Land use effect on dominance of native and exotic earthworm species in two contrasting rural landscapes

Lumbricids and several species of the genus Amynthas have spread over all continents and seem to be better competitors than natives in disturbed ecosystems and agricultural fields. More than half of Uruguay's 19 earthworm species recorded by 2014 are exotic. Aiming to contribute to the scarce information on earthworm ecology in the region, the objectives of this work were 1) to characterize the earthworm communities in agriculture and natural ecosystems, and 2) to assess the relationship between land use and richness of native and exotic earthworm species. Related to the latter objective, we hypothesized that the difference in the number of exotic and native species depended on the degree of disturbance, and predicted that exotic species would dominate in more disturbed soils. We sampled organic and nonorganic agricultural fields including wheat in the rotations in the South and the North-West of Uruguay. Undisturbed sites, i.e. with no recent agriculture activity, close to each sampling plot served as controls. Analyses were conducted to elucidate whether other variables, besides disturbance and location, could be influencing earthworm community structure and composition. In both locations, exotic species dominated in control plots, i.e. less or non-disturbed land, and were associated to higher N, C and soil porosity. Moreover, in the North-West, natives would dominate in terms of richness in most agriculture plots. The mean body weight was larger in the South, where there were more exotic species, than in the North-West, where there were more native species. Thirteen of the collected species had been reported for Uruguay, the four other species found, were reported for the first time in this paper: Microscolex phosphoreus and Glossodrilus parecis (natives); and Aporrectodea tuberculata and Murchieona minuscula (exotics). Finding four unrecorded species evidences the poor coverage of earthworm sampling in anthropic and natural landscapes of the country.