Prey size is more representative than prey taxa when measuring dietary overlap in sympatric forest bats

Abstract

AbstractIn temperate forests, insectivorous bats need to use variable hunting strategies as prey availability fluctuates during the growing season. At sites with variable amounts of forested habitat, sympatric bat species may exhibit high dietary overlap, but mechanisms of coexistence are unknown. We analyzed the diets of sympatric Myotis septentrionalis and Myotis sodalis in two different landscapes in central Indiana, USA: a riparian agricultural site and a managed forest site, aiming to assess interspecific dietary overlap. We collected fecal samples from 166 Myotis over four maternity seasons and used DNA metabarcoding to assess niche overlap by operational taxonomic units (OTUs, n = 708) and prey‐size taxa (n = 79). Analyzing diets by prey‐size classes, as opposed to only species, provided an alternative interpretation of dietary richness and overlap that may more accurately represent predator perceptions of prey. With overall prey sizes ranging from 2–36 mm, M. septentrionalis (n = 88) consumed larger prey (10.0 ± 5.5 mm, μ ± σ) than M. sodalis (n = 78; 8.9 ± 5.0 mm). Myotis sodalis had a more diverse diet (547 OTUs) compared to M. septentrionalis (453 OTUs) despite the smaller sample size. Of the 708 OTUs detected, 41% (292) were common across bat species. We found greater dietary overlap between species within each site than within either species across sites, suggesting both species mostly consume whatever insects are available on the landscape. Flexible hunting strategies may allow these species to coexist by consuming different sizes of prey at different rates in the tradeoff between travel cost and profitability. Prey size is an important measure for dietary overlap and resource partitioning in bats that few studies have yet considered, with implications for linking predators, prey, and habitats.