| Habitat alteration is considered the single greatest threat to the conservation of natural communities and thus understanding population response to habitat change is critical. In particular, studies are needed that address the effects of disturbance at multiple temporal and spatial scales. In this dissertation, I investigated landscape influence on population genetic structure in the two species of tailed frogs (genus Ascaphus), a pair of stream-associated amphibians that are hypothesized to be especially reliant on mesic forest conditions. This dissertation had three objectives: (1) examine the effect of timber harvest on coastal tailed frog gene flow across a relatively mild climate, (2) investigate patterns of genetic structure in response to both fire and timber harvest in the Rocky Mountain tailed frogs, and (3) understand what landscape and environmental factors facilitated colonization of the Mount St. Helens blast zone by coastal tailed frogs. In Chapter 1, I demonstrated that tailed frog populations had high overall genetic connectivity that occurred terrestrially, but loss of forest cover and high solar radiation impeded gene flow in both protected and managed areas. The managed landscape also led to declines in effective population size. In Chapter 2, I detected high gene flow across severely burned areas. However, population connectivity in intensively harvested forests was best explained by movement through riparian corridors that avoided the terrestrial environment. This shift to stream corridors was not seen in coastal tailed frogs in Chapter 1, and suggests an ecological difference between the coastal and Rocky Mountain species. Finally, in Chapter 3, we found high gene flow throughout the Mount St. Helens blast zone and inferred colonization from multiple sources in the outside intact forest. However, environmental influence on gene flow differed among disturbance types, as there was reduced landscape influence on genetic structure in the unmanaged blast zone, but connectivity in the managed blast zone was best described by the effects of several environmental variables. Collectively, this dissertation research demonstrates that dispersal is an important component of tailed frog population structure, and the extent of landscape influence on genetic connectivity is dependent on disturbance type. |
