The role of habitat simplification and seasonality in shaping interactions between ants, plants and herbivores in a neotropical savanna

Abstract

Protective interactions between ants and plants bearing extrafloral nectaries (EFNs) are highly conditional, and changes in abiotic conditions, including environmental seasonality, are known to influence their outcomes by changing plant phenology. Yet, there is still much to uncover, and despite living in the Anthropocene, we still know little about the effects of anthropogenic activities in shaping ant-plant interactions. We evaluated the influence of chronic anthropogenic disturbances (CAD) and seasonality in shaping the outcomes of interactions between ants and EFN-bearing plants in the Brazilian cerrado. For this, we assessed the diversity of ants (total and arboreal ant fauna) and herbivorous insects in trees of Qualea grandiflora located in preserved cerrado and pasture areas. In addition, we assessed the activity of EFNs, the rate of leaf herbivory, and the number of leaves from different stages (sprouting, new, old) monthly for 1 year. Ant diversity in the pasture increased during the dry season, while herbivore diversity increased in the rainy season, coinciding with higher EFN activity and leaf flushing. In the cerrado, EFN activity also peaked in the rainy season, and leaf herbivory levels were higher than in the pasture. Although ant abundance did not influence herbivore presence, greater arboreal ant diversity (especially in the pasture) was linked to lower herbivore richness but had no effect on leaf herbivory. Our study shows that CAD interacts with seasonality to shape multiple aspects of ant-plant interactions, ranging from EFN secretion to leaf herbivory, with potential pervasive consequences for tropical ecosystems.