Populations & ecosystems

Succession

The change in structure and species composition of a community over time

Climax community

A stable, self-perpetuating community that has reached equilibrium with its environment, and no further change occurs

What three traits does a climax community have

a great species diversity, complex food web and dominated by long-lived plants

Pioneer species

The first species to colonise a new area in an ecological succession

Primary succession

The change in structure and species composition of a community over time in an area that has not previously been colonised

Secondary succession

The recolonisation of a habitat previously occupied by a community that was disturbed by an event such as a fire, tree felling etc.

Which organisms are the pioneer species in primary succession

Lichens and algae

Stages of primary succession

Pioneer community, formation of primitive soil by weathering of rock and DOM, animals colonise, wind blows spores- moss forms, herbaceous plants outcompete moss, tall grasses grow, soil becomes thicker from DOM, humus in soil holds water, shrubs/small trees grow, large trees outcompete shrubs/small trees, climax community

How does secondary succession differ to primary?

In secondary succession there is already soil, seeds and spores. It is a much more rapid process because of this.

Stages of secondary succession

Rapid recolonisation by organisms- species depend on conditions prior to disturbance, seeds/spores/bulbs may still be in soil, shrubs/small trees grow, large trees outcompete small trees, climax community

Which species rapidly recolonise in secondary succession

grasses, heathers, brambles and birch trees

Disclimax

the prevention of the development of the climatic climax community by human interference

Which activities cause disclimax

Grazing maintains grassland and prevents shrubs/small trees from growing, farming removes most species, deforestation removes a community of large trees and smaller trees may be replanted