Influence of the leaf-cutting ant Atta sexdens Linnaeus (1758) on the taxonomic and functional diversity of woody plants in Atlantic Forest fragments

Abstract

There are reports suggesting that leaf-cutting ants can act as a biotic filter, selecting plant traits according to foraging preferences, and consequently affecting the species composition of plant communities. In order to test this hypothesis, we evaluated the relationship between the floristic and functional diversity of woody plants in fragments of Semideciduous Seasonal Atlantic Forest (SAF) with the presence or absence of Atta sexdens (Linnaeus, 1758) nests. We expected that, in places where A. sexdens nests is present, 1) floristic diversity is lower and 2) the plant community is dominated by species characterized by greater investment in anti-herbivore defenses and lower nutritional content. For this, we sampled nine SAF fragments in the north of Paraná state, in Brazil. The diversity of woody regenerants (> 1 m in height, < 2 cm diameter) was estimated and 10 functional traits were evaluated: gap dependence, deciduousness, leaf nitrogen and carbon content, leaf C/N ratio, presence of leaf trichomes, leaf thickness, specific leaf area, presence of latex and condensed tannins, for the 28 most abundant woody species. Contrary to expectations, there were no differences in floristic diversity between sites with or without A. sexdens, and functional diversity was also similar, reflecting the floristic similarity. We suggest that the herbivory pressure by A. sexdens on the woody regenerants of SAF fragments is not strong enough to cause significant mortality in individual species and, consequently, affect plant diversity and composition. This may in part be related to the fact that most nests of A. sexdens were established in the edges of the fragments and that ants from these nests forage not only in the forest but also in the agricultural matrix where food resources are abundant. We also suggest that longer-term studies are still needed to fully elucidate the effects of A. sexdens on the plant community of Atlantic Forest fragments.