Students hard at work on the "Mangrove Challenge"! (Sierpe River, SW Costa Rica)
Amphibians, especially frogs, are unique creatures that are especially sensitive to their ever-changing habitats. Many of these species’ populations are declining because of the carelessness of humans. Humans are the cause of global warming, water pollution, decreased biodiversity, water acidification, increased CO2 in the atmosphere, and habitat destruction. All of these problems are causing natural animal populations to form a downward slope, but frog populations seem to be getting hit the hardest. Frogs may get the reputation for being slimy and useless creatures, but they are one of the few animals that can give foreshadowing warning signals about the quality of our earth. Amphibian malformations have been reported in 44 states since 1996 (Khan, 2004). Much like the canaries in the coal mines, amphibians can warn us of the places where we need to clean up our act.
Amphibians are extremely vulnerable to change because their skin is not protected by hair or feathers and it must be kept moist in order to aid respiration. Frogs also breed in wetland habitats that naturally filter pollutants from the area. This natural filtration causes an increase in the concentration of harmful substances a frog and its offspring may absorb. Over the last thirty years, over 125 species of amphibians have become endangered or gone extinct (Kiesecker, 2004). There are several reasons for why this is happening and each one can be related to detrimental human activities.
One reason for the dwindling frog populations is the decrease in the ozone layer. Studies conducted on several different species of frog eggs found lower mortality rates in frog eggs sheltered from UVA and UVB rays than frog eggs that were unprotected from the ultraviolet radiation (Gannon, 1997). Frog and toad eggs existing at a high altitude had higher death rates because less atmosphere existed to filter out the ultraviolet rays. According to Robert Gannon’s article, the Pacific tree frog eggs had practically no response UVA and UVB radiation. This happened because their embryos contain high amounts of photolyase. Photolyase is an enzyme that rebuilds cells damaged by ultraviolet radiation. The toads that were studied had embryos with six times less photolyase than the Pacific tree frog egg, an adaptation that has helped ensure the tree frogs survival in our increasingly inhospitable world.
The increased levels of CO2 in our atmosphere are also to blame for the decline of countless amphibian populations. Global warming has changed the world’s weather patterns causing once moist areas to be lacking in sufficient surface water. Air pollution has also caused acid rain that becomes concentrated in ponds that collect runoff from large deforested areas. These smaller sparse ponds have lead to denser frog populations that are greatly susceptible to parasites and predators. Global warming can be directly blamed for the near extinction of the Golden Toad in Costa Rica. The slight increase in temperature over the years has caused the Montverde cloud forest to lose a significant amount of its moisture. The clouds now form at a higher altitude forcing the toads to immigrate to a new habitat. These denser populations are becoming disease and parasite ridden and the Golden toad will be lucky to ever be removed from the endangered species list.
When referring to frog parasites the major invader is the trematode or fluke. This microscopic flatworm borrows into the tadpoles at the end of the fluke’s life cycle. The adult trematodes live in the digestive systems of birds and the fluke eggs are excreted in the bird’s feces. The next developmental stage exists in snails. The cercariae leave the snail and then burrow into tiny tadpoles. When the burrowing happens occurs at limb buds, an extra leg may be added or one may be missing from the developing adult (Gannon, 1997).
Trematode infection rates have become higher in areas that receive agricultural runoff. The herbicides and pesticides cause many interesting problems that are not expected from a chemical that is meant to protect our crops from insect consumption. Deformities are just one result that occurs when frogs are exposed to herbicides and pesticides. Pesticide usage used to be around 50 million kilograms worldwide in the mid-1940s. Today, the usage is approximately 2.5 billion kilograms per year (Kiesecker, 2004). To test the effect of pesticides on the frog’s immune system Kiesecker and his colleagues added atrazine, malathion, and esfenvalerate to frog habitats in amounts that were equal to the EPA maximum for drinking water. The pesticides lowered the frogs’ immune systems and made the trematode infections three times as frequent as those tadpoles unexposed to the pesticides.
