Showing posts with label Australia. Show all posts
Showing posts with label Australia. Show all posts

Thursday, September 29, 2011

Australian Tree Frogs Collect Condensation for Hydration

Research published in the October issue of The American Naturalist shows that Australian green tree frogs survive the dry season with the help of the same phenomenon that fogs up eyeglasses in the winter.

Christopher R. Tracy and colleagues found the Australian Green Treefrog, Litoria caerulea, remain active during the dry season with apparently no available water and at temperatures that approach their lower critical temperature. The authors hypothesized that when the frogs retreated to their refugia condensation forms on their cold skin — just like it does on a eye glasses or the widows of your car.  They used frogs retrieved from natural dens and artificial dens and found the frogs absorb the condensing moisture through their skin, to maintain hydration during periods of little or no rain.

Before this study, the frogs' dry-season excursions were a bit mysterious.

"Every once in a while, we would find frogs sitting on a stick under the open sky, on nights when it was so cold they could barely move," said Dr. Chris Tracy, who led the research. "It was a real puzzle."

Tracy and his colleagues thought this behavior might enable the frogs collect condensation, but the hypothesis had never been tested.

The researchers designed a series of experiments using real frog dens in eucalyptus trees and artificial ones made from PVC pipe. They wanted to see if the frogs could collect enough moisture through condensation to compensate for what they lost being in the cold. They found that a cold night out cost a frog as much as .07 grams of water. However, a frog could gain nearly .4 grams, or nearly 1 percent of its total body weight, in water upon returning to the warm den.

The researchers also tested how well a frog's skin could absorb water, and found that as much as 60 percent of each water drop could be absorbed.

The results show that frogs can use condensation to hydrate themselves. And in a place as arid as the Australian savannahs during the dry season, where there is essentially no rain from June through August, every little bit counts.

"When there's no water available, even a small amount can mean the difference between surviving the dry season or not," Tracy said.

Citation
Christopher R. Tracy, Nathalie Laurence, Keith A. Christian, 2011, Condensation onto the Skin as a Means for Water Gain by Tree Frogs in Tropical Australia." The American Naturalist 178:553-558.(October 2011)

Friday, January 21, 2011

Monitor Lizard Mortality Due to the Cane Toad?


ABC Western Queensland is carrying the following story that reports anecdotal evidence that the Cane Toad is the cause of increased mortality in Varanus populations of the Cooper drainage. This is unedited.

20 January, 2011 3:37PM AEST

Cane toads in the Cooper threaten predators

By Nicole Bond and Julia Harris

Cane toads first arrived at Noonbah station homestead near Stonehenge, in March last year, although they were seen at a neighbouring property, Lochern, about six months earlier. Now, with a boom season in the district, the toad numbers are increasing, and Angus Emmott, a grazier and naturalist said he's starting to see their impact on goannas. He said the cane toads are just breeding like crazy.

"There's young ones everywhere but there's also lots of big ones," he said.

The issue of concern to Mr Emmott is he's now noticing that the goannas in particular are starting to die at Noonbah.

"I'm seeing goanna bodies lying around and anything like mulga snakes, De Vis banded snakes; any of those animals that have frogs as a significant component of their diet are really going to be hammered," he explained.

Mr Emmott said he hasn't seen a dead goanna with a cane toad in its mouth but the evidence from northern Australia is overwhelming.

"When the cane toads first move in, you get a mass die off of these particular groups of animals."

The promising part for Mr Emmott seems to be that over a period of about 20 years, the few goannas that do survive gradually learn to live with the cane toads and leave them alone.

He's hoping that will occur in the Cooper system over time as well.

"But we've probably got 15 to 20 years to wait until the goanna populations come back up to any sort of numbers again," he explained.

He said the goannas and other frog eating animals have a major role in the balance of the ecosystem and that's going to change.

"But without close, intense study we're probably not even going to be aware of what exactly those impacts are."

A number of scientists are interested in the invasion of cane toads into the Lake Eyre Basin catchments, and Mr Emmott said it's because it wasn't something that was predicted.

"It was thought that this part of the world would be too arid for them.

"They seem to be adapting quite well to the aridity; although it's not very arid at the moment!

"Sydney Uni had a student working around the Longreach area last summer and I'm sure if they can get some more money together they'll be doing some more work," said Mr Emmott.