Changing Ecosystems

Secondary succession

  • Starts where there has been vegetation before.

Secondary succession is much the same as primary succession, except it occurs when the current seral stage is removed abruptly. This may be due to a natural disaster such as a fire, or by human influence such as deforestation and strip mining.

This time, there is already soil and probably seeds present. This means the succession will happen more rapidly than primary succession. The pioneer plants are wind blown plants that are tolerant to high levels of sun and grow fast. Fast growing trees then develop, while shade-tolerant species develop in the understorey.

Explain how the change in species composition occurs in a succession.

  • species that are present change the habitat
  • other species able to colonise
  • new species better competitors

Explain what makes a climax community the most stable community.

  • there are more species present
  • more complex food webs
  • change in one species will have little effect on others
  • as there are alternative food sources

Explain why it would be more appropriate to use a transect rather than random quadrats when investigating succession.

  • series of changes over a distance;
  • environmental gradient present
  • ensures sampling of each community

The increase in the index of diversity is one indication that a biological succession is taking place in the area. Describe those features of a succession that would bring about an increase in the index of diversity.

  • Initial environment hostile / few organisms adapted
  • These organisms change the environment / suitable example
  • More niches / more habitats
  • Allowing other organisms to become established.