Leaf‐cutting ant nests support less dense and impoverished seed assemblages in a human‐modified Caatinga dry forest

Abstract

Regenerating forests make up an increasingly large portion of tropical landscapes worldwide and regeneration dynamics may be influenced by leaf-cutting ants (LCA), which proliferate in disturbed areas and collect seeds for fungus culturing. Here, we investigate how LCA influences seed fate in human-modified areas of Caatinga dry forest. We evaluate the seed deposition and predation on Atta opaciceps nests, foraging habitat surrounding nest and control habitat away of nest influence of 15 colonies located along a forest cover gradient during the rainy and dry seasons. For each habitat, four 50-cm 2 plots were established and all seeds on the soil surface were collected along 1 year. We recorded 13,628 seeds distributed among 47 species and 36.57% of the total seeds did not show any sign of predation. Nest mound habitats supported low-density and species-poor seed assemblages, which were taxonomically distinct from the control habitats. These effects only occurred in the rainy season. The proportion of undamaged seeds were similar across the habitats. While forest cover did not influence seed assemblage in terms of species richness or seed predation, it did interact with habitat type via increments in seed abundance as forest cover increased across the nests. Forest cover also affected seed composition, but only in the rainy season. These results indicate that LCA decrease seed deposition in areas under their influence, particularly on the nest mounds. As LCA profit from human disturbance in the Caatinga, their role as seed 'sinks' should be enhanced in disturbed Caatinga patches, particularly during the rainy season, when most of the plant recruitment occurs. Our findings reinforce the importance of LCA as drivers of forest dynamics and resilience in human-modified landscapes.

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

“…The herbivory pressure exerted by this species reaches over 30% of the stand leaf crop in their 1-3-ha sized foraging areas (Siqueira et al, 2018). Furthermore, it has been reported that A. opaciceps can reduce the seed bank (Oliveira et al, 2023) and seedling recruitment (Knoechelmann et al, 2020), thus negatively impacting the regeneration of the Caatinga. Colonies of A. opaciceps present external refuse dumps, which are annually renewed at the beginning of the rainy season when nest cleaning and maintenance are increased (Siqueira et al, 2018).…”

“…For A. opaciceps, an endemic species to the Caatinga dry forest, considerable herbivory rates have been documented, reaching over 30% of the standing leaf crop in foraging areas (Siqueira et al, 2018). In the Caatinga dry forest, these three ant species also create external dumps, resulting in mosaics of soil quality in their nesting areas (Knoechelmann et al, 2020;Oliveira et al, 2023;Siqueira et al, 2017Siqueira et al, , 2018. While the mounds at the nest entrances are composed of mineral soil with depleted soil carbon and reduced fertility (Meyer et al, 2013), the dumps consist of nutrient-rich materials from exhausted fungal gardens (Meyer et al, 2013;Siqueira et al, 2017Siqueira et al, , 2018.…”