Why are they threatened?

What makes amphibians vulnerable?

 

Many amphibians are highly susceptible to even slight changes in their habitat. If a species of amphibians is found in only one small area in the world (endemism), one bad year can mean extinction of that species. Below is a figure created by Heidi Rockney that shows several characteristics that make amphibians vulnerable using data collected in text books referenced at the bottom of the page.


 

 

 

• Because most amphibians have biphasic lifestyles, they rely on water in their larvae stage and after metamorphosis are often terrestrial.  This means damage to either environment will affect amphibians and they can get a double impact if both habitats are degraded.
• Many amphibians only disperse as far as the watersystem they inhabitat allows. This means they generally have low dispersal rates and small home ranges. This makes local extirpations particularly devastating as often times populations are etirpated from an area and no other amphibians will disperse and fill the open niche.
• Oftentimes amphibians need to migrate from overwintering sites to breeding sites.  This makes them vulnerable to habitat fragmentation and more easily spotted by predators.
• During the breeding season, amphibians congregate in high densities.  This provides an environment that can allow a single pathogen to get transmitted through an entire population.
• Amphibians have unshelled eggs and the water they are usually layed in is a great source of UV protection.  When water levels are lower, more UV radiation reaches developing amphibian eggs.  Increased UV exposure directly alters the expression of normal immune system development and function.
• Amphibians are charcterized as having permeable skin that allows water and oxygen exchange through their skin. Unfortunately, permeable skin also allows pollution and pathogens through their skin that can affect their health and fitness.

 

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References:

 

Dodd, K.C. (2010) Amphibian Ecology and Conservation. New York: Oxford University Press.

Groom, M.J., Meffe, G.K. Carroll, C.R. (2005) Principles of Conservation Biology. (3rd edition) Sunderland, MA: Sinauer Associates Inc.

Wells, K.D. (2007) The Ecology and Behavior of Amphibians. Chicago, London: The University of Chicago Press.