Biodiversity: Meaning, Levels & Measurement

There are 3 levels of biological diversity which are generally accepted: Genetic, Species, and Ecosystem. These levels are interconnected with each other but are still distinct enough to be studied as 3 separate components.

Genetic Diversity

• Genetic diversity is the variety of genes within a species. Genetic diversity can be measured at various levels such as population, species, community, and biome. The genetic diversity of Indian tigers has been reduced due to habitat fragmentation.
• Genetic diversity is important because it is the foundation for evolution and adaptation. Greater genetic diversity within a species or population increases the ability of some individuals to adapt to environmental changes. Lesser genetic diversity results in uniformity which poses a long-term problem as it is unlikely that any individual within the population could adapt to changing conditions.

Species Diversity

• Species diversity refers to the variety of species found within a habitat or a region. Some habitats have high species diversity such as rainforests and coral reefs. For Example: a good climate with good physical geography supports better species diversity.
• There are 2 levels of species diversity:
  • Regional Diversity: It is the diversity of whole nations or parts of continents within which many different communities exist.
  • Local Diversity: It is the diversity in a given nation where different communities exist at different latitudes.
• The 2 main components of Species Diversity are Faunal Diversity and Floral Diversity.

Ecosystem Diversity

• Ecosystem diversity is the variety of ecosystems at a given place. It includes both habitat and community diversity. Ecosystem diversity has both biotic (living) and abiotic (non-living) elements which distinguish it from genetic and species diversity.
• As the environment changes, the species best adapt to itself according to the environment thus the diversity of the species in an ecosystem is influenced by the ecosystem itself.
• Invertebrates (i.e. animals without backbones) comprise around 99% of all animal species, and most of them are insects.
• Invertebrates encompass a range of animals including crabs, snails, worms, corals, seastars, and insects like beetles and flies.
• Insects play crucial roles in ecosystems by acting as pollinators, nutrient recyclers, scavengers, and a food source for other organisms.

Biological diversity is defined and measured through two components: Richness and Evenness.

Simpson's Diversity Index

• Simpson's diversity index is often used to quantify the biological diversity of a habitat.
• According to this index, zero represents infinite diversity, whereas one represents only one species dominating the landscape and no diversity.

Spatial Components of Biological Diversity

R H Whittaker classified the spatial component of biological diversity into alpha, beta, and gamma diversity.

Alpha Diversity

Alpha diversity refers to the diversity within a specific area or ecosystem, typically measured by the number of species (species richness) present in that ecosystem.

Beta Diversity

• Beta Diversity refers to the change in species diversity between two ecosystems.
• For example, measuring species diversity between the grassland and terrain ecosystem.

Gamma Diversity

• Gamma diversity measures the overall diversity across different ecosystems within a region.
• Gamma diversity can also be defined as "geographic-scale species diversity.

Patterns of Biodiversity

Broadly, there are two kinds of biological diversity patterns -- Latitudinal Diversity Gradient and Species-Area Relationship.

Latitudinal Diversity Gradient

• According to the Latitudinal Diversity Gradient (LDG), the species diversity follows a regular pattern as we move from the equator to the polar regions.
• The plant and animal diversity is the maximum at the equator and decreases as we move towards the poles.
  • This increase in species richness is called the Latitudinal Diversity Gradient.

Species-Area Relationship

• The Species-Area Relationship describes the general trend and pattern of increase in species richness with increasing area of observation.
• Usually, the larger areas contain more species than smaller areas.

Sources of Biological Diversity

Mutation

• Mutations increase genetic diversity by altering the genetic material (mostly DNA) of organisms.
• It is an extremely slow process compared to the other ways in which local diversity increases.

Speciation

• The creation of a new species is known as speciation.
• It occurs when groups in a species become reproductively isolated and diverge.
• Speciation can occur through several different means, such as natural selection, competition, mutation, etc.

Immigration

• Immigration increases diversity as new individuals and perhaps even new species enter an area, increasing its diversity.
• The rate at which immigration happens depends on the size of the area in question, how many species are there already, and how close the area in question is to the source of immigration.

Succession

• Succession is the process through which an area gains species as successive communities of organisms replace one another until an end-point is reached.