Habitat selection in two species of short-horned grasshoppers : The role of thermal and hydric stresses.

The roles of thermal and hydric stress in habitat selection by two species of short-horned grasshoppers was investigated through field and laboratory studies and computer simulation experiments. Psoloessa delicatula was found to possess an elaborate repertoire of thermoregulatory postures and shade seeking behavior. This grasshopper was found in habitats in the shortgrass prairie in which bare patches of ground were common. It was found to regulate its body temperature to a relatively constant level over the course of a sunny day. Eritettix simplex was found in patches of dense vegetation, and its body temperature was usually similar to ambient temperature. During controlled laboratory experiments, E. simplex nymphs lost water rapidly and thus were presumed to be restricted to more mesic environments where desiccation stress is less. A thermal energy budget model was constructed and showed that the habitat selected by P. delicatula would allow behavioral thermoregulation whereas the habitat selected by E. simplex should preclude regulation of body temperature by behavioral means.