Evolutionary adaptation and stress: energy budgets and habitats preferred.

Natural populations are normally exposed to substantial environmental stress. The consequences of stress include elevated metabolic costs and additive genetic variability. From the former, preferred habitats should be located in environments corresponding to minimum total energy expenditure. This tendency occurs in the field for behavioral adaptation of Drosophila to variable temperature (and humidity) conditions. Laboratory studies of resource preference in Drosophila suggest a low genetic variability. However, under more stressful field conditions, genetic variability should be higher. Habitat preference studies under stressful conditions therefore need to be emphasized in modeling situations in nature.