Organisation of Ecosystems

There are four levels of organisation in an ecosystem:

  • Individual organism
  • Population
  • Community
  • Ecosystem

Components of the Ecosystem


A species is a group of similar organisms that are able to breed together and produce fertile offspring. This includes every plant and animal species that can be found on Earth.


A population is a number of organisms belonging to one species that live in a particular area at the same time.

  • The interaction of many different populations within the same habitat creates a community.


A community is a group of populations belonging to two or more species that are living and interacting with each other in the same area. Each species in a community depends on another species for factors that are essential for their survival and reproduction (e.g. food, shelter etc). So, if you remove one species, it can affect the whole community.

  • In a stable community, the populations of all the species remain relatively constant over time


An ecosystem is a biological community of organisms that interact with each other and their physical environment. Ecosystems include all of the abiotic and biotic components which live and interact within the same environment.

  • Abiotic components/factors – Non-living factors which can affect the size and distribution of populations (e.g. temperature, air currents, water and minerals).
  • Biotic components/factors – Living factors which can affect the size and distribution of populations (e.g. flora, fauna and bacteria).


An adaptation is a characteristic that helps an organism to survive and reproduce in their environment. Organisms can become more adapted to their environment over time.


Many organisms will require the same resources as each other, and due to a finite (limited) supply of resources (e.g. food), the organisms will have to compete for it.

There can be competition between the same species or competition between different species.

  • Animals – may compete for food (for energy), water, space (to live in) and mating partners (to produce offspring and pass on characteristics).
  • Plants – may compete for light (for photosynthesis), water (for photosynthesis), space (to grow in) and mineral ions (for growth).