Climate change could hit tropical wildlife hardest

Deborah Zabarenko, Reuters 5 May 08;

WASHINGTON (Reuters) - Polar bears may have it relatively easy. It's the tropical creatures that could really struggle if the climate warms even a few degrees in places that are already hot, scientists reported on Monday.

That doesn't mean polar bears and other wildlife in the polar regions won't feel the impact of climate change. They probably will, because that is where the warming is expected to be most extreme, as much as 18 degrees F (10 degrees C) by the end of this century.

But there are far fewer species living in the Arctic and Antarctic and in the temperate zones than in the tropics, said Curtis Deutsch of the University of California at Los Angeles.

Many of these tropical creatures are living at the edge of their temperature tolerance already. Even the slight tropical warming predicted by 2100 -- 5.4 degrees F (3 degrees C) -- could push them to the brink, Deutsch said in a telephone interview.

In research published in Proceedings of the National Academy of Sciences, Deutsch and his co-authors investigated what could happen to cold-blooded animals in the tropics over the next 100 years if the predictions of greenhouse warming hold true.

They chose cold-blooded creatures -- mostly insects but also frogs, lizards and turtles -- because warm-blooded animals have other ways of regulating their body temperatures, such as growing a thick coat of fur to guard against cold and shedding when it gets warm.

TROPICAL POPULATION CRASH

Cold-blooded organisms can either seek shade when it's hot or sun themselves when it's cool, but otherwise they are limited, Deutsch said.

"If nothing else happens, if they were just subjected to warming temperatures and everything else in their environment stayed the same, we would predict that their populations would crash more quickly," he said, meaning that many would die and their reproductive rates would plummet.

These animals do have other options besides a species crash, he said: they can migrate uphill or toward the poles to seek cooler climates, or they can evolve, and those with the best tolerance for heat would survive.

If they migrate or mutate, this could have an important impacts on humans living outside the tropics, Deutsch said, since insects particularly play key roles in pollinating agricultural crops and breaking down organic matter into essential nutrients for other creatures.

"The direct effects of climate change on the organisms we studied appear to depend a lot more on the organisms' flexibility than on the amount of warming predicted for where they live," said co-author Joshua Tewksbury of the University of Washington.

"The tropical species in our data were mostly thermal specialists, meaning that their current climate is nearly ideal and any temperature increases will spell trouble for them," Tewksbury said in a statement.

Tropical Trouble: Species to Struggle in Heat
Andrea Thompson, LiveScience.com Yahoo News 5 may 08;

Polar bears may be the poster children for the havoc that climate change could wreak on sensitive species, but animals and plants in the tropics could actually be in the greatest peril from global warming, a new study suggests.

While temperature changes in the tropics are expected to be much less extreme than those at higher latitudes, tropical species actually have a far greater risk of extinction from just a degree or two of warming, according to the results of the study, detailed in the May 5 issue of the journal Proceedings of the National Academy of Sciences.

Tropical species are accustomed to living within a much smaller temperature range than species at temperate and higher latitudes, so once temperatures exceed that range, many hot-zone species might not be able to cope, the authors said.

"There's a strong relationship between your physiology and the climate you live in," said study team member Joshua Tewksbury of the University of Washington. "In the tropics many species appear to be living at or near their thermal optimum, a temperature that lets them thrive. But once temperature gets above the thermal optimum, fitness levels most likely decline quickly and there may not be much they can do about it."

This threat to tropical species is particularly worrisome because, "unfortunately, the tropics also hold the large majority of species on the planet," said study team member Curtis Deutsch of the University of California, Los Angeles.

Tewksbury and Deutsch, who was a postdoctoral researcher at UW when the study was done, took temperature records from 1950 to 2000 and climate model projections from the Intergovernmental Panel on Climate Change for the first years of the 21st century and compared them to data describing the relationship between temperature and fitness for a variety of temperate and tropical species, including insects, frogs, lizards and turtles. Their research was funded in part by the National Science Foundation and the UW Program on Climate Change.

How a given species would fare in a warming world appeared to depend more on how a temperature change would affect population levels and a species' physical performance than the actual amount of warming predicted for where they lived.

Some tropical species can now shield themselves from the heat of the day by sitting under a shady leaf or burrowing into the soil. But if they are already living close to their critical high temperature, a slight increase in air temperature could make staying out of the sun a futile exercise, Tewksbury said. Warming may simply come too fast for the creatures to adapt.

Tropics insects 'face extinction'
BBC News 5 May 08;

Many tropical insects face extinction by the end of this century unless they adapt to the rising global temperatures predicted, US scientists have said.

Researchers led by the University of Washington said insects in the tropics were much more sensitive to temperature changes than those elsewhere.

In contrast, higher latitudes could experience an insect population boom.

The scientists said changes in insect numbers could have secondary effects on plant pollination and food supplies.

In the research published in Proceedings of the National Academy of Sciences, the US scientists studied how temperature changes between 1950 and 2000 had affected 38 species of insects.

Unlike warm-blooded animals, cold-blooded organisms cannot regulate their body temperatures by growing a coat of fur or shedding it when it gets warm. They are instead limited to either seek shade when hot or sun themselves when cool.

The scientists predicted such species would struggle to cope with the 5.4C rise in tropical temperatures expected by 2100.

"In the tropics, many species appear to be living at or near their thermal optimum, a temperature that lets them thrive," said Joshua Tewksbury of the University of Washington.

"But once temperature gets above the thermal optimum, fitness levels most likely decline quickly and there may not be much they can do about it," he added.

Although some species might be able to migrate uphill and towards higher latitudes, or evolve to cope with the warmer climate, others might eventually die out, the scientists said.

Tropical insects risk extinction with global warming: study
Jean-Louis Santini, Yahoo News 5 May 08;

Global warming could pose a greater risk to tropical insects and other species sensitive to the slightest shifts in temperature than to creatures living in the world's tundra, US scientists warned Monday.

While cold weather animals are used to huge temperature changes, tropical species live under a much smaller temperature range and face a bigger risk of extinction with an increase of just two or four degrees Celsius, according to a team led by University of Washington scientists.

"In the tropics many species appear to be living at or near their thermal optimum, a temperature that lets them thrive," said Joshua Tewksbury, an assistant professor of biology at the Seattle, Washington university.

"But once temperature gets above the thermal optimum, fitness levels most likely decline quickly and there may not be much they can do about it," he said.

For their research, published in the May 6 edition of the Proceedings of the National Academy of Sciences, the scientists examined daily and monthly global temperatures from 1950 to 2000.

They added climate model projections for warming in the first years of the 21st century drawn up by a United Nations group of international scientists, the Intergovernmental Panel on Climate Change.

The university researchers then compared the information with data describing the link between temperature and fitness for 38 temperate and tropical insects as well as cold-blooded animals such as frogs, lizards and turtles.

While polar bears can develop thicker fur to shield them from freezing temperatures, tropical species must use other tactics to protect themselves from higher temperatures such as staying out of direct sunlight or burrowing into the soil.

But hiding from the sun could prove useless to tropical animals already living so close to their temperature comfort zone as the warmer weather could come too fast for their physiologies to adapt, the scientists said.

"Many tropical species can only tolerate a narrow range of temperatures because the climate they experience is pretty constant throughout the year," said Curtis Deutsch, an assistant professor of atmospheric and oceanic sciences at the University of California, Los Angeles.

"Our calculations show that they will be harmed by rising temperatures more than would species in cold climates," he said.

"Unfortunately, the tropics also hold the large majority of species on the planet," said Deutsch, a co-author of the study who was a University of Washington postdoctoral researcher in oceanography.