Ant–plant interaction in the Neotropical savanna: direct beneficial effects of extrafloral nectar on ant colony fitness
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Current evidence suggests that ant–plant relationships may influence species composition, abundance, and interactions at the community scale. The main resource that plants offer to ants is extrafloral nectar (EFN) and the major part of published studies shown benefits from ants to plants possessing EFNs. However, the complementary question of whether and how ants benefit from EFNs is rarely addressed. Here, we present the results of a long-term study to demonstrate whether EFN has a positive effect on ant colony fitness. We quantified colony growth rate, survival and the final weight of individuals as measures of benefit derived from EFN. Our results provide clear evidence that EFN can have a significant positive impact on the survivorship, growth and reproduction of the Myrmicinae Cephalotes pusillus. In fact, a diet rich in EFN (providing at least 30 cal per day) resulted in five times more individuals per colony, greater body weights, and more eggs. These results have shed new light on the relationships between ants and EFN-bearing plants such as in tropical and temperate systems. The ant C. pusillus is the first case in which we have firm evidence that EFN improves colony growth and development, corroborating more than 100 years of experimental evidence of benefits to plants in these widespread relationships.
KeywordsCephalotes Chamaecrista Colony growth rate Mutualism Tropical
We thank to Judith Bronstein, Heraldo L. Vasconcelos, Sérvio P. Ribeiro, Gustavo Q. Romero and three anonymous referees for valuable comments on the early version of the manuscript. We specially thank Michele Lanan for suggestions and a strong English review. Authors thank financial support from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (J. Byk/graduate fellowship) and Conselho Nacional de Ciência e Tecnologia (K. Del-Claro, PQ/research grant).
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