Climate upsets: big model predicts many new neighbors.

For wildlife, the biggest wallop from global climate change may not be species extinctions but major shifts in the make-up of creature communities.

That's the prediction from the most ambitious application yet of the computer model for climate change and biodiversity developed by A. Townsend Peterson of the University of Kansas in Lawrence and his colleagues. They started with information on the current ranges of 1,870 birds, mammals, and butterflies in Mexico. Their model crunched the information under various scenarios of climate change to predict the ranges of the species in 2055.

Fewer than 3 percent of the species will get squeezed into extinction by then, according to the model, but the mix of animals in a lot of places will be different from what it is today. Lowlands, in particular, may have more than 40 percent turnover among their species, the researchers report in the April 11 Nature.

"I don't think anybody had suspected it would be so great," says Peterson. The extensive shakeup may bode ill for some species, exposing them to new predators and parasites or depriving migrants of vital partners.

The team's model, nicknamed GARP, takes a unique approach to predicting effects of climate change, says Peterson. Other models have either focused on a few species or lumped together all the species of an ecosystem as a unit. GARP, however, builds up its picture of broad landscape changes by adding predictions species by species.

From several dozen locations where a species has been found, GARP calculates where on the map a similar climate in 2055 might permit the species to live.

"We did it in Mexico because we could," says Peterson. The government's CONABIO biodiversity agency has surveyed museum collections to assemble data about species ranges. The United States offers nothing comparable, notes Peterson.

In their final analysis, the Kansas modelers considered climate change of intermediate severity. The modelers also created an intermediate case for how well animals will be able to move to escape tough conditions.

"The areas that are projected to get hammered are flatland areas," says Peterson. For example, the model predicts high species-turnover rates in the Chihuahuan desert, the valleys extending south to Oaxaca, and the Baja peninsula. Peterson speculates that flatlands may be especially vulnerable because creatures have to move many kilometers to find different climatic conditions instead of just climbing a little higher on a mountain.

Ecologist F. Stuart Chapin III of the University of Alaska-Fairbanks calls the new model "a really important step forward." However, he cautions that plenty of other factors will combine with climate to determine the ultimate ranges of species. An animal might find a more hospitable climate by moving, but that's no good if people have covered the escape route with houses and asphalt.

Chapin predicts that interactions of animals in new combinations will prove more important than climate in distribution of species. He finds the model's predictions of high species turnover "very likely." He says, "That's an important message that hasn't come through so clearly before."