Amphibians, reigning survivors of past mass extinctions, are sending a clear, unequivocal signal that something is wrong, as their extinction rates rise to unprecedented levels, according to a paper published this past month by the Proceedings of the National Academy of Sciences (PNAS). Humans are exacerbating two key natural threats – climate change and a deadly disease that is jumping from one species to another.
The authors confront the question of whether Earth is experiencing its sixth mass extinction and suggest that amphibians, as a case study for terrestrial life, provide a clear answer. "A general message from amphibians is that we may have little time to stave off a potential mass extinction," write co-authors Vance T. Vredenburg, assistant professor of biology at San Francisco State University, and David B. Wake, curator of herpetology in the Museum of Vertebrate Zoology at University of California, Berkeley, in the August 12th issue of PNAS.
Amphibians are among the oldest organisms on earth, having survived the last four mass extinctions. The current extinction rate of amphibians is cause for alarm, according to biologists.
"An ancient organism, which has survived past extinctions, is telling us that something is wrong right now" Vredenburg said. "We -- humans -- may be doing fine right now, but they are doing poorly. The question, really, is whether we'll listen before it's too late."
While many factors have been cited for the profound change in global amphibian populations, a new emerging infectious disease called chytridiomycosis, is thought to be directly responsible for wiping out more than 200 species. It poses the greatest threat to biodiversity of any known disease. An aquatic fungus of unknown origin, it's the first of its kind to infect vertebrates, and only amphibians.
Understanding the ecology of chytridiomycosis may not only help amphibians, but human health. Scientists seek to map how the pathogen is transmitted from one species to another to develop ways to prevent or control outbreaks.
The Sierra Nevada Yellow-legged Frog is an example of a species under threat of extinction. In 2001, chytridiomycosis was detected in the mountains of the Sierra Nevada, and subsequently the authors have documented mass die-offs and the collapse of populations because of outbreaks. The fungus is surprisingly virulent, according to authors, and how it causes death is not yet known.
"It's important for people to understand what's infecting and killing these frogs," Vredenburg said. "This disease is a remarkable example of a pathogen jumping boundaries and causing havoc. If we can understand how it is able to do so, we may be able to help the frogs as well as ourselves."
The way humans impact the environment is often discovered after the fact. It’s now being discovered that climate change has shifted the boundaries of plant and animal habitats, with some birds in North America extending their boundaries northward and trees moving farther up mountains into higher elevations.
This past week Andrea Thompson of LiveScience reported that between 2000 and 2005, New York state’s Department of Environmental Conservation had thousands of volunteers all over the state observe and report the birds they could identify, creating a Breeding Bird Atlas of the various species' breeding ranges.
Researchers at the State University of New York (SUNY) compared this atlas to another one conducted between 1980 and 1985 for 83 species of birds that traditionally have bred in New York and found that many had extended their range boundaries northward, some by as many as 40 miles (64 kilometers).
"But the real signal came out with some of the northerly species that are more common in Canada and the northern part of the U.S.," said Benjamin Zuckerberg, a Ph.D. student at SUNY. "Their southern range boundaries are actually moving northward as well, at a much faster clip."
Some of the species making this southern boundary shift are the Nashville warbler, a little bird with a yellow belly; the pine siskin, a common finch that resembles a sparrow; and the red-bellied woodpecker, considered the most common woodpecker in the Southeast.
The shifts, announced this past week, are occurring in a relatively short amount of time, the researchers also pointed out, and happening in a matter of decades. These changes are also consistent with the predictions of regional warming, they added.
Warming is also forcing some mountain plant species to adapt by moving to higher altitudes as it kills them in their traditional ranges. In Southern California, for example, warming temperatures and longer dry spells have killed thousands of trees and plants, while pushing their habitats an average of 213 feet up the Santa Rosa Mountains over the past 30 years, according to a new study detailed in the August 11th issue of the journal Proceedings of the National Academy of Sciences.
Previous studies have also catalogued the ways that climate change is changing natures behavior: birds are migrating earlier in the season; reptiles and amphibians are also heading for the hills to reach cooler environments; and the timing of plant blooms is shifting as the Earth heats up.
Greg Doltis also of LiveScience reported this week about an interesting study linked to the Douglas Fir. These trees are one of the most common in British Columbia, and can be found throughout the mixed forests of the Okanagan and Shuswap.
Findings from the study were presented this week in Proceedings of the National Academy of Sciences by a team of scientists from Oregon State University and the U.S.D.A. Forest Service.
The Douglas fir has earned a towering reputation for its ability to soar higher than most trees. But there's a limit to how tall it can grow, and a new study explains why: If it grows too tall, a tree cannot transport water to the highest leaves.
This study showed that somewhere between the height of a 30 or 35-story building, Douglas firs can't transport water any higher. This predicted range corresponds with the world's tallest Douglas fir, standing in at 326 feet. These giant old growth trees are becoming rare and are close to being the tallest trees on the planet coming close to the height of the tallest California redwoods, which stand at 379 feet.
"As you go higher and higher in a Douglas fir tree, it's almost like experiencing a drought," said Rick Meinzer, a Forest Service scientist at the Pacific Northwest Research Station.
Evaporation of water from leaves sucks both water and air bubbles. In a Douglas fir, this transport relies on dead cells that act like valves and make up most of this tree's wood and prevent air bubbles from traveling up through the tree. By rejecting the spread of air bubbles through these valves, this tree also prevents water from being pulled higher.
It will be interesting to follow this research as our climate changes and as we discover groundwater conditions and aquifers becoming depleted in our forests. As the forest ecosystem becomes drier our oldest trees may become even more starved for water leading to a higher mortality rate which would bring about another dynamic change to our planet.
.
(30)
Don Elzer writes and comments about the future, current affairs, lifestyle and the natural world. He is a director of the Watershed Intelligence Network publishers of The Monster Guide, which can be found at www.themonsterguide.com
He can also be reached by email at: treks@uniserve.com
