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!