Bats in the agricultural matrix: Factors driving species richness and activity

Background/Question/Methods

Agricultural intensification is a major driver of global species loss as complex, natural systems are converted to simple, homogeneous agricultural systems. Despite the negative impacts of agriculture on biodiversity, agricultural landscapes are critical to the long-term conservation of many species. As mobile organisms, bats can utilize roosting and foraging habitat that are distributed throughout the agricultural matrix. Bats are voracious predators of night-flying insects and provide economically important pest control services to agriculture. However, on-farm practices and surrounding habitat may influence the quality of the agricultural matrix for bat conservation, as well as pest control services provided by bats. I used bat detectors to compare bat species richness and activity in the Central Coast region of California. I monitored bats on paired organic and conventional farms during the summer for two years, and in nearby natural habitat patches for one year. I identified bat calls to species using Sonobat and visual identification. I categorized landscapes as simple or complex using a GIS and the National Land Cover Database, and then used linear mixed effects models to assess the impact of farm management and landscape complexity on bat species richness and activity.

Results/Conclusions

I recorded a total of 10,893 5-second bat call segments, and identified 4,661 calls. I identified 12 species, and the most common were Tadarida brasiliensis (45%) and Myotis yumanensis (41%). Species richness was significantly greater in complex than simple landscapes. Furthermore, natural habitat bolstered species richness more in simple than complex landscapes. Bat activity was strongly correlated with local land use and was lower on farms that in nearby remnant natural habitat. Additionally, bat activity was correlated with surrounding land use, and there was greater bat activity at sites with a lower percentage of surrounding agriculture and a higher percentage of surrounding forest within 1.5km. There was no significant response in bat species richness and activity to differences in farm management, although organic farms had greater bat species richness and activity than conventional farms. Bats utilize natural habitat more than open agricultural areas, which may be explained by the lack of linear landscape elements (e.g. trees and forest edges) that bats use as flyways. The retention of remnant natural habitat may be an important strategy to protect bats in agricultural landscapes, especially in simple landscapes dominated by agriculture where little natural habitat remains.