Non-feeding Relations Among Species

The overall structure of ecosystems is dominated by feeding relationships. However, different populations may interact in a way that one or both of them may benefit from the interaction (cooperation), or one or both may be negatively affected (competition). 

Commensalism is a relationship in which one member clearly benefits and the other apparently is neither benefited nor harmed. It often results 

Both populations benefit from the relationship, but the relationship is not an obligatory one, as both populations are capable of surviving in their natural environment on their own. For example, there are synergistic relationships among bacterial populations involved in the cycling of nitrogen. 

Mutualism is an obligatory relationship between two populations that benefits both. A mutualis-tic relationship requires close physical proximity it is highly specific, as one member cannot be replaced by another related species. A typical example is that of flowers and insects. Insects benefit by obtaining nectar from the flowers, and the plants benefit by being pollinated in the process. In some cases, the mutualistic relationship has become so close that the species involved are no longer 

Symbiosis refers to the intimate association between members of different species. It does not specify a mutual benefit or harm. Therefore, symbiotic relationships may include mutualism, commensalism, or parasitism. Symbiotic relationships often entail some degree of coevolution of the partners, shaping in part their structural and behavioral characteristics. 

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