GÖTTINGER ZENTRUM FÜR BIODIVERSITÄTSFORSCHUNG UND ÖKOLOGIE GÖTTINGEN CENTRE FOR BIODIVERSITY AND ECOLOGY Herb layer characteristics, fly communities and trophic interactions along a gradient of tree and herb diversity in a temperate deciduous forest Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultäten der Georg-August-Universität Göttingen vorgelegt von Mag. rer. nat. Elke Andrea Vockenhuber aus Wien Göttingen, Juli, 2011 Referent: Prof. Dr. Teja Tscharntke Korreferent: Prof. Dr. Stefan Vidal Tag der mündlichen Prüfung: 16.08.2011 2 CONTENTS Chapter 1: General Introduction............................................................................................ 5 Effects of plant diversity on ecosystem functioning and higher trophic levels ....................................................... 6 Study objectives and chapter outline ...................................................................................................................... 8 Study site and study design ................................................................................................................................... 11 Major hypotheses.................................................................................................................................................. 12 References............................................................................................................................................................. 13 Chapter 2: Tree diversity and environmental context predict herb species richness and cover in Germany’s largest connected deciduous forest .................................................... 16 Abstract................................................................................................................................................................. 17 Introduction .......................................................................................................................................................... 18 Methods................................................................................................................................................................. 19 Results................................................................................................................................................................... 25 Discussion............................................................................................................................................................. 30 Acknowledgements................................................................................................................................................ 35 References............................................................................................................................................................. 35 Appendix ............................................................................................................................................................... 42 Chapter 3: Richness, abundance, and community composition of flies (Diptera) across a tree and herb diversity gradient ........................................................................................... 57 Abstract................................................................................................................................................................. 58 Introduction .......................................................................................................................................................... 59 Materials and Methods ......................................................................................................................................... 60 Results................................................................................................................................................................... 65 Discussion............................................................................................................................................................. 72 Acknowledgements................................................................................................................................................ 77 References............................................................................................................................................................. 77 Appendix ............................................................................................................................................................... 83 3 Chapter 4: Herbivory, seed production and seed predation in forest herbs along a tree and herb diversity gradient ................................................................................................... 95 Summary ............................................................................................................................................................... 96 Introduction .......................................................................................................................................................... 97 Materials and Methods ......................................................................................................................................... 99 Results................................................................................................................................................................. 106 Discussion........................................................................................................................................................... 113 Acknowledgements.............................................................................................................................................. 118 References........................................................................................................................................................... 118 Appendix ............................................................................................................................................................. 124 Chapter 5: Synopsis ............................................................................................................. 128 Synopsis .............................................................................................................................................................. 129 References........................................................................................................................................................... 131 Summary............................................................................................................................... 132 Zusammenfassung................................................................................................................ 134 Acknowledgements............................................................................................................... 137 Curriculum Vitae ................................................................................................................. 138 Publication list ...................................................................................................................... 139 Thesis declarations ............................................................................................................... 140 4 CHAPTER 1 General Introduction 5 Effects of plant diversity on ecosystem functioning and higher trophic levels In the light of human-induced biodiversity loss, it is crucial to understand how changing biodiversity alters processes and components of ecosystems. Much research effort has gone into the field of biodiversity – ecosystem functioning relationships, and it was discovered that biodiversity can play a major role for ecosystem processes and properties such as biomass production, nutrient retention and ecosystem stability (Hooper et al. 2005). In many studies, the focus lies on the diversity of plants due to their vital role as primary producers. Biodiversity effects are generally ascribed to two potential mechanisms (Cardinale et al. 2011): (1) Due to differences in functional traits, different species exhibit complementarity in their resource requirements and adaptations to environmental conditions (niche differentiation). Therefore, combinations of species can exploit the resource space more effectively than communities of the same species. (2) Species-rich communities are more likely to contain species with particularly important traits that contribute disproportionally to ecosystem processes (sampling or selection effect). While this effect was first considered as an artefact in biodiversity experiments based on artificially assembled plant communities, some ecologists argue that it is also relevant in natural ecosystems because community composition can in part depend on stochastic processes (Hooper et al. 2005). Plant diversity not only affects ecosystem processes, but also communities of higher trophic level organisms, for instance arthropods associated with plants (Haddad et al. 2009). In particular, herbivore diversity has been shown to increase with increasing plant diversity (Scherber et al. 2010). It is not surprising that herbivores, a trophic group closely tied to plants, respond strongest to a greater variety of different feeding resources, considering that many herbivorous species show some degree of feeding specialisation. However,