Spatial movement patterns in frogs: Target-oriented dispersal in the pool frog, Rana lessonae

Abstract

The spatial movement pattern of pool frogs (Rana lessonae Camerano) was studied at two breeding ponds surrounded by drift fences at 60˚n in Sweden. Fence traps were classified according to (i) surrounding vegetation, or (ii) whether they were situated in a direction leading towards forest, adjacent marshes or neighboring pool frog localities. Observed captures per trap category were tested against numbers expected from random movements. Trap records of individually marked frogs were used in the analyses, which were performed separately for three time periods throughout the active season, each of two study-years. By separating captures during days with singly moving frogs (dispersers) from those during days with simultaneous group movements, the orientation of dispersal versus group (migration) movements were also compared. The movements of both adults and juveniles were significantly and consistently directed during all time periods, and generally the movements of singly-moving frogs were as target-oriented as those of frogs participating in simultaneous group movements. Significant deviations from random movements were also scored with respect to vegetation, but usually coincided with stronger deviations in the direction categories. This movement pattern, plus recaptures of marked frogs at neighboring breeding ponds, suggests that target-oriented movements prevail both among dispersing and migrating pool frogs. The behavior may have a significant role in observed metapopulation dynamics.