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University of Minnesota
December 14, 2010
Kenneth Kozak will go to great lengths--and heights--to study amphibians.
Salamanders show why the tropics are so rich in species
By Deane Morrison
The tiny salamanders in Kenneth Kozak's lab don't look very strong. But they've just helped overturn a powerful idea.
Ecologists have long known that the tropics have more species than temperate areas. But the reason may not be what they thought.
The traditional explanation was that organisms, armed with the extra solar energy and rain of the tropics, could use those resources to evolve into, and sustain, more species. It was as if the tropics were characterized by sunny, rain-splashed sameness.
But when researchers Kozak, of the University of Minnesota, and John J. Wiens of Stony Brook University looked closely at salamanders in temperate and tropical mountain regions of North America, this notion evaporated.
"It had nothing to do with the [energy input]," says Kozak, an assistant professor of fisheries, wildlife and conservation biology and curator of amphibians and reptiles at the U's Bell Museum of Natural History. "But because the seasonal temperature change is so slight in the tropics, [a variety of] habitats are stable, and organisms adapt to them."
For example, as one goes up a mountain in Central America, habitats get chillier and deciduous forest gives way to conifers. The lack of seasonal change stabilizes these habitats year-round, allowing salamanders to evolve into "specialists" adapted just to the specific conditions at their respective elevations. This leads to more salamander species.
What some salamanders lack in lungs, they make up for in looks.
But in the temperate southern Appalachians, mountains are low (the highest peak, Mt. Mitchell, reaches 6,800 feet), offering room for fewer climate-based habitats. And seasonal changes mix up the weather conditions so that salamanders at each elevation experience, at some point in the year, the conditions at every other elevation. None can survive by adapting to cold but not warmth, or to dry but not wet. This has a homogenizing effect that works against the evolution of new salamander species.
The researchers' data and insights could prove invaluable in finding suitable habitats for salamanders and other species threatened by climate change. They published their study in Ecology Letters.
Kozak and Wiens studied lungless salamanders, which account for about 70 percent of the world's salamander species. The ancestors of these salamanders originated in temperate areas of North America and moved into the subtropical and tropical highlands 30-40 million years ago. They now number some 225 species, compared to about 100 for the Appalachians and other eastern North American areas.
Highlands may seem a strange place for salamanders to thrive, but not when you consider that these little amphibians breathe through their skin.
"The efficiency of gas exchange [oxygen coming in, carbon dioxide going out] works best in cool, moist conditions, which tend to occur at higher elevations," Kozak explains.
By examining museum records of where various species were found and gathering GIS data about the environmental conditions in those places, the researchers were able to piece together where the most species live and how their numbers compared to the local climates.
Besides finding that mountains offer a variety of climates even in the tropics, they discovered that new species evolve faster when contact with related species is minimal.
"This finding is important for global climate change. It says that in predicting suitable habitats for species that may be displaced by climate change, you can't just look at the rate at which species adapt physiologically, you also have to look at interactions with other organisms, other species," says Kozak. "Unfortunately, this makes it harder to predict responses of species to climate change."
Kozak is a McKnight Land-Grant Professorship recipient for 2010-12.
Published in 2010