How fast do amphibians disperse? Introductions, distribution and dispersal of the common frog Rana temporaria and the common toad Bufo bufo on a coastal island in Central Norway

摘要

The common frog (Rana temporaria) and the common toad (Bufo bufo) were introduced successfully?to the coastal island of Fr?ya in Central Norway several times during 1960–2012. There is still a very?high degree of conformity between sites where they were introduced and the present distribution of?the two species. However, in western Fr?ya, a release of frogs about 1996 was followed by a quick?expansion of their distribution area; in 2012 and 2013, breeding was registered close to 7 km westwards?and eastwards, respectively, i.e. a population dispersal speed of approximately 0.4 km/yr. On eastern?Fr?ya and some small islands in the archipelago, area expansions at another four frog localities have?been prevented by ecological barriers like unfavourable limnetic or terrestrial habitats or salty water.?Two local common toad populations on eastern Fr?ya do not show any expansion either. However, an?apparently isolated record of the species on western Fr?ya in 2011 can possibly be explained by the?expansion westwards of a population in northern central Fr?ya, where toads were introduced around?1995. This stretch is about 9.9 km, i.e. an average population dispersal speed of 0.6 km/yr.