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Soil properties only weakly affect subterranean ant distribution at small spatial scales

Abstract:

Physico-chemical properties of soils have an indirect effect on ground-dwelling ant assemblages at regional scale. By contrast, little is known on their effect at the scale of the meter, at which direct interactions between subterranean ants and their environments occur.We aimed to study the effect of soil properties on the small-scale distribution of highly diverse subterranean ant assemblages. We expected ant species to be differentially associated with soil variables.This study was conducted in Bombuscaro and Copalinga (Ecuador), two premontane tropical forests 2. km apart, sharing the same climate and altitude. In each site, we delineated a 100. m line transect and every meter collected a sample of mineral soil (15. cm × 15. cm × 10. cm) and the associated ant fauna. Compared with traditional baiting this method should provide a relatively unbiased measure of subterranean ant diversity. Organic matter content, pH, electrical conductivity, degree of humification, soil texture and land slope were measured at each sampling point.Soil attributes of the two sites were contrasting and strongly spatially autocorrelated. The two ant assemblages shared only 12% of their 76 species. Ant diversity was higher in Bombuscaro (Fisher-α= 21.7 vs. 16 in Copalinga). Species turnover was remarkably high at both regional (intersite) and local (intrasite) scales. Ant species richness was not correlated with any of the measured variables. Soil properties were not associated with the occurrence of any ant species in Copalinga. In Bombuscaro, Hypoponera sp.01RI was correlated with lower pH values, and Acropyga fuhrmanni to higher clay content. A. fuhrmanni did not show correlation with this variable in Copalinga, where it is the dominant species (present in 48% of the samples). However, this species is associated with higher clay content at Copalinga (36.7 ± 6% SD) compared with Bombuscaro (6.5 ± 2%).Although weakly explained by the soil factors investigated, a high ant species turnover was observed at both small (1. m) and regional (2. km) spatial scales. The latter observation stresses the importance of designing large nature reserves including mosaics of habitats to conserve subterranean ant diversity in the Andes. © 2012 Elsevier B.V.