14 Newman, C. et al. (2003) Validating mammal monitoring methods and assessing the performance of volunteers in wildlife conservation— ‘‘Sed quis custodiet ipsos custodies?’’. Biol. Conserv 113, 189–197 15 Cook, L.M. et al. (1986) Postindustrial melanism in the peppered moth. Science 231, 611–613 16 Butcher, G.S. and Niven, D.K. (2007) Combining Data from the Christmas Bird Count and the Breeding Bird Survey to Determine the Continental Status and Trends of North America Birds. National Audubon Society 17 Klinkenborg, V. (2007) Millions of missing birds, vanishing in plain sight. New York Times 19 June 18 Jones, J.S. et al. (1977) Polymorphism in Cepaea—a problem with too many solutions. Annu. Rev. Ecol. Syst. 8, 109–143 0169-5347/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tree.2009.03.017 Available online 6 July 2009 Letters Assisted colonization: evaluating contrasting management actions (and values) in the face of uncertainty Martin A. Schlaepfer, William D. Helenbrook, Katherina B. Searing and Kevin T. Shoemaker College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210, USA In their recent Opinion article in Trends in Ecology & Evolution, Ricciardi and Simberloff [1] argue that assisted colonization is not an appropriate management option because the impacts of introduced species are too difficult to predict, and can have harmful consequences for recipi- ent ecosystems, including the extinction of native species. Invoking the precautionary principle, the authors argue that alternative conservation tactics must be pursued, even for species faced with extinction in their native range. We concur with the authors that there are risks associated with introducing species outside of their current range. However, we disagree for three reasons that these risks are so great that assisted colonization should not be considered among possible management options. First, the probability of translocated organisms causing significant damage to native species might be overstated. Indeed, the sources on which the authors base their analyses (http://www.issg.org and Ref. [2]) report impacts on native species that are sometimes based on anecdotal or correlative evidence, a common challenge when evaluating the impact of non-native species [3,4]. For example, the extinction of a Puerto Rican bullfinch subspecies from St. Kitts (Loxigilla portoricensis grandis) is attributed in the authors’ data set to the introduced green monkey (Cerco- pithecus aethiops) [2] even though the monkeys were uncommon within the bird’s range, the two species had coexisted for more than 200 years and the demise of the local Puerto Rican bullfinch population coincided with two catastrophic hurricanes [5]. Furthermore, for each species with multiple introductions, the authors scored only the most extreme impact, rather than an average one (Figure 1 caption in Ref. [1]). Reports of extreme examples are important because they describe worst-case scenarios, but these should also be accompanied by modal outcomes, which are more likely to occur. Second, there is a need to weigh the risks of assisted colonization versus the risk of extinction using more traditional conservation practices. Data provided by the authors (Figure 1 in Ref. [1]) suggest that 85% of intra- continental mammalian translocations resulted in no detectable effect in recipient ecosystems. Translocations within a species’ former range were not included in the authors’ analyses (A. Ricciardi, pers. commun.), and might have even lower probabilities of adverse effects. We suspect that if a species were under imminent threat of extinction, could not migrate to suitable habitat, was unlikely to cause ecological harm and benefited from broad public support, few would argue against assisted colonization. Third, risk assessments need to be evaluated and debated in a framework that recognizes that different stakeholders might place a premium on different outcomes. Even among conservation biologists, there appear to be divergent value systems that influence conservation targets and manage- ment tactics. Ricciardi and Simberloff appear to place a premium on protecting species in their native habitat, whereas proponents of assisted colonization are willing to translocate species to prevent their extinction even though in some cases this could result in adverse effects [6]. There is a need for a framework that integrates both biological information and socioeconomic data, and allows for debates regarding more subjective values surrounding species conservation. Hoegh-Guldberg et al. [6] proposed a relatively simple framework based on three categories: the need of a taxon (how imperiled is it?), technical feasibility (can it be translocated?) and suitability (do biological, social and economic benefits outweigh costs?). More com- prehensive (K.B.S. et al., unpublished) and alternative [7] frameworks are being proposed to help stakeholders evalu- ate the numerous, complex questions embedded within each of these three categories. Proponents and opponents of assisted colonization share a concern for biodiversity and, as the impacts of climate Corresponding author: Shoemaker, K.T. (mschlaepfer@esf.edu). Update Trends in Ecology and Evolution Vol.24 No.9 471