Sexual harassment in heterogeneous landscapes can mediate population regulation in a grasshopper

Population regulation has been related to differences in the quality among habitats, which mediate differences in vital rates such that in poor habitats reproductive rates are lower than those in high-quality habitats. The spatial distribution of animals in such habitats depends on their preferences and the degree to which individuals have a free choice of a particular habitat. The identified mechanisms that lead to a particular spatial distribution and eventually to regulation mainly include foraging-related interference, for example, ideal free distribution, or simple selection of available high-quality habitats, that is, site-dependent habitat selection. However, in insect species these mechanisms might not be applicable, but density-dependent habitat selection still occurs. We therefore suggest a mechanism that refers to the nearly universal observation that matings also bear fitness costs. Although these costs have been investigated on the individual level in many insect species, their consequences for population dynamics have not yet been addressed. In the grasshopper species Stenobothrus lineatus, females in a nonreceptive mating status escape sexually approaching males by undirected jumps. By including such avoidance behavior in a spatially-explicit simulation model, we investigated its potential to result in progressive use of low-quality habitats at increasing population densities. In particular, we show that (1) such behavior changes habitat selection, (2) altered habitat selection results in population regulation, and (3) the degree of habitat heterogeneity influences regulation such that (4) heterogeneous habitats show finetuned regulation and homogeneous habitats tend to support large fluctuations.