<unk>  is a biological interaction between individuals of two different species, where both individuals derive a fitness benefit, for example increased survivorship. Similar interactions within a species are known as co-operation.<unk>  plays a key part in ecology and evolutionary biology.  For example,<unk> ic interactions are vital for terrestrial ecosystem function as more than 90% of land plants rely on mycorrhizal relationships with fungi to provide them with inorganic compounds and trace elements.  In addition,<unk>  has driven the evolution of much of the biological diversity we see, such as flower forms (important for pollination<unk> s) and co-evolution between groups of species  However<unk>  has historically received less attention than other interactions such as predation and parasitism .
Measuring the exact fitness benefit to the individuals is not always straightforward, particularly when the individuals can receive benefits from a range of species, for example most plant-pollinator<unk> s.  It is therefore common to categorise<unk> s according to the closeness of the association, using terms such as obligate, facultative and symbiotic.  Defining "closeness", however, is also problematical. It can refer to mutual dependency (the species cannot live without one another) or the biological intimacy of the relationship in relation to physical closeness (e.g. one species living within the tissues of the other species).<unk>  and symbiosis are sometimes used to refer to the same thing but this is strictly incorrect: the term symbiosis was originally meant to include relationships which were<unk> ic, parasitic or commensal.
Mutualism
Pronunciation
Amplification 
Expressivity
Anise
Deconvolution
Homology 
Transactivation