Biodiversity within a community (3.4.6)

Biodiversity can be considered at three levels:

• Ecosystem biodiversity: the variety of different habitats in a defined area. This can range from a small local habitat to the whole Earth.
• Species biodiversity: the variety of species within a habitat or ecosystem. One way of measuring this is species richness, which quantifies the number of different species in a habitat.
• Genetic biodiversity: the genetic variation within the individuals of the same species or population.

Species richness is the number of different species present within a particular area or habitat. The greater the number of species, the higher the species richness, e.g., tropical rainforest.

However, it is important to note that species richness alone can be a misleading indicator of diversity. It shows how many species are present, but does not take into account how many individuals of each species are present.

The Index of Diversity (D) is used to measure the biodiversity of an area by considering both:

• Species richness: the number of different species in a given area.
• Species evenness: the number of individuals of each species in a given area.

This index provides a more accurate measure of biodiversity than species richness alone because it also takes into account the relative abundance of each species.

Where:

• = total number of individuals of all species
• = total number of individuals of each species

Modern farming practices significantly affect biodiversity.

Examples include:

• Monoculture: the cultivation of a single crop species across a large area supports fewer species compared to diverse natural habitats. A diverse area may be cleared and planted with a single species for farming.
• Selective breeding: farmers chose crops and livestock with desirable traits to breed over multiple generations. This aims to improve yield, resistance to disease, and growth rate but reduces genetic diversity over time.