In an ecosystem, no organism is living as an autonomous entity, isolated from its surroundings. It is part of is environment, rich in non living elements, rich in other organisms, from its species or another, with whom it is in interaction. Relationship between two species may be very different from one eating the other (predation), to both living together with mutual benefit (symbiosis).

Examples of interations are

  • Neutralism (lack of interactions)
  • Mutualism (non obligatory or temporary relationship between two populations that benefits both populations)
  • Symbiosis (obligatory relationship between two populations that benefits both populations)
  • Amensalism (Association which is detrimental to one species and neutral to the other)
  • Commensalism (Association in which one organism is benefitted and the other organism is neither benefitted nor harmed)
  • Competition (association between two species both of which need some limited environmental factor for growth and must share the growth limiting resource)
  • Predation (interaction between organisms in which one organism captures and feeds upon another organism. The predator is usually bigger than the prey)
  • Parasitism (interaction between organisms in which one benefits and one is harmed. The parasite is usually smaller than the host).