 151.85 0.4800 0.0 0.0 0.0 0.0 6 223.21 0.2000 0.0 0.0 0.0 0.0 13 344.10 0.3867 0.1067 0.0 0.0 0.0 20 436.22 0.5200 0.1600 0.0333 0.0 0.0 27 585.55 0.3333 0.1267 0.0733 0.0133 0.0 JULY 4 738.97 0.3733 0.1533 0.0800 0.0333 0.0 10 892.41 0.2800 0.1933 0.1200 0.0800 0.0067 18 1023.99 0.2133 0.1600 0.1533 0.1133 0.0267 24 1228.31 0.1067 0.1733 0.2200 0.1800 0.0733 AUGUST 1 1535.61 0.1733 0.0733 0.1800 0.2867 0.1400 15 1683.59 0.0800 0.0867 0.1267 0.1800 0.1600 22 1871.69 0.0533 0.0267 0.1000 0.2133 0.3200 SEPTEMBER 2 1954.55 0.0 0.0067 0.0667 0.0800 0.4133 8 2037.03 0.0 0.0 0.0333 0.0933 0.2133 12 2109.97 0.0 0.0 0.0133 0.0200 0.2067 19 2252.35 0.0 0.0 0.0 0.0400 0.1533 OCTOBER 3 2325.04 0.0 0.0 0.0 0.0067 0.1267 10 2444.95 0.0 0.0 0.0 0.0067 0.0733 17 2540.56 0.0 0.0 0.0 0.0 0.0067 24 2632.12 0.0 0.0 0.0 0.0 0.0133 31 2737.54 0.0 0.0 0.0 0.0 0.0 294. APPENDIX 3f : Continued. 3. Continued. C. brunneus - SITE 2, 1978 DATE DAY DEGREES I II III IV ADULTS JUNE 1 0.0 0.0 0.0 0.0 0.0 0.0 4 82.06 0.2 0.0 0.0 0.0 0.0 9 183.12 0.2667 0.0 0.0 0.0 0.0 19 333.72 0.6133 0.0800 0.0 0.0 0.0 26 450.75 0.3733 0.0800 0.0 0.0 0.0 JULY 3 565.83 0.1600 0.0933 0.0400 0.0 0.0 10 801.17 0.4533 0.0933 0.0400 0.0400 0.0133 17 931.74 0.1333 0.1067 0.0933 0.0133 0.0 25 1099.73 0.2400 0.0267 0.0400 0.0133 0.0 AUGUST 3 1264.18 0.3733 0.0533 0.0267 0.0400 0.0 14 1402.15 0.0800 0.0533 0.0267 0.0667 0.0533 21 1519.68 0.1067 0.0 0.0267 0.0267 0.0133 28 1603.50 0.0 0.0 0.0133 0.0400 0.0400 SEPTEMBER 4 1709.76 0.0 0.0 0.0133 0.0267 0.0667 11 1799.28 0.0 0.0 0.0 0.0 0.0133 18 1930.32 0.0 0.0 0.0 0.0 0.0133 OCTOBER 2 2124.46 0.0 0.0 0.0 0.0 0.0 C. brunneus - SITE 3, 1978 JUNE 12 0.0 0.0 0.0 0.0 0.0 0.0 14 27.2 0.2400 0.0 0.0 0.0 0.0 21 165.03 0.2134 0.0934 0.0 0.0 0.0 28 273.32 0.1066 0.0934 0.0134 0.0 0.0 JULY 5 436.35 0.0 0.0666 0.0334 0.0 0.0 10 552.48 0.0 0.0134 0.0134 0.0 0.0 13 662.16 0.0 0.0 0.0400 0.0 0.0 19 761.52 0.0 0.0 0.0134 0.0400 0.0 26 904.60 0.0 0.0 0.0 0.0268 0.0134 AUGUST 4 1186.45 0.0 0.0 0.0 0.0134 0.0134 16 1533.97 0.0 0.0 0.0 0.0134 0.0134 23 1681.95 0.0 0.0 0.0 0.0 0.0 APPENDIX 3e : Continued. 