Animals behaving strangely - climate change the culprit?
Reuters article; Stanford University release
August 11, 2005
OSLO, Norway (Reuters) - Salmon swim north into Arctic seas, locusts plague northern Italy and two heat-loving bee-eater birds nest in a hedge in Britain.
Scientists Find Direct Link Between Global Warming and Wildlife Evolution
For the first time, scientists have found a direct relationship between global warming and the evolution of contemporary wildlife. A research team led by Stanford University biologist Elizabeth Hadly published its findings in the September 7, 2004 online edition of the journal PloS Biology, says a Stanford press release.
Fossils reveal direct link between global warming and genetic diversity in wildlife
For the first time, scientists have found a direct relationship between global warming and the evolution of contemporary wildlife. A research team led by Stanford University biologist Elizabeth A. Hadly published its findings in the Sept. 7 online edition of the journal PloS Biology.
"We think we know a lot about how animals might respond to global warming, but we really have very little idea about their actual genetic response to environmental change," said Hadly, an assistant professor of biological sciences at Stanford.
In the study, she and her colleagues conducted a genetic analysis of two species of rodents commonly found in Wyoming's Yellowstone National Park -- the montane vole (Microtus montanus) and the northern pocket gopher (Thomomys talpoides). The researchers collected DNA from living animals and from the teeth of fossilized specimens whose remains were buried in Lamar Cave, a remote site near the northeast entrance to the park.
"The deposit in the cave is about nine yards deep and it took me seven years to excavate and identify the fossils," Hadly said. "It contains hundreds of thousands of bones and represents a continuous fossil record dating back 3,000 years. This timescale allows us to really investigate microevolution in a natural environment, the way you'd investigate it in a laboratory with something that has a much quicker generational timeline, such as bacteria or fruit flies."
Climate change and genetics
For the experiment, the research team compared DNA from voles and pocket gophers living near Lamar Cave with ancient DNA from fossilized rodents that inhabited the area at different times since 1000 B.C.
The researchers were particularly interested in animals that were alive during two recent climatic events -- the Medieval Warm Period (850-1350 A.D.), when the Northern Hemisphere experienced a slight warming trend; and the Little Ice Age (1350-1950), when the hemisphere cooled.
Since voles and pocket gophers prefer relatively wet grasslands, the scientists expected to see a decline in the population of both species during the Medieval Warm Period when their habitats dried up, and an increase during the Little Ice Age when the climate was wetter.
That prediction was confirmed by an analysis of fossil abundance in Lamar Cave, which revealed a 40 percent drop in the vole population during the warmer period, along with a 50 percent decline in the number of pocket gophers. As expected, fossil abundance for both species rose dramatically during the Little Ice Age as precipitation levels increased.
These findings established a direct correlation between climate change and population size, but how did individual voles and pocket gophers respond genetically to these episodes of global warming and cooling?
Earlier studies have shown that, when an isolated population shrinks, inbreeding increases. As a result, surviving offspring end up with similar DNA. Over time, this lack of genetic diversity can jeopardize the entire population, because each individual inherits the same vulnerability to diseases and other external threats.
"When you decrease population size, you have the potential of eliminating much genetic diversity," Hadly explained. "That's what happened to pocket gophers during the Medieval Warm Period. We found that they underwent a population size reduction and a decline in genetic diversity, which is what you would predict."
But voles had a different response to medieval warming. "They didn't show any reduction in genetic diversity, even though they did show a reduction in population size," Hadly said. That's because voles routinely look for mates from other colonies.
"Voles move around," Hadly noted. "They disperse quite freely, and that actually results in an elevation of genetic diversity during the time that their population sizes are undergoing reduction. Pocket gophers, on the other hand, are subterranean rodents. They dig underground burrows that are very energetically expensive to build, and they kind of stick in one place."
These results have important implications for wildlife biology and conservation, Hadly observed.
"There's a subtle message in this paper about the potential influence of warming on evolution," she said. "Voles show an influx of new genes and genetic diversity as their population declines, which means they're connected to other populations. But gophers haven't really recovered from the Medieval Warm Period, which ended less than 1,000 years ago. That means gophers are not getting any fresh, new genes from somewhere outside because they're isolated."
While previous studies have shown that interbreeding usually occurs among large populations of animals, "this study shows that gene flow is occurring when population sizes are low," Hadly said. "So the snapshot we have today about how populations are connected may not be how it actually persists through time." The study also has implications for wildlife managers in the greater Yellowstone ecosystem who are trying to maintain genetically diverse populations of elk, bison and other mammals.
"The landscape of Yellowstone -- arguably one of the largest relatively intact temperate zone ecosystems in the world -- is really chopped up and isolated, and there are fewer connections between populations," Hadly explained. "They really might not have anyplace to go because of development or habitat loss, and this has the potential to be exacerbated during global warming."
