When two or more organisms attempt to use the same limited resources (food, water and shelter). Both organisms are harmed. EX: A tiger and cheetah competing for a dead antelope.
When the predator hunts down prey and kills it to consume energy, predation occurs. This is one of the main ways energy moves throughout the ecosystem. EX: A polar bear hunts down a leopard seal to eat it.
The parasite harms it's host, sucking away its energy, usually slowly. Usually the parasite will not kill it's host. EX: A tick will hop onto a dog and bury itself into the skin and take it's energy.
Mutualism is when both organisms benefit. EX: After an alligators eats a meal, it will open it's mouth and birds will come to clean it's teeth. Both organisms benefit from this.
During commensalism, one organism benefits and the other is unaffected. EX: A human picking apples from a tree.
Symbiosis is a relationship in which two organisms live in a close association with eachother. Examples of symbiosis would be mutualism, predation, parasitism, competition and commensalism.