Habitat Segregation in Ground Crickets: Experimental Studies of Adult Survival, Reproductive Success, and Oviposition Preference

The closely related ground crickets Allonemobius allardi and A. fasciatus provide a striking example of habitat segregation. Both species are abundant in pastures and grasslands in the northeastern United States, but they occupy different parts of these habitats. At a site in northwestern Connecticut, we found nearly pure single—species populations at the extremes of a moisture gradient. Allonemobius allardi occurred in dry pasture, A. fasciatus in wet pasture. Distribution patterns remained constant from one developmental stage to another and from year to year. We undertook a series of experiments to define the factors that determine habitat associations in these crickets. By introducing single—species and mixed—species populations into enclosures in both wet and dry areas, we could demonstrate no significant differences in adult survival or reproductive success between species. Both A. allardi and A. fasciatus can survive and reproduce in wet and dry habitats. Laboartory choice experiments indicate that differences in oviposition preference also cannot account for field distribution patterns. Indeed, oviposition preference may be a consequence rather than a cause of habitat association.