Understanding the impact of invasive crayfish

In a rather provocative article, Parker et al. (1999) claimed that, up to then, little scientific attention had been placed on developing either theoretical or operational generalizations about the impact of invasive species. Specifically, the authors lamented the lack of a general framework in which to discuss “what impact is, or how we decide that the non-indigenous species exceeds that of another, or how we decide that the impact of a particular species is greater in one place than in another” (Parker et al. 1999, p. 4). Today, this scenario seems to have changed for several freshwater non-indigenous species (NIS), e.g. the zebra mussel Dreissena polymorpha (Pallas) (e.g. Karatayev et al. 2002, Ricciardi 2003), but it has remained practically unaltered for other widely diffused bioinvaders that have, however, attracted much scientific attention in these latest years, such as freshwater crayfish.