Ecological significance

Ecological Importance

Amphibians play a pivotal role in ecosystem as secondary consumers in many food chains. Tadpoles have significant impact in nutritional cycling. They are herbivorous to omnivorous and are the prey items for both invertebrates and vertebrates. Adult amphibians are the best biological pest controllers. Invertebrates and vertebrates also predate them. Because of their importance in ecosystem, decline or extinction of their population has significant impact on other organisms along with them. 

From the ecological perspective, amphibians are regarded as good ecological indicators. Due to high degree of sensitivity, either during tadpole stage or as adults, they respond to very slight change in the environment. Such responses have been used to indicate habitat fragmentation, ecosystem stress, impact of pesticides, and various anthropogenic activities.   

Human welfare

In human cultures, amphibians featured through ages in the form of poetry, songs or stories. Amphibians have been a good food source and few years ago India dominated in frogleg export (it is completely banned now) along with Southeast Asian countries. This has resulted in increased insect pest population. They are exploited as model organism in ecological, embryological, physiological and genetic research. Amines, alkaloids and polypeptides are found in skins of amphibians and have pharmacological importance. Epibatidine, a skin extract from Epipedobates tricolor, a south American frog blocks the pain 200 times more effectively than morphine.  Poison dart frogs of Dendrobatidae family have highly toxic skin compounds that are smeared to arrowheads to kill larger animals. 

Global amphibian decline

From the past two decades, amphibians have gained much importance for the declines in their population worldwide. There are clear evidence for such declines from North, Central and South America, Europe, Africa and Australia. Global amphibian decline can be attributed to those with obvious causes like habitat destruction, alteration, fragmentation, climate change, radiation, chemical contamination, pollution and diseases of viral, fungal, bacterial infection as evident from various parts of the world and those mysterious declines with no obvious cause. Looking from another perspective, the threat to the amphibians can be attributed to changes in physical environment and biotic environment. Changes in the physical environment include Ultra-Violet (UV) radiation, climate change, acid rain, pesticides, herbicides and fertilizers, where as the biotic environment includes, fragmentation, demographic effects (barriers for the movements of one population to other), genetic effects (fragmentation enhances isolation, isolation emphasises inbreeding, inbreeding results in stress, stress reduces viable population), diseases and synergistic interactions. The influence of these factors operates at two levels, either singly and/or synergistically.  

Possible factors influencing Global Amphibian Decline

 We are very much puzzled over mysterious decline of amphibians. Because, these declines have occurred in protected areas and moreover it occurred very rapidly and selectively. This ultimately points out that, some of these parameters are also going to threaten human welfare. 

Malformations in Amphibians

The studies have revealed that, some amphibians exhibit abnormalities or malformations. For example, existence of more limbs, misshapen or missing of limbs, etc. This is due to impact of ecosystem disruption on developing individuals and plausible agents include UV-B radiation, chemicals, pesticides and parasites

(http://www.npwrc.usgs.gov/narcam/backgrnd/backgrnd.htm).

Ultra-violet radiation:

In the Visible spectra (VIBGYOR), the region of radiation from 280 to 400 nm, is called Ultraviolet radiation. It falls under three categories separated by wavelength. UV-A has wavelengths from 320-400nm (nanometers), UV-B from 280-320nm, and UV-C below 280nm. In general, the shorter the wavelength the more energetic the radiation making it damaging to plants and animals. UV-C can do great damage but fortunately poses no risk to life on earth. It is completely filtered out by oxygen and ozone in the stratosphere. Ozone also plays a vital role in filtering UV-B, the ultraviolet radiation that is the greatest threat to life on earth. But even a fully functioning ozone layer does not absorb all the UV-B rays. UV-A surpasses the stratosphere virtually unfiltered. But compared to the shorter wavelengths, UV-A causes little harm and even plays an important role synthesizing vitamin D in humans. In amphibians, the eggs and tadpoles are susceptible to UV-B radiation damages. Due to UV-B radiation, DNA of the egg or tadpoles gets damaged. To some extent photolyase enzymes reduce this damage, but severe exposure leads to irreversible changes in DNA and results in death of egg or tadpole or even malformations. This ultimately leads to population decline.

Climate change:

Due to the process of global warming (rise in earth's mean temperature), drastic changes in the climate occur. This lead to decreased depth of pond water, increased intensity of UV-B radiation. Which ultimately reduce the immune system of the amphibians. Due to this amphibians are more prone to diseases and death.

Frogs became hermaphrodites

Atrazine, a widely used pesticide is making leopard frogs (Rana pipiens) hermaphrodite (bearing both male and female gonads in the same organism). Atrazine gets into aquatic water body, by means of agriculture runoff. It has the ability to disrupt sex hormones. Even the exposure of 0.1 ppb (parts per billion), has led to the mixed gonads in Rana pipiens. This may be one of the causal agent for amphibian decline, world over.