Effect of Road Proximity on Reproductive Effort and Movement Patterns of the Wood Frog (Rana sylvatica)

Abstract

Nearly half of the amphibian species in northeastern North America rely on vernal pools as their primary breeding habitat. The problem is that, because vernal pools are small and isolated, they are often left unmonitored and unprotected. A primary threat to both amphibians and vernal pools is habitat destruction and fragmentation, but our knowledge of the species-specific impacts of habitat loss and fragmentation on all phases of the amphibian life cycle are still rudimentary. The wood frog (Lithobates sylvaticus) was the focus of this research because it is considered the most common vernal pool indicator in Pennsylvania. The objectives of this study were to investigate the effect of road proximity on vernal pool hydrology and water chemistry, reproductive effort of wood frogs (i.e., numbers of egg masses deposited), and upland movement patterns of wood frogs. These parameters were compared between three isolated pools (> 1000 m from the nearest road) and two pools in a fragmented habitat (< 100 m from two roads) within a Pennsylvania state park. This study indicates that, although road proximity did not have a significant effect on vernal pool water chemistry and egg mass abundance was greater in the fragmented location, habitat fragmentation by roads did have a significant effect on the movement patterns of wood frogs in surrounding terrestrial habitat. At the isolated site where there were no barriers to movement, wood frogs were distributed randomly around the pools. However, wood frogs in the fragmented location were trapped at a lower frequency near roads than expected by chance, indicating that the presence of roads may reduce the amount of upland habitat utilized by adult wood frogs. Although this was a small and localized study, the results indicate the challenging nature of conserving species with complex life cycles in human dominated landscapes and highlight the importance of considering life-cycle and species-specific habitat requirements when designing vernal pool conservation plans.