Individual Mobility Prevents an Allee Effect in Sparse Populations of the Bush Cricket Metrioptera roeseli: An Experimental Study

The bush cricket, Metrioptera roeseli (Orthoptera, Tettigoniidae), occurs in patchy and heterogeneous agricultural landscapes. Such a mosaic of different types of grassland habitats causes spatial variation in local population density. Low population densities may result in fewer mating opportunities that can give rise to an Allee effect, possibly leading to a population decline or extinction. This experimental study shows that individuals can avoid an Allee effect by adjusting their movement behaviour in sparse populations. Even at a population density of five individuals per hectare, i.e. approximately one percent of normal population densities, no reduction of mating frequencies was detected. Observed net displacements made by different individuals in high and low population densities could successfully be predicted by a simple model of animal movement.