In the 1980’s scientists started noticing that amphibians were disappearing. Many theories have emerged regarding their decline, but none have been defined as the reason for all amphibian disappearances. Estimates of one third to one half of the 6,300 identified amphibian species are now threatened. This is extremely unusual in the evolutionary history of amphibians. The normal rate of extinction for amphibians is about one every 250 years! The worldwide decline in amphibians is a difficult subject to gain consensus on and many scientists argue that the majority of the decline is due to pollution, habitat destruction and human induced invasive species. These issues definitely play an integral role in amphibian declines, but the whole picture is more complicated. The fact that some of the most pristine habitats such as Yellowstone are now unable to sustain amphibian populations points to the conclusion that direct habitat destruction alone is not the culprit.The key factor to the demise of amphibians is probably the combination of climate change with habitat loss/degradation, disease, invasive species and overexploitation. Amphibians are more sensitive to environmental shifts than other species and their fast decline is a telling sign for how the earth’s ecosystems are shifting and the potential for further loss of biodiversity of all species is extensive.
There are basic life history traits that make amphibians more vulnerable then other species to declines. I have outlined what these traits are and how they relate to amphibians. There are seven main issues that are currently affecting the global loss of biodiversity. I will address each one in the context of how it affects and threatens amphibian species. The loss of amphibians has repercussions, many of which we are not yet aware of. Amphibians are important not only to local ecology, but also in ecosystem services they provide for us. I have outlined some amazing things that amphibians provide for us and what you can do to help them.
1) Climate change - The earth's climate regime is changing due to global warming from fossil fuel burning, which has massively increased carbon dioxide in the atmosphere. Carbon dioxide blocks heat from leaving the earth and the heat becomes 'trapped' on the surface leading to an overall warming of the planet. Photo credit: http://iucn.org/
2) Habitat fragmentation - The habitats of many species have and continue to be interrupted by human development. For example, dams and road systems isolate populations from one another. This prevents gene flow essential to maintaining healthy populations. When populations become isolated, there is a high change for inbreeding, this lowers overall reproductive output and health, which makes populations more susceptible to local extinctions. When there is no migration from other areas due to habitat fragmentation, species are not able to disperse into and restock devastated regions. Photo credit: Georgia Southern
3) Habitat degradation/loss - Human development has encroached and continues to onto wild habitats such as forests, wetlands, prairies, etc. which destroyed to make room for human neighborhoods or industry. This has limited the space available for many species that are now running out of areas to live. Photo credit: amphibiaweb
4) Invasive species - Humans have relocated many species into new habitats. Sometimes an introduced species will devastate ecosystem dynamics by outcompeting or outright killing off native species. When habitats get disturbed or degraded, they can leave an open niche in the ecosystem that can allow invasive species to invade. Photo credit: earthrangers
5) Pollution - Many manmade chemicals have entered the environment and caused anything from immediate death, to contamination of food or habitat of wildlife. This leads to either death, or decreased immunity. Pollution can also interfere with reproduction. Photo credit: inmagine
6) Pathogens - Degraded habitats, pollution and general stress from human disturbance leaves many species more susceptible to pathogens (an organism that causes disease). Sometimes species are crowded together because of habitat loss, and an invading pathogen can sweep in and wipe out entire populations. Photo credit: amphibiaweb
7) Overexploitation - Humans rely on other species for pretty much everything. Our food, clothing, housing, and gadgets are all made from materials that are found in the wild. With the human population exponentially increasing, many species have been removed from the wild, to the point that they are not able to recover and become endangered or threatened. Photo credit: hardwarezone
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References:
Amphibian Declines. Amphibiaweb [online] Available: http://www.amphibiaweb.org/declines/declines.html (3/1/2013)
Corn, P.S. 2005. Climate change and amphibians. Animal Biodiversity and Conservation. 28.1 pp59-67.
Groom, M.J., Meffe, G.K. Carroll, C.R. (2005) Principles of Conservation Biology. (3rd edition) Sunderland, MA: Sinauer Associates Inc.
Internaional Union for Conservation of Nature [online] Available: http://www.iucn.org/ (3/1/2013)
Skerratt, Lee Francis, Berger, Lee, Speare, Richard, Cashins, Scott, Raymond McDonald, Keith, Phillott, Andrea Dawn, Hines, Harry Bryan, Kenyon, Nichole. 2007. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. Ecohealth. 4pp125-134.
Sodhi, Navjot S., Bickford, David, Diesmos, Arvin C., Lee, Tien Ming, Koh, Lian Pin, Brook, Barry W., Sekercioglu, Cagan H., Bradshaw, Corey J. A. 2008. Measuring the meltdown: Drivers of Global Amphibian Extinction and Decline. PLoS One. 3(2) e 1636.
Stuart, Simon N., Chanson, Janice S., Cox, Nail A., Young, Bruce E., Rodrigues, Ana S.L., Fischman, Debra L., Waller, Robert W. 2004. Status and Trends of Amphibian Declines and Extinctions worldwide. Science Magazine. 306 (5702)pp 1783-1786.
Wake, David B., Vredenburg, Vance T. 2008. Are we in the midst of the sixthmass extinction? A view from the world of amphibians. PNAS. 105.
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