Populations, Communities & Ecosystems (Cambridge O Level Biology)

• There are several key terms that we use when referring to the different components of an ecosystem and their levels of organisation:
  • A population is defined as a group of organisms of the same species living in the same place at the same time
  • A community includes all of the populations living in the same area at the same time
    • Within a community, each species depends on other species for food, shelter, pollination, seed dispersal etc
    • If one species is removed it can affect the whole community
    • This is called interdependence

  • A habitat is the place where an organism lives
    • E.g. badgers, deer, oak trees and ants are all species that would live in a woodland habitat

  • An ecosystem is defined as a unit containing the community of organisms and their environment,
    interacting together
  • This means,all the biotic factors and all the abiotic factors that interact within an area at one time
    • The term 'biotic factors' includes all the living components such as plants and animals
    • The term 'abiotic factors' includes all the non-living components such as light intensity, mineral ions, water availability
    • Ecosystems can vary greatly in size and scale
      • A small ecosystem might be a garden pond
      • A large ecosystem might be the whole of Antarctica

Ecology Definitions Diagram

Levels of organisation in an ecosystem

• All living organisms compete with each other for food, water and living space
• Those who are the best adapted to their environments generally increase their populations at the expense of those less well-adapted
• Population growth in most organisms is controlled by the following four factors:
  • Food supply
  • Competition
  • Predation
  • Disease