10.3 changes in ecosystems

• What is an abiotic factor?

  physical and non living factors within an ecosystem

  e.g.

  • climactic factors (temp,pH)
  • soil factors (pH, composition
  • human factors (pollution)
• what are biotic factors?

  living features in an ecosystem
• how do biotic factors affect population size?

  • predator / prey population changes
  • disease causing reduced population
  • availability of mates to reproduce
• interspecific competition


  competition for resources between different species

  competitive exclusion principle:

  two species can't coexist in the same habitat with the same niche. one species will out-compete the other.
• intraspecific competition


  competition for resources within the same species

  • as population increases, intraspecific competition increases
  • population then decreases, causing less intraspeffic competition
  • ocilates
• what is carry capacity?

  the maximum population size that can survive indefinitely in an environment
• what is primary succession?

  when an area which was previously devoid of life, is colonised by different organisms
• how does succession occur?

  • pioneer species (lichen) arrive, survive harsh conditions and colonise bare rock
  • death and decomposition increases mineral content  and forms humus in the soil and soil depth increases
  • so larger plants grow more bigger due to minerals
  • these provide niches 
  • and form a climax community
• what is a plagioclimax?


  • human activity which interferes with succession
  • preventing the formation of a climax community
• what is a climax community? How is it reached?

  final stage of succession, when a stable ecosystem has been established.

  • soil is rich enough to form large plants
  • environment stops changing