Occupancy of freshwater turtles across a gradient of altered landscapes

ABSTRACT

Turtles are one of the most threatened groups of vertebrates worldwide. In the northeastern United States, a legacy of centuries of dramatic landscape alteration has affected freshwater turtle populations, but the relationships between the current landscape and distributions and abundances of freshwater turtles remain poorly understood. We used a stratified random approach to select 88 small, isolated wetlands across a gradient of forest cover throughout Rhode Island, USA, and systematically sampled freshwater turtles in these wetlands. We report estimates of relative abundance and used a canonical correspondence analysis to investigate relationships between species relative abundance and environmental covariates. We also investigated which environmental covariates affect the occurrence and detection probabilities of each species. Eastern painted turtles (Chrysemys picta picta) and common snapping turtles (Chelydra serpentina) were widespread (occurring in 83% and 63% of wetlands, respectively) and relatively abundant. Spotted turtles (Clemmys guttata) were far less common, occurring in 8% of wetlands, and exhibited a positive association with shallow wetlands surrounded by forest. Non-native red-eared sliders (Trachemys scripta elegans) occurred in 10% of wetlands and exhibited a positive association with road density, likely reflecting a positive relationship between slider occurrence and human population density. Identifying landscape-scale habitat features that are associated with the occurrence of sensitive species can improve the ability of biologists to identify and protect turtle populations. © 2018 The Wildlife Society.