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

Abstract

The 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.

Genetic variability in geographic populations of the natterjack toad (Bufo calamita)

“…These results have been supported in studies about migratory ranges carried out in populations from Britain, which considered that these populations cannot maintain connectivity of neighboring local populations (Sinsch et al. ). On the contrary, metapopulation dynamics seem to be much greater in populations from the Iberian Peninsula (Sinsch et al.…”

“…In fact, connectivity of local populations by dispersers is great in the Iberian Peninsula indicating a considerably large metapopulation system (Sinsch et al. ). The differentiation among natterjack toad populations is only remarkable in fragmented habitats where populations are isolated (Allentoft et al.…”

“…On the contrary, metapopulation dynamics seem to be much greater in populations from the Iberian Peninsula (Sinsch et al. ) with high genetic diversity and gene flow (Marangoni ).…”

When new human‐modified habitats favour the expansion of an amphibian pioneer species: Evolutionary history of the natterjack toad (Bufo calamita) in a coal basin

“…Among the few available comparable studies, this process of colonization has been suggested in Suaeda maritima , a halophyte plant species that repeatedly colonized former potash mining dumps in Germany (Prinz et al., ; see also Esfeld et al., ). In our case study, B. calamita is known to be a pioneer species with high dispersal capabilities (Miaud, Sanuy, Avrillier, Sanuy, & Miaud, ; Sinsch, Oromi, Miaud, Denton, & Sanuy, ). Thus, the most parsimonious hypothesis is that toads successfully dispersed from natural populations initially established in former semi‐natural habitats (humid meadows or pastures) located in the vicinity of the coalfields (Godin, ).…”

Amphibian decline, pond loss and reduced population connectivity under agricultural intensification over a 38 year period

“…They will, on one hand, not be able to oversee longer routes, such as pond to pond dispersals, but may make well-informed decisions on the basis of the local environment they find themselves in. As data on individual paths are rare for amphibians and may refer to migration rather than dispersal, it is not possible to confirm whether dispersal routes are informed or naïve (Mazerolle and Vos 2006;Vos et al 2007;Sinsch et al 2012;Sinsch 2014). As a consequence, it is necessary to explore both options (Decout et al 2012).…”