Increased dispersal rates and distances in density-stressed bush crickets (Metriophera brachyptera).

Abstract

The limitation of dispersal due to habitat fragmentation is considered as one key factor for an increasing risk of extinction especially in sedentary species with low dispersal ability. A few studies on grasshoppers and crickets indicate that dispersal ability even of sedentary species may have been underestimated in the past. It is argued that certain environmental conditions can trigger and increase dispersal in such species. In a first set of experiments emigration rates of the bush cricket Metrioptera brachyptera (L., 1761) were recorded in 'microcosms' (cage-populations) with various 'population' densities. The proportion of emigrants was correlated with increasing densities. In a second set of experiments individuals stressed by high densities as well as individuals that were not submitted to this stress were released on a soccer field and dispersal patterns of both groups were recorded. Stressed individuals dispersed significantly faster and further than unstressed ones. The results indicate that dispersal is induced by certain environmental conditions suggesting episodic colonization patterns which occur even in sedentary species.

Keywords

Dispersal, emigration, experimental approach, metapopulation, microcosm.