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

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.Abundancia y Riqueza de Especies de Insectos Nocturnos en Granjas Orgánicas y Convencionales: Efectos de la Intensificación Agrícola sobre el Forrajeo de Murciélagos Resumen: Los insectos son el alimento principal de muchos animales, incluyendo murciélagos (Chiroptera), y todas las especies de murciélagos en el Reino Unido se alimentan en hábitats agrícolas. Las poblaciones de murciélagos están declinando en toda Europa, en parte probablemente debido a la intensificación agrícola. La agricultura orgánica prohíbe el uso de agroquímicos, un componente mayor de la intensificación agrícola, haciéndolos un control ideal para un estudio de sistemas agrícolas intensivos. Para evaluar el impacto de la intensificación agrícola sobre el forrajeo de murciélagos, cuantificamos la disponibilidad de sus presas mediante la comparación de insectos aéreos nocturnos capturados en hábitats en 24 pares similares de granjas orgánicas y convencionales. Los insectos fueron iden...

Nocturnal Risks-High Bat Activity in the Agricultural Landscape Indicates Potential Pesticide Exposure

“…This appears to be in contrast to other studies reporting insect abundances and diversity being negatively associated with agricultural intensification (e.g., Benton et al, 2002;Wickramasinghe et al, 2004). However, we compared abundance of nocturnal insects with more than 70% being Diptera.…”

Benefits of organic farming to biodiversity vary among taxa

“…Our findings differ from those of Bengtsson et al (2005) mainly in that predatory invertebrates only infrequently showed a significant response. Bats were not included in the meta-analysis of Bengtsson et al but Wickramasinghe et al (2004) have also suggested that organic farming is beneficial to bats, both through provision of more structured habitats and higher abundance of insect prey.…”

Moths and management of a grassland reserve: regular mowing and temporary abandonment support different species

“…Some studies targeted entire landscapes, comparing management impacts on insects over large scales (Bergman et al 2004;Wickramasinghe et al 2004). They typically relied on a few model groups, such as butterflies (Öckinger & Smith 2006;Rundlöf et al 2008), or bumblebees (Haaland & Gyllin 2010), although multi-taxa comparisons also exist (Meek et al 2002;Roth et al 2008;Sjodin et al 2008;Čížek et al 2012).…”