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T a b l e o f c o n t e n t s

1. Introduction 1

2. Material and methods 8

2.1. Study sites 8

2.2. Climate measurements and sampling of arthropods 10

2.3. Sampling and processing of Evernia prunastri thalli 13

2.4. Processing of data and statistical analysis 14

2.4.1. Analysis of climate measurements 14

2.4.2. Analysis of the animals' use of different climates 16

2.4.3. Analysis of the animals' microhabitat use 17

2.5. Determination and nomenclature 19

2.6. Species list and sample size 19

3. Results 22

3.1. Analysis of microclimatic living conditions on exposed tree trunks 22

3.1.1. Absolute microclimatic conditions 22

3.1.1.1. Multiple regression analysis 22

3.1.1.2. Univariate analysis of categorial factors 25

3.1.2. Climatic differences between the trunk and the macroclimate 26

3.1.2.1. Multiple regression analysis 26

3.1.2.2. Univariate analysis of categorial factors 29

3.1.3. Climatic zonations at the trunk surface 30

3.1.4. An example of microclimatic patterns 31

3.1.5. Balances of direct and indirect effects of single variables 32

3.2. Use of climatic gradients by corticolous arthropods 34

3.2.1. Use of the microclimate: heat, humidity, scale and zonations 34

3.2.2. Use of the seasonal climates: opportunities for migration between soil

and crown 42

3.2.3. Use of moist macroclimates: foraging opportunities for drought-sensitive

animals 43

3.2.4. Use of rainy weather: opportunities to avoid soil soaking 44

3.2.5. Use of wind exposure: opportunities to achieve wind dispersal 46

3.3. Use of discrete microhabitats (cryptogam species, crevice types) by

corticolous arthropods 47

3.3.1. Average use of microhabitat types 47

3.3.2. Microhabitat use of different age-classes 50

3.3.3. Effect of climate on microhabitat use 50

3.3.3.1. Univariate analysis 50

3.3.3.2. Discriminant function analysis 58

3.3.4. Effect of patch size on the microhabitat use 62

3.4. Morphogenesis of the heavily grazed and wind-exposed lichen

Evernia prunastri 64

3.4.1. Morphogenetic patterns of branches 64

3.4.2. Correlation between arthropod grazing and the growth of branches 64

3.4.3. Correlation between climatic exposure, the growth of branches and the

growth form of whole thalli 66

4. Discussion 71

4.1. Analysis of microclimatic living conditions on exposed tree trunks 71

4.1.1. Causes of temperature differences between trunk and macroclimate 71

4.1.2. Causes of water vapour pressure differences between trunk and

macroclimate 72

4.1.3. Conclusions on the climatic suitability of exposed tree trunks for

arthropods 75

4.1.3.1. Climatic disadvantages compared to alternative habitats 75

4.1.3.2. Climatic advantages and possible adaptive strategies of arthropods 77

 

