Biodiversity is the variety of living organisms in an area. It can be considered at three levels:
• genetic diversity: the variety of alleles within a species.
• species diversity: the number of different species and how evenly individuals are spread between them.
• ecosystem diversity: the variety of habitats and ecosystems in an area.The simplest measure of biodiversity in a habitat is species richness, the number of different species present. It is found by sampling the habitat and counting the species identified. It does not take into account how many individuals of each species there are.Genetic diversity within a species can be measured using the heterozygosity index, H:H = number of heterozygotes ÷ number of individuals in the population A higher value means more individuals are heterozygous, so there is more genetic diversity.Worked example: in a sample of 120 individuals, 42 are heterozygous at a particular gene locus.
H = 42 ÷ 120 = 0.35High biodiversity makes ecosystems more stable, because there are many feeding relationships and more species to fill roles if one is lost. High genetic diversity lets a population adapt to change, such as a new disease or a change in climate. A small population, for example of an endangered species, often has low genetic diversity and so is at greater risk of extinction.
• genetic diversity: the variety of alleles within a species.
• species diversity: the number of different species and how evenly individuals are spread between them.
• ecosystem diversity: the variety of habitats and ecosystems in an area.The simplest measure of biodiversity in a habitat is species richness, the number of different species present. It is found by sampling the habitat and counting the species identified. It does not take into account how many individuals of each species there are.Genetic diversity within a species can be measured using the heterozygosity index, H:
H = 42 ÷ 120 = 0.35High biodiversity makes ecosystems more stable, because there are many feeding relationships and more species to fill roles if one is lost. High genetic diversity lets a population adapt to change, such as a new disease or a change in climate. A small population, for example of an endangered species, often has low genetic diversity and so is at greater risk of extinction.