CIE A Level Biology复习笔记18.2.2 Biodiversity

Biodiversity can be thought of as a study of all the variation that exists within and between all forms of life

Biodiversity looks at the range and variety of genes, species and habitats within a particular region

It can be assessed at three different levels:

The number and range of different ecosystems and habitats

The number of species and their relative abundance

The genetic variation within each species

Biodiversity is very important for the resilience of ecosystems, in that it allows them to resist changes in the environment

Ecosystem or habitat diversity

This is the range of different ecosystems or habitats within a particular area or region

If there is a large number of different habitats within an area, then that area has high biodiversity

A good example of this is a coral reef. They are very complex with lots of microhabitats and niches to be exploited

If there is only one or two different habitats then an area has low biodiversity

Large sandy deserts typically have very low biodiversity as the conditions are basically the same throughout the whole area

Species diversity

An ecosystem such as a tropical rainforest that has a very high number of different species would be described as species-rich

Species richness is the number of species within an ecosystem

Species diversity looks at the number of different species in an ecosystem, and also the evenness of abundance across the different species present

The greater the number of species in an ecosystem, and the more evenly distributed the number of organisms are among each species, then the greater the species diversity

For example, an ecosystem can have a large number of different species but for some species, there may only be 3 or 4 individuals. As a result, this ecosystem does not necessarily have high species diversity

Ecosystems with high species diversity are usually more stable than those with lower species diversity as they are more resilient to environmental changes

For example in the Pine forests of Florida, the ecosystem is dominated by one or two tree species. If a pathogen comes along that targets one of the two dominant species of trees, then the whole population could be wiped out and the ecosystem it is a part of could collapse

Genetic diversity

The genetic diversity within a species is the diversity of alleles and genes in the genome of species

Although individuals of the same species will have the same genes they will not necessarily have the same alleles for each gene

Genetic diversity is measured by working out the proportion of genes that have more than one form (allele) and how many possible alleles each gene has

There can be genetic differences or diversity between populations of the same species

This may be because the two populations occupy slightly different ranges in their habitat and so are subject to slightly different selection pressures that affect the allele frequencies in their populations

Genetic diversity within a single population has also been observed

This diversity in a species is important as it can help the population adapt to, and survive, changes in the environment

The changes could be in biotic factors such as new predators, pathogens and competition with other species

Or the changes could be through abiotic factors like temperature, humidity and rainfall