• Mutualism is a symbiotic relationship when both species benefit. An example is a moth obtaining nectar from a flower and carrying pollen for the plant.

• Parasitism occurs when one species benefits and the other (host) is harmed. Leeches are parasites that drain blood from their hosts.

• Commensalism occurs when one species benefits and the other is unaffected.

A healthy ecosystem is a complex web with countless symbiotic relationships.