Extinction in the Finnish Daphnia magna metapopulation
Robinson, John David
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Metapopulation studies typically employ long-term presence-absence datasets, or snapshot presence-absence data along with characteristics of habitat patches, for estimating extinction rates. Both of these approaches place demands on the amount of data available for the system of interest. In this dissertation, genetic datasets were used in an attempt to estimate the rate of extinction in the Finnish Daphnia magna metapopulation. If successful, these methods would allow for rapid characterizations of systems of conservation importance. In addition, the relative influences of genetic and environmental factors on short-term colonization success in newly founded D. magna populations were assessed in a laboratory experiment. In Chapter 2, simple population genetic summary statistics were applied to simulated and empirical datasets in an attempt to estimate population ages. Simulated datasets show that the potential for this sort of analysis is good when even moderate numbers of loci are considered. Ages estimated from empirical data were biased upwards in all cases, but remained correlated to known ages for mismatch distribution-derived estimates. In Chapter 3, approximate Bayesian computation (ABC) methods were used to compare a strict metapopulation model with a representation that included a persistent source population. Model selection using ABC strongly supported the latter of these two structures. Parameter estimates using the persistent source model largely agreed with previous data in the system, particularly for the rate of extinction, but estimated rates of gene flow were higher than expected. The combination of persistent sources and (apparent) gene flow between patches may be responsible for the upwards bias in ages estimated in Chapter 2. Finally, in Chapter 4, an experiment was undertaken to assess the influences of genotypic diversity and environmental variation on short-term population persistence. This experiment revealed no significant effects of genotypic diversity on time to extinction in the Daphnia system. The data for environmental variation are difficult to reconcile with previous studies, as significant effects of block and a block-by-environmental variation interaction in the model showed a reversal in the direction of the effect of increased temporal variation in food input. Variable environments increased hazards in the first, but not the second, experimental block.