Investigating Causal Relationships between Global Change and Insect Interaction Networks: Insights into Dietary Specialization, Interaction Diversity, and Disturbances
Anthropogenic activities over the past century have driven accelerated global change, including dramatic losses of biodiversity. In this dissertation, I investigated causal relationships between global change and diversity of insect interaction networks through quantifying effects of biotic and abiotic gradients on dietary specialization, interaction diversity, and related attributes of arthropod communities. My focus on how specialization varies across gradients and is affected by global change addressed a classic hypothesis, the "jack-of-all-trades is a master of none" assumption about specialization in insect herbivores. I estimated associations between dietary specialization and abundance of caterpillars using 18-years of plant-caterpillar data from Ecuadorian forests across elevational gradients and found that specialists are locally more abundant than generalists, and generalists occupy more space across all elevations and habitats. At a larger scale, I examined latitudinal gradients in network specialization and interaction diversity using long-term plant-caterpillar-parasitoid datasets from temperate and tropical regions. I found a weak but detectable latitudinal gradient in interaction diversity with the highest interaction diversity at low latitudes due to the combination of greater species diversity and greater abundance of specialists towards the equator. As a more direct test of future global change on arthropod networks, I examined a temporal gradient in arthropod networks before and after fire disturbance in the eastern Sierra Nevada mountains. I found that a prescribed fire created classic early successional habitat, allowing for random recruitment of arthropods using post-fire plants and detritus. The initial increase in primary consumers and taxonomic diversity 1 year post fire was followed by a reduction in the abundance of primary producers due to increases in other trophic levels and a move towards pre-fire network structure. These fire community results are consistent with a healthy 10-year fire return interval for Sierra Nevada communities, and continued suppression or increased drought and fire intensity are likely to disrupt that interval. The results from all the dissertation research reported here are relevant to conservation and habitat management, as interactions are more tightly linked to ecosystem function and ecosystem services and are likely to be more susceptible to anthropogenic stressors.
Biodiversity, Dietary specialization, Environmental disturbance, Interaction diversity, Plant-insect interaction
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