A Test of Intersexual Trophic Niche Partitioning within a Population of Wood Turtles (Glyptemys insculpta)

The Wood Turtle (Glyptemys insculpta) is a semiaquatic turtle species that has been known to exhibit intersexual variation in habitat use during summer. Males often remain near watercourses in riparian areas, whereas females tend to move upland and spend more time in terrestrial environments postnesting. Dietary niche partitioning is one of several hypotheses proposed to explain why females leave aquatic habitats in search of terrestrial food resources. The presence of dietary niche partitioning within a population of Wood Turtles in central New Brunswick, Canada, was assessed using stable isotope analysis. Male and female Wood Turtles were sampled in spring and summer 2021. Potential invertebrate foods were sampled and grouped into pond, stream, and terrestrial food sources. Using stable carbon (delta C-13) and nitrogen (delta N-15) isotopic ratios of extracted red blood corpuscle and blood plasma, the resource use and isotopic niche widths of individuals within the population were compared between seasons and sexes. Results indicated no significant differences in delta C-13 and delta N-15 values, dietary contributions, or isotopic niche widths between spring and summer samples or between males and females. We determined that terrestrial invertebrates were an important food source (>72% mean diet contribution) across the entire sampled population, with invasive Arion slug species constituting a large portion of turtle diets. Our findings indicate that dietary niche partitioning is most likely not the explanation for sexual variation in habitat use by Wood Turtles.