DISSERTATION RESEARCH: Soil resource variability as a driver of interactions within, and emergent properties of, tritrophic ecological networks

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A key goal in ecology is understanding how and why environmental variation shapes species interactions. Food webs describe the feeding relationships between organisms, and illustrate the ecological roles of plants and animals in natural communities. Food webs also describe how the entire suite of feeding interactions might function. Understanding how and why food webs differ between places is important because it can help predict ecological impacts of environmental change such as species loss or habitat change. In this project, researchers will study how changes in soil nutrients cause differences in food webs. The research focuses on the feeding interactions between plants and caterpillars, and between caterpillars and their predators. By documenting "who eats whom" in Northern California soils of low versus high fertility, this project will be able to describe complex food webs and ask how these webs are different across soil types. Because most of our understanding of this topic comes from agricultural ecosystems that have soils impacted by fertilizer, this project will provide new insights as it is based on soils that naturally vary in fertility. This research will involve several undergraduate students and an ecology club. Variation in soil resources is a ubiquitous form of environmental heterogeneity, with strong direct and indirect effects on organismal traits and species interactions. Multiple theories address the effects of resource level on trophic interactions: the Resource Availability Hypothesis (RAH) suggests that resource availability should shape plant traits and, consequently, their quality to herbivores; in turn, the Slow Growth, High Mortality (SGHM) and High Performance, High Mortality Hypotheses (HPHM) relate plant quality to interactions between herbivores and natural enemies. Based on these theories, this research will disentangle the interacting roles of predation and nutritive and defensive plant traits in shaping plant-caterpillar-top predator tri-trophic interactions. Using a natural mosaic of low fertility serpentine and higher fertility non-serpentine soils in California, this project will build exclusion cages to assess how top-predators affect plant-caterpillar interactions across different soil types. Plant nutritive and defensive traits will be measured simultaneously to disentangle the relative importance of traits and predation in driving food web structure across different resource contexts. Together, these experiments will advance our understanding of how and why species interactions vary across heterogeneous landscapes.