Spatial and temporal dynamics of turtle nest predation: edge effects

Abstract

We determined the effect of distance from ecological edges, both wooded and water edges, on nest predation for 862 painted turtle, Chrysemys picta, nests from 1995 to 1999 at an ∼1.5 ha study site. In three of five years and overall, nests closer to the water edge had a higher probability of predation; and in one year nests closer to the wooded edge had a higher probability of predation. Although more turtles nested closer to the water edge as the nesting season progressed in some years and overall, this behavior does not explain the observed patterns of nest predation. We present a novel application of the cubic spline analysis to address the dynamics of predation across continuous distances from an edge and identify threshold values where the predation rate levels off. Threshold values of ∼25–40 m were detected in 1995, 1998, and with all five years combined. However, even though a significant edge effect was detected in 1997, a threshold was not clear. While an edge effect on predation was not detected in each year, this study provides evidence for a strong effect of distance from the water edge on nest predation over significant ecological time. Focusing on turtle nest predation and smaller spatial scales addresses previous taxonomic and spatial bias in edge effects research, and provides further support for the ecological importance of edge effects.