According to Edward Wilson “Biodiversity is the combined diversity at all the levels of biological organization.”
Types of Biodiversity
- Genetic diversity: Diversity of Genes in a species
*A single species might show high diversity at the genetic level over its distributional range.
*India has more than 50,000 genetically different strains of rice, and 1,000 varieties of mango.
- Species diversity: The diversity at the species level.
*The Western Ghats has greater amphibian species diversity than the Eastern Ghats.
- Ecological diversity: Diversity at the ecosystem level,
*India, for instance, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows have greater ecosystem diversity than a Scandinavian country like Norway.
Species on Earth and in India
*According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million. Robert May places the global species diversity at about 7 million.
*More than 70 per cent of all the species recorded are animals, while plants (including algae, Fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22 per cent of the total. Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent of the total.
*Although India has only 2.4 per cent of the world’s land area, its share of the global species diversity is an impressive 8.1 per cent.
*India is one of the 12-mega diversity countries of the world. Nearly 45,000 species of plants and twice as many of animals have been recorded from India.
Patterns of Biodiversity
- Latitudinal gradients: The diversity of plants and animals is not uniform throughout the world but shows a rather uneven distribution.
*Tropics (latitudinal range of 23.5° N to 23.5° S) harbor more species than temperate or polar areas.
Ecologists and evolutionary biologists have proposed various hypotheses;
(a) Speciation- A function of time, unlike temperate regions subjected to frequent glaciations in the past, tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification,
(b) Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialization and lead to a greater species diversity and
(c) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.
- Species-Area relationships:
German naturalist and geographer Alexander von Humboldt observed that within a region species richness increases with increasing explored area, but only up to a limit.
On a logarithmic scale, the relationship is a straight line described by the equation
log S = log C + Z log A
where S= Species richness A= Area
Z = slope of the line (regression coefficient)
C = Y-intercept
Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region.
But the species-area relationships among very large areas like the entire continents, you will find that the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2).
The importance of Species Diversity to the Ecosystem
–Communities with more species are more stable than with less species.
-Source of food and improved varieties.
-Aesthetic and cultural benefits.
Loss of Biodiversity
-The IUCN Red List (2004) documents the extinction of 784 species (including 338 vertebrates, 359 invertebrates and 87 plants) in the last 500 years.
– The current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times.
– Examples of recent extinctions include the Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller’s Sea Cow (Russia) and three sub species (Bali, Javan, Caspian) of tiger.
Effect of loss of biodiversity in a region may lead to
a) Decline in plant production,
b) Lowered resistance to environmental perturbations such as drought and
c) Increased variability in certain ecosystem processes such as plant productivity, water use, and pest and disease cycles.
Causes of biodiversity losses:
The accelerated rates of species extinctions that the world is facing now are largely due to human activities. There are four major causes (‘The Evil Quartet’ is the sobriquet used to describe them).
i) Habitat loss and fragmentation
(iii) Alien species invasions