On June 8, 2007, PED Seminar Series Presents

Population ecology and the evolutionary tragedy of the commons

by Dr. Daniel Rankin

Adaptation does not necessarily lead to traits which are optimal for the population. This is because selection is often the strongest at the individual or gene level. The evolution of selfishness can lead to a ‘tragedy of the commons’, where traits such as aggression or social cheating reduce population size and may lead to extinction, a phenomenon known as evolutionary suicide. Here, I first present a model of the evolutionary tragedy of the commons that explicitly considers the population dynamics where individuals invest in individually costly competitive traits. I incorporate a feedback between population ecology and the evolution of conflict, and show that this feedback may be an important mechanism in resolving the level of competition and conflict among individuals. However, if conflict does have an effect on population densities, it will also affect extinction risk, and may lead to higher-levels of selection, such as species-level selection. I explore this idea in a simple model that combines individual-level selection with ecology in two interacting species. The model shows that individual selection in combination with competitive exclusion greatly increases the likelihood that selfish species go extinct. A simple example of this would be a vertebrate species that invests heavily into squabbles over breeding sites, which is then excluded by a species that invests more into direct reproduction. A multi-species simulation shows that these extinctions result in communities containing species that are much less selfish. These results suggest that species-level selection and community dynamics play an important role in regulating the intensity of conflicts in natural populations. These models suggest that the interaction of behaviours with population ecology can have important long-term evolutionary consequences.

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