Do deterministic processes influence the phenotypic patterns of animalivorous bat ensembles at urban rivers?

Abstract

Although urbanization is perhaps the most damaging, persistent, and rapidly  expanding form of anthropogenic pressure on natural ecosystems, data on the patterns and processes of sympatric bat species in urban landscapes are relatively scant. We quantified the packing and dispersion of sympatric animalivorous bats based on flight and echolocation parameters at two urban rivers in Durban, South Africa. We used null models to test if the observed phenotypic patterns deviated significantly from the random  patterns expected in the absence of competition or prey defences at ensemble and functional group scales. As we predicted,  species packing increased in the species-rich ensemble comprising many morphologically similar species that grouped together, with a few morphologically distinct species dispersed further away. Furthermore, we found evidence that competition influenced flight patterns of the open-air bats at the species-rich river ensemble, and prey defences influenced echolocation patterns of   coexisting bats at the ensemble and functional group scales. However, non-deterministic processes such as habitat structure and the physics of sound and flight probably mediated these deterministic processes to influence the phenotypic structure of sympatric bats in urban  landscapes.

Key words: bats, urban landscape, rivers, competition, prey defences, null models.