Species move high and low to escape the heat

In the tropics, many species will soon face population declines and extinction due to the warming global climate if they lack a cooler place to migrate, researchers report in the Oct. 9 issue of Science. These tropical regions of the planet present unique challenges for species because latitudinal migration (north or south) does not provide enough relief, and species must shift their ranges upward in elevation in order to escape the heat. Robert Colwell and colleagues analyzed data for 1,902 species of plants, insects, and fungi in the tropics to conclude that lowland populations will soon experience decreases in biodiversity and species richness because there is no source of species adapted to higher temperatures to replace those driven upslope by warming. Meanwhile, the researchers suggest that species at higher elevations will simultaneously be faced with “mountaintop extinctions,” when they run out of room to climb higher.

Also, a new survey indicates that the ranges of small mammals within Yosemite National Park have changed substantially after a century's worth of climate warming. Ranges for some high-elevation mammals such as the alpine chipmunk have shrunk, while animals living at low elevations, such as the harvest mouse, have expanded their ranges into higher elevations. Craig Moritz and colleagues say that warming has scrambled the composition of other mid- and high-elevation mammal communities as well. To document these changes, the researchers compared their survey data with an extensive data set collected at Yosemite in the early 20th century by Joseph Grinnell, a field biologist whose work led to the concept of the "ecological niche." Despite significant range fluctuations, Yosemite has maintained its diversity of small mammal species over the past 100 years. The large area protected by the park may preserve animal diversity by allowing mammals to migrate into new elevations in response to climate change, Moritz and colleagues suggest. A Perspective by Jens-Christian Svenning explains these findings in more detail.

ARTICLE #11: "Global Warming, Elevational Range Shifts, and Lowland Biotic Attrition in the Wet Tropics," by R.K. Colwell at University of Connecticut in Storrs, CT; G. Brehm at Friedrich-Schiller-Universität Jena in Jena, Germany; C.L. Cardelus at Colgate University in Hamilton, NY; A.C. Gilman at University of California, Los Angeles in Los Angeles, CA; J.T. Longino at Evergreen State College in Olympia, WA.

ARTICLE #12: "Impact of a Century of Climate Change on Small Mammal Communities in Yosemite National Park," by C. Moritz; J.L. Patton; C.J. Conroy; J.L. Parra; S.R. Beissinger at University of California, Berkeley in Berkeley, CA; G.C. White at Colorado State University in Fort Collins, CO.

ARTICLE #3: "Biodiversity in a Warmer World," by J. Svenning at University of Aarhus in Aarhus, Denmark; R. Condit at Smithsonian Tropical Research Institute in Balboa, Ancon, Panama.