To share or not to share: DNA metabarcoding reveals trophic niche overlap between sympatric trawling bats

Understanding ecological niches is essential to comprehend the processes that allow similar species to occur sympatrically. Niche overlap can result in some degree of competition when resources are limited, and therefore, sympatric species must differ to some extent at some niche level in order to co-exist. The two trawling bats that co-occur along the Mediterranean region share their foraging strategy and feeding grounds, potentially consuming similar prey species. However, no research has been conducted to elucidate their dietary niche similarities or differences to test whether these may shape their sympatric foraging occurrence and distribution. We used DNA metabarcoding to study the dietary composition and niche overlap of Myotis capaccinii (an exceptionally endangered species) and M. daubentonii (a relatively common species) during the breeding season in northeastern Iberia. Unlike previous studies, Trichoptera was the most frequently consumed prey order for both bat species, followed by Diptera (mainly Chironomidae). We also report, for the second time, fish consumption by M. capaccinii in the Iberian Peninsula, and provide the fourth report of piscivory for European bats . Although minor differences in diet composition between both trawling bats were found, they presented highly overlapping dietary niches and similar dietary niche breadths, suggesting that they exploit similar trophic resources. Overall, the current results suggest that both species may have found a balance to co-occur in the same foraging niche without interspecific competition being a limiting factor.