Indirect ant-protection against crab herbivory: damage-induced susceptibility to crab grazing may lead to its reduction on ant-colonized trees

1. Mangrove trees colonized by weaver ants (Oecophylla smaragdina) experience less insect and crab herbivory compared with trees without ants. However, it is unlikely that ants prey on and deter crabs as they do insects. Protection could be indirect if leaves damaged by insects are more susceptible to crab herbivory. 2. In the field and in laboratory tests, leaves with artificial holes simulating leaf beetle-feeding marks were more susceptible than intact leaves to damage by the crab Episesarma versicolor. 3. The study further revealed that damaged leaves showed increased susceptibility only to male crab feeding whereas females were indiscriminate, probably because of differences in claw morphology between the sexes. 4. Combined with previous findings at the same field site, these results suggest that ants can indirectly protect trees against crab herbivory by directly removing insect herbivores and thus decreasing the leaf damage they inflict. The system illustrates a complex trophic cascade involving density and trait-mediated indirect interactions.