She noted that the methods developed for the study offer wildlife biologists a unique approach to understanding the long-range effects of climate change on genetics.
"In looking at wild organisms in nature, I don't really know of another study like this," she said. "No one has really looked specifically at how the environment has influenced genes over a 3,000-year timescale. And our expectation is that other species will also show genetic responses to warming. Whether these effects are reversible may have to do with life history and how connected populations are, and for many species that remains to be seen."
Other co-authors of the PloS Biology study are Stanford postdoctoral fellows Uma Ramakrishnan and Marcel van Tuinen; Stanford graduate students Yvonne L. Chan, Kim O'Keefe and Paula A. Spaeth; and Chris J. Conroy of the University of California-Berkeley. The study was supported by a grant from the National Science Foundation.
The study, "Genetic Response to Climatic Change: Insights from Ancient DNA and Phylochronology," is posted on the PloS Biology website at http://www.plosbiology.org.
This is a Stanford University release. It appeared on Sept 7, 2004.
Signs of global warming fed by greenhouse gases produced by human activity, or just summertime oddities?
In the United States, some warblers are flying north to Canada. In Costa Rica, toucans are moving higher up into the mountains, apparently because of rising temperatures.
In July, a Norwegian man fishing in a fjord had a shock when he landed a John Dory, a fish more usually found in temperate waters off southern Europe or Africa.
"There's a long list of migratory species ending up further north. It's certainly a sign of warmer temperatures," said Steve Sawyer, climate policy director at the Greenpeace environmental group.
He said salmon had been swimming through the Bering Strait between Alaska and Russia into the Chukchi Sea, apparently because the frigid water had warmed up.
Such shifts could have vast long-term implications for farmers and fishing fleets.
However, some experts are skeptical that unusual sightings of everything from bears to butterflies support theories that temperatures are rising because of a build-up of heat-trapping gases emitted by cars, factories and power plants.
"If you want to measure temperatures, you use a thermometer, not a bird," said Fred Singer, who heads the U.S. Science and Environmental Policy Project. "Birds have all sorts of reasons for moving north, south, sideways or whatever."
Singer says people and creatures have adapted to unexplained changes in temperature, linked to natural variation, throughout history. Some species simply move in unexpected directions or unwittingly stow away on trucks, planes or ships.
ROBINS IN ARCTIC
However, U.N. data show that the warmest year since records began in the 1860s was 1998, followed by 2002, 2003 and 2004. Most scientists link the rise in temperatures to human emissions of carbon dioxide from burning fossil fuels, rather than natural change.
The panel that advises the United Nations says that rising temperatures may drive thousands of species to extinction and cause more storms, floods and deserts while raising sea levels, perhaps by 3 feet by 2100.
Inuit peoples have noted southerly species of wildlife reaching the Arctic in summertime in recent years, including robins, hornets and barn owls.
Anecdotal evidence from further south is piling up.
Two yellow, green and brown bee-eater birds, usually found in southern Europe, have nested in a hedge in southern England -- the fourth time a bee-eater nest has been found in Britain.
"It looks as if it's linked to climate change," John Lanchbery, head of climate policy at Britain's Royal Society for the Protection of Birds, said of a general shift northwards of birds in Europe.
Growing seasons have extended and seas have become warmer, he said.
However, some examples are misleading.
In the Piedmont region of northern Italy this summer, residents were surprised by swarms of locusts, suspecting they had flown over from Africa.
Insect experts said they were an Italian species and did not migrate over long distances. Still, an exceptionally hot summer in 2003 has meant more parched ground, ideal conditions for the pests to lay their eggs.
"Global warming could also be a reason," said Vincenzo Girolami, an entomologist at Padua University. If there were more hotter, drier summers, there were likely to be more swarms of locusts in Italy, he said.
HEADACHE FOR RANGERS
In the United States, birds such as the Cape May warbler and Blackburnian warbler are moving north into Canada, causing a headache for forest rangers.
If the birds leave, spruce forests in the United States could be vulnerable to attacks by spruce budworm caterpillars, normally eaten by the birds. If the caterpillars are left to thrive they will eat, and dry out, the trees.
"The trees could be more stressed which could lead to more fires," said Terry Root, a professor at Stanford University in the United States. "We could really have a difficult situation."
In Costa Rica's Monteverde cloud forest, toucans, with their brightly-colored, banana-shaped bills, are threatening another species, the spectacular green quetzal, by moving to higher altitudes where the quetzals nest, she said.
(Additional reporting by Timothy Gardner in New York, Robin Pomeroy in Rome and Ed Stoddard in Johannesburg)
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