As global change accelerates and with it species extinctions, it seems that new measures may be needed in conservation practice. One such measure -- a controversial one -- is that of ‘assisted colonization’. Loss et al. review the potential means to implement such an approach. They feel that there may be some scope for careful use of assisted colonization in conjunction with other landscape-scale conservation measures.
Species that are in small, isolated, non-mobile or low-dispersing populations situated in fragmented landscapes are characterised as species that are threatened by the potential impacts of climate change. Assisted colonization is suggested as a useful conservation strategy for such species, but only when combined in an ‘integrated approach’. Loss et al. conclude that short-distance translocations are less likely to result in biological invasions, that a consideration of the full range of a species rather than only peripheral populations should be made and that assisted colonization is best combined with other approaches, like habitat corridors. They liken assisted colonization to ‘integrated pest management’, where a strategy of employing a range of control measures is likely to produce the most effective long-term outcome and minimise the risk of damage to the environment.
Some authors have argued strongly against ideas of assisted colonization, likening it to ‘ecological roulette’ (Ricciardi and Simberloff, TREE 24, 2009), which may, for example, result in the species becoming invasive in its new range. In recognition of this, Loss et al. argue that assisted colonization must be preceded by a thorough risk assessment. However, the reliability of frameworks for risk assessments of introduced species is questionable ( Groves et al. Chapters 3 and 5 in: “Weed Risk Assessment.” Collingwood: CSIRO Publishing, 2001). In addition, it is not clear to us that the integrated approach Loss et al. advocate will reduce uncertainty. Rather, by introducing multiple processes that may interact unpredictably, it could compound it.
Overall, this article is a notable manifestation of the controversy in the literature on this strategy (see also Vilà and Hulme, TREE 2011, Jul 13 (Epub ahead of print) and Thomas CD, TREE 2011, 26).