Disturbance-dependent species regularly colonize ephemeral habitat patches. In this research, I used patterns of genetic variation to estimate the dispersal dynamics of black-backed woodpeckers (Picoides arcticus), a fire specialist, and compared these patterns to hairy woodpeckers (Picoides villosus), a generalist. I then examined how frequent colonization of ephemeral habitat patches versus stable migration among static habitat patches shapes the genetic structure of species.
I examined patterns of genetic variation in mtDNA and microsatellites in both black-backed and hairy woodpeckers to determine large-scale spatial structure. Black-backed woodpeckers have high genetic connectivity across the boreal forest and lower genetic connectivity among sites separated by large gaps in forested habitat. Across the boreal forest, hairy woodpeckers have low genetic differentiation in mtDNA that lacks spatial structure, but moderate genetic differentiation in an isolation by distance pattern in microsatellite data. These results suggest that large gaps in forest act as a movement barrier to black-backed woodpeckers; movement patterns of hairy woodpeckers are primarily driven by geographic distance as opposed to landscape composition.
Once I understood the primary mechanisms driving large-scale patterns, I determined the fine-scale spatial structure in both species. Black-backed woodpeckers apparently disperse twice as far as hairy woodpeckers based on patterns of fine-scale geneticstructure. Female black-backed woodpeckers have limited dispersal, with long-distance dispersal being male-biased. A weak pattern of female-biased dispersal was observed in hairy woodpeckers.
I used simulations to evaluate how effective population size and dispersal distance interact with two models of dispersal, frequent colonization of ephemeral patches and stable migration, to shape large-scale genetic structure. Frequent colonization of ephemeral habitats resulted in lower spatial structure and higher genetic differentiation among patches in comparison to stable migration. Low genetic differentiation with little spatial structure occurred at an intermediate dispersal distance in the frequent colonization model, the pattern observed in black-backed woodpeckers. Stable migration with short dispersal distance results in isolation by distance, the pattern observed in hairy woodpeckers.
Disturbance-dependent species have evolved with a natural mosaic of shifting habitat patches. As anthropogenic disturbance increasingly changes this mosaic, ecologists need to consider how this shift may affect connectivity for disturbance-dependent species.
|Advisor:||Allendorf, Fred W., Schwartz, Michael K.|
|Commitee:||Hutto, Richard L., Mills, L. Scott, Saab, Victoria A.|
|School:||University of Montana|
|Department:||Fish & Wildlife Biology|
|School Location:||United States -- Montana|
|Source:||DAI-B 71/02, Dissertation Abstracts International|
|Keywords:||Black-backed woodpecker, Dispersal, Genetic structure, Hairy woodpecker, Picoides arcticus, Picoides villosus, Population genetics, Wildfire|
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