UC San Diego

The compensation hypothesis predicts that the value of a nutrient increases with its scarcity in the environment. Organisms will thus seek out limiting nutrients in order to maximize their growth. In this study, we evaluated this hypothesis by examining Argentine ant (Linepithema humile) foraging preferences in three different habitats (intertidal beach, riparian woodland, and scrub) in southern California. We used standardized baiting (protein, carbohydrate) transects and stable isotope analysis to determine if short-term behavioral responses at baits reflect longer-term patterns of resource assimilation. Habitats were replicated in eight blocks of each of the three habitats. Ants showed strong preferences for carbohydrate

baits in all three habitats, but the δ15N values significantly differed as a function of habitat. The δ15N values of the Argentine ant were highest in beach habitats, reflecting assimilation of marine-derived resources, intermediate in riparian woodlands, and lowest in scrub. Carbohydrate preferences exhibited by the Argentine ant across the environmental gradient reflect the well-known preferences for sugar exhibited by this species and more generally reflect how short-term behavioral responses may not always reflect longer patterns of resource assimilation.