Slow natal dispersal across a homogeneous landscape suggests the use of mixed movement behaviours during dispersal in the Darwin's frog
Résumé
Dispersal is a key process in ecology and evolution. Both theoretical and empirical evidence in actively dispersing organisms support the general notion that the use of nearly straight dispersal paths is a highly ef␣cient way to maximize dispersal success in heterogenous landscapes. In homogeneous landscapes, in contrast, the bene␣ts of a straighter dispersal path could be outweighed by an increase in risk costs, favouring the evolution of tortuous dispersal paths resulting in a relatively slow dispersal. Empirical support for this theoretical prediction, however, has remained elusive. To explore this theoretical pre- diction, we studied the movement behaviour of the southern Darwin's frog, Rhinoderma darwinii, a fully terrestrial amphibian inhabiting a highly homogeneous environment (i.e. South American temperate forest). Using spatial captureerecapture data collected over a 4-year period in wild populations, in combination with statistical and simulation modelling, we found evidence of a slow natal dispersal lasting one year or more. In contrast, adults exhibited high site ␣delity, having a median annual displacement of 3.64 m. A correlated random walk model produced synthetic distributions of juvenile annual displacement that were nearly identical to the empirical data, suggesting that a plausible explanation of juvenile dispersal is the use of routine movements (with high path tortuosity) over short temporal scales (<3 months) integrated over the year along a relatively straight dispersal path. We predict that for species living in homogenous landscapes, this behaviour likely reduces many of the costs associated with the transient stage of dispersal. Speci␣cally, periods of routine movements might reduce risk costs (e.g. dying due to starvation or predation), while the integration of these periods along a straight line maximizes dispersal distance while minimizing energetic costs.