Dissertation Research: The Roles of Local and Metapopulation Forces in Determining Regional Scale Aphid Population Dynamics

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Morris9801089The range of many organisms consists of collections of populations in suitable habitat patches connected through migration. Such collections are called metapopulations. In order to understand and predict how metapopulations will behave over time it is necessary to understand both processes affecting each of the populations separately (e.g. predator-prey relations) and processes affecting migration between patches. Preliminary studies on the aphid, Aphis lugentis, reveal that both predation pressure and patch distribution affect metapopulation dynamics. Observational and experimental data collected over two years is being used to fit a simulation model describing the A. lugentis system. The model will be used to predict the results of large-scale manipulations of predator density and patch arrangement which will be carried out in the field. The proposed manipulations will be the first explicit experimental test of the role of migration in controlling metapopulation dynamics. When the simulation model is able to accurately predict the results of the large-scale manipulations it will be used to answer two closely related questions. First, under what conditions do factors affecting migration between patches play an important role in metapopulation dynamics? Second, under what conditions do within patch processes become so important as to mask the affects of migration in determining metapopulation dynamics? This study will provide crucial experimental evidence for the importance of migration in determining metapopulation dynamics. While a great deal of theory predicts a critical role for migration rates in determining metapopulation dynamics that theory has gone largely untested. Nevertheless metapopulation models are widely used in species management and conservation plans. Beyond providing experimental evidence that migration does indeed play an important role in determining metapopulation dynamics, this study will explore how the relative importance of within patch processes and migration change under a variety of conditions. In so doing it will take a large step towards predicting when large-scale population dynamics can be predicted based on information about within patch processes alone, migration and extinction rates alone, and when more detailed information at both scales is necessary.