The effects of urbanisation on the diversity and abundance of nocturnal insects: Implications for microbat conservation

Background/Question/Methods

The few studies focusing on microbats in cities indicate that urbanisation has a negative effect on species richness and diversity, probably due to a reduction in the availability of prey and roost sites.  However, quantitative data on the effect of urbanisation on resource availability and how this influences microbat populations is currently lacking. Therefore we aim to quantify the relationship between the diversity and foraging activity of microbats in urban areas and the diversity and abundance of their invertebrate prey.  We also aim to investigate the habitat and landscape variables which influence insect distribution. This study was carried out between January and March in 2010 and 2011 in the city of Melbourne, south-east Australia. Nocturnal aerial insects and microbats were sampled at 60 study sites distributed along an urban-rural gradient (based on human population density).  Ten sites each were located within six land-use categories (industrial areas, residential areas, golf courses, recreational parks, remnant bush reserves and riparian vegetation), representing varying levels of human modification. Light traps were used to survey insects, and ultrasonic detectors were set up simultaneously to record microbat activity. Insects were counted and identified to Order and microbat species were identified using an automated echolocation key.

Results/Conclusions

A total of 70,494 nocturnal aerial insects were captured from 17 different Orders, with Lepidoptera (49%), Diptera (17%) and Hemiptera (16%) being the most abundant. We found that urbanisation had a negative effect on insect abundance, with greater numbers of insects in less urbanised areas. A positive relationship was found between insect abundance and microbat species richness, and with microbat activity. Insect abundance was found to vary among the different habitats, with more insects in riparian, remnant and residential areas than in golf courses, recreational parks and industrial areas. These habitat types also had a higher density and diversity of vegetation than golf courses, recreational parks and industrial areas. Results from this study indicate that urbanisation has a negative impact on potential microbat prey. The positive relationship between insects and bats imply that a reduction in prey availability through urbanisation will also negatively affect bat populations. Results suggest that managing urban areas to maximise insect abundance, by maintaining diverse and structurally varied habitats, would benefit bat populations.