Does mixed diffuse pollution degrease ground beetle diversity?

The variation in species diversity pattern of over 120 ground beetles species in heavy metal pollution gradient (Zn, Cu, Cd, Pb and Ni) was investigated in Poland and Great Britain. The carabid beetles were collected on 124 sites in forest and meadow gradients. Forward selection of canonical correspondence analysis indicated that species composition seems to be influenced mostly by geographic region and land use history meanwhile heavy metals, however significantly, described smaller part of species variation. Indicator species of certain pollutant groups (zinc, nickel, cooper) and certain concentration levels (high, medium, low) were identified using Indicator Species Analysis (IndVal). Most of them, characteristic for highly contaminated soils belong to small sized carnivores or granivores from genus Amara and Harpalus. We found a significant decrease in species diversity in more contaminated nickel soils, meanwhile zink and copper gradients indicated highest values for the lowest and highest amounts of both stressors. We conclude that in most cases directional replacement of species can occur in contaminated sites. Species more competitive but less tolerant are replaced by less competitive but more flexible species.