As Earth’s climate cycles between warm and cool periods, species often must move to stay within suitable conditions. Scientists have now mapped how fast species have had to migrate in the past to keep up with changing climate. They found that small-ranged species – which constitute much of Earth’s biodiversity – are concentrated in regions where little migration has been required. Climate change due to human activities will drastically increase the required migration rates in many of these locations, putting their unique faunas at risk.
During the Last Glacial Maximum (21,000 years ago) Earth's climate was much cooler and many species were forced to occupy very different areas than they do today. In northern Europe, for example, many of the species found today are relatively recent arrivals from their refuges in southern Europe. A team of ecologists and computer scientists have asked how fast species around the world have had to migrate to keep up with this massive historical climate change and whether there are differences in the modern communities between places with low and high required migration rates.
Required migration rates were estimated by calculating how fast climate conditions have moved over Earth's surface at a point. This velocity depends on both the rate of temperature change through time and on local topography. On steep topography, a short distance traveled can produce a large difference in temperature, leading to small climate-change velocities.
What happens if a species cannot migrate as fast as it must to keep up with the velocity of climate change? Its range may shrink and, in some cases, the species may go extinct. This is most likely when climate-change velocity is high relative to species' dispersal abilities. The researchers tested this by mapping patterns of small-ranged species diversity for all terrestrial amphibians, mammals and birds. High concentrations of small-ranged species occurred where velocities were low (for example, the South American Andes), and small-ranged species rarely occurred at all where velocities were high (much of northern Europe, for example). Weak dispersers (amphibians) were most strongly affected by velocity, while the strongest dispersers (birds) were least affected.Within the mammals, bats showed patterns more similar to birds, while non-flying mammals were more like the amphibians. Thus, there appears to be a direct connection between the required migration velocity, a species' ability to disperse in response, and ultimately, the probability that a species will be driven to extinction by climate change.
This research provides the first evidence that past regional climate shifts interact with local topography and species dispersal abilities with long-lasting important consequences for the global distribution of biodiversity.
Anthropogenic climate change is leading to increased climate-change velocities. Moreover, there are several regions in the world including the Amazon basin and much of Africa where velocities have historically been rather low but are expected to increase rapidly in the next 70 years. These areas, by virtue of their historically low velocities, have high concentrations of small-ranged species. These species will likely be at particular risk as velocities increase over the next several decades.