Succession

• Succession: change in species composition & structure of a community over time. Overtime species diversity increases.
• Primary succession: when newly formed/ exposed land (with no species present) is gradually colonised (inhabited) by an increasing number of species.
• 1.Pioneer species colonise rocks like lichens, moss, fungi.

  2.Pioneer species slowly erode the rock & accumulation of dead & decomposing organic material leads to primitive soil.

  Habitat is less hostile.

  3.Soil develops allowing for less complex, small plant, grasses like ferns to appear.

  4.Soil builds up & nutrient levels increase, deep rooted shrubs appear.

  5.Over long period trees and woodlands establish as they outcompete smaller plants e.g. for light intensity.

  6. Climax community is reached where there is a stable long lived community.
• Secondary succession: Reintroduction & recolonisation of organisms after ecological disturbance of an established ecosystem.

  Presence of bare soil with seeds already dispersed & spores remain allowing for germination.

  Existing bare soil is high in nitrates from migrating animals producing droppings.
• Succession is affected by:

  1.Migration-arrival of seeds, spores & animals.

  2.Interspecific competition-

  3.Facilitation- Mutualism between species becomes increasingly significant as succession progresses.
• Humans interference can affect development of climax community-

  1.Grazing- Livestock eat grasses & other plants.

  2.Farming- ploughing & growth of crops by monoculture stops trees & shrubs from establishing.

  3.Deforestation- trees cut cause soil erosion.
• Some Conservation projects require the deliberate, artificial prevention of succession in order to preserve an ecosystem in its current stage of succession.

  E.G. if succession was allowed to occur, this valuable moorland would be replaced by a climax community dominated by spruce forest, which cannot support the same species as the moorlands

  both ecosystems can bemaintained, giving ahigher overall species diversity
• Each stage of succession when a particular community dominates =Sere