The diversity of insectivorous bat assemblages among habitats within a subtropical urban landscape

We investigated the bat (Microchiroptera) diversity of four major habitat types within a large Australian subtropical city (Brisbane, Australia) to determine whether species richness was affected by habitat changes associated with urbanization, as suggested from studies elsewhere. Forty sites, ten in each habitat type (remnant bushland, parkland, low-density residential and high-density residential) were surveyed using acoustic bat detectors on six non-consecutive occasions. Fourteen bat species were recorded. The species accumulation curve of the entire Brisbane bat assemblage reached a plateau at 14 species. The total numbers of species in bushland, parkland, low-density residential and high-density residential habitats were 14, 13, 14 and 11 species, respectively. Asymptotic estimates of species richness for each habitat were close or equal to these totals. Mean asymptotic estimated species richness differed significantly among habitats, being lowest in high-density residential sites and highest in low-density residential sites. Evenness profiles were similar across habitats, and were not strongly dominated by a few species. Partitioning of diversity components showed that landscape (gamma) diversity was mainly determined by the high species richness of low-density residential and bushland habitats (alpha diversity), rather than high beta (beta) diversity among habitats. These findings contradict those of other studies on bat diversity in which species richness was highest within 'natural' areas of the urban landscape and assemblages were dominated by one or two species. This highlights the need for caution in making generalizations based on existing information, which is dominated by studies in temperate regions.