Stop and ask for directions: factors affecting anuran detection and occupancy in Pampa farmland ponds

There is a great need to understand the effects of man-made land transformation on freshwater biodiversity, because agricultural landscapes provide habitat for many aquatic and semi-aquatic organisms. However, not all forms of land use are equal in their capacity to support wildlife. Cattle grazing leads to a change in pasture vegetation structure, whereas conversion to commercial crop-based agriculture promotes structural and chemical degradation of the ecosystem. From 2010 to 2012, in the Pampa biome, southern Brazil, we modelled anuran occupancy for 39 farmland ponds. Specifically, we determined detection probabilities associated with survey- and pond-specific variables and examined tadpole occupancy in relation to land use in southern Brazil. We recorded eleven anuran species, but only five were detected at levels suitable for occupancy modelling. Species detectability varied with water temperature, extent of floating macrophyte cover, and sampling date. For three species, detection-adjusted occupancy models indicated a relationship between occupancy and agricultural activities and/or livestock management. Agriculture areas negatively affected occupancy by Odontophrynus americanus and Physalaemus gracilis. The presence of livestock within a 500 m radius positively affected pond occupancy by Hypsiboas pulchellus. Other species were negatively associated with pond area or fish presence. Our results demonstrate that traditional extensive livestock farming can provide a buffer that protects freshwater environments, because it did not greatly modify the grassland matrix. We argue that further species-based approaches will be critical for developing effective conservation strategies for anurans, particularly in the context of the expanding rice production/exotic forests in southern Brazil.