Habitat Usage, Dietary Niche Overlap, and Potential Partitioning between the Endangered Spotted Turtle (Clemmys guttata) and Other Turtle Species

Abstract

Habitat loss and degradation affect populations in isolation while also modifying the intensity of interspecific interactions, which may be especially relevant for species of conservation concern coexisting with more common species. We explored habitat preferences and potential interspecific resource competition in the endangered Spotted Turtle (Clemmys guttata). For habitat data, water quality measurements were recorded once per trapping session, while canopy cover and vegetation data were recorded once per field season. We also investigated niche overlap in habitat and food resources between C. guttata and other, more common, turtle species. Our data indicated that the abundance of C. guttata was negatively correlated with dissolved O2 and pH levels and positively correlated with body of water depth and canopy cover. The investigation of niche overlap revealed that Mud Turtles (Kinosternon subrubrum) and Painted Turtles (Chrysemys picta), but not Snapping Turtles (Chelydra serpentina), were negatively correlated with the abundance of C. guttata despite differences in characteristics of bodies of water used by each species. We used structural equation modeling to better understand if the relationships between C. guttata and other turtles were due to direct interactions or simply reflected environmental influences. We then used stable isotope analyses to compare similarities in δ13C and δ15N isotopes as proxies for diet overlap between C. guttata and other turtles and ultimately found that all species had similar, broad diets. The inverse relationship between abundance of C. guttata and other species, paired with the overlap in dietary niche space, suggests there is potential for interspecific interactions to negatively impact the abundance of C. guttata within turtle communities on the Atlantic Coastal Plain. The results of this study highlight that management efforts may need to consider that species of conservation concern coexist with more common species, especially as habitat loss decreases the breadth of habitat available.