Collaborative Research: Maintaining High Species Diversity in Communities

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ABSTRACTCOLLABORATIVE RESEARCH: MAINTAINING HIGH SPECIES DIVERSITY IN COMMUNITIESEcosystems frequently contain species that are evolutionarily and ecologically similar. However, whether this diversity is actually maintained by mechanisms that directly promote coexistence or rather is lost very slowly from systems is unclear. Many mechanisms have been proposed that could promote the indefinite coexistence of species on both local and regional scales. These mechanisms of coexistence are only present when vital rates (survival, growth, reproduction) vary with the environment and when individual species have different responses to the same environment change. The alternative is that species do not differ in their responses to the environment and are slowly being lost through a random process called "ecological drift" in which the population size of one species relative to another is determined by the unpredictability inherent in survival, growth, and reproduction. This process is akin to "random genetic drift" in which random evolutionary changes among the relative abundances of so-called neutral genes occur due to unpredictability in the process of inheritance. This project will elaborate recent models of ecological drift by incorporating mechanisms of coexistence into these "neutral" ecological models. Like the neutral models, development of the new theory will take advantage of analogies between the ecological mechanisms that determine species diversity patterns and the evolutionary processes that determine genetic diversity. The goal of the research is to develop a set of predictions that incorporates both ecological drift and various coexistence mechanisms that operate on local and regional scales. These predictions will be statistically compared with existing data on community diversity across local and regional scales. The research will provide indirect but highly practical tests for mechanisms that shape community diversity.