4.2. Use of climatic gradients by corticolous arthropods 79

4.2.1. Significance of climate use: Which benefits of trunk colonisation are

achieved? 79

4.2.1.1. Interpretability of the data 79

4.2.1.2. Microclimatic benefits 82

4.2.1.3. Connection between soil and crown 86

4.2.1.4. Access to food due to moist macroclimates 86

4.2.1.5. Shelter from soil soaking 87

4.2.1.6. Access to wind dispersal 88

4.2.2. Prerequisites: Does the climate use depend on r/K/A-life strategy traits

(taken from the literature) 88

4.3. Use of discrete microhabitats (cryptogam species, crevice types) by

corticolous arthropods 91

4.3.1. Significance of microhabitat use for the supply of food and climatic

microshelters 91

4.3.2. Alternative explanations for microhabitat use 91

4.3.3. Conclusions: adaptive value and prerequisites of microhabitat use 98

4.4. Morphogenesis of the heavily grazed and wind-exposed lichen

Evernia prunastri 100

4.4.1. Growth of branches 100

4.4.2. Growth form of whole thalli 102

4.4.3. Fruticose (shrub-like) growth in other exposed cryptogams 103

4.5. Resumé 104

5. SUMMARY 105

6. ZUSAMMENFASSUNG 109

7. Acknowledgements 114

8. Literature 115

List of tables

Tab. 1: Multiple regression analyses of temperature and saturation

deficits at the trunk 23

Tab. 2: Multiple regression analyses of differences in temperature and

water vapour pressure between boundary layer and macroclimate 27

Tab. 3: Path analyses of the multiple and indirect effects of climatic

variables on the trunk microclimate 33

Tab. 4: Summary of the climatic patterns, which are most relevant for the

heat and humidity supply and are used for comparison to the

animals' distribution 36

Tab. 5: Summary of average microhabitat use patterns 49

Tab. 6: Discriminant function analyses of the spatio-temporal use of

microhabitats 59

Tab. 7: Typical morphological features of Evernia prunastri branches 65

Tab. 8: Correlation between cross-section and growth type of Evernia

prunastri branches 65

Tab. 9: Correlation of wind exposure and grazing with the growth of

branches and complete thalli of Evernia prunastri 101

List of figures

Fig. 1: Structure of the investigated microhabitats 9

Fig. 2: Differentiation of climatic exposures on a trunk (scheme) 11

Microclimatology:

Fig. 3: Compensation of temperature increase between trunk faces by an

increase in water vapour pressure 24

Fig. 4: Effect of sun exposure of a trunk face on saturation deficits 25

Fig. 5: Monthly changes of trunk climate 26

Fig. 6: Diurnal changes of trunk climate 26

Fig. 7: Water vapour pressure differences between trunk and

macroclimate depending on the macroclimate 28

Fig. 8: Water vapour pressure and temperature differences between

trunk and macroclimate depending on season and tree type 29

Fig. 9: Strength of microclimatic zonations on different scales and

during different wind speeds 30

Fig. 10: Reduction of wind speed on different tree types 31

Fig. 11: Example of a microclimatic zonation 32

Arthropod distribution:

Fig. 12: Distributions along microclimatically relevant climatic patterns 37,38

Fig. 13: Distributions within the microclimatic profile at the bark surface 39

Fig. 14: Diurnal abundance dynamic of Entomobrya nivalis on tree types

of different diurnal upheating 40

Fig. 15: Phenology of arthropod species on trunks 43

Fig. 16: Percentage of age classes during different weather conditions

and daytimes 45

Fig. 17: Average densities on different microhabitats 48

Fig. 18: Age class distribution in different microhabitats 51

Fig. 19: Relative use of microhabitats during different climates 53-55

Fig. 20: Discriminant function analyses of microhabitat use 61

Fig. 21: Use of cryptogams of different dominance 63

Growth of Evernia prunastri thalli

Fig. 22: Distribution and development of different types of

Evernia prunastri branches over a thallus 66

Fig. 23: Regeneration of feeding traces 67

Fig. 24: Development of branches with artificial and natural feeding traces 68

Fig. 25: Growth and rupture of differently wind exposed thalli 69

Fig. 26: Profile of water vapour fluxes at the trunk surface (scheme) 74

Fig. 27: Interaction of processes determining Evernia prunastri's growth 103

form and adaptability to wind exposure

"Insects are especially vulnerable to all these factors of the weather because of their small size and proportionately large surface area; the compensation for this is their ability to exploit much more finely graded habitats, escaping from the harsh ambient conditions into more favourable microniches." (WILLMER 1982) "I hope to put microclimatic effects back into the picture as part of an integrated approach to the studies of insects' distributions and herbivory patterns." (WILLMER 1986)

"Soil animals are not organized into well defined communities. The centres and boundaries of species populations are scattered along macro-environmental gradients such that at any points at the gradient a species assemblage is found which has proved extremely difficult to associate with vegetation type or physicochemical factors of the habitat. This situation may be partially the result of failing to define the environmental variables at a scale which is meaningful to the animals and/or not choosing the correct variables to describe the habitat." (ANDERSON 1977)

"The soil and its associated habitats are immensely complex, from the ecological point of view. We are beginning to understand the extent of the microhabitat diversity, but there is still much more to be learned about the reaction of species populations to this diversity." (WALLWORK 1976)

"Some of the more important areas in which information [on lichen-invertebrate associations] is in demand are:

1. Feeding and sheltering specifity...." (GERSON & SEAWARD 1977)

"As information accumulates, however, it is becoming apparent that lichen/moss-arthropod interactions are unique in many ways, and this uniqueness demands a level of investigator creativity at least equal to that of higher-plant-arthropod workers." (LAWREY 1987)

 


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