Atrazine is also used as an herbicide and has been found to gender bend wild frogs. Studies done at University of California, Berkeley found male tadpoles that had developed into female frogs over time. Adult male frogs were also found with testes invaded by ovary cells. These male frogs became infertile and unable to mate with other females or males. Atrazine is sprayed over seventy-five percent of the United States’ corn crop despite its gender bending effects (Sissell, 2002). Many European countries outlawed the chemical years ago. A ban would be the only way to effectively ensure that the frogs are not transformed and would also protect the still unnoticeable effects that atrazine may have on humans (Withgott, 2002).
Apalachicola National Forest is home to the very rare Rana capito, known as the gopher frog in Florida. Florida is claimed to have more frogs and snakes than any place in the United States and Canada. The gopher frog has gained attention because of the way it throws its arms up when disturbed. The frogs look to be covering their eyes like a child would do when playing peek-a-boo. Bruce Means conducted a study to find out why the gopher frog population was declining in a part of the National Forest called the Munson Sand Hills. His findings were that the frogs cannot flourish in the area were Sand Pines grow because the trees’ increased density crowds out the smaller ground-cover plants that shelter the frog from predators. Means works for the Coastal Plains Institute and Land Conservancy in Tallahassee Florida and is quoted as saying “Wrecking an ecosystem causes many species to decline. Since we all live in the same world, this will eventually come back to harm us (Means, 2003).” I agree completely with what he says and believe that the bad karma is racking up and nature will eventually come back to bite our development crazed economy in the butts.
Although the outlook of amphibian populations looks less than optimistic, many efforts are being made to improve their future. Florida State University has used a forty-thousand dollar grant to construct an amphibian passage under the U.S. highway 319. This will help the endangered spotted salamander, gopher frog, and striped newt to travel to breeding grounds at a small pond in the Apalachicola National Forest (FSU, 1998). In my area, the Redback salamander is being protected by closing off streets in specific areas of the Cleveland Metroparks. Cars are restricted to certain areas in order for these amphibians to travel to their moist breeding grounds during the months of June and July. I am pleased to see that these creatures are being protected because Cleveland does not usually have the reputation for being a friend of nature. It is encouraging to hear that we are moving in the right direction.
As travel and communication become easier and more frequent, humans need to pay attention to the unique ecosystems that exist throughout our planet. Every action we make has an unimaginable effect on the rest of the world. We need to be aware that biodiversity is decreasing while disease outbreaks are increasing. This disease increase and biodiversity decrease relationship is still debatable, but amphibians can help us investigate the connection because of their sensitivity to environmental changes (Kiesecker, 2004). Amphibians should not be ignored because they have a lot to tell us about what we are doing to our precious planet.
Just as Osha Gray Davidson was unsure whether to be hopeful of full of despair towards the degradation of the coral reefs, I am trying to remain optimistic when considering the future of amphibians on the earth. They have survived up to this point but humans are more talented destroyers than we may realize. Hopefully nature will win over and frogs, toads and salamanders will be here for decades to come. The only way for that to happen is for more people to become educated on the extent to which we are ruining the natural world for our descendants. The educated people of the earth need to come together and stop taking the natural world for granted. That way our precious wildlife can be saved.
Florida State University press release. (1998, March ). How did the frog cross the road?. Environment, 40. Retrieved Jun 3, 2005.
Gannon, R. (1997, Dec 01). Frogs in peril. Popular Science, Retrieved May 30, 2005, from http://elibrary.bigchalk.com.oh0195.oplin.org/libweb/elib/do/document.
Khan, O. (2004). Frogs in peril follow-up. Green Living, 64.
Keisecker, H. M., Belden L. K., Shea K., and Rubbo, M. J. (2004, March ). Amphibian decline and emerging disease. American Scientist, 92. Retrieved Jun 03, 2005, from www.americanscientist.org.
Means, B. (2003). Hopping experiment. Science World, Retrieved May 30, 2005.
Sissell, K. (2002, Nov 06). Malformed frogs linked to atrazine. Chemical Week, 164. Retrieved Jun 08, 2005, from http://web28.epnet.com/citation.asp.
Withgott, J. (2002, Nov 2). Popular herbicide may gender bend wild frogs. New Scientist, 176. Retrieved Jun 08, 2005, from http://web28.epnet.com/citation.asp.
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