International A Level Biology / Biodiversity and conservation
Biodiversity and endemism revision notes
Edexcel International A Level Biology (YBI11), chapter 12: Biodiversity and conservation, specification point 4.15, 4.16. Free lesson.
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Biodiversity is the variety of species and genetic variation in an area, built up through evolution over billions of years. Knowing how human activities reduce biodiversity, and why endemic species are especially vulnerable, helps you explain conservation problems.
How evolution built up the variety of life
Life on Earth began over 3.5 billion years ago as simple single cells. Mutations created new alleles, which are different versions of a gene. This variation gave natural selection differences to act on. As populations adapted to different environments, they became more different, and over enough time some formed new species. There are millions of species today, most of which have not yet been named. Human activity is now removing species far faster than new ones form.
How human activity threatens species
Four major human threats reduce species numbers. In an exam answer, name the threat and explain how it affects the organisms in the question. Naming a threat alone is not enough. Habitat loss: clearing forests for farms, towns or roads removes food, shelter and breeding sites, so populations fall. Climate change: shifts in temperature and rainfall can make conditions unsuitable. A species that needs cool, wet conditions may find its habitat too hot or dry, and may not be able to move. Overexploitation: overfishing, hunting or logging takes organisms faster than they can reproduce,…
How biodiversity differs from genetic diversity
Biodiversity is the variety of life in an area. It includes the variety of species and the genetic variation within them. Genetic diversity is only the variety of alleles within a species. A gene pool means all the alleles in a population. These terms describe different things, and biodiversity is not the same as population size. Biodiversity can be measured using species richness or an index of diversity. A coral reef can have high biodiversity. Genetic diversity can be measured using the heterozygosity index. Cheetahs have very little genetic diversity. A gene pool can…
Why endemic species are vulnerable
A species is endemic to a place if it is found there naturally and nowhere else. Ring-tailed lemurs are endemic to Madagascar because wild populations live only on that island. An endemic species often has a small range and may also have a small population. It may be specialised for local conditions, so it cannot easily move elsewhere when conditions change. A threat can then affect the whole species, with no other population to survive elsewhere. If the only habitat is cleared, the species may become extinct everywhere. A new predator could also affect the whole species if it is limited…
Applying the ideas to examples
When you explain a change in biodiversity, connect what organisms lose to what happens to species and alleles. Also distinguish the reason a species is endangered from the fact that it is endemic. Grandidier's baobab is endangered because its forest is being cleared for farming. Its endemism makes this more serious because there is no population elsewhere. When mangroves are cleared for shrimp farms, organisms lose food, shelter and breeding sites. Populations fall, some species disappear from the area, and the smaller surviving populations have less genetic diversity.