Global Change Impacts on Ecological Systems

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My research tests how biotic and abiotic mechanisms interact to regulate the diversity and functioning of ecological systems, and how those mechanisms are transformed by human-based change. At the simplest level, all biological systems are shaped by the pool sizes and flows rates of limiting resources (light, nitrogen, prey). Humans affect diversity and function by dramatically altering these pools and flows, in complicated ways because factors such as climate change, eutrophication, species introductions, and trophic collapse often occur simultaneously. Our lab uses empirical approaches, at scales from local to global, to investigate these issues, targeting both fundamental theory and its application to management. For the next five years, my lab will focus on three objectives: (i) Resource-based plant responses to Arctic change: how warming, precipitation, and N deposition variously affect "Arctic greening" (ii) Diversity, resource retention, and farm impacts: the capacity of diversity to regulate resource uptake on agricultural landscapes, reducing environmental impacts on water, (iii) Resiliency to co-varying changes in resources. How niche-based compensatory responses buffer, or are overwhelmed by, the combined effects of drought and N pollution. These objectives are unified in their goal of untangling the relative influences of biotic processes (species interactions, diversity) and abiotic processes (climate, nutrients) on regulating limiting resources, with implications for ecosystem function (e.g., resistance, resilience, total production). The regulation of resources has always been a central tenet of ecological models describing the creation and maintenance of biological diversity, via ecological and evolutionary pathways. Resource regulation has also become a gateway to understand the mechanistic impacts of global change. This is felt especially acutely with nutrients, with N and P - two of the most important limiting resources for primary productivity - now acting as major pollutants globally. Our work tests reciprocal connections between biotic and abiotic influences on resources in anthropogenic environments. This includes how diversity affects resources via niche complementarity, maximizing uptake and thus production, while reducing availability for invading species (e.g., biotic resistance). It also includes how abiotic factors affect resources, especially when supply exceeds the demand of the plant community (e.g., eutrophication) or fails to meet it (e.g., intense drought).The reciprocal relationship between diversity affecting the environment (via the demand for resources) and the environment affecting diversity (via the supply of resources) captures many of the fundamental mechanisms central to models of community assembly, species coexistence, and niche evolution. It should also predict how human-based environmental change affects these processes, a theme that is central to my research program.