Biodiversity and conservationEdexcel A-Level Biology B: Revision notes

Biodiversity is the variety of living organisms. It can be assessed at different scales:

• Species diversity within a habitat: the number of species (species richness) and how evenly individuals are spread between them (evenness).
• Genetic diversity within a species: the variety of alleles in the gene pool of a population. A population with many alleles can adapt to change, whereas a population with little genetic diversity, e.g. after a population bottleneck, is vulnerable to disease and environmental change and may suffer inbreeding.

An index of diversity takes account of both the number of species and their relative abundance. Simpson's index is:

$D = \dfrac{N(N-1)}{\sum n(n-1)}$

where N = total number of individuals of all species and n = number of individuals of each species.

Worked example: a sample has four species with 10, 5, 3 and 2 individuals. N = 20, so N(N-1) = 380. Σn(n-1) = 90 + 20 + 6 + 2 = 118. D = 380 / 118 = 3.2.

A higher D means greater diversity. A habitat dominated by one species has a lower D than one with the same species spread evenly.

Ethical reasons: species have an intrinsic right to exist, and we have a responsibility to pass on a diverse natural world to future generations.

Economic reasons (ecosystem services):

• Provisioning: food, timber, fibres, and genetic resources and medicines (e.g. vincristine from the rosy periwinkle).
• Regulating: carbon storage, climate and water regulation, flood prevention, pollination, soil protection.
• Cultural: tourism, recreation and education, which provide jobs and income.

Loss of biodiversity can remove species whose uses are not yet discovered.

Ex-situ conservation protects species outside their natural habitat.

• Zoos run captive breeding programmes, using studbooks to avoid inbreeding and maintain genetic diversity, and may reintroduce animals to the wild.
• Seed banks store seeds dry and at low temperatures to keep them viable, taking little space.

Issues: small captive populations may lose genetic diversity; animals may lose natural behaviours and fail to survive when released; some seeds cannot be stored; it is expensive and does not protect the habitat.

In-situ conservation protects species within their natural habitat, e.g. national parks, marine reserves and protected areas.

Advantages: the whole ecosystem and its food webs are protected; populations are larger so genetic diversity is higher; species keep their natural behaviours and can continue to adapt.

Issues: poaching and illegal logging are hard to police; cost of patrols; conflict with local people who need the land; small or fragmented reserves, disease and climate change.

The two approaches are usually combined, with ex-situ methods as a back-up.