Can temperature modify the strength of density‐dependent habitat selection in ectotherms? A test with red flour beetles

Habitat selection is an important aspect of the ecology of animals and models predict that density dependence is a strong force shaping patterns of habitat selection. In ectotherms, however, density dependence of fitness tends to weaken as temperature deviates from the species’ optimal temperature ( T o ). This may have important implications for density‐dependent habitat selection because the underlying mechanism for density‐dependent habitat selection is density dependence in fitness. We examine how temperature can modify the predictions from isodar theory and obtain temperature‐dependent predictions for density‐dependent habitat selection. We specifically predict that the isodar's intercept will be furthest from zero and the slope will be steepest at the optimal temperature. As temperature deviates from the optimal temperature, we predict that the intercept will approach zero and the slope will approach one. We then test these predictions with experiments on habitat selection based on food abundance by red flour beetles in the laboratory. We also confirm that fitness decreases as density increases and that density dependence weakens as temperature deviates from T o . In agreement with our predictions, preference for habitats with more food weakened as density dependence weakened. Our results have implications for habitat selection by ectotherms because we demonstrate that variation in environmental temperature can weaken markedly the effect of density on both fitness and habitat selection. High density may entail no fitness costs for ectotherms that cannot maintain their optimal temperature.