The biosphere is the part of the earth inhabited by living organisms.

Ecosystems exist in the biosphere, and within ecosystems, there can be different habitats, each with its own distinct conditions. A community of organisms live in ecosystems because they are adapted to the conditions.

Ecosystems are made of biotic and abiotic factors:



Non-living elements of the habitat of an organism, physical or chemical

  • Solar energy input
  • Climate
  • Oxygen availability
  • Edaphic – soil pH, mineral availability
  • Temperature
  • Wind
  • Pollution

When abiotic conditions are suitable, organisms can grow and reproduce quickly. Organisms can only exist where the abiotic conditions are suitable.



Living elements of a habitat which affects the ability of organisms to survive. They are density dependent

  • Predation – as the prey population increases, more food is available – predator population grows – so more prey is eaten – prey falls – predators fall as well.
  • Parasitism – diseased animals will be weakened and not reproduce successfully. They cannot hunt well and are more likely to be caught. Parasites can wipe out whole populations and spread fast when there is a high population (close proximity).
  • Competition for resources
  • Grazing


Anthropogenic factors arise from human activity and can be both abiotic and biotic.


  • Interspecific competition: Between species – different species within a community compete for the same resources – limits food so less energy for growth and reproduction – population sizes will be smaller. The better adapted species will out-compete the other
  • Intraspecific competition – Within a species – for limited resource between members of the same population of a species.


The various populations in an ecosystem or habitat make up a community.

A niche is the requirements that an animals has to survive in a habitat.