Relative Fitness and Behavioral Compensation of Amphibians in a Managed Forest

Habitat loss and degradation are two of the most important factors leading to the imperilment of species worldwide including amphibians, but mechanisms underlying these changes are poorly understood. To understand the fitness potential of harvested forests, I conducted studies of a forest specialist, Rana sylvatica (Wood Frogs) and compared these results with those from identical studies with an open canopy specialist, R. pipiens (Northern Leopard Frogs) in response to an unharvested control and three forest harvesting treatments: clearcutting (with removal of all merchantable timber > 10 cm diameter), clearcutting with coarse woody debris retention, and partial harvesting with removal of < 25% canopy cover. First, I used radio-telemetry data collected on 72 adult R. sylvatica and 40 R. pipiens and logistic regression modeling to assess habitat selection Second, I predicted and quantified the plasticity of the two frogs with respect to survival, time to metamorphosis, and growth rate. My results suggest that R. pipiens may use clearcut areas during the spring and summer that are within migration distance of breeding and overwintering habitats if dense ground vegetation has regenerated. However, the fitness potential of the clearcut treatments for R. sylvatica is lower than that of the forested treatments, and coarse woody debris retention may ameliorate some of the effects of clearcut harvesting. Further, partial harvesting with removal of < 25% canopy cover is a forest management technique that may not adversely influence the fitness of R. sylvatica. Larval R. sylvatica from open-canopy treatments reached a minimum size and metamorphosed earlier than other treatments, but ultimately, juveniles attained the same mass in all four treatments; open-canopy treatments, however, had 35 ± 2% fewer survivors than forested treatments. In contrast, survival of R. pipiens larvae increased with decreasing canopy cover, increasing water temperature, and increasing food availability, and juveniles remained larger and had higher survival in open-canopy treatments. In summary, the treatments induced opposing changes in the fitness correlates at the aquatic and terrestrial life stages of R. sylvatica but not R. pipiens. Further, each species selected different harvest treatments, and havesting affected the habitat selection of both species at multiple scales.