Stratification of insects and bats reveals vertical trophic structuring in beech forests

Vertical stratification offers an overlooked dimension of trophic niche partitioning in forests, potentially enabling predators to track prey distributed at different heights. Although bats are known to partition forest airspace vertically, whether their activity matches the vertical distribution of insect prey in line with their diets and foraging strategies has rarely been tested directly. We quantified flying insects and bat activity at ground and canopy levels across 20 plots in an old-growth beech forest in the central Apennines, Italy. We collected 1123 insects representing 23 taxa and recorded 1301 bat passes from 17 species or acoustic groups. Both prey and predators showed clear vertical stratification. Dipterans were about 18 times more abundant near the ground (on average, 32.9 vs 1.8 individuals), whereas lepidopterans were approximately 1.6 times more abundant in the canopy (on average, 11.8 vs 7.2 individuals). Bat activity closely mirrored these patterns: the moth specialist Barbastella barbastellus was 2.4 times more active in the canopy, whereas the whiskered bat species group, dominated by Myotis mystacinus , and Pipistrellus pipistrellus , were 1.9 and 2.5 times more active near the ground, respectively. Myotis myotis showed no statistically significant difference in activity between the two strata. By revealing concordant vertical distributions of insect prey and bats, we show that trophic resources may help structure three-dimensional habitat use in temperate forests. These patterns also suggest that vertical niches are flexible rather than fixed, reflecting behavioural plasticity in bats and context-dependent stratification in insects. Maintaining vertical forest heterogeneity may therefore preserve complementary prey resources and foraging opportunities for diverse bat assemblages.