Dying for conservation: eradicating invasive alien species in the face of opposition

In 2002, Parties to the Convention on Biological Diversity committed themselves to achieve, by 2010, a significant reduction in the current rate of biodiversity loss at global, regional and national levels. While it is clear that this target has not been achieved, 2010 may nevertheless be important if this International Year of Biodiversity prompts countries and international bodies to take proactive measures against the primary drivers of biodiversity loss. This certainly seems to be happening for one such driver, invasive alien species (IAS). [IAS are organisms introduced by man into places out of their natural geographic range, where they become established and disperse, negatively impacting on local ecosystems and species (http://www.iucn.org). ] For example, Brazil approved a national strategy for IAS earlier this year (http://www.gisp.org/) and this national measure echoes several recent reports on IAS monitoring and management, as well as recent recommendations on policy options to minimize the negative impacts of IAS on biodiversity (IUCN, 2009; Shine et al., 2009; Tu, 2009; McGeoch et al., 2010). History shows that IAS can have a range of impacts on ecosystems, including the extinction of native species. In 2005, the IUCN Red List database described causes of extinction for 170 species: IAS contributed to the loss of 54% of them, and were the sole cause of extinction for 20% (Clavero & Garcı́a-Berthou, 2005). In comparison, habitat destruction contributed to the extinction of 48%. IAS present an on-going threat, and have caused 31 bird species, nine mammal species and 205 amphibian species to be listed in higher categories of threat since the initial IUCNRed List assessment for each of these taxa (McGeoch et al., 2010). IAS can drive native species extinct through predation, by vectoring or causing disease, by genetic introgression or hybridization, by habitat modification and perhaps also by competition (Davis, 2009). Their presence can affect ecosystems at multiple trophic levels: for example, alien rats (kiore Rattus exulans) introduced to Little Barrier Island, New Zealand, had population-level impacts on everything from trees (Campbell & Atkinson, 2002) to seabirds (Jones et al., 2008). The native species that suffer the greatest effects of IAS tend to be distinctive and localized endemics, whereas the IAS themselves are frequently widespread and abundant. Thus, IAS are homogenizing the natural world, so that areas that have evolved or acquired distinctive faunas over thousands or millions of years are increasingly losing their unique identities. Addressing the threat posed by IAS can lead to positive conservation outcomes: for example, 17 vertebrate species have seen their risk of extinction downgraded on the IUCN Red List following efforts to control invasive species (McGeoch et al., 2010). There are many more such opportunities. The threats to native species posed by IAS can be mitigated in a variety of ways, including eradication or on-going control of the IAS population, translocation (of native or invader), managing the invaded environment or directed evolution of the native species (Davis, 2009). From the perspective of the species of conservation concern, eradication of the IAS is an efficient solution. If done properly, and if the IAS has not brought infectious diseases into native populations, eradication is definitive: it eliminates the threat and the threatening