Biodiversity is used to describe every living thing, including plants, bacteria, animals, humans; more specifically used to refer to the diversity of biological organization in cellular macromolecules or biomes.
Biodiversity is defined as ‘the variability among organisms from all sources, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part, this includes diversity within species between species and of ecosystems.’
–UN Earth Summit 
Levels of Biodiversity
- Genetic diversity
- Species diversity
- Ecosystem/Ecological diversity
1. Genetic Diversity
It is diversity of genes within a species.Genes are the basic unit of whole diversity as the cell is the basic unit of life. Genes are responsible for transfer of traits to next generations in different species i.e., they are responsible for variations in between the organisms.
These variations in genes within a species due to which there is diversity among the individuals is called Genetic Diversity.
- Rauwolfia vomitoria [medicinal plant] growing in different Himalayan ranges might be in terms of potency and concentration of active chemical [reserpine] that plant produces.
- There are more than 50,000 genetically different strains of rice and 1,000 varieties of mango in India.
2. Species Diversity
The diversity at species level. Species are different from one another due to different genetic makeup and their members can’t interbreed.
Some species exhibit more diversity of species as compared to other regions, such areas are called Biodiversity Hotspot like Tropical Rainforest.
Example: a) Amphibian diversity in Western Ghats is greater than the Eastern Ghats
3. Ecological Diversity
It represents different types of ecosystems in a particular region i.e. diversity of a habitat in the given unit area.
India, for instance, with its deserts, rainforests, mangroves, coral reefs, wetlands, estuaries and alpine meadows has greater ecosystem diversity than a Scandinavian country like Norway.
Scientists have estimated that there are around 8.7 million species of plants and animals in existence, however, only around 1.2 million species have been identified and described so far.
Species exist in particular ecosystems that have ideal environmental conditions.
1. Latitudinal Gradients
On moving from equator to poles Species Diversity decreases.
- Tropical Amazonian Rainforest, South America has the greatest biodiversity pn earth- 40,000 plant species; 3,000 fishes; more than 1,200 birds; 427 mammals; 427 amphibians, 378 reptiles; more than 1,25,000 invertebrates.
2. Species-area relationship
Within a region species richness increases with area, but only upto a limit, this was observed by Alexander von Humboldt [German naturalist and geographer]
log S = log C + Z log A
S = species richness
A = area
Z = regression coefficient [slope of line]
C = Y-intercept
Importance of Species Diversity to the Ecosystem
For this let’s see “Rivet popper hypothesis”-
This was proposed by Paul Ehrlich.
- In an airplane [here ecosystem] all parts are joined together using thousand of rivets [species]. If every passenger traveling in airplane starts popping a rivet to take home [causing a species to become extinct]. Initially, it may not effect flight safety [proper functioning of ecosystem], but as more rivets are removed the plane becomes dangerously weak over a period of time.