Commensalism: Interaction in which one species benefits and other is neither harmed nor benefitted. The species which is benefitted is termed commensal and the other species is called the host. Such a population interaction is represented as (+,0). E.g. clown fish that lives among sea anemone gets protection from predators as they stay away from the stinging tentacles of sea anemone. Sea anemone doesn’t derive any benefit from clown fish.
Association between algae and fungi called Lichen shows mutualism. A snake feeds on frog and thus shows predator and prey relationship, and the population interaction is called predation. Lice is an ectoparasite on the human scalp and thus shows parasitism.