Background/Question/Methods - Food availability often influences competitive outcomes through differential effects on growth and reproductive output. Although it has received less attention, resource conditions may also influence competition through nutritional effects on behavioral performance. The link between nutrition and competition may be particularly important for ants because of their dietary diversity and often substantial investment in competitive interactions. One hypothesis linking nutrition and competitive performance in ants posits that increased access to carbohydrates allows colonies to invest more in worker traits underlying behavioral dominance; we label this the metabolic fuel hypothesis. This hypothesis leads to the prediction that interference competition should be particularly costly for ant colonies with less access to metabolic fuels such as carbohydrates because such colonies have fewer worker resources for patrolling territories and defending food finds. We tested this prediction by varying diet protein:carbohydrate (P:C) ratio and exposure to interference competition for colonies of the Argentine ant (Linepithema humile), a widespread invasive species.
Results/Conclusions - Consistent with the metabolic fuel hypothesis, we found that when facing interference, Argentine ant colonies increased patrolling activity much more when reared on higher carbohydrate (lower P:C) diets. However, diet had little effect on per capita patrolling, suggesting dietary effects were due primarily to the large diet-related changes in colony size. Using performance assays, we found that in fact diet composition had little effect on individual worker activity and aggression; instead, these traits depended primarily on whether colonies had previously been exposed to competitors. Our results suggest that dietary P:C ratio has an important influence on Argentine ant colony–level performance in a competitive environment and thus access to carbohydrate resources may be an important factor underlying the success of this invasive species. However, this effect stems primarily from changes in worker number rather than changes in individual worker behavior.