In habitats where prey is either rare or difficult to predict spatiotemporally, such as open habitats, predators must be adapted to react effectively to variations in prey abundance. Open-habitat foraging bats have a wing morphology adapted for covering long distances, possibly use information transfer to locate patches of high prey abundance, and would therefore be expected to show an aggregative response at these patches. Here, we examined the effects of prey abundance on foraging activities of open-habitat foragers in comparison to that of edge-habitat foragers and closed-habitat foragers. Bat activity was estimated by counting foraging calls recorded with bat call recorders (38,371 calls). Prey abundance was estimated concurrently at each site using light and pitfall traps. The habitat was characterized by terrestrial laser scanning. Prey abundance increased with vegetation density. As expected, recordings of open-habitat foragers clearly decreased with increasing vegetation density. The foraging activity of edge- and closed-habitat foragers was not significantly affected by the vegetation density, i.e., these guilds were able to forage from open habitats to habitats with dense vegetation. Only open-habitat foragers displayed a significant and proportional aggregative response to increasing prey abundance. Our results suggest that adaptations for effective and low-cost foraging constrains habitat use and excludes the guild of open-habitat foragers from foraging in habitats with high prey abundance, such as dense forest stands.

a b s t r a c tThe decline of bat populations across Europe has generated considerable interest and activities for the conservation of this enigmatic group of mammals. However, the factors influencing their distribution and species richness are still poorly understood, particularly on regional scales. We used the presence/absence data of the bat atlas of the German federal state of Bavaria (grid cell area ∼34 km 2 ) to estimate the species-area curve and to compare the predictive power of environmental and climatic data sets for species richness and composition of bat assemblages within grid cells. We used as predictors land-use data extracted from CORINE, and climatic information from the WorldClim database. We found a species-area relationship with a slope very similar to that of other vertebrate assemblages (S = 2.56 × A 0.209 ). By using variance partitioning for species richness and predictive canonical correspondence analysis, we found that on the scale considered, land use is more important than climate for bat assemblages. Nevertheless, the amount of explained variance is low. Concentrating on the land-use data, we found that the relative amount of the grid cell area dominated by human activities (e.g., settlements, traffic) was associated with increasing species richness as well as the probability of occurrence of several single bat species. Furthermore, broadleaf forests and mixed forests increased species richness, and even small proportions (>5%) of these land-use types within a grid cell are sufficient for a positive influence on species richness. Our results underline the importance of urban areas for the conservation of bats on regional scales. Furthermore, the results underline the importance of small forest patches as habitats for bats.

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