2.1 Species and populations

Significant ideas:

  • A species interacts with its abiotic and biotic environments, and its niche is described by these interactions.
  • Populations change and respond to interactions with the environment.
  • Any system has a carrying capacity for a given species.

Knowledge and understanding:

  1. A species is a group of organisms that share common characteristics and that interbreed to produce fertile offspring.
  2. A habitat is the environment in which a species normally lives.
  3. A niche describes the particular set of abiotic and biotic conditions and resources to which an organism or population responds.
  4. The fundamental niche describes the full range of conditions and resources in which a species could survive and reproduce. The realized niche describes the actual conditions and resources in which a species exists due to biotic interactions.
  5. The non-living, physical factors that influence the organisms and ecosystem—such as temperature, sunlight, pH, salinity, and precipitation—are termed abiotic factors.
  6. The interactions between the organisms—such as predation, herbivory, parasitism, mutualism, disease, and competition—are termed biotic factors.
  7. Interactions should be understood in terms of the influences each species has on the population dynamics of others, and upon the carrying capacity of the others’ environment.
  8. A population is a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.
  9. S and J population curves describe a generalized response of populations to a particular set of conditions (abiotic and biotic factors).
  10. Limiting factors will slow population growth as it approaches the carrying capacity of the system.

Applications and skills:

  • Interpret graphical representations or models of factors that affect an organism’s niche. Examples include predator–prey relationships, competition, and organism abundance over time.
  • Explain population growth curves in terms of numbers and rates.


  • The change in one community can impact on other communities (butterfly effect).

Theory of knowledge:

  • Through the use of specialized vocabulary, is the shaping of knowledge more dramatic in some areas of knowledge compared to others?


  • Human population carrying capacity (8.4)