October 15, 2011 — andyextance

Fast rates of warming pose the greatest threat to species that occupy small areas of similar climate, researchers in Denmark and the UK showed last week. Brody Sandel from Aarhus University and his colleagues compared where amphibians, birds, and mammals can be found today with how fast climate has changed over the past 21,000 years. They found that fewer “endemic” species, which only inhabit tightly defined locations, live in areas where climate has changed fastest since the peak of the last ice age. “As we embark on these upcoming decades of rapid climate change, we can expect that it should continue to have major consequences on weakly-dispersing species and species living in flat regions,” Sandel said.

Sandel and his colleagues set out to try and understand how greatly species’ current homes are determined by events that happened long ago or more recently. “People often talk about historical effects, but it’s been difficult to measure exactly relative to the effect of modern climate, so we wanted to be able to put those two things side-by-side,” he explained. To do this, the scientists studied a property they call climate-change velocity, that brings together the rate at which warming creeps over the planet with landscape shape.

“If you’re standing at a point on the Earth’s surface, you can think of that climate as moving over you,” Sandel said. “For example, at one point the mean annual temperature might be 10°C, and 100 years later that climate condition will have moved a certain distance. You can take that distance that it moved and divide it by the time it took to move there, and that gives you a velocity measurement. It describes the minimum migration rate that a species would have to obtain to keep up with climate as it changes over it.”

Flying beats slithering

Terrain shape plays an important role in climate-change velocity, as temperature changes rapidly with altitude. “If you need to get to a place that’s 1°C cooler you just move up the mountain slope, and that could require only a very small movement,” Sandel said. “Whereas, if you’re in a really flat area and you need to get to somewhere that’s 1°C cooler you might have to move a very large distance to get there.”

With co-workers from Aarhus, Cambridge and Exeter Universities, as well as the University of East Anglia, Sandel analysed reconstructed temperature changes from since the world was last at its iciest . “We combined that with current estimates of average annual temperature globally, and those together give us our velocity map,” he explained. The researchers also mapped the ranges that 21,000 species of amphibians, mammals, and birds inhabit, revealing how many of them are endemic.

The findings that came from analysing the two maps together reported in top research journal Science last week largely met the team’s expectations, Sandel explained. “Climate change velocity is the rate at which a species would have to move to keep up with climate change,” he told the Science podcast. “If the species dispersal ability doesn’t let it keep up with that rate, then we expect possibly the species range to shrink, or possibly for the species to go extinct. If you look at amphibians, mammals, and birds, our hypothesis going in was that amphibians, which are generally the weakest dispersers of the three, will respond most strongly to variation in velocity. And birds, which are strong dispersers, will have a relatively weak relationship with velocity. And in fact, that’s what we found.”

Future destabilised

The ranges where species can be found today looks to have been strongly influenced by this effect. “We see very, very low numbers of endemic species when climate-change velocity is high, and the areas where we see high concentrations of endemic species, those are almost exclusively areas where climate-change velocity is very low,” Sandel said. For example, endemic species are nearly absent from largely flat areas like northeastern North America and a swathe of Europe from Belgium through to Russia. By contrast, places with low climate-change velocity are more likely to harbour endemic species. These include mountainous areas like the Andes, but also flatter regions where climate has been relatively stable over the past 21,000 years, like parts of the Amazon basin and central Africa.

With climate-change velocities set to increase, these flatter areas that still host endemic species are a particular conservation concern, Sandel and his colleagues write. That’s in part because creatures with small ranges provide most of Earth’s species diversity. “If you compare climate change and velocities since the last glacial maximum to the velocities we expect over the next century, overall we see a huge increase,” he commented. “In general, the same areas that have experienced high velocity in the past should also be experiencing high velocities in the future. But there are some exceptions, and those are important because the areas that have been stable in the past have endemic species, and those will be at the most risk in the future. Two of the most notable are the Amazon Basin, much of it will be experiencing much higher velocities than it ever has in the past, and actually a good portion of Africa.”