Composition of terrestrial isopod assemblages along an urbanisation gradient in Denmark

Abstract

The effects of urbanisation on isopods were studied in Sorø, Zealand, Denmark in 2004. We sampled woodlice using pitfall traps in a natural beech forest, a suburban beech forest remnant and forest “islands” of the original habitat in a public park. A total of 31 848 individuals comprising six species were collected. Two additional, small-bodied species were excluded from analyses due to their low number in the traps. Three species ( Porcellio scaber , Oniscus asellus , Philoscia muscorum ) dominated the assemblages accounting for 95.7% of the total specimens. Although, we found no difference among the habitats based on species richness or species composition, they did differ according to the Rényi scalable diversity index. This index was highest in the suburban habitat, followed by the urban forest islands and lowest in the natural forest. This was due to the significantly higher total isopod abundance in urban and suburban sites, compared to the forest habitat. The forest woodlice assemblage formed a distinct group in the hierarchical cluster analysis while the assemblages of suburban and urban sites did not separate into distinct groups. We conclude that the effect of urbanisation on woodlice assemblages manifests itself through the abundance and the relative distribution of isopod species, which are both appropriately represented by the scalable diversity index approach.