NEET Biology Notes Biodiversity and Wildlife Conservation-Concept of Biodiversity
Concept of Biodiversity
- The term biodiversity was popularised by the sociobiologist Edward Wilson.
- Biodiversity is the heterogeneity which exists at different levels of biological organisations in our biosphere.
- The scientific estimation of total numbm of species made by Robert Mayer is about 7 million.
- More than 70% of all the species recorded are animals, while plants (algae, fungi, bryophytes, gymnosperms and angiosperms) comprise not more than 22% of total.
- Among animals, insects are the most species-rich taxonomic group making up more than 70% of the total.
- Fungi species in the world are more than the combined total of the species of fishes, amphibians, reptiles and mammals.
- India shares 8.1% of global species diversity and it makes India one of the 12 mega diversity countries of the world.
- Nearly 45000 species of plants and twice as many of animals have been recorded from India. There are probably more than 100000 plant
- species and more than 300000 animal species yet to be discovered and described.
- The biological diversity includes following three hierarchical levels :
- Genetic Diversity
It is the diversity in the number and types of genes present in different species and the genetic variations in the same species.
For example, genetic variation in medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges occurs in terms of the potency and concentration of reserpine (active chemical). India has more than 50000 genetically different strains of rice and 1000 varieties of mango.
- Species Diversity
It is the variety of species within a region. It indicates the species richness in any habitat. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
It is the diversity at ecosystem level. Diversity abfhe level of community and ecosystem has three perspectives
α- diversity (within community diversity), which is also called local diversity and is the diversity within a community.
β – diversity diversity (between community diversity) is the diversity between two communities.
γ – diversity diversity, which is also called regional diversity, represents the total richness of species in all the habitats found within a region,
- geographical area or landscape.
According to World Conservation Network (WCN; 2004), the total number of plant and animal species defined so far is slightly more than 1.5 million and yet more are to be discovered.
Patterns of Biodiversity
.Species diversity decreases as we move away from the equator towards the poles. Therefore according to non-uniform diversity on the earth the biodiversity is divided into following patterns as:
- Latitudinal Gradients
- Generally, tropics'(latitudinal range of 23.5°N to 23.5°S) harbour more species than temperate or polar areas.
- Columbia located near the equator has nearly 1400 species of birds, whereas New York at 41°N has 105 species andGjreenland at 71°N only 56 species.
- India with much of its land area in the tropical latitudes, has more than 1200 species of birds.
- The tropical Amazonian rain forest in South America has the greatest biodiversity on earth.
- Species-Area Relationships
Alexander von Humboldt observed that within a region species richness increased with increasing explored areas upto a limit.
On a logarithmic scale, the relationship is a straight line deseribed by the equation.
Reasons of Biodiversity
The main reasons for more diversity in tropics than temperate regions are
- Species formation (speciation) is a part of evolution. Unlike temperate regions subjected to frequent glaciation for much time period in the past, tropics remained relatively undisturbed for millions of years and had a long evolutionary time for species diversification.
- Tropical environments are less seasonal, relatively more constant and predictable, which promote niche specialisation and lead to a greater species diversity. .
- There is more solar energy available in the tropics, which contributes to higher productivity and in turn greater diversity.
Importance of Biodiversity
Ecologists believe that communities with more species tend tobba more stable than those with less species. A stable community has the following attributes:
- It shall not show too much variations in the year-to-year productivity.
- It must be either resistant or resilient to seasonal disturbances.
- It must be also resistant to invasion by alien species.
- The species richness and diversity are essential for ecosystem health as well as survival of human race on the earth.
Loss of Biodiversity
- Biodiversity has been declining rapidly, the colonisation of tropical Pacific islands by humans is said to have led to the extinction of more than 2000 species of native birds.
- IUCN (International Union for Conservation of Nature and Natural Resources), Red List (2004) documented the extinction of 784 species (338 vertebrates, „ 359 invertebrates and 87 plants) in the last 500 years.
- Dodo (Mauritius), Ouagga (Africa), Thylacine (Australia), Steller’s sea cow (Russia) and three sub-species (Bali, Javan and Caspian) of tiger are the examples of recent extinction.
- About 27 species have been extincted during last 20 years. Some groups like amphibians appear to be more vulnerable to extinction.
The major causes of biodiversity loss (The Evil Quartet) are
- Habitat Loss and Fragmentation
- Alien Species Invasions