Toads, roads, and nodes: Collaborative assessment of amphibian diversity in the Eastern and Central U.S.A. reveals pervasive effects of roads and traffic

Background/Question/Methods

Habitat loss and fragmentation represent significant threats to amphibians. Fragmentation is particularly harmful because many amphibians migrate between aquatic and terrestrial habitats, and even narrow bands of unsuitable habitat can act as barriers to movement.  Additionally, amphibians are slow-moving and prone to road mortality, and many species are unable to travel long distances to leave unsuitable areas.  We addressed several questions, including: 1) Does the number of roads or volume of traffic more strongly affect amphibian populations?, 2) Are roads detrimental to amphibian populations when they separate wetlands from uplands (i.e., habitat split)?, and 3) Are amphibians more sensitive to landscape composition or configuration?  This project was integrated into undergraduate biology curricula; students from nine U.S. colleges summarized North American Amphibian Monitoring Program (NAAMP) data in the Eastern and Central U.S. and used GIS to extract and compile landscape data for 1620 survey locations across 14 states.  We built generalized linear models to test hypotheses concerning the influence of landscape variables on amphibian species richness and site occupancy by individual species.

Results/Conclusions

We found that models incorporating local traffic volume, development, and wetland area were the best predictors of amphibian species richness and site occupancy by individual species.  For overall species richness in 10 of 11 species examined, traffic volume in the vicinity of a survey site was more closely associated with site occupancy than was road length.  We found little evidence for distinct effects of habitat split by roads or development, and in general, landscape composition variables were more useful than landscape configuration variables for predicting amphibian occupancy.  Our results suggest that roads, and particularly traffic, exert strong negative effects on calling amphibians across the Eastern and Central U.S., affecting even species considered disturbance-tolerant.  Our project demonstrates that networks of undergraduate students can be enlisted to analyze large ecological data sets and can provide students with a meaningful research experience in large-scale ecology. We plan to continue our investigation by addressing the importance of landscape connectivity to amphibian populations using this collaborative course-based research model.