Amphibians

Why are amphibians important? Why should we care if they are declining or go extinct?

Valuable source of human medicine.
All amphibians have poison glands. There is, however, an incredible diversity in the structure and function of the toxins produced, both among species and even among populations of the same species. The difference between a poison and a drug is generally a matter of dose, so it is not surprising to find that dilute amphibian toxins have been used by humans for medicinal purposes for thousands of years. A recipe from a 15th-century leechbook recommends boiled toads to cure edema and leprosy. Martin Luther, from 16th-century Germany, applied dried toads onto tumors. The Chinese have used the digitalis-like chemicals found in toad skin to treat heart ailments. Today many scientists are studying the chemicals found in the skin of different species of frogs and toads, and some of the chemicals they find are in the process of being refined for use as human medicine. For example, the tricolor dart-poison frog (Epipedobates tricolor) produces a skin secretion that acts as a non-addictive painkiller 200x more effective than morphine.

Indicators of environmental health.
Amphibians have relatively permeable skin, which allows the easy passage of water and gases, but also makes the animals susceptible to pollutants and other environmental hazards. Moreover, because of the dual lifestyle of many amphibian species (daily and/or within their lifetime), they are doubly susceptible to pollutants on the land and in the water. There was a time, antedating the use of sensitive gas detectors, when coal miners brought caged canaries with them down into the mines. The birds are significantly more sensitive to toxic gases (carbon monoxide) than humans, so the miners used them as living meters of working conditions: if the birds suddenly died, they knew they too were at risk and it was time to get out. Some people have likened this to our current situation with amphibians. Because amphibians are more susceptible to environmental hazards than are other animals, perhaps we should take heed to their sudden and catastrophic declines. Are they succumbing to stressors that might affect us at higher levels? Or are we being affected already?

Control of insects and insect-borne diseases.
Amphibians feed primarily on insects and other invertebrates. It was estimated that a single population of cricket frogs (Acris crepitans) could consume almost 5 million invertebrates in one year. Because amphibians can form such a significant component of their ecosystems, it seems logical that their prey items might prosper in areas where population declines, extirpations, and extinctions have relieved predation pressures by amphibians.

Indeed, scientists have observed that areas where local anurans have been eliminated have witnessed large population increases in some kinds of insects.

Vital link in food webs.
Amphibians play a vital role in their ecosystems because they are unique re-packagers of energy, unique due to (1) the small body sizes they can achieve, (2) the efficiency with which they create new body tissue, (3) the percent of the biomass they can represent in a given ecosystem. The low energy needs of amphibians allow them to convert over 50% of that consumed food into body tissue, whereas less than 2% of ingested food in birds and mammals goes to growth.

In one New England forest, a single species of salamander consumes 1/5 the amount of food consumed by all the birds, but because of their efficiency at converting food to body tissue, the salamanders produce more new animal tissue mass each year than do the birds and mammals!

Role in nutrient cycles.
As precipitation falls on the land, it carries with it soil and nutrients as it seeks a state of lower potential gravity, e.g., ponds, swamps, and lakes. Such erosion gradually causes the filling-in of these bodies of water and their conversion into meadows and eventually forests. This is succession, a natural process whereby one habitat is converted into another. Most amphibians have aquatic larvae, and many species utilize ponds, swamps, and lakes for reproduction. Their larvae grow there and incorporate into their body tissues some of the nutrients that were washed into these bodies of water by erosion. When they metamorphose, they carry these nutrients back up onto the land, thereby subtly slowing the process of succession. Loss of amphibian larvae from a community not only cancels this effect, but since most tadpoles are herbivorous, it can also lead to algae blooms, hypoxia (low oxygen), and fish kills, all of which can accelerate succession.

Role in culture and religion.
Humans have viewed amphibians in a variety of fascinating roles. While in some cultures frogs and toads have been despised and regarded as evil, other cultures have embraced them as life-giving keepers of the rains or agents of fertility and good luck. Some simply use them for food. Amphibians have been both cherished and persecuted by different cultures as characters in fantasy stories, ingredients in folk medicine, and as spiritual beings. Shamanism, dating back to the Stone Age, is believed to have given rise to all religions. The Shaman was the leader whose essential role was that of mediator between his people and the spirit world. Toads were important to the Shaman for their symbolic value and for creating hallucinogenic brews. In early asiatic cultures and in the pre-Columbian civilizations of the Americas the toad was regarded as a divinity, the great Mother Earth, the source and the end of all life. The Egyptian goddess of childbirth, Heqet, is usually pictured with a frog's head. Lamps and amulets with frog shapes were placed in Egyptian tombs to repel demons from the underworld. Christian religion does not portray amphibians in such a positive light. One of the plagues of Egypt was an army of frogs sweeping over the land. Note though that the plague of the frogs' mass exodus from water was preceded by a plague of water pollution and succeeded by a plague of insects - how prophetic! Since the Middle Ages, witches and toads have been closely connected. By some accounts, witches cohabited with and even dressed their amphibian associates. Chemicals in the toads' skin made them popular ingredients in magical concoctions (e.g., the famous scene from Shakespeare's Macbeth). The hunters in some indigenous tribes of the Amazon rub the skin secretions of the giant monkey frog (Phyllomedusa bicolor) into self-inflicted burns. The toxins in the skin secretions induce nausea and hallucinations in the hunters, who claim to then have heightened awareness and increased hunting success. And of course, today amphibians enjoy pop culture as Kermit the Frog, Michigan J. Frog, and the Budweiser frogs.

Amphibians are declining.
The world's amphibians are in grave danger. Populations of frogs, toads, and salamanders around the planet have been declining in recent years, and in some regions, entire
communities of amphibians have disappeared. Forests that once rang with whistles and chirps are now silent. Scientists are just now beginning to unravel some of the proximate causes for declines, but species are going extinct faster than we can determine why.

Aesthetics.
Amphibians are simply beautiful in form and function. They come in a dazzling array of shapes, sizes, and colors, and their physical beauty is matched only by the multitude of ways in which they fill so many diverse niches.