Spatial distribution of bat activity in agricultural fields: implications for ecosystem service estimates

Abstract

Bats provide a number of ecosystem services in agricultural areas, including the predation of night-flying insects, for which they are estimated to save agricultural industries billions of dollars per year. Intensive agriculture has many negative effects on biodiversity, and it is important to understand how wildlife exploit available habitats to allow persistence in these human-modified landscapes. To better evaluate the effectiveness of bats’ pest-controlling services, and to increase understanding of bat foraging behavior in these historically open grassland landscapes, we estimated bat activity and insect abundance in and around crop fields in southeast Nebraska, USA. Specifically, we used a novel acoustic grid sampling approach to document and visualize spatiotemporal activity patterns by different bat species over agricultural fields and forested habitat along crop field edges. Bat activity was highest in areas with the most forested edge habitat, and sites with more trees and water typically had more species present. Bat species and activity was low in isolated forest fragments and sites with minimal habitat edges, but overall insect volume did not decline away from field edges, suggesting that ecosystem services provided by bats likely diminish not because of a decline in resource availability, but because of the lack of structure. Woodland interfaces are important habitats for bats, and the invasion of grasslands by woody species in the Great Plains has increased available bat habitat, and therefore services provided by bats, but with a cost to grasslands and the ecological services they provide. However, although bats are clearly important insect predators that benefit agricultural activities, our ability to quantify the ecosystem services they provide will be greatly improved with a more nuanced understanding of how their activity varies relative to habitat structure and scale within the landscapes where these services are required.