Human disturbance promotes herbivory by leaf‐cutting ants in the Caatinga dry forest

Abstract

Anthropogenic disturbances are known to modify plant–animal interactions such as those involving the leaf‐cutting ants, the most voracious and proliferating herbivore across human‐modified landscapes in the Neotropics. Here, we evaluate the effect of chronic anthropogenic disturbance (e.g., firewood collection, livestock grazing) and vegetation seasonality on foraging area, foliage availability in the foraging area, leaf consumption and herbivory rate of the leaf‐cutting ant Atta opaciceps in the semiarid Caatinga, a mosaic of dry forest and scrub vegetation in northeast Brazil. Contrary to our initial expectation, the foraging area was not affected by either disturbance intensity or the interaction between season and disturbance intensity. However, leaf consumption and herbivory rate were higher in more disturbed areas. We also found a strong effect of seasonality, with higher leaf consumption and herbivory rate in the dry season. Our results suggest that the foraging ecology of leaf‐cutting ants is modulated by human disturbance and seasonality as these two drivers affect the spectrum and the amount of resources available for these ants in the Caatinga. Despite the low productivity of Caatinga vegetation, the annual rates of biomass consumption by A. opaciceps are similar to those reported from other leaf‐cutting ants in rain forests and savannas. This is made possible by maintaining high foraging activity even in the peak of the dry season and taking benefit from any resource available, including low‐quality items. Such compensation highlights the adaptive capacity of LCA to persist or even proliferate in human‐modified landscapes from dry to rain forests.

Rainfall reduction increases insect herbivory in tropical herb communities

“…For example, Barton et al (2009) observed that reduced water availability strengthened the herbivorous effect on the overall plant total biomass. In another study, leaf‐cutting ants preferentially attacked plants from habitats with water limitation (Ribeiro‐Neto, Pinho, Meyer, Wirth, & Leal, 2012), and at our study area, leaf‐cutting ants pressure on woody plants (leaf consumption and herbivory rate) is higher in the dry season (Siqueira et al, 2018). The challenge arises in predicting the outcome of increased herbivory on the long‐term persistence of herbs and the insects themselves.…”

Functional organization of woody plant assemblages along precipitation and human disturbance gradients in a seasonally dry tropical forest

“…Recent studies in the Caatinga have documented the influence of CAD and changes in precipitation levels as drivers of plant community organization, including taxonomic (Ribeiro et al, 2015;Ribeiro-Neto, Arnan, Tabarelli, & Leal, 2016;Rito, Arroyo-Rodríguez, et al, 2017a;Siqueira et al, 2018), phylogenetic , and functional patterns (Ribeiro et al, 2019;Sfair et al, 2018). Overall, these findings suggest environmental filtering and intraspecific trait variation as key drivers of the spatial distribution of plants along environmental and disturbance gradients.…”

“…Moreover, slash‐and‐burn agriculture and the exploitation of forest products have converted most of the Caatinga old growth forest into a mosaic of forest patches exposed to varying levels of chronic disturbance (Ribeiro et al, ; da Silva et al, ; Sobrinho et al, ). Recent studies in the Caatinga have documented the influence of CAD and changes in precipitation levels as drivers of plant community organization, including taxonomic (Ribeiro et al, ; Ribeiro‐Neto, Arnan, Tabarelli, & Leal, ; Rito, Arroyo‐Rodríguez, et al, ; Siqueira et al, ), phylogenetic (Ribeiro et al, ), and functional patterns (Ribeiro et al, ; Sfair et al, ). Overall, these findings suggest environmental filtering and intraspecific trait variation as key drivers of the spatial distribution of plants along environmental and disturbance gradients.…”

Phylogenetic signal in leaf-cutting ant diet in the fragmented Atlantic rain forest

“…Leaf-cutting ants (LCA) are dominant herbivores in the Neotropical rain and dry forests and savannas, removing up to 30% of green biomass in the foraging area of a colony (Siqueira et al 2018, Urbas et al 2007, Wirth et al 2003. In human-modified landscapes their impact is amplified by the fact that LCA colonies proliferate in disturbed habitats such as early-successional forests (Vasconcelos & Cherrett 1995), forest remnants (Terborgh et al 2001) and forest edges (Wirth et al 2007).…”