Matching Pairs Define Ecological RelationshipOnline version Define Ecological Relationships by Amanda O'Malley 1 Commensalism 2 Competition 3 Parasitism 4 Predation 5 Mutualism One organism eats another organism. Both organisms benefit by their association with eachother. One organism is harmed and the other benefits. One organism benefits, the other is neutral (unharmed but does not benefit). Organisms competing for the same limited resource.