Stable isotopes suggest a sustained diet shift among ants exposed to drought in a tropical rainforest

Abstract

Abstract With higher frequency and intensity of droughts predicted for many tropical forests, understanding the responses of plants and animals to changed conditions will be increasingly important. Ants are considered ecosystem engineers in tropical rainforests due to their abundance and the diversity of functional roles they perform. Diets of rainforest ants can range from purely carnivorous, to mostly plant-based, with stable isotopes now being used to distinguish these differences. We sampled ant communities in a lowland rainforest in an insitu drought experiment and compared diets using stable isotope analyses. We found that 14 of the 18 species sampled had higher δ15N levels in the drought experiment. Importantly, the two most common species in the region showed a significant effect of the drought experiment on δ15N, which was similar to the dry season response in the control plot. There was no detectable difference of the experiment for ant δ13C values. The observed changes in ants δ15N in response to drought may be caused by ants shifting to a more predatory diet, or a drought-induced shift in δ15N in plants for which we did not test. Further analysis of changes in δ15N in plants with drought is required to determine if one or both factors are involved. Since ants are a dominant force in rainforests, trophic shifts may have broad implications for the impact of climate change on species interactions and food webs.