Tropical birds, trees may not be adapting fast enough to climate change.
In response to global climate change, many plants and animals are already adapting to a new, warmer reality. Scientists in Europe and in North America, for example, have observed plant species flowering earlier, animals breeding sooner, and both plants and animals shifting northward as temperatures rise. But two studies from Duke's Nicholas School of the Environment suggest that for some species those changes may not be happening fast enough.
One sign of trouble comes from tropical birds. Because of the gradual change in temperatures across tropical latitudes, birds threatened by changing climates aren't able to easily shift habitats northward. "So moving up to higher elevations is the only way to go," says German Forero-Medina, a Ph.D. student at the Nicholas School.
In a study that compared where tropical birds live now to habitat records from the 1970s, Forero-Medina found that while birds are moving higher, they aren't migrating as rapidly as scientists expected they would need to in response to recorded temperature increases. The animals instead may be tracking changes in vegetation, which can move only slowly via seed dispersal.
"This may be bad news," says Stuart Pimm, Doris Duke Professor of conservation ecology at the Nicholas School and a coauthor of the study. "Species may be damned if they move to higher elevations to keep cool and then simply run out of habitat. But, by staying put, they may have more habitat but they may overheat."
About half of all bird species live at 3,500 feet or more above sea level, and of these species, more than 80 percent may live within the tropics.
Meanwhile, another Duke-led study finds that many eastern U.S. tree species aren't adapting to climate change as quickly or consistently as predicted.
The study, which analyzed data on ninety-two tree species in thirty-one states, found that the geographic boundaries of most tree species are shrinking, rather than shifting northward as predicted. Nearly 59 percent of the species studied had boundaries that are constricting on both their northern and southern limits. Only about 21 percent of the species appeared to be shifting northward. About 16 percent seemed to be advancing southward, and around 4 percent appeared to be expanding in both directions.
"Many models have suggested that trees will migrate rapidly to higher latitudes and elevations in response to warming temperatures, but evidence for a consistent, climatedriven northward migration is essentially absent in this large analysis," says James S. Clark, H.L. Blomquist Professor of environment at the Nicholas School.