Influence of Landscape Structure and Human Modifications on Insect Biomass and Bat Foraging Activity in an Urban Landscape

Urban landscapes are often located in biologically diverse, productive regions. As such, urbanization may have dramatic consequences for this diversity, largely due to changes in the structure and function of urban communities. We examined the influence of landscape productivity (indexed by geology), housing density and vegetation clearing on the spatial distribution of nocturnal insect biomass and the foraging activity of insectivorous bats in the urban landscape of Sydney, Australia. Nocturnal insect biomass (g) and bat foraging activity were sampled from 113 sites representing backyard, open space, bushland and riparian landscape elements, across urban, suburban and vegetated landscapes within 60 km of Sydney's Central Business District. We found that insect biomass was at least an order of magnitude greater within suburban landscapes in bushland and backyard elements located on the most fertile shale influenced geologies (both p<0.001) compared to nutrient poor sandstone landscapes. Similarly, the feeding activity of bats was greatest in bushland, and riparian elements within suburbs on fertile geologies (p = 0.039). Regression tree analysis indicated that the same three variables explained the major proportion of the variation in insect biomass and bat foraging activity. These were ambient temperature (positive), housing density (negative) and the percent of fertile shale geologies (positive) in the landscape; however variation in insect biomass did not directly explain bat foraging activity. We suggest that prey may be unavailable to bats in highly urbanized areas if these areas are avoided by many species, suggesting that reduced feeding activity may reflect under-use of urban habitats by bats. Restoration activities to improve ecological function and maintain the activity of a diversity of bat species should focus on maintaining and restoring bushland and riparian habitat, particularly in areas with fertile geology as these were key bat foraging habitats

Determinants of microbat communities in urban forest remnants: a rapid landscape scale assessment

Urbanisation affects fauna in many ways; with some species persisting and going on to dominate urban habitats, while other species decline over time due to habitat disturbance and modification. Microbats comprise a major component of remnant mammalian fauna in urban areas but we have a comparatively poor understanding of how they respond to urbanisation compared to other taxonomic groups. We investigated the impacts of an urban gradient on microbat communities of habitat remnants on the Gold Coast, south-east Queensland, Australia. We conducted acoustic surveys of 34 sites categorised as urban, peri-urban or rural, with an additional five reference sites. A combination of landscape and habitat elements were quantified for each site and their influence on the richness and calling activity of microbats determined. Overall, more microbat species were detected in reference sites followed by peri-urban sites. Rural and urban sites had similar richness, but only 50 % overlap in species recorded. After accounting for sampling effort peri-urban sites were found to have the greatest species richness and calling activity. Three species accounted for 45.4 % of the variation in microbat species detected. Using generalised linear mixed models we found that site area and the extent of urban development in the landscape (i.e. urbanisation index) had the greatest impact on microbat richness and calling activity. Models including logging (clearfelling) and hollow-bearing tree measures were also important. Our results support the use of the urbanisation gradient as a key measure to quantify the impacts of urbanisation on biodiversity. Logging history plays an important role across the landscape as it is a potential driver of other landscape variables such as tree species diversity, stand density and hollow-bearing tree density.Griffith Sciences, Griffith School of EnvironmentNo Full Tex