Spatially Heterogeneous Nest-Clearing Behavior Coincides with Rain Event in the Leaf-Cutting Ant Atta cephalotes (L.) (Hymenoptera: Formicidae) (original) (raw)
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Austral Ecology, 2011
Leaf-cutting ants (Atta spp.) have become a topical issue in Neotropical ecology, particularly because they are reaching hyper-abundance due to escalating levels of fragmentation in recent years. Yet, despite intensive research on their role as dominant herbivores, there is still insuYcient documentation on the impacts of their large, long-lived nests on plant assemblage structure and ecosystem functioning. Our study aimed at investigating the magnitude, nature, and spatial extent of nest inXuence by assessing 11 attributes of ant nest, canopy structure, light environment and sapling assemblage for 20 colonies in four plots along nest-understorey gradients in a large remnant of Atlantic forest. We also monitored the performance of seeds and seedlings of Chrysophyllum viride, an abundant shade-tolerant species. Previously unrecognized canopy gaps above ant nests (0.04-87.9 m 2 ) occurred in 95% of all colonies surveyed. Overall, canopy openness and light availability at least doubled in ant nest plots compared with distant understorey plots. These drastic changes in the light environment paralleled those in plant assemblage: sapling density almost tripled (mean § SE: 0.42 § 0.1 saplings m ¡2 ) and sapling species richness doubled (0.16 § 0.02 species m ¡2 ) in distant plots, as did shade-tolerant species. After a 1-year period, only 33 § 15.6% of the seeds germinated and all seedlings died on nests, whereas seed germination reached 68 § 5.1% in distant plots and 66.4 § 7.6% of their seedlings survived after 12 months. Therefore, plot location was the most signiWcant explanatory variable for predictable and conspicuous changes in the light environment and structure of sapling assemblages. Our Wndings greatly extend knowledge on the role played by leaf-cutting ants as ecosystem engineers by demonstrating that ant nest-mediated disturbance promotes environmental modiWcations in tens of meters around nests and is thus, strong enough to drive plant recruitment and consequently alter both the Xoristic and functional signature of plant assemblages.
Oecologia, 2010
Leaf-cutting ants (Atta spp.) have become a topical issue in Neotropical ecology, particularly because they are reaching hyper-abundance due to escalating levels of fragmentation in recent years. Yet, despite intensive research on their role as dominant herbivores, there is still insuYcient documentation on the impacts of their large, long-lived nests on plant assemblage structure and ecosystem functioning. Our study aimed at investigating the magnitude, nature, and spatial extent of nest inXuence by assessing 11 attributes of ant nest, canopy structure, light environment and sapling assemblage for 20 colonies in four plots along nest-understorey gradients in a large remnant of Atlantic forest. We also monitored the performance of seeds and seedlings of Chrysophyllum viride, an abundant shade-tolerant species. Previously unrecognized canopy gaps above ant nests (0.04-87.9 m 2 ) occurred in 95% of all colonies surveyed. Overall, canopy openness and light availability at least doubled in ant nest plots compared with distant understorey plots. These drastic changes in the light environment paralleled those in plant assemblage: sapling density almost tripled (mean § SE: 0.42 § 0.1 saplings m ¡2 ) and sapling species richness doubled (0.16 § 0.02 species m ¡2 ) in distant plots, as did shade-tolerant species. After a 1-year period, only 33 § 15.6% of the seeds germinated and all seedlings died on nests, whereas seed germination reached 68 § 5.1% in distant plots and 66.4 § 7.6% of their seedlings survived after 12 months. Therefore, plot location was the most signiWcant explanatory variable for predictable and conspicuous changes in the light environment and structure of sapling assemblages. Our Wndings greatly extend knowledge on the role played by leaf-cutting ants as ecosystem engineers by demonstrating that ant nest-mediated disturbance promotes environmental modiWcations in tens of meters around nests and is thus, strong enough to drive plant recruitment and consequently alter both the Xoristic and functional signature of plant assemblages.
Nearly half of the ant species present in a tropical forest are directly in contact with the ground for nesting or foraging, with evidence of vertical stratification among ground layers (i.e., surface, litter, and soil). How ants in each layer respond to environmental factors and to seasonality remains little studied. We hypothesized that ant species distribution varied spatially and seasonally among the three ground layers and that their distribution was distinctly affected by various abiotic and biotic factors. Ants were collected in an Ecuadorian premontane tropical forest and their distribution was analyzed spatio-temporally: vertically (between the ground surface, leaf-litter, and mineral soil, using pitfalls, Winkler, and soil cores), horizontally (every meter along a 100 m transect) and seasonally (between the dry and the rainy seasons). Four environmental parameters were measured every meter along the transect: canopy openness, slope, leaf-litter depth, and leaf-litter volume. Correlations between species distribution, richness, abundance, and environmental variables were calculated. Species richness was high, with 176 species collected along the transect. Our results show a clear vertical stratification, with distinct faunal composition in each layer and a strong seasonal effect. Stable distribution of several dominant species between seasons suggests a low nest relocation rate. During the dry season, higher ant richness and abundance were found in pitfall traps suggesting higher activity on the surface of the forest floor. Similarly, higher ant richness and abundance found in the soil during the dry season suggest the migration of drought-sensitive species downwards deeper into the soil. Species richness and dominant species distribution were related to distinct factors according to the layer considered; we found strong correlations between the quantity of leaf-litter and dominant ant species distribution and species richness in the leaf-litter layer, while no correlation was found with any factor in the soil layer. Our results show that ant faunal composition and the response of ants to environmental factors vary vertically at small spatial scale and seasonally, which emphasizes the importance of distinguishing layers in the ground matrix.
