August 22, 2011

Tracking species as they flee


Species are escaping to higher elevations at an average rate of 36 feet per decade and moving away from the equator at a rate of 10.1 miles per decade. This is 2 to 3 times faster than they were fleeing in 2003 - the last time a similar analysis was conducted. 


In the early nineties, a young PhD student at the University of Texas in Austin spent four and a half years following a small black butterfly with red and yellow spots up and down the west coast, from southern California in March to Canada in August. In 1996 she published the results of her laborious fieldwork in a paper titled "Climate and Species Range" in the journal Nature.


The PhD student's name was Camille Parmesan, and her paper offered one of the first documented examples of a species' having shifted its range in response to climate change. Dr. Parmesan's work (she is now an associate professor at the university) showed that over the previous 100 years, the entire range of the butterfly, the Edith's Checkerspot, had moved northward and to higher elevations. In fact, 80 percent of the populations in Mexico and Southern California had disappeared.


Dr. Parmesan's pioneering work helped to unleash a flood of similar research documenting the geographical adaptations of plants and animals to a warming world.


The resulting body of research also provided the data for a new meta-analysisled by Chris D. Thomas of York University in Britain, whose findings were just published in the journal Science.


The paper compiled 23 studies involving latitudinal measures and 31 studies on elevation range shifts for plants, birds, mammals, fish, arthropods, amphibians, reptiles and mollusks from around the world.


The findings indicate that among the plants and animals tracked in the studies, species over all were escaping to higher elevations at an average rate of 36.1 feet per decade and moving away from the equator at a rate of 10.1 miles per decade. That's a steady march poleward of eight inches per hour. Those two rates are respectively two and three greater than those found in the last similar meta-analysis in 2003.


The data also clearly indicates that the species changing their distribution the most rapidly are those in regions where the most warming has occurred.


While the study pulled together literature from around the world, the vast majority of available research comes from Europe and North America, leaving big holes in global understanding how species in one of the most biologically rich areas, the tropics, are responding to climate change.


These unanswered questions are further complicated by the primary role of precipitation, as opposed to temperature, in distributing most species in the tropics. The precise effects of climate change on precipitation are still a source of debate and uncertainty.


What is more, a large minority of species were observed to move in the opposite direction from what was predicted — for instance, to lower elevations and closer to the equators.


"It's an important reminder that there are a whole host of other pressures beyond climate change which determine species distribution," Dr. Thomas said. "Land use change, habitat loss — there's a long list of pressures which must all be balanced. Climate change is a huge pressure, but it's just one pressure facing species around the world."
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