Protein matters: ants remove herbivores more frequently from extrafloral nectary-bearing plants when habitats are protein poor

Abstract

More aggressive and competitive ant species are better bodyguards for extrafloral nectary (EFN)-bearing plants. Therefore, any factor that increases the relative value of EFNs to ants should benefit the plants, because it would increase the probability of the plant interacting with more aggressive ants. We hypothesized that the frequency of plant attendance by more aggressive ants and the efficiency of plant defence by ants will be higher when the availability of carbohydrates and/or proteins to ants is low. We established 19 plots with five focal plants from the EFN-bearing species Turnera subulata per plot. For each focal plant, we recorded the identity of the attending ants and their efficiency in removing simulated herbivores from the plant. In each site, we estimated the biomass of soil arthropods and the number of apical meristems with active EFNs as proxies of protein and carbohydrate availability, respectively. The probability of interacting with more aggressive ant species was not influenced by the number of meristems with active EFNs or by arthropod biomass. However, simulated herbivores were removed more frequently in plots with lower arthropod biomass. This suggests that overall ant aggressiveness towards other arthropods increases in protein-poor sites, potentially increasing the efficiency with which EFN-bearing plants are defended against herbivores.

anti-herbivory defence, carbohydrate availability, ecological stoichiometry, generalized mutualism, partner quality, Turnera subulata