Ant nest distribution and richness have opposite effects on a Neotropical plant with extrafloral nectaries

Studies assessing the effects of the spatial distribution of ant nests on ant-plant mutualisms are rare, even though they could be decisive to the outcomes of such interactions. Here, we investigated how ant nest abundance and richness affected a Neotropical plant with extrafloral nectaries (EFN), Smilax polyantha (Smilacaceae). We used baits to sample all nests of mutualistic ants within a 12 m radius of each plant. All neighbouring plants with EFN within 10 m of each tagged plant were also sampled. We measured foliar herbivory and fruit production of each S. polyantha. We hypothesized that (i) high numbers of ant nests near S. polyantha individuals would reduce foliar herbivory and increase fruit production, and that (ii) high ant nest richness would increase foliar herbivory and reduce fruit production. Results showed that plants surrounded by more ant nests had lower foliar herbivory and higher fruit production. However, ant nest richness was associated with higher foliar herbivory. Furthermore, plants producing more leaves and those surrounded by more neighbouring plants with EFN had reduced herbivory. Despite this, S. polyantha had low numbers of ant nests and reduced fruit production when surrounded by high numbers of neighbours with EFN. We suggest that the spatial distribution of ant nests and resources (plants with EFN) play an important role in ant-mediated mutualisms, where both ants and plants are likely competing for each other's services. Thus, incorporating these two variables in ecological models should provide insights into how protective mutualisms are structured.

Automated summary

This study investigated the effects of ant nest abundance and richness on a Neotropical plant. The results showed that an increase in ant nest abundance reduced foliar herbivory and increased fruit production, while an increase in ant nest richness was associated with higher foliar herbivory and reduced fruit production. Furthermore, plants with higher leaf production and surrounded by more neighboring plants with extrafloral nectaries had reduced herbivory.