Differential responses of anuran assemblages to land use in agroecosystems of central Argentina

Agriculture has been identified as one of the largest contributors to the current global biodiversity crisis. Amphibians are declining worldwide, and the loss of habitat and water contamination related to agricultural land uses have been suggested as the main drivers of this phenomenon. In central Argentina, the Pampean Region combines the highest rates of grassland replacement of South America, the lowest percentage of protected areas of the country, and the lack of studies exploring diversity patterns of native amphibians occurring in agroecosystems. To fill these gaps, we surveyed anuran (frogs and toads) assemblages from 342 breeding ponds located in three ecological units from central Argentina (Rolling, Flooding, and Inland Pampas) during three breeding seasons (2015-2018). We aimed to evaluate the importance of breeding habitat characteristics (ponds) and the surrounding landscape features as drivers of anuran diversity occurring in agricultural landscapes under the primary land uses of the region (cattle grazing and soybean cropping). We tested for the effects of breeding habitat characteristics and landscape features on anuran richness, abundance, and individual species occurrence, using GLMM models and information-theoretic procedures. Results indicated that species richness and total abundances were differently influenced by the habitat and landscape features across the ecological units. Overall, vegetation cover of the ponds and land use were the most important variables influencing richness and anuran abundance. The positive influence of pond vegetation cover on anuran assemblages was registered for all the ecological units, while different patterns emerged when we analyzed the effects of land use surrounding the ponds. Land use expressed as the percentage of soy crop surrounding the ponds negatively affected richness and abundance of anurans of the Flooding Pampas, but the inverse relation was found for assemblages occurring in the Inland Pampas. Moreover, multiple competing models suggested a positive correlation between anuran diversity and land-use heterogeneity, and pond density. The differential responses of anuran assemblages among the ecological units can be related to a combination of several factors encompassing regional soil characteristics (i.e., soil texture), land-use intensity as well as requirements of anuran species. We discussed the particularities of each ecological unit in order to recognize those conservation efforts that will favor anuran diversity in these altered landscapes and further contribute to achieving agricultural sustainability.