“Assisted colonization” (AC) may not be a household term yet, but chances are it will become an increasingly common topic over the next few years—or, at least, it should, according to scientists writing in a recent issue of the journal Frontiers in Ecology and the Environment. The main goal of the researchers, both of whom are affiliated with Seattle’s University of Washington, was not to take a pro- or anti-AC stance, but to argue that it is time for discussions about this topic to be moved out of the ivory tower and into the community at large.

Assisted colonization is a wildlife management technique whereby individuals are intentionally relocated to places outside their native ranges in an effort to protect them from anthropogenic threats. The main threat considered here was climate change, which is projected to alter some habitats so quickly that their inhabitants will not be able to adjust in time (by adapting or by moving themselves to more suitable areas, for instance). Within the scientific community, the concept of AC has been met with both praise and alarm. Some researchers feel that it is an excellent tool for species conservation, while others believe it will cause more harm than good. One particular worry is that assisted colonization efforts are merely sanctioned introductions of potentially destructive nonnative species that may have adverse impacts on local species and, potentially, entire ecological processes.


(The Florida Torreya, Torreya taxifolia. To combat the “shrinking native range” of this species, an environmental group called the Torreya Guardians has transplanted seedlings to North Carolina.)


While the authors feel that this is one of many valid and important questions, they also believe that it is time to take a step back and take a broader view of the debate. They suggest that we need to focus our attention on three activities: weighing the consequences of action versus inaction; deciding, as a society, the extent of “ecosystem engineering” that we feel is appropriate; and considering alternative approaches to AC.

The action vs. inaction debate is particularly fraught because it involves so much conjecture. Predictions about the outcomes of ACs (or lack thereof) can be informed by forecasts of climate change, data collected from previous reintroductions (for instance, of critically endangered species that are raised in captivity and then released into the wild), experiments, and historical records associated with previous climate shifts. Despite these potential sources of information, it is not always easy to identify which species are at the greatest risk, let alone determine how they might respond to, or influence, a new habitat—a habitat that, itself, will continue to change as climatic patterns shift. Furthermore, there are also moral and ethic issues to consider: Is it better to prevent the global extinction of one species even when it causes the local extinction of another, or is it tolerable to lose a single species if doing so prevents potential loss of ecosystem function at its proposed AC site?


 (The Iberian lynx, Lynx pardinus, is a critically endangered species that has become “trapped” in pockets of subpar habitat in Spain. Researchers have proposed assisted colonization as a method for reducing the likelihood that this species will go extinct.)

The second issue, ecosystem engineering, revolves around the need to decide what we want for our ecosystems. They provide us with a variety of services (including, but not limited to, space for recreation, carbon sequestration, water filtering, and the production of clean air) upon which we are extremely reliant. Thus, do we want to maximize one or more of these services even if that means allowing species to go extinct? Do we want to protect or preserve as many species as possible, even if that means we need to find alternative sources of particular services? Or do we want to “let the chips fall where they may” and refuse to interfere? Rather than arguing for or against any of these options, the authors simply point out that these are big decisions that impact everyone; thus, while scientific research can help educate people about the pros and cons of the different choices, debates on these issues should not just be held among researchers.

Finally, the authors focus on landscape connectivity, a topic that they say has been “noticeably absent” from the AC debate. Connectivity of habitats has been achieved for a number of organisms using techniques such as wildlife crossing structures and dam removal. Although these methods are often focused on allowing individuals to utilize and recolonize native habitats from which they have been cut off by anthropogenic structures, this practice—like assisted colonization—can also result in access of new areas by nonnative species. Despite this, fewer people object to connectivity efforts than to ACs. The authors ask whether these objections are associated with the amount of intervention (since building a connecting overpass, for instance, allows animals to move themselves, in contrast to having humans physically relocate animals during AC efforts), or with the potential effects of intervention. They point out that proponents of connectivity may also feel that it is a morally superior option as it restores “the natural order of things.” Ultimately, the authors feel that both options should be kept on the table, since particular species may respond better to one method than the other.


 (Managers in northern England investigated the utility of assisted colonization for the marbled white, or Melanargia galathea. Individuals were relocated as far as 65 km beyond the margins of their native range to sites that were “predicted to be climatically suitable.”)

Overall, the authors hope that the assisted colonization debate can be “reframed” in the context of these three major issues. By focusing on these ideas and broadening the dialogue to include both non-scientists and scientists, it should be possible to shift from a “purely academic” debate to one that will yield concrete plans about how to proceed.


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Lawler, J.J. and Olden, J.D. 2011. Reframing the debate over assisted colonization. Frontiers in Ecology and Environment 9(10):569-574.

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