Measuring the impact of freshwater NIS: what are we missing?

Within the last two decades, the dangers that some non-indigenous species (NIS) pose to indigenous species, ecosystem functioning, economic interests, and public health have been abundantly publicized in both the scientific and the popular literatures. A flood of publications, under the format of both synthetic overviews and detailed accounts of some species, accompanied the heightened interest in biological invasions (e.g. Williamson 1996, Mack et al. 2000, Cox 2004). Several underlined the dramatic effects that these species induce to the recipient environment and ascribed them to the potential of NIS to (1) alter and disrupt the biotic structure of ecosystems; (2) affect the wellbeing of other species; (3) push many species toward extinction; (4) reduce the productivity of agriculture and aquaculture; and (5) pose threats to human health and to the health of domesticated or semidomesticated plants and animals (Cox 2004). The media often featured both general problems (e.g. Bright 1998, Devine 1999, Di Justo 2006) and “the invader of the week” (Simberloff 2003a).