4.1  Species, Communities and Ecosystems

big ninja

Essential Idea:

The continued survival of living organisms including 

humans depends on sustainable communities


  • Species are groups of organisms that can potentially interbreed to produce fertile offspring
  • Members of a species may be reproductively isolated in separate populations
  • A community is formed by populations of different species living together and interacting with each other
  • A community forms an ecosystem by its interactions with the abiotic environment
  • Species have either an autotrophic or heterotrophic method of nutrition (a few species have both methods)
  • Autotrophs obtain inorganic nutrients from the abiotic environment
  • Consumers are heterotrophs that feed on living organisms by ingestion
  • Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion
  • Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion
  • The supply of inorganic nutrients is maintained by nutrient cycling
  • Ecosystems have the potential to be sustainable over long periods of time


  • Classifying species as autotrophs, consumers, detritivores or saprotrophs from a knowledge of their mode of nutrition
  • Setting up sealed mesocosms to try to establish sustainability
  • Testing for association between two species using the chi-squared test with data obtained by quadrat sampling
  • Recognising and interpreting statistical significance