ASSESSING SEASONAL VARIATION IN THE ISOTOPIC BASELINE OF AN EASTERN OHIO WOODLAND

Foraging ecology studies of small and nocturnal organisms, like terrestrial gastropods and other invertebrates, can be challenging or inefficient using traditional field observation methods alone. Instead, stable isotope analyses are often used to indirectly study and quantify different aspects of organisms’ diets. However, these studies rely on an intimate understanding of the isotopic baseline of the ecosystem, which can vary due to a wide range of environmental factors including temperature, precipitation, humidity, and more. This research investigates seasonal variation in the carbon and nitrogen isotopic composition of primary producers and decomposers in an effort to set an isotopic baseline for future studies of terrestrial gastropod diets. Terrestrial gastropod species are known to eat a variety of food sources in temperature forests, including fresh and decayed vascular plants, fungi, molds, mosses, and lichens, among others. We tested the hypothesis that food resources will be enriched in ¹⁵N and ¹³C during the drier months of the year. The preliminary nitrogen and carbon results suggest that both fungi and C₃ plants from the same locale indeed exhibit a ~2-3 per mil difference between spring and fall. The isotopic difference is present even when comparing months with similar weather regimes. This investigation illustrates that seasonal isotopic shifts in food sources are significant in temperature forests and should be taken into account when approximating an organism’s diet based on isotopic analyses.