Abstract

--- - Theory predicts that in resource-limited environments, coexisting species may overlap their niche dimensions but must differ in at least one to avoid competitive exclusion. Specifically, it has been suggested that the coexistence of competing species within a guild, could be sustained with mechanisms of resource partitioning, such as segregation along a trophic dimension. Among the most gregarious mammals are bats, which present diversification in their diet based on habitat choice and body size. Despite differences that could explain specialization in prey selection, there are insufficient studies that explore food overlap in mixed bat colonies and the factors that determine the selection of prey, both at intra- and inter-specific levels. To fill this gap, we analyzed the isotope signal (delta 13C and delta 15N) in feces collected in a mixed colony of Tadarida brasiliensis and Myotis chiloensis. To understand how several factors could influence these isotopic signals, intrinsic explanatory variables were analyzed, including body mass, body length, age, and sex. Also, extrinsic variables were analyzed, including monthly temporality and moonlight intensity. Our findings support age-dependent specialization in M. chiloensis, with a significant role of moonlight intensity and sex on delta 15N. In T. brasiliensis, we identified a significant effect of size, sex, and ear length on delta 15N. Our analysis indicates that both species of bats experience diverse degrees of overlap through austral summer months, affected by several factors that explain the variability in their fecal isotopic signals. - This study analyzed the isotope signal in feces collected from a mixed colony of Tadarida brasiliensis and Myotis chiloensis to explore feeding overlap and the factors that determine prey selection. The results showed that age-dependent specialization exists in Myotis chiloensis, with a significant role in moonlight intensity and sex. The study also identified an important effect of size, sex, and ear length in Tadarida brasiliensis. Both species of bats experience diverse degrees of overlapping through the months of austral summer, affected by several factors that explain the variability in their feces isotopic signals.image