3. Continued. C. parallelus - SITE 1, 1979 DATE DAY DEGREES I II III IV ADULTS MAY 20 0.0 0.0 0.0 0.0 0.0 0.0 22 46.24 0.1867 0.0 0.0 0.0 0.0 28 198.16 0.0400 0.0 0.0 0.0 0.0 29 219.02 0.1600 0.0 0.0 0.0 0.0 JUNE 1 281.60 0.1733 0.0133 0.0 0.0 0.0 4 344.18 0.2533 0.0600 0.0 0.0 0.0 8 451.86 0.7333 0.0800 0.0 0.0 0.0 14 613.59 0.4533 0.0600 0.0 0.0 0.0 18 721.55 0.7867 0.2467 0.0 0.0 0.0 21 800.21 0.8533 0.1867 0.0067 0.0 0.0 JULY 2 1088.63 0.9600 0.6067 0.1467 0.0200 0.0 5 1171.33 1.0400 O.6800 0.2333 0.0333 0.0 9 1284.29 0.5733 0.7067 0.3933 0.0600 0.0133 12 1368.92 0.5867 0.7667 0.3467 0.1000 0.0200 16 1481.76 0.4533 0.5533 0.4533 0.2267 0.0667 19 1544.88 0.2667 0.2600 0.2267 0.1933 0.1200 23 1628.32 0.1467 0.2800 0.3133 0.2400 0.1400 26 1709.92 0.2400 0.2867 0.2533 0.1667 0.1800 30 1817.82 0.2400 0.2133 0.2400 0.2133 0.4333 AUGUST 6 1993.52 0.0800 0.1333 0.0533 0.1600 0.2933 9 2052.62 0.0933 0.0733 0.0800 0.1467 0.4133 12 2111.72 0.0133 0.0267 0.1000 0.0867 0.3933 16 2190.37 0.0 0.0667 0.0467 0.0933 0.2867 20 2268.97 0.0 0.0400 0.0800 0.0800 0.5067 23 2328.13 0.0 0.0067 0.0333 0.1067 0.3533 26 2387.29 0.0 0.0067 0.0800 0.0600 0.4400 30 2466.92 0.0 0.0467 0.0467 0.0600 0.4667 SEPTEMBER 4 2566.77 0.0 0.0133 0.0067 0.0053 0.4333 6 2606.71 0.0 0.0133 0.0200 0.0200 0.3733 9 '2666.62 0.0 0.0 0.0 0.0267 0.3600 13 2742.99 0.0 0.0 0.0 0.0200 0.2733 17 2818.19 0.0 0.0 0.0 0.0 0.1600 27 2977.79 0.0 0.0 0.0 0.0 0.3000 OCTOBER 1 3033.79 0.0 0.0 0.0 0.0 0.1333 4 3075.79 0.0 0.0 0.0 0.0 0.2000 11 3161.79 0.0 0.0 0.0 0.0 0.0933 15 3246.24 0.0 0.0 0.0 0.0 0.0 296. APPENDIX 3e : Continued. 3. Continued. C. parallelus - SITE 2, 1979 DATE DAY DEGREES I II III IV ADULTS JUNE 1 0.0 0.0 0.0 0.0 0.0 0.0 5 104.68 0.1600 0.0 0.0 0.0 0.0 8 183.95 0.0400 0.0 0.0 0.0 0.0 15 372.46 0.3067 0.0 0.0 0.0 0.0 18 458.77 0.1867 0.0400 0.0 0.0 0.0 19 487.54 0.2133 0.0200 0.0 0.0 0.0 22 547.21 0.3200 0.0333 0.0 0.0 0.0 JULY 3 766.00 0.4533 0.1133 0.0067 0.0 0.0 6 850.81 0.4667 0.1400 0.0067 0.0200 0.0 10 963.89 0.4800 0.1600 0.1000 0.0667 0.0067 13 1039.97 0.5867 0.1133 0.1267 0.1067 0.0400 17 1141.41 0.3200 0.1467 0.2133 0.1933 0.0533 20 1191.21 0.1600 0.1733 0.1467 0.1800 0.0733 24 1257.61 0.2400 0.1733 0.1933 0.2000 0.2133 27 1316.41 0.1733 0.1000 0.1133 0.1133 0.1000 AUGUST 7 1532.01 0.2000 