Life originated on earth about 3.8 billion years ago, since then, there has been diversification of life forms. More than 1.5 million species of plants and animals have been recorded so far.
Ecologists believe that communities with more species tend to be more stable than those with fewer species. A stable community has the following features. A widespread species with minimal variation in productivity from year to year. Tolerance to occasional disturbances, which could be natural or manmade and resistance to invasions by exotic species. David Tilman showed that greater diversity leads to increased productivity.
Paul Ehrlich with the help of an analogy – the ‘rivet popper hypothesis’ says the loss of one species in the ecosystem may not hamper its functioning but the extinction of more species will have a great impact on the functioning of the ecosystem.
According to IUCN Red List 2004, about 784 species have become extinct in the last 500 years.
At present, there are more than 15,500 species worldwide that are on the verge of extinction.
Ever since life originated on earth, there have been five episodes of mass extinction of species.
We are currently undergoing the Sixth Episode of Extinction. The difference is in the rate of extinction, which is 100 to 1,000 times faster than in pre-human times. If such high rates of extinction continue, ecologists have warned that nearly 50 per cent of species on earth might be extinct in the next 100 years. Sudden climate change and various human activities have accelerated the rate of species extinction. These human activities, which include habitat loss and fragmentation, over-exploitation, alien species invasion and co-extinction.
Habitat loss and fragmentation is the most important factor responsible for species extinction. The second major cause of loss of biodiversity is over-exploitation of natural resources. Another cause of loss of biodiversity is invasion of alien species. When an alien or exotic species is introduced accidentally or deliberately into a habitat, it may turn invasive and cause the decline or extinction of indigenous species. Another cause of loss of biodiversity is co-extinction, which occurs when the extinction of one species results in the extinction of associated species. Apart from all these factors, pollution in habitats has threatened the survival of many terrestrial and aquatic species. We are losing our rich biological wealth at an alarming rate. It is essential to control and prevent the loss of our biodiversity to save our planet.