Mitigating the impacts of agriculture on biodiversity: bats and their potential role as bioindicators

Agriculture is a dominant land use worldwide with approximately 40% of the land's surface used for farming. In many countries, particularly parts of Europe, this figure is substantially higher and most agricultural land is under intensive practices aimed at maximising the production of food. The intensification and expansion of modern agricultural practices led to the biological simplification of the farmed environment, which has resulted in declines in farmland biodiversity during the last century. As with other taxa, many bat species have suffered severe population declines during the 20th century, with agriculture believed to be one of the main drivers reducing roost availability and foraging habitat. Lower intensity farming methods, and the creation or management of habitat features on farmland could potentially mitigate some of these negative impacts but the effects of this on bats, in comparison to other taxa, have received relatively little attention. Here, I review evidence on the impacts of efforts to increase biodiversity in agricultural landscapes on bat populations, and explore whether responses of bats to agricultural activities are similar to those of other taxa, a necessary requirement if they are to be used as bioindicator species. There are relatively few studies with which to assess the effects of management interventions on bats in agricultural landscapes, and these are restricted to only a few countries. Nevertheless, there is evidence that bats benefit from lower intensity agricultural systems, specifically organic farming and shaded agroforestry: these systems tend to be associated with higher bat abundance, species richness and diversity, and are more heavily utilised by foraging bats. Whilst very few studies have explicitly tested the utility of bats as bioindicators in agricultural landscapes, overall, the response of bats to lower intensity agricultural systems also reflects responses by other taxa. These studies have been largely restricted to temperate regions, however. The review highlights several major gaps in our knowledge of bats in agricultural landscapes and where future research could be usefully directed including: (1) a broader geographical range of studies examining both the efficacy, and the underlying mechanisms through which lower intensity agricultural systems may benefit bats; (2) the potential for lower intensity systems in key crops such as oil-palm; (3) studies of the demographic effects of conservation management on bats; (4) in order to assess the potential of bats as bioindicators, studies quantifying the response of both bats and other taxa to environmental change in a wider range of biomes and regions are needed.