Net benefits of a mutualism: Influence of the quality of extrafloral nectar on the colony fitness of a mutualistic ant

Aim Extrafloral nectar, a carbohydrate-rich liquid, is the main plant-based resource offered in exchange for ant protection. The positive results of this protection provided by ants are widely studied and supported; however, studies showing the benefits that ants and their colonies have from the resources offered by plants such as extrafloral nectar are scarce. Here, we evaluated how extrafloral nectar and artificial food resources with different nutrient concentration benefit short- and long-term Camponotus crassus colony fitness (number and weight of individuals) and survival. Methods We conducted two sets of experiments: (1) in the field we attached artificial ant nests to plants with clogged and unclogged extrafloral nectaries; and (2) in the laboratory we offered artificial food resources with different carbohydrate-protein ratios to ant colonies. With these experiments, we evaluated the number and weight of queens, adult workers, pupae, larvae, and eggs, as well as the survival probability of the colonies. Results In the first experiment, the short-term provision of extrafloral nectar resulted in a larger number and weight of individuals with access to this resource. In the second experiment, regardless of time, the supply of more concentrated carbohydrate and nitrogen food increased ant colony fitness and survival. Conclusion: We provided new evidence that extrafloral nectar significantly benefits ant colonies. Our results corroborate the assertion that these relationships are reciprocally beneficial.