Successsion

Succession is the sequence of changes that occurs in a community over a period of time. Each new change is known as a sere and ususally involves a new species inhabiting the area. 

Primary Succession: This happens on an area of land is devoid of life for example bare rock. The first species to inhabit the area is known as the pioneer species. They can cope with the extreme conditions and break up organic matter in order to create soil which can then help more complex species begin to establish there. 

As soil mass increases and more nutrients and minerals are added, more complex species inhabit the area with each sere, replacing the existing community. This continues until a climax community is reached, which is the final stage in succession and consists of a stable and self-sustaining community.

Secondary Succession: This occurs only when an exisiting community has been cleared, for example as a result of a forest fire or a ploughed field. Seeds and spores will lie dormant in the soil and this means that the community can re-establish itself as succession happens again.  

Deflected Succession: A community that only remains stable as a result of human activity preventing succession is called a deflected succession. For example sheep grazing in a field prevents succession from occuring past a certain point, and therefore it's deflected. If the sheep are taken away, succession will progress and deflected succession no longer occurs. 

Succession occurs in many different environments. For example on a beach, sand dune succession takes place, during which smaller embryo dunes eventually get replaced by shrubs and in turn forestry. Succession can also occur in other places such as peat bogs and other such areas.

Succession can be analysed using qudrats in a technique known as a transect. A transect is used to investigate the distribution and abundance or organisms in a certain area. Where there appears to be a distinct change in an area, a transect is used in which quadrats are placed at measured intervals. If there is no distinct change in conditions in an area, then random sampling takes place during which quadrats are placed at random at certain points and organisms counted. 

Both biotic and abiotic factors can affect the distribution and abundance of species in a habitat. Biotic factors are living factors which affect this, and abiotic factors are non-living factors which affect this. 

Abiotic Factors

• Solar energy input - measured with a light metre
• Oxygen availability - measured using an oxygen probe 
• Edaphic factors such as pH - measured using a pH probe 
• Topography - Surveyors levelling equipment used to measure the shape of land 

Biotic Factors

• Competition for resources such as food, light and water
• Grazing, predation and parasitism are all relationships where one organism benefits at the other's expense
• Mutualism which is a relationship where both organisms benefit