Quantitative population and community dynamics

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On ecological timescales, the distribution and abundance of species depends on local species interactions like competition which determine birth and death rates, and dispersal among local sites. The focus of my research program is to understand how larger-scale patterns in ecology emerge from the fundamental processes that determine abundances: birth, death, and movement. This is a challenging problem because rates of birth, death, and movement depend on many factors and can vary greatly among species, locations, and times. My proposal describes two short-term objectives that further my long-term research program: (1) Spatial synchrony. One of the most striking large-scale patterns in ecology is spatial synchrony: spatially-separated populations of the same species all increasing, and decreasing, in abundance in concert, even though some populations are hundreds or even thousands of km from others. Species as different as birds, insects, and human pathogens exhibit spatial synchrony, suggesting that the explanation for synchrony lies in general principles rather than system-specific biology. Building on my previous work, I propose to test previously-untested hypotheses for how spatial synchrony arises from movement of organisms from place to place, and from spatially-synchronized weather fluctuations. If the proposed hypotheses hold, much current thinking will require revisiting. (2) Species coexistence. Competing species from microbes to mammals often coexist for many generations. The mechanisms explaining coexistence often are system-specific. To identify general principles, modern coexistence theory summarizes the consequences of these system-specific mechanisms in terms of a smaller set of abstract, “higher level” mechanisms that can be quantified in any system. New methods make it feasible to quantify these high-level mechanisms. I propose to test hypotheses about how environmental fluctuations, and the number of coexisting species, mediate the strength of high-level coexistence mechanisms. Few studies test hypotheses about the strengths of coexistence mechanisms. I propose to address both objectives with laboratory microcosm communities comprised of fast-growing protists and bacteria. This system allows me to directly manipulate the hypothesized determinants of spatial synchrony and species coexistence, manipulations that are impossible in most other systems. Laboratory microcosms play by the same fundamental rules as natural systems. Microcosm experiments complement field studies by allowing powerful, direct experimental tests of hypothesized general principles. Those general principles apply to species in Canada and elsewhere. Understanding general principles underpins our ability to conserve and manage Canadian species and ecosystems. Besides contributing to fundamental understanding, the proposed work will provide training and research experience for 3 Ph.D. students, 3 M.Sc. students, and 13 undergraduate research assistants.