Picky City Bats: Variation in Urban Conditions Generates a Suitability Gradient that Structures the Bat Community.

Abstract

The transformation of natural systems into urban cities represents a radical habitat modification and one that generates species-specific effects on bat communities. Cities present heterogeneous mosaics of urban conditions, which the bats can inhabit differentially by utilizing their intrinsic characteristics. We expected bat species richness, number of abundant species and feeding guilds to be positively impacted by an increased degree of suitability for bats in certain areas interspersed in the city. We also expected that the number of dominant species would follow an inverse pattern, with some species being fostered in less suitable areas for bats. We determined the levels of suitability for the presence of bats in urban-based basic geostatistical units (BGUs) in the Neotropical city of Morelia, in Michoacán state, Mexico. We identified three levels of suitability for bats, low, medium and high, using the percentage of arboreal vegetation and constructed and open areas in the BGUs. We monitored the bat assemblage monthly over an annual cycle using autonomous ultrasonic recorders to assess the abundance of each species at each suitability level. Across all three suitability levels throughout the year, we found a high dominance of three insectivorous bat species that forage in open areas. Diversity measures supported our predictions, agreeing with bat flight and foraging functional traits. These results highlight the importance of city features in driving bat diversity and how urban planning that fails to consider key city features, such as arboreal areas in the city, may reduce suitability for bats, leading changes in diversity.