The relative availabilities of complementary resources affect the feeding preferences of ant colonies

Theory predicts that consumers selecting among complementary resources will show stronger preferences for items that become relatively less available. I tested this hypothesis in a field study that compared the preferences of ant colonies given simultaneous access to experimental foods differing in carbohydrate and protein content. In the first part of the study, I examined the effect of nutrient supplementation on colony-level preference in the ant Dorymyrmex smithi. Colonies that had received a protein solution for 24 h consumed proportionally more carbohydrates than control colonies that had been given access to water, suggesting that colonies preferred nutrients when they became relatively rare. In the second part of the study, I compared colony-level preference among eight species of ants that differ in their relative access to carbohydrates and protein in the field. I found that species with relatively easy access to carbohydrates preferred protein, whereas species with greater access to protein preferred carbohydrates. These results suggest that the benefits of a nutritionally mixed diet coupled with differences in the relative availability of nutrients may explain variation in feeding decisions both within and among ant species.