Divergent landscape effects on population connectivity in two co-occurring amphibian species

The physical and environmental attributes of landscapes often shape patterns of population connectivity by influencing dispersal and gene flow. Landscape effects on movement are typically evaluated for single species. However, inferences from multiple species are required for multi-species management strategies increasingly being applied in conservation. In this study, I compared the spatial genetic patterns of two amphibian species across the northeastern United States and estimated the influence of specific landscape features on the observed genetic structure. The spotted salamander (Ambystoma maculatum) and wood frog (Rana sylvatica) share many ecological attributes related to habitat use, phenology and site fidelity. However, I hypothesized that important differences in their movement patterns and life history would create distinct genetic patterns for each species. Using 14 microsatellite loci, I tested for differences in the level of genetic differentiation between the two species across 22 breeding ponds. The effects of eight landscape features were also estimated by evaluating 32 landscape resistance models. Spotted salamanders exhibited significantly higher genetic differentiation than wood frogs. Different landscape features were also identified as potential drivers of the genetic patterns in each species, with little overlap in model support between species. Collectively, these results provide strong evidence that these two amphibian species interact with the landscape in measurably different ways. The distinct genetic patterns observed are consistent with key differences in movement ability and life history between A. maculatum and R. sylvatica. These results highlight the importance of considering more than one species when assessing the impacts of the landscape matrix on population connectivity, even for ecologically similar species within the same habitats.

Winter snowfall determines the occupancy of northern prairie wetlands by tadpoles of the Wood Frog (Lithobates sylvaticus)

In the northern plains of North America, the wetland breeding habitat of amphibians and their populations could be reduced by a change in climate that included decreased precipitation. To test this hypothesis, relative abundance of late-stage tadpoles of the Wood Frog ( Lithobates sylvaticus (LeConte, 1825)) was monitored from 1997 to 2010 during a wet–dry–wet cycle in 29 wetlands distributed throughout central Saskatchewan, Canada. The wetlands were dry for up to 7 consecutive years, and for a mean of 3.8 consecutive years. Consequently, tadpole occupancy of the wetlands was reduced to less than 40% for 5 consecutive years and none of the wetlands had tadpoles during the severe drought of 2001 and 2002. However, the drought had no observable long-term effect on either tadpole occupancy of wetlands or tadpole abundance. In 2007, 93% of the wetlands supported tadpoles, and in 2008 the highest mean relative abundance of tadpoles was recorded. Tadpole occupancy of wetlands was related to winter and spring precipitation (R2 = 0.84) with 67% of long-term variation in occupancy related to snowfall from November to February and 17% related to rainfall from March to June. Less than 45 mm of winter precipitation for 6 consecutive years would probably cause regional extinction of populations of the Wood Frog.