0.2867 0.2933 0.1667 0.2933 10 1604.22 0.1733 0.1667 0.1333 0.1733 0.3200 14 1700.50 0.0889 0.0444 0.0778 0.1222 0.3222 21 1867.66 0.0933 0.1200 0.2133 0.1933 0.3000 28 2042.80 0.0933 0.0667 0.1600 0.1933 0.3667 31 2094.25 0.0 0.1400 0.1667 0.1600 0.3067 SEPTEMBER 4 2162.85 0.0267 0.0600 0.0467 0.1067 0.3333 7 2214.30 0.0133 0.0400 0.0800 0.0733 0.3267 10 2265.75 0.0 0.0133 0.0600 0.0667 0.2867 14 2355.70 0.0 0.0 0.0067 0.0400 0.2733 21 2477.10 0.0 0.0 0.0 0.0133 0.0867 25 2541.90 0.0 0.0 0.0 0.0200 0.1467 28 2586.90 0.0 0.0 0.0 0.0 0.0 297. APPENDIX 3e : Continued. 3. Continued. C. parallelus - SITE 3, 1979 DATE DAY DEGREES I II III IV ADULTS JUNE 14 0.0 0.0 0.0 0.0 0.0 0.0 17 69.69 0.1333 0.0 0.0 0.0 0.0 20 139.38 0.2000 0.0267 0.0 0.0 0.0 23 232.30 0.2133 0.0800 0.0 0.0 0.0 JULY 1 302.23 0.1600 0.1333 0.0200 0.0 0.0 4 469.15 0.0533 0.1933 0.0267 0.0 0.0 8 567.39 0.0667 0.0933 0.1467 0.0200 0.0 11 643.83 0.0 0.1400 0.1867 0.1067 0.0 15 745.75 0.0 0.0133 0.1200 0.1333 0.0200 18 809.74 0.0 0.0133 0.0733 0.1267 0.0067 22 895.06 0.0 0.0 0.0467 0.1067 0.0133 25 960.34 0.0 0.0 0.0200 0.0600 0.0200 AUGUST 5 1199.46 0.0 0.0 0.0 0.0600 0.1267 10 1333.21 0.0 0.0 0.0 0.0333 0.2000 15 1460.78 0.0 0.0 0.0 0.0133 0.0800 19 1559.54 0.0 0.0 0.0 0.0133 0.0533 23 1657.98 0.0 0.0 0.0 0.0067 0.0333 27 1756.42 0.0 0.0 0.0 0.0 0.0533 SEPTEMBER 1 1867.67 0.0 0.0 0.0 0.0 0.0467 13 2153.62 0.0 0.0 0.0 0.0 0.0333 17 2232.04 0.0 0.0 0.0 0.0 0.0 APPENDIX 3e : Continued. 3. Continued. C. brunneus - SITE 1, 1979 DATE DAY DEGREES I II III IV ADULTS MAY 25 0.0 0.0 0.0 0.0 0.0 0.0 28 75.96 0.0267 0.0 0.0 0.0 0.0 29 96.82 0.1200 0.0 0.0 0.0 0.0 JUNE 1 159.40 0.2267 0.0 0.0 0.0 0.0 4 221.98 0.2667 0.0 0.0 0.0 0.0 8 329.66 0.5200 0.0 0.0 0.0 0.0 14 491.39 0.3600 0.0200 0.0 0.0 0.0 18 599.35 0.8100 0.0400 0.0 0.0 0.0 21 678.01 0.7067 0.0267 0.0 0.0 0.0 JULY 2 966.43 1.3333 0.1867 0.0067 0.0 0.0 5 1049.13 1.1067 0.2000 0.0133 0.0 0.0 9 1162.09 1.1200 0.1933 0.0800 0.0267 0.0 12 1246.72 1.2267 0.2133 0.0800 0.0267 0.0 16 1359.56 0.8400 0.1733 0.1533 0.0267 0.0134 19 1422.68 0.3067 0.1333 0.0600 0.0933 0.0134 23 1506.84 0.1733 0.2533 0.0800 0.0800 0.0333 26 1587.72 0.2933 0.1667 0.1067 0.1133 0.0467 