Biodiversity and variation (4.1, 4.2)

Biodiversity is the variety of life in a particular habitat or across the whole Earth. It can also refer to diversity within a single species.

Biodiversity is not distributed evenly around the Earth’s surface.

Biodiversity hotspots are regions with exceptionally high biodiversity, often containing many endemic species, and can be under threat from human activities.

Endemic species are only found naturally in one particular geographic area and nowhere else.

The exponential growth of the global human population has significantly impacted biodiversity by increasing the demand for natural resources such as land, water, wood, and fossil fuels.

This has led to environmental degradation, negatively affecting terrestrial and aquatic ecosystems and contributing to climate change.

The major factors reducing biodiversity include:

• habitat destruction
• habitat fragmentation
• polluting the atmosphere
• overexploitation of resources.

Ex situ conservation involves protecting species by relocating them from their natural habitats to controlled environments.

Examples include:

• Zoos – can carry out captive breeding programs and research on species’ behaviour, genetics, and needs.
• Botanic gardens – plant species are grown from seeds or cuttings. Methods such as tissue culture and cloning help propagate large numbers of plants from small samples.
• Seed banks – seeds are dried and stored in temperature–controlled environments to preserve genetic diversity.

Captive populations may suffer from reduced genetic diversity and maintaining controlled environments can be costly and resource-intensive.

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.

Biodiversity can be measured within a species using genetic diversity.

The heterozygosity index (H) is the proportion of gene loci or individuals that are heterozygous (contain two different alleles).

A high heterozygosity index indicates high genetic diversity meaning that there is greater genetic variation within the population. This increases the population’s ability to adapt to environmental change.

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