Assisted colonisation to help species combat climate change

By Joern Fischer

Hewitt et al. just published a very nice paper on assisted colonisation as a strategy to help species cope with climate change. The basic idea of assisted colonisation is to help species move in response to climate change — e.g. because parts of their old range are getting too warm. When species can’t keep up with climate change (e.g. because landscapes are too fragmented or because species cannot disperse very well), assisted colonisation has been suggested as a possible solution.

There are two things I like about the paper by Hewitt et al. First, it actually is a very thorough review of a complex debate. Opinions are greatly divided on assisted colonisation, and range from extremely negative to extremely enthusiastic. In the meantime, agencies and NGOs are starting to ‘just get on with it’ … even though the science is far from clear. (That shouldn’t be surprising — Soule argued in 1985 that conservation biology was a crisis discipline, which couldn’t always wait for all the facts!)

I have taken the liberty to copy one table from the paper, as an overview of the really thorough analysis the authors did. Go ahead and read the paper if you think this is useful …. (i.e. sorry Elsevier, forgive me for copying this figure):

Fig. 3. Reasons for and against assisted migration and relationships between opposing arguments. Reasons for consist of benefits, either ecological or socio-economic (far left), and other arguments for assisted migration or counter-arguments to the opposition (middle left). Reasons against consist of risks, either ecological or socio-economic (far right) and other arguments against or counter-arguments to proponents (middle right). The size of the boxes corresponds to the number of articles stating the arguments, and numbers indicate references, as shown below. Arrows point to arguments on the opposite side of the debate that the positions were made in response to. Solid lines indicate responses that were more directly related, and dotted lines, those that were less directly related. Arrows are intended to be illustrative rather than exhaustive treatments of key connections among arguments and counter-arguments. References 1: Peters and Darling (1985), 2: Davis and Zabinski (1992), 3: Honnay et al. (2002), 4: Savolainen et al. (2004), 5: Hulme (2005), 6: Pearson and Dawson (2005), 7: Chapin et al. (2007), 8:Hunter (2007), 9: McLachlan et al. (2007), 10: Williams et al. (2007), 11: Aitken et al. (2008), 12: Chapron and Samelius (2008), 13: Davidson and Simkanin (2008), 14: Hellman et al. (2008), 15: Hoegh-Guldberg et al. (2008a), 16: Hoegh-Guldberg et al. (2008b), 17: Huang (2008), 18: Mueller and Hellmann (2008), 19: Parker (2008), 20: Petit et al. (2008), 21: Rahel et al. (2008), 22: Van der Veken et al., 2008, 23: Bradley and Wilcove (2009), 24: Carroll et al. (2009), 25: Chen et al. (2009), 26: Donaldson (2009), 27: Fazey and Fischer (2009), 28: Galatowitsch et al. (2009), 29: Hayward (2009), 30: Heller and Zavaleta (2009), 31: Lawler (2009), 32: Marsico and Hellman (2009), 33:Mawdsley et al. (2009), 34: Ricciardi and Simberloff (2009a), 35: Ricciardi and Simberloff (2009b), 36: Richardson et al. (2009), 37: Sax et al. (2009), 38: Schlaepfer et al. (2009), 39: Schwartz et al. (2009), 40: Seddon et al. (2009), 41: Spear and Chown (2009), 42: Swarts and Dixon (2009), 43: Vitt et al. (2009), 44: Hagerman et al. (2010), 45: Parker et al. (2010), 46: Sandler (2010), 47: Vitt et al. (2010).


The second aspect about this paper that I like is that it explicitly looks to inform a debate through figuring out shades of grey (a point I recently argued in this blog about another polarised debate, namely land sparing vs wildlife-friendly farming…) — rather than joining a false black and white dichotomy. The authors state that the debate is complex, and rather than proposing a simple solution, they try to provide a framework which can help to reach case-specific solutions. Hooray …! I wish more scientists did this.

