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Demographic and Genetic Consequences of Fragmentation in Spatially Structured Populations

  • Author(s): Spring-Pearson, Senanu Mark
  • Advisor(s): Nunney, Leonard
  • et al.
Abstract

The spatial arrangement of individuals is an important aspect of their biology and understanding this arrangement can inform us about their ecology and conservation - explored here in three studies. In the first, the population viability analysis that was conducted for the habitat conservation plan of the Stephens' kangaroo rat (Dipodomys stephensi) was found to be seriously flawed resulting in overly optimistic predictions regarding population persistence. Inclusion of spatial structure, as in the original, resulted in much shorter persistence times than when it was excluded. Addition of age-structure using a model that was unavailable at the time of the original habitat conservation plan allowed determination that the model was most sensitive to juvenile mortality and adult fertility - parameters for which reliable estimates are not currently known. In the second study, a method to utilize genetic differences among subpopulations in order to estimate the standardized variance in reproductive success is developed. The method combines genetic and ecological effects of polygyny on the effective sizes of mitochondrial and autosomal genomes. The method was tested using the lekking Greater sage-grouse (Centrocercus urophasianus), in which it was found that the standardized variance was substantially higher than many field estimates, suggesting that such field studies may undercount the number of subordinate males in the population. In the third study, the ability to genetically detect migrants in populations that are structured by limited dispersal was investigated. Using computer simulations, it was found that the genetic differences generated by isolation-by-distance allowed quick and reliable detection of migrants across a barrier that limited dispersal. This finding was extended to develop a method for detecting the presence of such a barrier. The method relies on differences between likelihood of assignment within vs. between subpopulations. With structured populations, barriers could be statistically detected within approximately 10 generations after their construction.

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