30 1695.62 0.0933 0.0867 0.1400 0.1000 0.0467 AUGUST 6 1871.32 0.1200 0.0667 0.1067 0.1067 0.0800 9 1930.42 0.0667 0.0400 0.0667 0.0667 0.1000 12 1989.52 0.0 0.0467 0.0800 0.0400 0.0867 16 2068.17 0.0133 0.0533 0.0400 0.1067 0.0800 20 2146.77 0.0 0.0400 0.0467 0.0800 0.0800 23 2205.93 0.0 0.0400 0.0267 0.0733 0.1200 26 2265.09 0.0 0.0133 0.0667 0.0867 0.1067 30 2344.72 0.0 0.0133 0.0133 0.0600 0.1066 SEPTEMBER 4 2444.57 0.0 0.0133 0.0133 0.0133 0.1333 6 2484.51 0.0 0.0 0.0067 0.0067 0.1000 9 2544.42 0.0 0.0 0.0 0.0200 0.0667 13 2620.79 0.0 0.0 0.0 0.0133 0.0800 17 2695.99 0.0 0.0 0.0 0.0 0.0667 27 2855.59 0.0 0.0 0.0 0.0 0.0733 OCTOBER 1 2911.59 0.0 0.0 0.0 0.0 0.0933 4 2953.59 0.0 0.0 0.0 0.0 0.0667 11 3039.59 0.0 0.0 0.0 0.0 0.0467 15 3085.96 0.0 0.0 0.0 0.0 0.0 APPENDIX 3e : Continued. 3. Continued. C. brunneus - SITE 2, 1979 DATE DAY DEGREES I II III IV ADULTS JUNE 12 0.0 0.0 0.0 0.0 0.0 0.0 15 80.79 0.1333 0.0 0.0 0.0 0.0 18 167.10 0.0800 0.0 0.0 0.0 0.0 19 195.87 0.0533 0.0 0.0 0.0 0.0 22 255.54 0.1600 0.0 0.0 0.0 0.0 JULY 3 474.33 0.4533 0.0133 0.0 0.0 0.0 6 559.14 0.4533 0.0400 0.0267 0.0 0.0 10 672.22 0.5600 0.0800 0.0133 0.0267 0.0 13 748.30 0.8267 0.1067 0.0533 0.0400 0.0 17 849.74 0.4533 0.1067 0.0533 0.0800 0.0133 24 965.94 0.3467 0.0800 0.0800 0.0667 0.0133 27 1024.74 0.1333 0.0133 0.0267 0.0667 0.0533 AUGUST 7 1240.34 0.0267 0.0133 0.0400 0.0400 0.0267 10 1312.55 0.0267 0.0533 0.0133 0.0133 0.0933 14 1408.83 0.0 0.0 0.0 0.0667 0.1333 21 1575.99 0.0 0.0 0.0 0.0133 0.0934 28 1751.13 0.0 0.0 0.0 0.0133 0.1200 31 1802.58 0.0 0.0 0.0 0.0 0.0933 SEPTEMBER 4 1871.18 0.0 0.0 0.0 0.0 0.0400 13 1981.58 0.0 0.0 0.0 0.0 0.0 300. APPENDIX 3e : Continued. 3. Continued. C. brunneus - SITE 3, 1979 DATE DAY DEGREES I II III IV ADULTS JUNE 14 0.0 0.0 0.0 0.0 0.0 0.0 17 64.86 0.0800 0.0 0.0 0.0 0.0 20 134.55 0.0533 0.0 0.0 0.0 0.0 24 227.47 0.1600 0.0 0.0 0.0 0.0 27 297.40 0.2667 0.0400 0.0 0.0 0.0 JULY 4 464.32 0.2933 0.0400 0.0 0.0 0.0 8 562.56 0.1333 0.0667 0.0133 0.0 0.0 11 639.00 0.2400 0.0933 0.0133 0.0 0.0 15 740.92 0.0267 0.0677 0.0667 0.0133 0.0 18 804.91 0.0533 0.0267 0.0400 0.0533 0.0 22 890.23 0.0533 0.0133 0.0533 0.0533 0.0 25 955.51 0.1067 0.0133 0.0267 