Global Change and trophic interaction diversity: complex local and regional processes
AuthorPardikes, Nicholas Alexander
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The structure and functioning of ecosystems across the globe are rapidly changing due to several components of global environmental change (GEC). My dissertation aims to illustrate how regional and local aspects of GEC impact diverse assemblages of species and species interactions. All organisms are embedded in complex networks of species interactions, and future efforts to predict and mitigate the impacts of GEC on ecological communities will be facilitated by such studies that incorporate a suite of species and species interactions. This study advances our understanding of how GEC will impact ecological communities by investigating two questions about GEC: 1) How will shifts in global climate cycles (e.g., El Nino Southern Oscillation), as a consequence of global warming, impact a diverse assemblage of butterflies that exist across a heterogeneous landscape? 2) What are the consequences of woody plant encroachment on complex, specialized interactions between plants, insect herbivores, and natural enemies (e.g., insect parasitoids)? Furthermore, I helped develop a tool to identify characteristics of ecological communities that are essential for promoting the diversity of trophic interactions. While the loss of species diversity is well recognized, interactions among species are vanishing at an astonishing rate, yet we know little about factors that determine the diversity of interactions within a community. Using data from a long-term butterfly monitoring dataset, I was able to demonstrate the utility of large-scale climate indices (e.g., ENSO) for modeling biotic/abiotic relationships for migratory butterfly species. Next, I used encroaching juniper woodlands in the Intermountain West to uncover that population age structure of dominant tress, such as juniper, can affect plant-insect dynamics and have implications for future control efforts in the expanding woodlands. Additionally, reductions of understory plant diversity, as a consequence of juniper expansion, resulted in significantly lower parasitism rates and parasitoid species diversity. Finally, simulated food webs revealed that species diversity and, to a lesser degree, consumer diet breadth, promote the diversity of trophic interactions. As ecosystems across the globe experience changes and the loss of species diversity continues, these findings offer insight into how GEC will impact species and species interactions.