In 2009 I wrote about two diverse research studies, conducted on different continents, that demonstrated the poleward migration of animals in response to a warming climate. We now have a more exhaustive meta-study(1) that describes significantly faster migration toward the poles and toward higher elevations than previously reported. With 2,000 species included in the study, poleward migration in response to climate change was found to be an average rate of 17.6 kilometers (10.9 miles) per decade and the upwards rate of migration averaged 12.2 meters (40 feet) per decade. According to the Dr. Chris Thomas, lead investigator of the study,"These changes are equivalent to animals and plants shifting away from the Equator at around 20 cm (8 inches) per hour, for every hour of the day, for every day of the year. This has been going on for the last 40 years and is set to continue for at least the rest of this century” .
In contrast to field studies, “meta-studies” analyze the results of a collection of previous studies. In other words, they pull together and analyze data from a bunch of different studies, rather than undertake field or laboratory investigations. Obviously the data included in meta-studies are often collected by different methods, in different locations and at different times, however when properly analyzed, these differences can strengthen the findings of meta-studies. This meta-study, conducted by investigators at the University of York, England included data from over a 100 studies in Europe, North America, Chile and Malaysia and included both plant and animal species.
As would be expected, there was a great deal of variation in migration among species, with some moving little, or not at all, or even retreating over several decades. But over all, the trend of migration toward cooler climates was clear. Additionally, the rate of migration was correlated with the amount of climate change in species range. According to Dr. Thomas “the more warming there’s been in an area, the more you would expect a species to move, and the more they have moved”.
Accelerating rates of upward migration have recently been described elsewhere, for instance a recent investigation(2) revisited upward migration of American pikas in the Great Basin ecoregion of the North American west. Records from the period 1898 to 2008 showed a near 5-fold increase of extinction of local populations and an 11-fold increase in the rate of upward migration during the past 10 years. Pika populations are now moving upwards at an average rate of 145 meters (475.7 feet) per decade in response to a warming climate.
Dependence upon upward migration is little more than a short-cut to extinction, as the physical amount of potential habitat declines with increasing elevation until it becomes zero – at the top of the mountain. As populations and communities migrate upward, they become increasingly physically isolated, and the gene pools of individual species tend to become increasingly unique. The term “disjunct” is frequently applied to such isolated communities, and with the passage of time they become “relics” of ecosystems found under previous regional climates. Often called “Islands in the Sky” by the popular press, mountain-top relic communities are a biological refuge, offering a window into the past. As they have reached the top, many of the species comprising these ancient communities are now being “pushed off” the mountains, and into extinction, by a warming climate.
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1.) I-C. Chen, J. K. Hill, R. Ohlemuller, D. B. Roy, C. D. Thomas. Rapid Range Shifts of Species Associated with High Levels of Climate Warming. Science, 2011; 333 (6045): 1024 DOI: 10.1126/science.12064321.
2.) Beever, E. A., Ray C., Wilkening, J. L., Brusssard, P. F. and Mote, P. W. (2011), Contemporary climate change alters the pace and drivers of extinction. Global Change Biology, 17: 2054–2070. doi: 10.1111/j.1365-2486.2010.02389.x
