Species Roles and Link Roles: a Richer Perspective on Network Ecology
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Species roles and link roles: a richer perspective on network ecology Alyssa R. Cirtwill Submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at the University of Canterbury School of Biological Sciences University of Canterbury New Zealand 2016 Dedicated to my family and to my friends near and far. Your love, support, and encouragement made this possible. The more accurate the map, the more it resembles the territory. The most accurate map possible would be the territory, and thus would be perfectly accurate and per- fectly useless. The tale is the map that is the territory. –Neil Gaiman Table of Contents Contents v Abstract ix Preface xi Co-authorship statements xiii General introduction 1 Bibliography............................. 8 Chapter 1: Species’ roles in food webs 13 Introduction ............................. 14 Concepts of species’ roles in networks . 15 Grouping species with similar roles . 24 Limitations to role concepts and future directions . 30 Conclusions ............................. 33 Acknowledgements. 34 Box 1:Glossary ........................... 35 Bibliography............................. 36 Chapter 2: Knowledge of predator-prey interactions improves predictions of immigration and extinction in island biogeography 51 Abstract................................ 52 Keywords .............................. 52 Introduction ............................. 53 Methods ............................... 55 Results ................................ 62 Discussion .............................. 68 Acknowledgements. 71 Supportinginformation . 71 Bibliography............................. 72 vi Chapter 3: Conservation of interaction partners between related plants varies widely across communities and be- tween plant families. 77 Summary............................... 78 Keywords .............................. 78 Introduction ............................. 79 Materialsandmethods . 81 Results ................................ 86 Discussion .............................. 89 Acknowledgements. 93 Authorcontribution. 93 Supportinginformation . 93 Bibliography............................. 94 Chapter 4: Are high-arctic plant-pollinator networks unravel- ling in a warming climate? 99 Abstract................................ 100 Keywords .............................. 100 Introduction ............................. 101 MaterialsandMethods. 103 Results ................................ 111 Discussion .............................. 118 Acknowledgements. 122 Supportinginformation . 122 Bibliography............................. 123 Chapter 5: Concomitant predation on parasites is highly variable but constrains the ways in which parasites contribute to food-web structure. 129 Summary............................... 130 Keywords .............................. 130 Introduction ............................. 131 Materialsandmethods . 137 Results ................................ 142 Discussion .............................. 144 Conclusions ............................. 147 Acknowledgements. 148 Dataaccessibility . 148 SupportingInformation . 148 Bibliography............................. 150 Chapter 6: Taking the scenic route: trophic transmission of parasites and the properties of links along which they travel. 157 Abstract................................ 158 Keywords .............................. 158 vii Introduction ............................. 159 Methods ............................... 161 Results ................................ 167 Discussion .............................. 170 Acknowledgements. 174 Supportinginformation . 174 Bibliography............................. 175 General discussion 179 Summaryofresults. ... .... .... .... ... .... .. 179 Implications ............................. 181 Nextsteps .............................. 183 Conclusion.............................. 186 Bibliography............................. 187 Appendix: Are parasite richness and abundance linked to prey species richness and individual feeding preferences in fish hosts? 191 Summary............................... 192 Keywords .............................. 192 Introduction ............................. 193 MaterialandMethods . 196 Results ................................ 201 Discussion .............................. 206 Acknowledgements. 211 FinancialSupport . 211 Bibliography............................. 212 Supporting Information S2 219 S2.1:Fullmodels .......................... 220 S2.2:Best-fitmodels ........................ 224 S2.3:Summarytablesforbest-fitmodels . 226 S2.4: Details of models not described in the main text . 228 S2.5: Cumulative species richness plots for islands not showninthemaintext. 235 Supporting Information S3 239 S3.1. Original sources for networks . 240 S3.2. Supplemental within-network results . 242 S3.3. Supplemental within-family results . 243 Bibliography............................. 245 Supporting information S4 251 S4.1 - Simulated dates of first interaction . 252 S4.2 - Tentatively-dated observations: methods . 258 viii S4.3 - Tentatively-dated observations: results . 259 S4.4 -Supplementalfigures . 262 Supporting Information S5 263 S5.1. Additional References and Description of Food Webs . 264 S5.2. Supplemental methods: quantifying species’ and links’ roles............................... 266 S5.3. Supplemental methods: role dispersion & diversity . 267 S5.4. Supplemental results: median roles . 269 S5.5. Supplementalresults: speciesroles. 271 S5.6.Linkroles ........................... 273 Bibliography............................. 276 Supporting Information S6 279 S6.1: Detailed methods for data collection . 280 S6.2: Supplemental methods and results for links’ structural properties ........................... 294 S6.3:Resultsofmodelselection . 297 S6.4: Testing for correlations between link properties . 298 Bibliography............................. 301 Supporting Information SA 305 S7.1. Supplemental results: biomass of trophically transmit- tedparasites .......................... 306 Acknowledgements 309 Abstract Food webs and other ecological networks can be seen as maps of species and their interactions (e.g., predation, pollination, and parasitism). Such mappings frame the complex intricacies of biological communities in a way that is analytically tractable, but also obscure species-level information. This can lead to a gap between studies of networks and the deep literature surrounding species’ idiosyncratic ecologies. Species roles— descriptions of the way each species is embedded into its community —offer one way to bridge this gap. As roles provide a species-level perspective on network structure, patterns in species roles can often be related to species traits in a way that the overall structure of a network usually cannot. Thus, role-based approaches give network ecologists a way to use species’ natural histories to understand patterns in network structure while also making network analyses more approachable for ecologists with different specialities. This thesis uses a variety of definitions of species roles to explore a variety of ecological networks, demonstrating the broad range of questions to which species roles may be applied. The first chapter provides an overview of several different role concepts used in network ecology, and the second through fifth chapters each use one or more role concept to investigate specific ecological questions. Chapter two uses species roles to incorporate a predator-prey network into the Theory of Island Biogeography. Chapter three uses species roles to compare the overlap of plants’ interaction partners in plant-pollinator and plant-herbivore networks, while chapter four explores the changes to plants’ and insects’ roles in a single plant- pollinator network over 15 years of climate change. Chapters five and six are focused on aquatic food webs that include parasites. Chapter five compares the roles of parasites and free-living species, as well as different types of interactions between them (i.e., predation among free-living species, parasitism, antagonism among parasites, and x concomitant predation on parasites inside their hosts). Chapter six uses the roles of feeding links between free-living species to better understand the trophic transmission of parasites. Finally, in an appendix we show how individual variation in fishes diets affect their parasite loads. The key findings of this thesis are i) that using species roles to incorporate information from food webs improves the predictions of the Theory of Island Biogeography, ii) that more closely related plants had more similar sets of interaction partners despite a great deal of variation across networks and between plant families, iii) that the roles of plants and pollinators have shown different changes after 15 years of warming, suggesting that phenological uncoupling may be a risk for this system, iv) that parasites and free-living species have different roles in food webs, but only when concomitant predation was considered, and v) that many properties of feeding links between free-living species affect the outcomes of these links for parasites. As well as providing answers to the driving questions behind each chapter, this thesis demonstrates the breadth of potential applications for species roles. We conclude species roles provide a framework that speaks to the heart of one of the fundamental unsolved questions in ecology— how species’ traits relate to the structure of ecological networks. Preface This thesis has been written as a series of stand-alone scientific articles which nevertheless