Melting Ice and... Lemmings!

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So, we’ve established that the changing climate is causing problems for some poor plants and animals, but what’s all this got to do with the refugial hypothesis? Well, as I’ve mentioned before, species responses to climate change in the past can provide us with clues to how they may respond to present and future climatic change. I’ve come across a study that demonstrates this perfectly with reference to Arctic populations of the collared lemming. 

Prost et al (2010) first draw attention to the recent global temperature increase and the effects that it has had on ecological and biological systems, noting that the effects on Arctic ecosystems have been greater than in other parts of the world. They extracted DNA from both fossil and modern day lemming samples from Russia. They analysed the DNA and created a ‘temporal network’ to show the ‘haplotype composition through time’ (see Figure 1 for this, each circle represents one single haplotype) – for a reminder of what a haplotype is click here, but basically the more haplotypes, the higher the genetic diversity. As you can see from the image in Figure 1, genetic diversity among the lemmings dramatically decreased with time. 

Source: Prost et al (2010)

During the Late Pleistocene, the lemmings had a much more widespread distribution, occupying large parts of Eurasia as well as the area around the Arctic. The fossil record shows that the lemming populations expanded during glacial advances and contracted during interglacials. The DNA evidence points to a distinct decline in lemming populations as the temperature began to increase after the LGM, with the lowest lemming population coinciding with the Bølling/Allerød warm phase. Present day populations of lemmings are restricted to refugial areas of the Arctic, characterised by dry, treeless tundra. Prost et al (2010) found that the populations within these areas had low genetic diversity.

So, how does this relate to what’s happening in the Arctic today? If past increases in global temperature (such as following the LGM) had such a dramatic effect on lemming population sizes and the genetic diversity of remaining populations, then future increases in temperature could have similar repercussions. This time, however, the consequences could be much worse because the refugial populations are much smaller and less genetically diverse than the pre-LGM distribution of lemmings. If changes in climate were to result in large numbers of present-day lemming populations to die out then the remaining genetic diversity could be ‘completely abolished’. Understanding how the little lemmings may respond to climate change is particularly important because of the role that they play in the Arctic food chain – if there's no food for the larger mammals then their populations will also decline. I think it’s really interesting to see how the studies of past populations can warn us about dangers facing certain species in the future – after all, a changing climate is nothing new and species have had to deal with it before. I wonder, though, if findings like this ever really have an impact when it comes to developing climate change policies, or whether people really feel that saving the little lemmings is a valuable use of resources over the conservation of more charismatic mega-fauna?