Of course, I can’t write a blog entry about this without also giving my personal opinion… Together with Ioan Fazey, I have written a short note on this issue, which you can view here. Our view is rather negative. But not so much because of the likely risks (which is what most people focus on): perhaps those could be managed. But rather because assisted colonisation appears a band-aid. If the problem is fragmentation of natural habitats and climate change, then we ought to deal with those, rather than find a technological solution around these problems. Our biggest criticism is that assisted colonisation takes up important brain space (and will take up lots of funding, no doubt): we’re writing about it right now, instead of writing about the root causes of biodiversity decline, namely human landscape modification and (in this case) climate change. Like many issues, this is a bit of a bandwagon, but an exceptionally expensive one! To be of most use, do we need governments to spend money on moving species, or to spend money on making landscapes more traversable to species, and reducing climate change? I think the latter would be more useful — and that’s why I’m skeptical about assisted colonisation.

But obviously, other opinions exist and are valid. Hewitt et al. have done a great job of giving an authoritative overview of many relevant arguments. I highly recommend their paper!


5 thoughts on “Assisted colonisation to help species combat climate change

  1. Pingback: “Buzzword concepts” and their pitfalls | Ideas for Sustainability

  2. I think it’s all well and good for you to describe assisted migration as a ‘band-aid’ solution, but I’d like to wonder what further measures you propose that are immediate and extensive enough to right some of the damage that is causing the need to translocate species? Evidently anthropogenic effects are causal here, but as the population continues to boom at alarming rates, where are we going to house people/grow food? Not all farmers can afford to grow organic, or leave remnant patches of forest in their fields. I am a massive advocate for sustainability and appreciating the intrinsic value of nature, but it’s one thing to say “we should be focussing more on x issue” without proposing exactly HOW to fix the problem. Where do you propose the government cuts money from to channel into further climate change projects? And such as what – more solar panels, more tax schemes…? Do you propose wildlife corridors be established through every farm/urban landscape? If so, who will assist those that are losing land/money from these reserves transecting their land and where will we make up for this loss of potential produce?

    • Dear Ais, thank you for your comment! To my mind, the question is not whether we do something about climate change and species extinctions, but what we ought to do. I think it is important to focus on the drivers of sustainability problems, rather than its symptoms. One of those drivers is indeed human population growth, and I think it needs to be addressed (i.e. that is one area where governments should be spending money). Other issues relate to the amount of natural habitat loss. There, the main cause of the problem is not smallholder farmers (who indeed may be too poor to be asked to do the work themselves) but consumption patterns in rich countries and those with growing economies. Land clearance in the tropics, for example, is primarily driven by high economic demand for agricultural “luxury” goods such as palm oil and soy beans used to feed livestock (so that rich people can eat meat). The problem here certainly is not poor smallholder farmers, and I do agree with you that asking such farmers to plant big corridors etc is simply unrealistic (and probably unethical). The challenge, as I see it, relates to society much more broadly. There are a range of interconnected issues to be addressed for sustainability, and climate change and habitat loss are just two of the symptoms — the whole thing is driven by excessive consumption levels and material growth (and intensified by a growing human population). I wrote a bit about this here:
      So, how do we fix this problem instead if not via assisted colonisation? Well, depends on the region, so first of all, we need to be clear that there is not one-size-fits-all solution, but that we need regional solutions. Then, depending on where you work, it may become clearer. I am not proposing we blindly and uncritically roll out corridors everywhere. Society needs to be involved in deciding what ought to be prioritised. BUT — the bottom line is (I think) that if you have major internal bleeding, you can’t happily stick on band-aids and think you’re done. Assisted colonisation is needed because of the interaction of climate change with habitat loss. So, we must address climate change and habitat loss, ultimately.
      I am not ruling out there would not be situations where assisted colonisation would be useful, but as a “general solution”, it strikes me as too short-sighted and may distract from more important activities addressing more fundamental drivers of extinction. (Assisted colonisation is not cost-neutral either by the way — so to star with, that’s the money I propose to spend on habitat restoration instead.)

  3. Pingback: IRIS researchers help make sense of assisted migration debate | Institute for Research and Innovation in Sustainability

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