A predictive approach to the continental distributions of species

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Species are distributed very unevenly over the Earth. What determines the spatial distributions of species? Why are there more species in some places than in others? Why do ranges sizes vary? How do human activities affect the capacity of the environment to accommodate species? These are among the most fundamental questions about natural ecological systems. Their answers are crucial to predicting the effects of global climate change and habitat modification. ******The long-term goals of my research are: 1) to document the main patterns in the geographic distribution of biodiversity; 2) to identify predictive relationships between biodiversity and characteristics of the environment; and 3) to propose and test simple, process-based models that accurately predict those variations. My research has four main themes:******Theme I: Earlier work from my lab showed that broad-scale geographic variation in species richness is strongly correlated to contemporary climate. These correlations probably reflect a causal link, because they accurately predict variations of richness through time and in other geographic regions. We have tested and rejected several hypotheses about underlying mechanisms, but we have not yet identified the processes that produce variations of biodiversity in nature.******To identify these processes, I plan to develop and test a model of continental biogeography, inspired by MacArthur and Wilson's Equilibrium Theory of Island Biogeography (ETIB). ETIB has been extremely fruitful, both conceptually, and because of its management implications. My students and I will hypothesize analogous sets of constraints on the geographic ranges of species on continents. Using a simulation model, we will derive predicted patterns of biodiversity from these hypotheses, and will compare the predictions to observed patterns of mammal and bird diversity in the Americas. Further, we will test whether our hypothesized constraints are observed in nature. ******Theme II: We also propose to test how human activities (e.g., climate change and natural habitat removal) affect species' distributions and species richness at the landscape scale. In previous work, we found that mixtures of 50% natural forest, and 50% human-dominated land cover maximize avian biodiversity in southern Ontario. Here, we will test whether this relationship holds in other biomes, and for other taxa. ******Theme III: The studies discussed above are based on statistical descriptions of patterns in nature. However, the predictive ability of these models is rarely tested. Inferences drawn from them may be incorrect. We propose to review, and to re-evaluate the predictive accuracy of published papers in biogeography. ******Theme IV: Finally, I wish to develop a synthesis (in monograph form) of the ecological literature on the predictable patterns of ecology. What can we predict about the structure and functioning of ecological systems?