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 (δ13C) and nitrogen (δ15N) 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 δ13C and δ15N 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.Abstract
δ13C and δ15N isotope ratios and isotopic niche areas of four groups of Wood Turtles (Glyptemys insculpta) sampled in central New Brunswick, Canada, in spring and summer 2021. Blood corpuscle (RBC) and plasma samples were extracted from individual Wood Turtles. Whole invertebrates from three different sources (pond, stream, terrestrial) were also sampled from the study site. The δ13C and δ15N isotope ratios of all samples were analyzed via SIA. Individual data points reflect the isotopic ratios of individual Wood Turtles. SEAs were quantified for the four groups of Wood Turtles by using a Bayesian statistical framework, applied using the statistical software R’s SIBER package. Isotopic ratios of all turtle samples and SEAs were corrected for trophic enrichment. The mean isotopic ratios and their corresponding error bars of invertebrates from each of the three sources are also represented.
Estimated resource use of pond, stream, and terrestrial invertebrates by four groups of Wood Turtles (Glyptemys insculpta) sampled in central New Brunswick, Canada, in spring and summer 2021. Blood corpuscle (RBC) and plasma samples were extracted from individual Wood Turtles, and their isotopic ratios were analyzed via SIA. Using the Bayesian model SIMMR, the three food sources’ dietary contribution to the four groups of Wood Turtles were estimated and are expressed as a proportion of 0–1.
Isotopic niche areas of four groups of Wood Turtles (Glyptemys insculpta) sampled in central New Brunswick, Canada, in spring and summer 2021. Individual data points reflect δ13C and δ15N isotope ratios of individual Wood Turtles. SEAs were quantified using a Bayesian statistical framework, applied using the statistical software R’s SIBER package.
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