Seeing the Small: Investigating the Diffuse Effects of Inga-Ant Mutualism in Seedling Communities of the Ecuadorian Amazon

Mutualisms between plants and animals work to the benefit of both parties, but their broader impacts are not often considered. For example, plants in the neotropical tree genus Inga have specialized nectar-producing glands on their leaves called extrafloral nectaries (EFNs) that provide food to ants in return for defense from herbivorous insects. Such ant-plant interactions can alter the mutualist ants’ behavior and spatial dynamics, impacting surrounding insects and plants. The Inga tree is often studied in agroforestry contexts, but few studies have been conducted on the potential diffuse impacts of the Inga-ant mutualism in non-cultivated contexts. In the lowland rainforests of Amazonia, Inga is one of the most abundant and diverse tree genera, suggesting the potential for a large effect. In this study, I measured rates of standing herbivory in seedling plots based around 102 focal Inga plants. I found differences in the likelihood of attack by herbivores, but no difference in the extent of damage between seedlings near and far from an Inga. These results indicate little support for the hypothesis that ant defense of leaves extends beyond their direct mutualism, but that further study may reveal other effects of EFN-mediated ant–plant mutualisms in plant communities.