Comparing little brown and big brown bat isotopic niches over the past century in an agriculturally dominated landscape

Abstract

Abstract Agricultural intensification has caused population declines and reduced species diversity in both arthropods and their predators. Despite conservation and habitat management implications, the effects of land-use change on the trophic relationships between nocturnal arthropod predators and their prey have seldom been described. To assess how arthropodivorous bats may have shifted their diets in response to land-use changes, we compared bulk δ 13C and δ 15N values from little brown and big brown bat museum specimens and carcasses collected in the Upper Midwestern region of the United States from 1898 to 2019. As an exploratory analysis, we also investigated relationships between isotopic values and climate or landcover variables to quantify potential correlations with changes in arthropodivorous bat foraging patterns over time. Overall, we found that isotopic niche overlap of little brown and big brown bats increased from 24% to 45% between historical and contemporary time periods. Our results indicate that the isotopic niches of little brown bats have been largely conserved, whereas the isotopic niches of big brown bats are more flexible and became more similar to little brown bats over time. Further analyses showed that stable isotope values from arthropodivorous bat tissues were also correlated with certain landcover variables such as the prevalence of wetland, forest, and grassland habitats, but not with the prevalence of agricultural land on a local scale. These findings suggest that the foraging patterns of some aerial arthropodivores have shifted in response to the loss of habitat diversity and corresponding changes in prey resources.