Athena Aktipis: University of Arizona Department of Ecology and Evolutionary Biology

Models such as Maynard Smith’s Haystack model have shown that high rates of movement (i.e., migration, mixing, dispersal) undermine the evolution of cooperation. However, these models generally assume that movement is unconditional. The present model replaces the assumption of unconditional movement with conditional movement; individuals stay in groups that provide higher returns (by virtue of having more cooperators), and ‘Walk Away’ from groups providing low returns. Implementing this conditional movement rule generates a number of findings including: 1) when individuals have high thresholds, corresponding to low tolerance for defectors, this lead to selection for cooperation, 2) high thresholds lead to high rates of movement initially and lower rates of movement after selection for cooperators, and 3) population structure becomes more stable after selection increases the proportion of cooperators in the population. These findings challenge the standard view derived from Maynard Smith’s Haystack model and others that high rates of movement undermine selection for cooperation. In contrast, the current model demonstrates that high rates of conditional movement can be associated with stronger selection for cooperation. These results show that high rates of migration observed in nature are not prohibitive for the evolution of cooperation, as standard group selection models have assumed.
http://www.bec.ucla.edu/AktipisWalkingAwayTextAndFigs.doc