Divergent effects of leaf‐cutting ant herbivory and soil engineering on the reproductive success of plants in a Caatinga dry forest

Abstract

Plant reproduction is influenced by resource availability, environment and interactions with pollinators, pathogens and herbivores. In the Neotropical region, the leaf‐cutting ants are voracious herbivores and soil engineers, potentially affecting plant performance. This study investigated the effects of herbivory and soil changes via nest construction and maintenance linked to Atta opaciceps (Hymenoptera: Formicidae) (Bormeier, 1939) on the reproductive success of two Leguminosae species (Cenostigma pyramidale (Tul.) E. Gagnon & G.P. Lewis and Indigofera suffruticosa Mill. Mill.) widely distributed in the Caatinga dry forest. We selected eight nests from A. opaciceps colonies, with both plant species nearby. For each colony, we selected similar‐sized adult plants from foraging trail ends, where ants concentrate foraging efforts and herbivory is pronounced. We also selected plants located 20 m away from the foraging trail ends, representing herbivory‐protected scenarios, secured by tanglefoot barriers. Additionally, to assess ant‐related soil effects, we selected individuals from different nest‐associated soils (i.e., nest mounds and external refuse dumps) and from locations 20 m away from the aforementioned locations. All these individuals were shielded with tanglefoot barriers. Herbivory and soil changes from A. opaciceps did not affect any metric evaluated of C. pyramidale. Yet, for I. suffruticosa, ant herbivory boosted fruit set, and nest‐related soil changes, notably from refuse dumps, increased the number of flowers and fruits. Our findings indicate that leaf‐cutting ant effects on plant performance are species‐specific and may eventually benefit plant reproduction. Given the proliferation of leaf‐cutting ants in human‐modified landscapes of the Caatinga dry forest, positive interactions with plants might be vital to improving plant recruitment and forest regeneration dynamics.