In class we discussed the role of evolutionary stability as it applies to a one on one encounter with two distinct alternative strategies. Often when we consider evolution and evolutionary stability, we consider members of the plant and animal world. This world is often much more complex than the simple scenario we discussed, involving multiple interacting species and varying individual payoffs. When considering the evolutionary stability of a single species, we must consider its enemies and friends, including predators, prey, parasites, and symbiotic organisms.

                In an article published by ScienceDaily, the effects of predators and parasites on evolutionary stability are studied to reveal some surprising findings. In their studies, the authors found that predators and parasites, along with other natural enemies, can often be found to increase the evolutionary stability of a population. While at first thought this seems counterintuitive, the procedure actually makes a lot of sense. Predators will often prey on the easiest prey they can find. This tendency will lead to a Darwinian elimination of weaker strains of a species, providing an evolutionary advantage to stronger strains. If the species is evolutionarily stable to begin with, the effect of these predators will not be to eliminate the species, but rather to promote its evolutionary stability through Darwinian evolution.

                The more interesting part of the study is divulged with the consideration of hermaphroditic plants and animals (organisms capable of self and cross fertilization). In these situations not only will the natural enemies of the organism promote evolutionary stability through trait expression, as discussed above, but they also have an impact on the evolutionary stability of mating procedures. The study finds that the impact of the natural enemies of a given species tends to improve the evolutionary stability of mixed mating through alterations in mate availability and natural selection through cross breeding. For more information on the study, see the full article and its related links:

http://www.sciencedaily.com/releases/2007/10/071026124003.htm