Abundance and Species Richness of Nocturnal Insects on Organic and Conventional Farms: Effects of Agricultural Intensification on Bat Foraging

Abstract

Abstract: Insects are the principal food for many animals, including bats (Chiroptera), and all species of bats in the United Kingdom feed over agricultural habitats. Bat populations are declining throughout Europe, probably in part as a result of agricultural intensification. Organic farming prohibits the use of agrochemicals, a major component of agricultural intensification, making it an ideal control for a study of intensive agricultural systems. To evaluate the impact of agricultural intensification on bat foraging, we quantified the availability of bat prey by comparing nocturnal aerial insects captured within habitats on 24 matched pairs of organic and conventional farms. Insects were identified to family and moths to species. We compared the abundance of 18 insect families commonly eaten by bats in the United Kingdom between farm types and tested for correlations of abundance with bat activity. Insect abundance, species richness, and moth species diversity were significantly higher on organic farms than on conventional farms. Insect abundance was significantly higher in pastural and water habitats on organic farms than in the same habitats on conventional farms. Of the 18 insect families that are important components of the bat diet, 5 were significantly more abundant on organic farms overall. Some were also more abundant within organic pastural, woodland, and water habitats than on conventional farmland habitats. The activity of bats that mainly ate Lepidoptera was significantly correlated with the abundance of this order. Our observations suggest that agricultural intensification has a profound impact on nocturnal insect communities. Because bats are resource limited, a reduction in prey availability through agricultural intensification will adversely affect bat populations. Less‐intensive farming benefits British bat populations by providing and maintaining diverse and structurally varied habitats, which in turn support a wide selection of insect prey for bats, including insect families that are significant components of the diet of a number of rare bat species.