Connectivity of local amphibian populations: modelling the migratory capacity of radio‐tracked natterjack toads

Abstract

AbstractThe delimitation of the spatial equivalent of isolated populations or interacting sets of local populations is crucial for conservation management. In Amphibia, spatial organization in metapopulations requires knowledge on the individual variation of annual migratory capacity within local populations to delimit core habitats around the breeding site and to estimate the connectivity among neighbouring populations. The migratory behaviour of 143 adult Bufo calamita was monitored using radio‐telemetry at eight localities covering a latitudinal range from 41° to 54°N. Aims of the study were to assess the geographic variation of migratory distance moved by males and females and to model their capacity for dispersal assuming exclusively unidirectional movements. Migratory range was not sex‐biased, but was three times lower in population inhabiting sandy areas than in those on clay soils, probably because of the scarcity of moist shelters causing more frequent and more distant movements. For conservation management of local natterjack populations, we propose to use the migratory capacity of the 50% most sedentary individuals to delimit the core area around a given breeding site. To estimate the potential genetic connectivity between neighbouring local population, we propose to use the minimum migratory capacity of the 5% of individuals that moved most. Estimates obtained for populations in central Europe and the UK indicate a core area of 600 m around the breeding site and a maximum distance of 2250 m between the breeding ponds to maintain connectivity. Thus, the principal conservation problem in the UK is that most populations are isolated by distance and prone to local extinction. In contrast, core areas of populations in Spain extend to distances of about 5 km and connectivity is maintained up to a distance 12 km between neighbouring breeding ponds.