Biology - Succession

  • Created by: Hanna W
  • Created on: 03-03-17 14:15

Types of succession

Primary succession -------- newly formed/exposed land --- there is no soil or organic material.

Pioneer species in primary succession ----- first to colonise the area. They are adapted to the harsh conditions. They change the abiotic conditions, when they decompose they form the base for the soil. The creation of the soil makes the conditions less harsh, so that other less adapted organisms can then move in.

Secondary succession ------- there is soil present but the ara is cleared of vegetation. 

Pioneer species in secondary succession ----- pioneer species are larger are larger shrubs and plants.

Climax community ----- the ecosystem is carrying the most complex community that it can. The climax community rarely changes.

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Sampling a population

Types of sampling techniques:

  • Quadrat sampling ----- Line or belt transect 
  • Mark, release, recapture ------ motile organisms
  • Point quadrat ----- smaller sample size

Total popultion size =    No. caught in 1st sample x No. caught in 2nd sample 


                                     No. marked individuals caught in the 2nd sample

Random sampling - Have to use a computer generated number used to choose coordinates to throw the quadrat at. Humans can be influenced by weather or by looking at the area they are investigating.

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Mark, release, recapture

* Used for observing motile organisms e.g. mice or birds

Rely on several assumptions when using this method:

  • That the marked sample has had enough time to mix back into the population.
  • That the marking hasn't affected the individuals chances of survival or that the mark hasn't rubbed off.
  • That there are no changes in population size. E.g. deaths and births and migration.
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The founder effect - ecosystems and genetic bottle

* Is what happenes when a small number of individuals begin a new colony.

Can occur for a number of reasons:

  • Habitat fragmentation
  • Religious seclusion e.g. the Amish
  • Hunting to near extinction - the famous AQA otter (Lutra lutra) question.
  • Disease wiping out most of the population.


  • Only a small number of allels are left in the population gene pool.
  • Can result in the number of rare alle insidences increasing becuase of it being inherited through a smaller population. e.g. The Pingelap island people and their colour blindness. A tsunami wiped out the whole population of the island apart from 20.
  • A higher incidence of genetic faults could occur.
  • Inbreeding brings with it a higher chance of genetic mutation. Few partners means that inbreeding is inevitable.
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