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 Melastoma malabathricum flowers, pollinated by large carpenter bees, Xylocopa spp., produce ant attractants that recruit weaver ants, Oecophylla 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 Xylocopa 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.
Summary
1.Although theoretical models suggest that ambush predators could have a wide range of ecological and evolutionary effects on plant-pollinator interactions, these models require predators that are both abundant and mobile. Crab spiders, the main model system for studying the effects of ambush predators on plant-pollinator interactions, are neither of these. 2. The weaver ant Oecophylla smaragdina is a keystone predator in South-East Asian forests. It uses the flowers of a wide range of native and introduced species as hunting platforms for incoming pollinators. Weaver ants affect the behaviour of flower visitors and the reproductive success of their host plants.3. Due to their ubiquity and mobility, O. smaragdina ants satisfy the assumptions of the theoretical models. They have the potential to affect the structure of pollination networks. 4. Synthesis. Oecophylla smaragdina in South-East Asia, and possibly other predatory ant species in African and American tropical forests, may play a key role in shaping the ecological and evolutionary trajectories of plant-pollinator interactions.
Predator avoidance and foraging often pose conflicting demands. Animals can decrease mortality risk searching for predators, but searching decreases foraging time and hence intake. We used this principle to investigate how prey should use information to detect, assess and respond to predation risk from an optimal foraging perspective. A mathematical model showed that solitary bees should increase flower examination time in response to predator cues and that the rate of false alarms should be negatively correlated with the relative value of the flower explored. The predatory ant, Oecophylla smaragdina, and the harmless ant, Polyrhachis dives, differ in the profile of volatiles they emit and in their visual appearance. As predicted, the solitary bee Nomia strigata spent more time examining virgin flowers in presence of predator cues than in their absence. Furthermore, the proportion of flowers rejected decreased from morning to noon, as the relative value of virgin flowers increased. In addition, bees responded differently to visual and chemical cues. While chemical cues induced bees to search around flowers, bees detecting visual cues hovered in front of them. These strategies may allow prey to identify the nature of visual cues and to locate the source of chemical cues.
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