Food limitation and starvation independently affect predator macronutrient selection.

Predators are often food limited in their habitat, and some are limited by specific macronutrients (protein, lipid or carbohydrate). It is unresolved, however, to what extent and in what way food and macronutrient limitation are connected. Using a carabid beetle (Nebria brevicollis), we compared macronutrient self-selection of the animals three times: immediately after collection in the field, after being fed to satiation and nutritional balance and after a subsequent period of starvation. Both sexes were food and females lipid limited in the field; after 7-21 days of starvation both sexes increased proportional carbohydrate intake significantly. Thus, starvation created a nutrient deficit that was different from what the animals had experienced in the field. We conclude that while macronutrient limitation in nature may be influenced by hunger due to food limitation, this is not its main determinant. A nutritional imbalance of available food may override this effect.