Community: consists of interacting species, usually living with a defined area. Species in a community interact almost constantly, therefore, the fate of a particular population may be tightly linked to the other species that share its habitat. Commensalism (+/0): one specie has a positive influence and the other species doesn"t really care. Types: intraspecific: members of the same species. Agent of natural selection: interspecific: members of different species using the same limiting resources. Niche: the range of resources that the species is able to use or the range of conditions it can tolerate. Occurs when two species interact in a way that confers fitness benefits to both. Species interactions may affect the distribution and abundance. Species act as agents of natural selection when they interact (predators and prey, parasites and hosts, etc. ) Evolutionary pressure (individuals are at a less advantage and ar eless fit) The outcome of interactions among species is dynamics and conditional.