Flowers attract weaver ants that deter less effective pollinators

Summary 1. Many flowers produce ant‐repellent substances that prevent ants from discouraging pollinator visits. When a flower's most effective pollinator is unaffected by predatory ants, however, flowers should benefit from the presence of ants that deter less effective pollinators from consuming resources. 2. Behavioural assays revealed that M elastoma malabathricum flowers, pollinated by large carpenter bees, X ylocopa spp., produce ant attractants that recruit weaver ants, O ecophylla smaragdina . 3. The presence of ants was associated with an increase in the reproductive success of M . malabathricum flowers. This outcome likely resulted from the filtering effect of ants on the community of flower visitors: ants deter less effective pollinators and attract X ylocopa bees through an indirect effect on resource depletion. 4. Synthesis . Although plant–pollinator interactions are classified as mutualisms, not all flower visitors are effective pollinators, and some can be parasites or conditional parasites. As a result, predators that deter flower visitors can have positive or negative effects on plant fitness, depending on whether they deter all visitors or a subset of them, and on the relative effectiveness of deterred and undeterred visitors.