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Lepitdoptera on an Asteracae, San Jose, Costa Rica.  Photo by Nicholas Friedenberg.

Pollinators and flowers are common examples of mutualists; one could not persist without the other. The strength of this link, however, can be weak. Many mutualisms are "diffuse," meaning that each player may have many alternative species with which it may interacts.

Mutualism and the dynamics
of ecological communities

Mutualism, a reciprocal positive interaction between two organisms, has posed an ecological and evolutionary quandary since Darwin's time. Not only are some mutualisms the result of highly specialized morphologies, physiologies, and behaviors, but the interaction itself is commonly considered unstable. A lot of work has gone into describing examples of mutualisms in nature and deciphering their evolution. However, the paradigm of community ecology remains dogmatically exploitative rather than facilitative. The importance given to "plus-minus" interactions such as competition or predation, wherein one organism benefits at the expense of another, is no doubt partly spurious, a product of community ecology's historical emphasis on stable equilibria.

As ecology moves away from the desire for point stability, it may be that facilitative "plus-plus" interactions gain more notoriety. Not only are they common, but what instability they induce in a system may explain such phenomena as pollination limitation and population outbreaks of pests and disease.

In the coming months, Archidictus will host an online collaborative project on the community consequences of mutualism. Participants will include Matt Ayres and Nicholas Friednberg of Dartmouth College. The project will focus on a destructive forest pest, the southern pine beetle, that displays outbreak dynamics approximately every seven years. The beetle plays host to fungi that feed its larvae. The beetle also transports, accidentally, mites that carry their own nutritional fungus. The mite's fungus can outcompete the beetle's fungus, preventing the development of beetle larvae. The system can be reduced to two compartments: beetles and their mutualists in one module and mites and their mutualist in the other. The net interaction between the two compartments is a classic plus-minus antagonistism. Does the inclusion of detail (postitive interactions) within these compartments affect the dynamics of the system?

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