BIOTROPICA, 2000
The location of the nutrient-rich organic refuse produced by a leaf-cutting ant colony varies among ant species. Atta cephalotes locate their organic refuse in subterranean chambers, whereas A. colombica place their organic refuse on the soil surface near the nest. We studied the effect of the absence or presence of external organic refuse on the abundance of fine roots and seed bank composition in the superficial horizons of ant nests. We sampled soils from ant nests or dumps and adjacent areas of 15 adult nests of A. cephalotes at La Selva (LS), Costa Rica, and of 15 of A. colombica nests on Barro Colorado Island (BCI), Panama. Soils from A. cephalotes nests did not differ from adjacent soils in abundance of fine-root and seed diversity. In contrast, organic refuse from A. colombica nests was less diverse in seed composition (due to the great abundance of Miconia argentea) and had a greater abundance of fine roots than adjacent areas. Thus the external location of the ant-nest organic refuse is potentially important in determining the different types of plant recolonization in abandoned or dead ant nests. The relative abundance of these Atta species may influence the structure and/or composition of tropical forests.
Journal of Tropical Ecology, 2014
. Does inundation risk affect leaf-cutting ant distribution? A study along a topographic gradient of a Costa Rican tropical wet forest. Abstract: Successional state of forest and availability of pioneer plants are recognized factors affecting densities of leaf-cutting ants. However little is known about how abiotic factors can shape nest distributions. We investigated the effect of topography, soil, forest successional state and inundation risk on nest density and size of Atta cephalotes colonies along streams in a tropical wet forest in Costa Rica. In each forest type, we surveyed 12 sites, each site comprising five transects (10 × 100 m) varying in topography and proximity to streambeds. We found no difference regarding nest size or density between forest types or soil consociation. Nest density varied with topographic environment, with significantly higher nest density on slope tops (farther from streambeds) and without colonies in valley bottoms (closer to streambeds). Nests found in areas affected by the last great inundation before our study were scarcer and smaller than nests in non-flooded areas. We showed that inundation events favour an accumulation of Atta colonies towards higher sites, where they are also allowed to become larger and may survive longer. Inundation risk may be a strong force shaping the distribution of leaf-cutting ant nests in tropical floodplain forests, even concealing the relevance of successional state of forest.
In tropical forests, the leaf-litter stratum exhibits one of the greatest abundances of ant species. This diversity is associated with the variety of available locations for nest building. Ant nests can be found in various microhabitats, including tree trunks and fallen twigs in different stages of decomposition. In this study, we aimed to investigate undecomposed twigs as nest-building resources in the leaf litter of dense ombrophilous forest areas in the southeastern region of Brazil. Demographic data concerning the ant colonies, the physical characteristics of the nests, and the population and structural of the forest were observed. Collections were performed manually over four months in closed canopy locations that did not have trails or flooded areas. A total of 294 nests were collected, and 34 ant species were recorded. Pheidole, Camponotus, and Hypoponera were the richest genera observed; these genera were also among the most populous and exhibited the greatest abundance of nests. We found no association between population size and nest diameter. Only tree cover influenced the nest abundance and species richness. Our data indicate that undecomposed twigs may be part of the life cycle of many species and are important for maintaining ant diversity in the leaf litter.
Twigs in the Leaf Litter as Ant Habitats in Different Vegetation Habitats in Southeastern Brazil
Tropical Conservation Science, 2017
Vegetation structure and microhabitat availability and diversity affect ant assemblage diversity, growth, and dispersal. In this study, we described assemblages of ants nesting in twigs found in the leaf litter, comparing nest characteristics and ant colony sizes among different vegetation habitats at a regional scale. Twigs were collected in urban parks, Eucalyptus plantations, and preserved areas of native Atlantic Forest. We measured the twigs, counted the number of ant colonies, and estimated canopy openness. A total of 51,213 ants from 22 genera and 61 species were recorded. We collected 74, 141, and 283 nests in urban parks, Eucalyptus plantations, and native forest areas, respectively. The richest genera were Pheidole, Camponotus, and Solenopsis. Linepithema neotropicum, Gnamptogenys striatula, and Solenopsis sp.2 were recorded in all study areas. We found only one invasive species, Cardiocondyla wroughtonii. Typically, the canopy in urban park areas was more open, and these areas had lower species richness, lower rate of twig occupancy, and smaller diameter twigs occupied by smaller colonies compared to Eucalyptus plantations or native forest. Ant assemblages were determined mainly by vegetation habitat, followed by twig characteristics. As many ant species use twigs as nest site, twigs are critical habitats for maintaining ant diversity in the leaf litter of areas with varying degrees of complexity in the vegetation structure. However, the availability of twigs as nest resource depended on vegetation structure. In addition, twigs may increase the area occupied by the colonies of some ant species, including Wasmannia auropunctata, which was very frequent in urban parks.