DIETARY SHIFTS IN A GRAZING RODENT AFTER THE TERMINAL PLEISTOCENE MEGAFAUNA EXTINCTION

Recent rapid biodiversity losses coupled with anthropogenic climate change poses significant problems for the conservation of modern ecosystems. Studies on trophic downgrading demonstrate that ecosystems can be held in a delicate balance by as little as a single keystone species. Characterizing these changes is a challenge for contemporary biology. Here, we use the terminal Pleistocene extinction of megafauna as a proxy for understanding how the removal of millions of large-bodied animals from the landscape influenced the ecology and interactions among surviving species. Using a unique fine-grained temporal record from Hall’s Cave in the Edward’s Plateau in Texas, we characterized the dietary niche within a species of rodent, the cotton rat (Sigmodon hispidus), prior to and following the extinction. For eight different time bins spanning ~15ka to present, we measured bone collagen carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values and quantified isotopic (dietary) niche space using Bayesian standard ellipse areas. We find a significant 2X expansion in the isotopic niche of S. hispidus after the extinction as well as a time-transgressive decrease in mean δ¹⁵N values. This expansion in isotopic niche may indicate a possible competitive release in the use of available resources, while the decrease in mean δ¹⁵N values may be connected to shifts in δ¹⁵N or change in species composition of the local plant community. Broadly, our results suggest that species such as S.hispidus will likely show a high level of adaptive behavioral plasticity in response to the loss of taxa inhabiting upper trophic levels.