The exploitation of mutualisms

Mutualisms (interspecific cooperative interactions) are ubiquitously exploi ted by organisms that obtain the benefits mutualists offer, while deliverin g no benefits in return. The natural history of these exploiters is well-de scribed, but relatively little effort has yet been devoted to analysing the ir ecological or evolutionary significance for mutualism. Exploitation is n ot a unitary phenomenon, but a set of loosely related phenomena: exploiters may follow mixed strategies or pure strategies at either the species or in dividual level, may or may not be derived from mutualists, and may or may n ot inflict significant costs on mutualisms. The evolutionary implications o f these different forms of exploitation, especially the threats they pose t o the stability of mutualism, have as yet been minimally explored. Studies of this issue are usually framed in terms of a "temptation to defect" that generates a destabilizing conflict of interest between partners. I argue th at this idea is in fact rather inappropriate for interpreting most observed forms of exploitation in mutualisms. I suggest several alternative and tes table ideas for how mutualism can persist in the face of exploitation,