by Leif L. Richardson And Judith L. Bronstein
|A female mason bee (Osmia species) foraging at manzanita flowers that have been previously nectar robbed. Photo by Dorit Eliyahu|
Mutualism is a biological phenomenon in which two species interact to their mutual benefit. A classic example is pollination, in which plants exchange a food reward (usually pollen or nectar) for pollen transport between flowers. Mutualisms are ubiquitous in nature, but so is their exploitation by organisms (often individuals of the mutualist species pair) that benefit from the exchange while not reciprocating with either partner. Despite their prevalence, theoretical models predict that these ‘cheaters’ should drive mutualisms to extinction because deriving a benefit without paying a cost should spread. How do mutualisms persist in the face of this pervasive exploitation?