Biotic interactions in a changing world: the role of feeding interactions in the response of multitrophic communities to rising temperature and nitrogen deposition A thesis submitted in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in the University of Canterbury by Claudio de Sassi School of Biological Sciences University of Canterbury 2012 We can't solve problems by using the same kind of thinking we used when we created them A. Einstein Table of contents Table of contents ........................................................................................................ ii List of figures .............................................................................................................. v List of tables .............................................................................................................. vi Abstract ..................................................................................................................... vii Acknowledgements ................................................................................................... ix Authorship declaration ............................................................................................. xi Chapter I: Introduction ............................................................................................. 1 1.1 A perspective of climate change in ecological research.................................. 1 1.2 How does climate change affect us?................................................................ 2 1.3 The multiple axes of real-world complexity.................................................... 4 1.3.1 Biodiversity and the importance of interactions among species............ 4 1.3.2 Biotic complexity: from species to networks ........................................ 5 1.3.3 Synergistic global environmental change drivers.................................. 7 1.4 Thesis objectives and outline........................................................................... 8 Chapter II: Plant-mediated and non-additive effects of two global change drivers on an insect herbivore community ............................................................ 12 2.1 Abstract.......................................................................................................... 12 2.2 Introduction.................................................................................................... 13 2.3 Material and Methods .................................................................................... 15 2.3.1 Study site.............................................................................................. 15 2.3.2 Experimental design ............................................................................ 16 2.3.3 Vegetation survey ................................................................................ 18 2.3.4 Data analysis........................................................................................ 18 2.4 Results............................................................................................................ 20 2.4.1 Plant community response to the environmental change drivers: ....... 22 ii 2.4.2 Herbivore assemblage response to global change drivers: .................. 22 2.4.3 Relative importance of direct vs. plant mediated effects..................... 23 2.4.4 Phenology of herbivore assemblage and common species.................. 23 2.4.5 Total herbivore biomass....................................................................... 25 2.5 Discussion...................................................................................................... 26 Chapter III: Climate change disproportionately increases herbivore over plant or parasitoid biomass ............................................................................................... 30 3.1 Abstract.......................................................................................................... 30 3.2 Introduction.................................................................................................... 31 3.3 Material and Methods .................................................................................... 33 3.3.1 Study site: altitudinal gradient experiment .......................................... 33 3.3.2 Experimental design and sampling of altitudinal gradient experiment 34 3.3.3 Study site: artificial warming experiment............................................ 35 3.3.4 Experimental design and sampling of warming experiment ............... 36 3.3.5 Insect rearing........................................................................................ 38 3.3.6 Biomass measurements........................................................................ 39 3.3.7 Data analysis........................................................................................ 40 3.4 Results............................................................................................................ 42 3.4.1 Altitudinal gradient experiment........................................................... 42 3.4.2 Warming experiment ........................................................................... 44 3.5 Discussion...................................................................................................... 47 Chapter IV: Bottom-up effects mediate response of food-web structure and resilience to climate change and nitrogen deposition ........................................... 51 4.1 Abstract.......................................................................................................... 51 4.2 Introduction.................................................................................................... 52 4.3 Material and Methods .................................................................................... 55 4.3.1 Study sites and sampling: altitudinal gradient experiment.................. 55 4.3.2 Study sites and sampling: artificial warming experiment.................... 56 4.3.3 Insect identification and quantification of feeding links ..................... 57 4.4.4 Data analysis........................................................................................ 58 4.4 Results:........................................................................................................... 67 iii 4.5 Discussion...................................................................................................... 76 Chapter V: Climate and nitrogen affect size-structuring of a host parasitoid food web .................................................................................................................... 80 5.1 Abstract.......................................................................................................... 80 5.2 Introduction.................................................................................................... 81 5.3 Material and Methods .................................................................................... 83 5.3.1 Study site and experimental set up ...................................................... 83 5.3.2 Insect identification and body size measures....................................... 85 5.3.3 Data analysis........................................................................................ 86 5.4 Results............................................................................................................ 90 5.5 Discussion...................................................................................................... 99 Chapter VI: Discussion ......................................................................................... 102 6.1 Summary...................................................................................................... 104 6.1.1 Plant-mediated and non-additive effects of two global change drivers on an herbivore community............................................................. 104 6.1.2 Climate change disproportionately increases herbivore over plant or parasitoid biomass............................................................................ 105 6.1.3 Bottom-up effects mediate the response of food-web structure and resilience to climate change and nitrogen deposition ...................... 106 6.1.4 Climate and nitrogen affect size-structuring of a host-parasitoid food web................................................................................................... 107 6.2 Outlook ........................................................................................................ 108 6.3 Final conclusions ......................................................................................... 110 Bibliography ........................................................................................................... 112 Appendix 1 .............................................................................................................. 135 Appendix 2 .............................................................................................................. 158 Appendix 3 .............................................................................................................. 162 iv List of figures Figure 1.1: Publication report..................................................................................... 2 Figure 2.1: Flow diagram ......................................................................................... 21 Figure 2.2: Herbivore phenological response..........................................................