The immigrant triclad flatworm Dugesia tigrina (Girard) (Plathelminthes, Turbellaria). Range-extension and ecological position in The Netherlands

Abstract

The possible routes which could have been followed by D. tigrina in the course of its immigration in the Netherlands are discussed (Fig. 1). The species is almost restricted to the larger, eutrophic waters and is found usually under stones. The absence of species in smaller waters, such as ditches, could be explained by an interaction of various factors. The succesful immigration of D. tigrina in the larger waters is partly due to the very catholic and opportunistic manner of feeding, by which the species can co-exist with D. polychroa. The distribution pattern and habitat of D. tigrina in the Netherlands is similar to that of Planaria torva (this species is, however, more widely distributed in the Netherlands). The two species probably have solved the problem of co-existing with D. polychroa in a different way. The thermal pollution of today is favourable for a thermophilous species, such as D. tigrina. © 1975 Netherlands Hydrobiological Society.