January 23, 2005

Death To Kermit

Amphibians, as you may or may not have heard, are going the way of the Dodo at an alarming rate. It'd be a shame if we failed to do anything until the insects really start getting on our nerves, or the birds that feed on them start dying off, as well.

According to an article in the December 6, 2004 issue of Science, entitled "Status and Trends of Amphibian Declines and Extinctions Worldwide"*, this has been a concern since the 1970s. Because rapid die-offs were occuring even then across what were considered relatively pristine areas, the problem was that much more vexing.

Today, the authors of this global survey of amphibian populations were able to quantify the decline. A whopping 42% of all amphibian species are facing some kind of decrease, and 7% are listed as critically endangered. The researchers felt that even these numbers might be underestimates though. There isn't enough data available to assess the population trends of another 22% of amphibian species.

For a comparison, the article listed the percentages of other types of animals that are listed by the IUCN as either Vulnerable, Endangered, or Critically Endangered. These categories apply to 32% of amphibians, as opposed to 23% of mammals, and 12% of birds.

Species who are in decline for no apparent reason, such as those living in protected national parks, seem to be disappearing at an even more rapid pace. Disease and climate change are more frequently suspected, particularly fungal infections caused by water molds, but a single cause doesn't present itself. The study speaks of disappearances so rapid that species vanish from some survey areas between between one ecological survey and the next. Those families most threatened include toads, tree frogs, true frogs, and salamanders.

What is perhaps another piece of this puzzle came from an article in the April 2004 issue of Scientific American entitled, "Double Distress." The piece noted the work of a biologist at the University of Pittsburgh, Rick A. Relyea [2], who investigated the effect of pesticides on tadpoles.

Pesticide concentrations have long been suspected of being responsible for the disappearance of amphibians, but only very rarely had the chemicals been directly linked to these die-offs. The standard toxicity guidelines often indicate that pesticides are present in levels too low to directly affect these species. Relyea went looking for an indirect link, and he found one.

He added the pesticide carbaryl, sold commonly as Sevin, in varying amounts to tanks with tadpoles in them. When the amounts were small enough that they shouldn't have any direct affect, they didn't, at least when the tadpoles were by themselves. If predators were added to the water, red-spotted newts separated by a barrier, the toxin became up to 46 times more deadly to the tadpoles.

The added stress, in addition to amounts of toxin harmless by itself, made the tadpoles far more susceptible to carbaryl's effects. It seems far-fetched to me that a tadpole in the wild would be in water that didn't contain predators, and considering the contamination of the Arctic and the epidemic diseases killing coral, hard to believe that anywhere on the planet is truly pristine anymore.

Now animals are dying not only because their habitats are being exploited, not because of excessive hunting, but because mysterious stressors in their environment are just killing them off. Disease organisms are taking advantage of weakened species and off-kilter climates. It's no longer enough to just designate a national park and keep developers and poachers out, we need to rethink our addiction to inefficient manufacturing processes and the billions of tons of toxins we produce every year.

[1] Stuart, Simon N., et al. 10.1126/science.1103538

[2] First appeared in the journal Ecological Applications, December, 2003

Posted by natasha at January 23, 2005 04:22 AM | Environment | TrackBack(3) | Technorati links |