Incidental nest predation in freshwater turtles: inter- and intraspecific differences in vulnerability are explained by relative crypsis |
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Authors: | Aaron J Wirsing Julia R Phillips Martyn E Obbard Dennis L Murray |
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Institution: | (1) School of Forest Resources, University of Washington, Box 352100, Seattle, WA 98103, USA;(2) Department of Biology, Trent University, 1600 West Bank Drive, Peterborough, ON, K9J 7B8, Canada;(3) Wildlife Research and Development Section, Ontario Ministry of Natural Resources, Trent University, 2140 East Bank Drive, Peterborough, ON, K9J 7B8, Canada |
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Abstract: | There has long been interest in the influence of predators on prey populations, although most predator–prey studies have focused
on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after
incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric
freshwater turtle species whose nests are differentially prone to opportunistic detection—painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)—is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging
behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2
years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated.
Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping
turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed
to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey.
Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration
of undisturbed conditions that are less likely to expose nests to incidental predators. |
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