A type of mutualism in which the interacting species derive benefit from each other but not being fully dependent that each cannot survive without the symbiotic partner.
This is the more common type of mutualism exemplified by plants producing fruits eaten by birds while the birds help on dispersing the seeds of the fruit when they excrete them on places far from the parent plant.
Word origin: L mūtu(us): mutual, reciprocal + Gk -ismos, -isma: often directly, often through.
Related forms: mutualist (noun), mutualistic (adjective).
Compare: obligative mutualism.
See also: symbiosis.