A-Level Biology OCR Notes

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Succession

Succession is the variety of processes that occur over time in a species that occupy a certain area.
Primary succession is the progressive colonisation of bare rock or other barren terrain by living organisms.
- The area is first colonised by the pioneer species, changing the abiotic factors to be less hostile for other species to survive.
- Different species may be present at each stage, who change the environment so that it becomes more suitable for other species with different adaptations but less suitable for the previous species- changing biodiversity.
- The climax community is when a stable state is reached, where there is high biodiversity and a number of new species.
Secondary succession is the recolonization of an area after an earlier community has been removed or destroyed.

Conservation

Conversations is the maintenance of biodiversity, including diversity between species, genetic diversity within species and maintenance of a variety of habitats and ecosystems.
Preservation is the maintenance of habitats and ecosystems in their present condition, minimising human impact

The rate of growth of the human population creates an increasing demand for raw material and food. A balance between conversation and human needs is necessary in order to maintain the sustainability of natural resources

Timber can be managed by:
- Coppicing- cutting tree stems close to the ground
- Pollarding – cutting the stem higher from the ground to prevent animals eating the shoots
- Rotational coppicing- coppicing different areas each time, to allow time for growth
Fish stocks can be managed by:
- Preventing overfishing
- Aquacultures
In in situ conservation species are conserved within (inside) their natural habitat, maintaining biodiversity. This includes creating legislations, wildlife reserves and repopulating areas via reintroduction.

Advantage	Disadvantage
Conserves species without removing them from their habitat	The habitat may be too fragmented to ensure a sustainable population
Ecosystem integrity is also maintained as the species are able to play a vital role in the functioning of the ecosystem	Too much genetic diversity may have already been lost to allow the species to adapt to change in their natural environment
Cheaper than ex situ conservation	Wildlife reserves may be damaged by ecotourism
Protects the biodiversity and the crucial elements of the ecosystem	The conditions that caused the area to have a loss of species may still be present

In ex situ conservation species are conserved outside their natural habitat, maintaining biodiversity. This can occur in zoos, botanic gardens and seed banks.

Advantage	Disadvantage
Protects organisms from predation and poaching	Limited genetic diversity
Help attract funding and awareness	It may be difficult to provide a suitable environment
Techniques such as artificial insemination are used to maximise reproductive success and genetic diversity	Many animals may also be unable to be re-introduced into the wild as they will not have learnt the necessary behaviour

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