Multispecies interactions: causes and effects of species fluctuations in space and time

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One of the most perplexing challenges to understanding biodiversity lies in determining the importance of fluctuations in species abundances through time and space. Scientists have shown that species-specific fluctuations are necessary to maintain diversity, yet fluctuations are known to contribute to species extinctions. Moreover, most species occur in spatially patchy habitats, which are prone to large fluctuations. Reconciling the opposing consequences of fluctuations requires identifying processes that drive fluctuations, determining when and how these processes dominate ecological dynamics, and understanding why different processes lead to divergent outcomes. In this proposal, my lab will test the prevalence and consequences two poorly-understood sources of fluctuations that are common in patchy habitats. The first, ecological drift, is the process of random change in communities that results from demographic stochasticity, and how this stochasticity is dampened or propagated through ecological interactions. There have been several calls for formalizing drift as a fundamental process in ecology. Our research test the importance of drift in competitive communities, and identify the conditions in which drift overwhelms deterministic processes. This will be complemented by parallel research on drift in food webs, with a focus on how stochasticity scales across trophic levels. Both empirical studies will be used to inform theoretical models that will formalize the importance of habitat patch size, species interactions, among-species differences in demographic stochasticity, and body size on ecological drift. The second part of the proposed research will test the prevalence and effects of fluctuations that result from dynamic feedbacks between local interactions and dispersal. These feedbacks are poorly understood for most systems, yet structure diversity within patches and across landscapes. Importantly, local interactions and dispersal are dependent on temperature, providing a unique opportunity to understand their dynamic feedbacks but also making this understanding imperative for conservation. We will use a specialist plant-herbivore system that is naturally fragmented to estimate the temperature-dependence of herbivore feeding rates, dispersal rates and impacts on plants, and resulting changes in plant patchiness and local abundances of herbivore species. We will use these parameters to predict how chronic temperature change and fluctuating temperatures alter dynamic feedbacks between local interactions and dispersal, and test these predictions using observational studies and large-scale experimental metacommunities. Overall, these studies of causes and consequences of species fluctuations will address fundamental gaps in understanding how biodiversity is maintained, and provide new insights for conservation in an era of global change.