Mobility and metapopulation structure of Geocrinia alba and Geocrinia vitellina, two endangered frog species from southwestern Australia

Dispersal rates can have an important impact on many population processes. Dispersal can lead to population regulation and regional stability in the face of local instability through the formation of a metapopulation. This may be particularly true for frogs because they often have patchy distributions. In this paper I investigate dispersal by male Geocrinia alba and Geocrinia vitellina, using a mark-recapture study. Pit traps were used to determine whether frogs move out of their breeding habitat. I found that both species were very philopatric. Between the 1993 and 1994 breeding seasons, 76-86% of individuals were displaced less than 10m and 90-97% were displaced less than 20m. Dispersal was even lower within each breeding season, with 92-95% of individuals being displaced less than 5 m. Pit trapping indicated that some individuals of both species move out of the swamps in late autumn and return at the beginning of the breeding season, in late winter and early spring. Therefore, although displacement may be very restricted, the frogs are likely to move greater distances. The extreme breeding-site philopatry exhibited by G. alba and G. vitellina suggests that movement between disjunct populations is unlikely and that populations in continuous habitat may be relatively isolated from one another by distance alone. This is consistent with previous predictions based on genetic studies, which suggested there was very little migration between populations. These data support the contention that neither species is likely to exist as a metapopulation because recolonization of vacant habitat is improbable.