Red flour beetles balance thermoregulation and food acquisition via density‐dependent habitat selection

Abstract Theories of habitat selection assume that habitat selection patterns are based on the fitness consequences of selecting a particular habitat, and predict that individuals should be distributed between habitats so that each individual obtains the same fitness. The predictions are relatively simple when habitat suitability is based upon the quantity of depletable resources, such as food, in a habitat: individuals should be distributed between habitats in proportion to the depletable resources in those habitats. Yet, non‐depletable resources can also be important in habitat selection. For example, ectotherms must obtain heat from the environment, which causes them to select habitats based, at least partly, upon thermal quality. Non‐depletable resources can cause habitat selection that is independent of density and may modify the value of depletable resources. We used red flour beetles Tribolium castaneum to test the hypothesis that habitat selection by ectotherms depends upon both food abundance and temperature. We determined the thermal preference of red flour beetles. We then conducted habitat selection experiments with beetles when habitats were set at their preferred temperature and 10°C below their preferred temperature. We simultaneously manipulated food abundance in both habitats, and varied population density. We also examined the fitness effects of habitat selection by measuring oviposition rates of beetles. Beetles selected the habitat within their preferred temperature when food was equal between habitats and when food was higher in that habitat across all population densities. Beetles showed equal preference for high‐ and low‐temperature habitats when food was higher in the low‐temperature habitat across all population densities. Fecundity was always higher at the preferred temperature of beetles, regardless of food abundance or population density. Temperature is clearly an important factor in habitat selection of ectotherms and should be considered whenever thermal differences exist between habitats.