0.0400 0.0267 AUGUST 5 1194.63 0.0 0.0400 0.0533 0.0133 0.0667 10 1328.38 0.0 0.0533 0.0533 0.0267 0.0800 15 1455.95 0.0 0.0133 0.0533 0.0533 0.0800 19 1554.71 0.0 0.0133 0.1067 0.0400 0.0533 23 1653.15 0.0 0.0 0.0267 0.0133 0.0400 27 1751.59 0.0 0.0 0.0267 0.0400 0.0400 SEPTEMBER 1 1862.84 0.0 0.0 0.0 0.0 0.0533 6 1992.09 0.0 0.0 0.0 0.0 0.0 301. APPENDIX 3f : Change in nymphal cohorts of C. parallelus and C. brunneus in field cages, 1978. C. parallelus SITE 1 SITE 2 DAY DAY DATE I II III IV AD. TOTAL DATE I II III IV AD. TOTAL DEGREES DEGREES CAGE 1 CAGE 1 20/6 30 30 0 10/7 30 30 0 27/6 12 4 16 92.12 17/7 9 4 13 117.67 4/7 4 4 8 241.45 24/7 4 1 5 231.92 11/7 8 8 394.87 31/7 4 1 5 365.84 18/7 2 1 3 548.31 7/8 4 1 5 476.04 25/7 2 1 3 679.89 14/8 3 1 4 580.69 1/8 1 1 2 884.21 21/8 1 1 2 718.60 8/8 2 2 1037.86 28/8 1 1 836.19 15/8 1 1 1191.51 22/8 1 1 1339.49 CAGE 2 CAGE 2 27/6 30 30 0 10/7 30 30 0 4/7 12 4 16 147.33 17/7 16 7 23 117.67 11/7 4 9 13 302.75 24/7 2 17 19 231.92 18/7 1 8 9 456.19 31/7 8 8 16 365.84 25/7 2 7 9 587.77 7/8 2 9 11 476.04 1/8 5 2 7 792.09 14/8 7 7 580.69 8/8 7 7 945.74 21/8 5 5 718.60 15/8 6 1 7 1099.39 28/8 4 4 836.19 22/8 6 6 1247.37 4/9 4 4 920.06 11/9 2 2 1026.32 CAGE 3 4/7 30 30 0 11/7 10 13 23 153.42 18/7 11 11 306.88 25/7 6 1 7 438.46 1/8 5 2 7 642.78 8/8 5 1 6 798.43 15/8 1 3 4 950.08 22/8 1 1 1098.04 302. APPENDIX 3f : Continued. C. brunneus SITE 1 SITE 2 DAY DAY DATE I II III IV AD. TOTAL DATE I II III IV AD. TOTAL DEGREES DEGREES CAGE 1 CAGE 1 20/6 30 30 0 10/7 30 30 0 27/6 13 1 14 92.12 17/7 15 2 17 117.67 4/7 5 7 12 241.45 24/7 2 5 7 231.92 11/7 12 12 394.87 31/7 4 1 5 365.84 18/7 3 2 5 548.31 7/8 1 3 4 476.04 25/7 2 3 5 679.89 14/8 2 2 580.69 1/8 3 1 4 884.21 21/8 2 2 718.60 8/8 2 2 1037.36 28/8 1 1 2 836.19 15/8 2 2 1191.51 4/9 2 2 920.06 22/8 2 2 1339.49 11/9 2 2 1026.32 CAGE 2 27/6 30 30 0 4/7 9 3 12 149.33 11/7 11 11 302.75 18/7 9 2 11 456.19 25/7 4 3 7 587.77 1/8 3 2 5 792.09 8/8 1 1 2 945.74 15/8 1 1 1099.39 22/8 1 1 1247.37 CAGE 3 20/6 30 30 0 27/6 11 6 17 92.12 4/7 4 12 16 241.45 11/7 16 16 394.87 18/7 8 5 13 548.31 25/7 5 6 11 679.89 1/8 5 5 10 884.21 8/8 2 8 10 1037.86 15/8 8 2 10 1191.51 22/8 3 4 7 1339.49 29/8 7 7 1433.54