Biological interactions are the effects that the organisms in a community have on one another through their interaction. These interactions need not be direct; individuals may affect each other indirectly through intermediaries such as shared resources, common enemies, or their effect on some abiotic element of the system. Interactions between organisms can produce both conflict and cooperation. Within systems theory, these interactions can be understood in terms of synergies. A positive synergy is when two creatures interact to produce a combined effect greater than the sum of their effects in isolation. A negative synergy, what can also be called interferences, is an interaction that generates a combined output that is less than the simple additive combination of inputs in isolation. Between­species ecological interactions can be divided according to their synergy into three different types, predation, competition, and mutualism.