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. Copyright © Cambridge University Press 2013.3018992Adis, J., Eco-entomological observations from the Amazon: III. How do leaf-cutting ants of inundation forest survive flooding? (1982) Acta Amazonica, 12, pp. 839-840Bitancourt, A.A., Expressao mateḿatica do crescimento de formigueiros de Atta sexdens rubropilosa representado pelo aumento do ńumero de olheiros (1941) Arquivos Do Instituto Bioĺogico de Sao Paulo, 12, pp. 229-237Corella, O., (2001) Elaboracíon de un Mapa Hist́orico Del Cambio de Uso Del Suelo en la Estacíon Bioĺogica la Selva, PuertoViejo de Sarapiqú?, Heredia, , Doctoral thesis, Instituto Tecnoĺogico de Costa RicaCosarinsky, M.I., Roces, F., Neighbor leaf-cutting ants and mound-building termites: Comparative nest micromorphology (2007) Geoderma, 141 (3-4), pp. 224-234. , DOI 10.1016/j.geoderma.2007.06.006, PII S0016706107001644Denslow, J.S., Tropical rainforest gaps and tree species diversity (1987) Annual Review of Ecology and Systematics, 18, pp. 431-451Farji-Brener, A.G., Why are leaf-cutting ants more common in early secondary forests than in old-growth tropical forests? An evaluation of the palatable forage hypothesis (2001) Oikos, 92 (1), pp. 169-177(2006) World Reference Base for Soil Resources. World Soil Resources Reports, (103), 128p. , IUSS WORKING GROUP WRB FAO, RomeKleineidam, C., Roces, F., Carbon dioxide concentrations and nest ventilation in nests of the leaf-cutting ant Atta vollenweideri (2000) Insectes Sociaux, 47, pp. 241-248Laurance, W.F., Ferreira, L.V., Rankin-de Merona, J.M., Laurance, S.G., Rain forest fragmentation and the dynamics of Amazonian tree communities (1998) Ecology, 79 (6), pp. 2032-2040McDade, L.A., Bawa, K.S., Hespenheide, H.A., Hartshorn, G.S., (1994) La Selva: Ecology and Natural History of A Neotropical Rain Forest, 493p. , University of Chicago Press, ChicagoPenaloza, C., Farji-Brener, A.G., The importance of treefall gaps as foraging sites for leaf-cutting ants depends on forest age (2003) Journal of Tropical Ecology, 19 (5), pp. 603-605. , DOI 10.1017/S0266467403003675Schnitzer, S.A., Carson, W.P., Treefall gaps and the maintenance of species diversity in a tropical forest (2001) Ecology, 82 (4), pp. 913-919Silva, P.S.D., Bieber, A.G.D., Leal, R., Wirth, I.R., Tabarelli, M., Decreasing abundance of leaf-cutting ants across a chronosequence of advancing Atlantic forest regeneration (2009) Journal of Tropical Ecology, 25, pp. 223-227Sokal, R.R., Rohlf, F.J., (1995) Biometry: The Principles and Practice of Statistics in Biological Research, p. 887. , (Third edition W. H. Freeman and Co., New YorkSollins, P., Sancho, F.M., Mata, R.C., Sanford, R., Soils and soil process research (1994) La Selva: Ecology and Natural History of A Neotropical Rain Forest, pp. 34-53. , McDade, L. A., Bawa, K. S., Hespenheide, H. A. & Hartshorn, G. S. (eds. University of Chicago Press, ChicagoVan Gils, H.A.J.A., Gaigl, A., Ǵomez, L.E., The relationship between soil variables and leafcutter ant (Atta sexdens) nest distribution in the Colombian Amazon (2010) Insectes Sociaux, 57, pp. 487-49

Simple does not mean poor: grasslands and forests harbor similar ant species richness and distinct composition in highlands of southern Brazil

Several studies addressed ant communities in the dense Atlantic Forest that runs along the Brazilian coast. However, comparatively little is known about the mixed forests and grasslands that occur in the southern range of the Atlantic Forest domain. In this study we performed the first standardized assessment of ants in the forest- grassland mosaic found in the highlands of the state of Santa Catarina. We aimed to investigate and compare ant richness and composition between mixed forests and grasslands in the main mountain range of south Brazil. Ants were collected in two years with ground pitfalls, tree pitfalls and litter samples. Sixty ant species were recorded, resulting in 22 new records for “Planalto Serrano” region and three for the state of Santa Catarina: Eurhopalothrix depressa , Pheidole radoszkowskii and Wasmannia williamsoni . There was significant dissimilarity in ant species composition between grasslands and forests, but no difference in ant species richness, even considering the higher number of strata in mixed forests. Similar richness and low number of arboreal species suggest that this ant community is structured similarly to temperate ones. Both habitats presented a large proportion of exclusive species. The fact that species composition between grassland and forest areas differed, coupled with the similarity in species richness between habitats and the record of new ant species for the region, calls for strong conservation efforts in grasslands of southern Brazil, which still are little protected by conservation areas