Species within a community may interact in various ways. These interactions can be categorized by the possible effects two interacting species may have on each other, positive (+), negative (-), or neutral (0). Two species may interact as predator and prey or parasite and host. A predator is typically larger than its prey and kills it whereas a parasite is typically smaller than its host and may not kill it. In this interaction, one species benefits and the other is negatively effected. Two species may share resources and thus compete. In this interaction both species are negatively affected. In a relationship called commensalism the activities of one species benefit a second species while the first species is unaffected by the second. Species may also engage in mutually beneficial interactions. There are also many cases in which two species have no effect on each other.