Combining landscape genetics, radio-tracking and long-term monitoring to derive management implications for Natterjack toads (Epidalea calamita) in agricultural landscapes

Understanding the influence of landscape elements on movement and connectivity of potentially isolated populations is essential for successful conservation management, especially in agricultural landscapes. Here, we assessed the movement and genetic structure of the endangered Natterjack toad (Epidalea calamita) in an intensively managed agricultural landscape of the Central Plateau in Switzerland. Movement was analysed on the basis of molecular markers and radio-tracking, supplemented by long-term monitoring data describing population trends. A total of 19 migration events were detected by genetic first-generation assignment tests (11), by unintentional repeated genetic sampling of individuals (6) and by radio-tracking between predefined populations (2). None of the breeding sites was genetically isolated, although there was a trend that, in addition to geographic distances > 2.5 km, built-up areas enhanced genetic differentiation. Analysing the toad populations as a spatial network supported the inference that the two largest populations were sources, suggesting population size as a major driver of the movement pattern. We conclude that the Natterjack toad is well established in the intensely managed agricultural landscape, given that (i) large populations are maintained which may act as sources to spatially distributed occurrences, and (ii) the intensively managed landscape is sufficiently interspersed with suitable breeding habitats.