A paleoecological perspective to bat conservation: Revealing diet shifts in Myotine bats through guano

Understanding how land use change impacts bat diet is vital to bat conservation efforts. Little is known about trophic level shifts that occur within bat diets due to variations in the extent of agriculture. Here, we measured ẟ¹³C and ẟ¹⁵N stable isotopic compositions from a modern, post-bomb (after 1950 CE) bat guano core over a 65-year period to answer the following research questions: 1) What vegetation changes are revealed by the ẟ¹³C and ẟ¹⁵N stable isotope compositions? 2) What changes in bat diet occurred in the southeastern Appalachian region? Using this data we also suggest bat conservation recommendations. Based on stratigraphic changes in isotopic values, we determined three distinct phases when bat diet shifted between predatory and herbivorous insect prey. After comparing the stable isotopic compositions to cropland data, we found that changes in the trophic level of bat diet are coeval with changes in agricultural land use. We attribute increased consumption of predatory insects to phases with increased C₄ plants (i.e., crops such as maize). We show that increased agricultural diversity (i.e., crops with high C₃ to C₄ plant mixtures), add structural complexity to a landscape, providing greater food availability and refugia for a diversity of insects. Overall, we found that C₃ to C₄ crop diversity, acted as the mechanism driving bat diet variation between 1952 and 2018 CE. Our recommendations to improve bat conservation include increasing agricultural diversity and increasing vegetative field boundaries in agricultural areas. From this study, we demonstrate that applying paleoecological methods can inform bat conservation efforts.