Responses of anurans to composition and configuration of agricultural landscapes

It is imperative to identify farming systems that support biodiversity. Amphibians are the most threatened class of vertebrates globally and are particularly sensitive to the impacts of agricultural intensification. While it is known that areas of natural cover are important for amphibians in farmland, it is unknown whether cropped areas of the landscape can be structured in ways that benefit them. We examine relationships between anurans (frogs and toads) and farmland heterogeneity (structural complexity of cropped areas). We hypothesize that anurans benefit from higher compositional and configurational heterogeneity via increased prey resources and refuge habitat, and facilitation of movement. We measure compositional heterogeneity as crop diversity and configurational heterogeneity as mean field size in agricultural landscapes. We predicted that anuran richness and abundance are positively related to crop diversity and negatively related to mean field size. We surveyed 34 agricultural landscapes in eastern Ontario, Canada, representing gradients in farmland heterogeneity, for anuran richness and abundance. We used a multi-model inference approach to calculate and compare model-weighted mean coefficients to determine the direction and relative importance of landscape variables on anuran response variables. While species richness and abundance were most strongly related to the amount of forest in the landscapes, anuran abundance was also negatively related to mean field size (i.e. positive association with configurational heterogeneity). In addition, the presence of one species, the American toad, was positively associated with crop diversity. Our results suggest that conserving natural habitats such as forest is the most effective means of maintaining anuran diversity and abundance in agricultural landscapes, but that increasing the landscape configurational heterogeneity through reduction of crop field sizes can provide an additional strategy to enhance anuran abundance.