Biodiversity is defined as ‘the variability among living organisms from all sources, including terrestrial, marine and other aquatic ecosystems and the ecological complexes of
which they are a part; this includes diversity within species, between species and of ecosystems’.

United Nations Earth Summit (1992)

Conservation and sustainable use of biodiversity is fundamental to ecologically sustainable development. Biodiversity is part of our daily lives and livelihood, and constitutes
resources upon which families, communities, nations and future generations depend.


Levels of Biodiversity:
Biodiversity is considered to exist at three levels: genetics, species, and ecosystems.

(a) Genetic diversity:
• It is concerned with the variation in genes within a particular species.

• Genetic diversity allows species to adapt to changing environments.

• This diversity aims to ensure that some species survive drastic changes and thus carry on desirable

• The survival of individuals ensures the survival of the population.

• The genetic diversity gives us beautiful butterflies, roses, parakeets or coral in a myriad hues, shapes
and sizes.

(b) Species diversity:
• It refers to the variety of living organisms on earth.

• Species differ from one another, markedly in their genetic makeup, do not inter-breed in nature.

• Closely-related species however have in common much of their hereditary characteristics. For in-
stance, about 98.4 per cent of the genes of humans and chimpanzees are the same.

• It is the ratio of one species population over total
number of organisms across all species in the given

• ‘Zero’ would be infinite diversity, and ‘one’ represents only one species present.

(c) Ecosystem/ Community diversity:
• This refers to the different types of habitats. A habitat is the cumulative factor of the climate, vegetation
and geography of a region.

• There are several kinds of habitats around the world. Corals, grasslands, wetland, desert, mangrove and
tropical rain forests are examples of ecosystems.

• Change in climatic conditions is accompanied by a change in vegetation as well. Each species adapts itself to a particular kind of environment.

• As the environment changes, species best adapted to that environment becomes predominant. Thus the
variety or diversity of species in the ecosystem is influenced by the nature of the ecosystem.


Measurement of Biodiversity:
Biodiversity is measured by two major components:
i. species richness and
ii. species evenness.

(i) Species richness:
It is the measure of number of species found in a community.
a) Alpha diversity:
It refers to the diversity within a particular area or ecosystem, and is usually expressed by the number of species (i.e. species richness) in that ecosystem.

b) Beta diversity:
It is a comparison of diversity between ecosystems, usually
measured as the change in amount of species between the ecosystems.

c) Gamma diversity:
It is a measure of the overall diversity for the different ecosystems within a region.

(ii) Species evenness:
It measures the proportion of species at a given site e.g. low evenness indicates that a few species dominate the site.