Slow natal dispersal across a homogeneous landscape suggests the use of mixed movement behaviours during dispersal in the Darwin's frog

Abstract

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 efficient way to maximize dispersal success in heterogenous landscapes. In homogeneous landscapes, in contrast, the benefits 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 prediction, 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 capture–recapture 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 fidelity, 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 (