The Debate Over Assisted Colonization
    By Caitlin Kight | December 2nd 2011 07:58 AM | 3 comments | Print | E-mail | Track Comments
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    “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.


    For supplemental images associated with this post, pleasevisit the Anthrophysis pin board at Pinterest.

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

    Thanks to the following websites for providing the images used in this post:


    Gerhard Adam
    I find that much of this discussion suggests a level of knowledge that simply doesn't exist and that we are proposing "solutions" to problems that we can't possibly foresee.
    Or do we want to “let the chips fall where they may” and refuse to interfere?
    I found this statement interesting, because what makes anyone think that there is any other possible outcome?  Regardless of what we do, it is impossible to predict exactly how any particular variation or modification will manifest itself over the years or decades.

    One way or another, we are interfering.  One way or another, species will adapt, go extinct, or diverge from current forms/practices, etc. regardless of what we think we are doing, because life isn't static.  No matter how we think we will "manage" this, it will do what it has always done ... find the best way for each organism to survive regardless of the expected outcomes.

    I find the use of the term "engineering" to be somewhat fanciful, since our knowledge about ecosystems is hardly sufficient to judge that anything we do could be rightfully considered "engineering".  For a species that failed to recognize their obvious culpability (1) in giving rise to antibiotic resistant strains of bacteria, I find this notion of preserving ecosystems somewhat quaint.

    (1)  In this context I mean that we possessed all the knowledge about biology and evolution we needed to recognize the inevitable consequences of our use of antibiotics, but instead we persisted in believing that we had somehow "conquered" human diseases.  Such terminology, as well as that employed in the article illustrates hubris, not science.
    Mundus vult decipi
    Let's put our minds to the service of nature by not characterizing our relationship as one of server and served.

    Until conservation biologists and conservation enthusiasts begin looking at current climate change issues with an eye to "deep time", irresponsible scare tactics will continue to catapault the "dangers" of assisted migration to Fox News stridency, not PBS style rationality. I am the founder of Torreya Guardians, and the paper I coauthored (with Paul Martin) that preceded any action on our part to move Torreya taxifolia north fully grounded our advocacy on the rational proposition that because "native range" for this critically endangered species is also regarded by paleoecologists as one of three "pocket refuges" that all species of America's great eastern forests retreated to during the peak glacial periods, then at this stage of interglacial the tree should already have moved back north. Why it didn't manage to follow hemlock north is a subject of speculation. But no ecologist with any training in paleoecology could rationally argue that Torreya taxifolia might become invasive as an alien plant. For a detailed report on this perspective, google the comments I filed in 2011 to USF&WS on the revision of the mgmt plan for this endangered species: "Paleoecology and the Assisted Migration Debate: Why a Deep-Time Perspective Is Vital," which is published on the website.