Amphibians
in danger
Once-thriving aquatic population nearing extinction
By Callan Bentley
Flat Hat Staff Writer
I can tell you exactly where I was 16 years, one month, and two days ago. I was puttering about in my backyard in Arlington, Virginia. As was my habit, I poked around among the fallen leaves looking for creepy-crawlies. The basement windows of my house had small sunken "window wells" and in once of these two-foot-deep holes, I found a toad. Apparently, he had jumped in and become trapped.
My father then stuck his head out the door and called to me. We were going to the hospital to visit my mother and my new baby brother, who had been born the day before. As I was only three years old, I wasn't really thinking about what I was doing, and I stuffed the toad into the pocket of my jeans. After half an hour at the hospital, I remembered the poor toad and pulled it out of my pocket, expecting to find it dead. Gratefully, it seemed none the worse for wear. Being the fast thinking three-year-old that I was, I immediately presented it to my mother as a gift. She acted honored, although she later revealed to me that she had a nurse release it outside.
"Amphibian" is a general term applying to frogs, toads, and salamanders, all of which share several characteristics. Many species are aquatic, and those that are not aquatic must return to the water to breed. Their skin is not waterproof, unlike their relatives (and evolutionary higher-ups) the reptiles. Similarly, reptilian eggs can be laid in dry areas because they are impermeable to water, whereas amphibians must lay their eggs in water lest they dry out.
Worldwide, there have been reports of declining amphibian populations. Apparently, some force is putting amphibians in peril, and either threatening or endangering many species. Biologists have proposed several different reasons for the sudden decrease in numbers, including habitat destruction, pollution, and natural population fluctuations, but no single reason has come to be apparent as the root cause.
Amphibians are particularly vulnerable to these forces because their permeable skin can easily absorb waterborne pollutants, they lack protective hair, feathers, or scales, and their shell-less eggs are especially vulnerable.
There have been several studies that have sought to determine why these animals are dropping in numbers so drastically. One, which is described in the October issue of Natural History magazine, describes work taken to determine what was causing one particular amphibian, the Oregon Western Toad, to decline.
The scientists performing the studies think that the answer lies in ultraviolet (UV) radiation. This toad lays its eggs in shallow water, where sunlight penetrates them. Throughout their development, these eggs and the embryos they contain would be exposed to sunlight and the UV radiation it contains. For years, it has been well documented that the middle portion of the UV spectrum, called UV-B, is especially dangerous. Excessive exposure causes sunburn, skin cancer, and weakening of the immune system. When subjected to UV-B radiation, the toad embryos developed abnormally.
So the natural experiment to test this theory is to let one group of eggs develop exposed to UV-B radiation and to cover another group that otherwise develops in exactly the same conditions. When scientists performed this experiment, they found that more than 40 percent of the exposed embryos died, as opposed to only 10 percent of the shielded embryos.
Another study, published in the August 23, 1991 issue of the journal Science, spent 11 years examining "fluctuations of substantial magnitude in both the size of breeding populations and in the recruitment of juveniles." It found no overall trend in breeding population sizes, aside from fluctuations that could be explained by droughts at the time of the study. The study concluded by suggesting longer-term studies. Although this study found no overall trend it failed to check into whether UV radiation could be the culprit.
The possibility that human depletion of the ozone layer (which screens out a substantial portion of solar radiation) could be at fault has been raised as well. Ozone is vital because it is the only portion of the atmosphere that does anything to stop UV radiation from reaching us. The depletion of the ozone layer, even by tiny amounts, can be disastrous for many organisms, especially ones as fragile as amphibians.
Natural History noted that between the winter of 1989-90 and the winter of 1992-93, ozone levels in the stratosphere "dropped by 11 percent, but the amount of UVB radiation reaching the ground climbed by 90 percent."
Current concern about environmental
issues has reached a peak on campus in the past week due to concern over the
Matoaka / College Woods area. Preservation of natural areas is essential to
preserving biodiversity in general and amphibian populations in particular.
Whether man is at fault of populations are naturally fluctuating, amphibians
are disappearing at alarming rates. Only time and more research will tell what
is behind it.