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United we stand, divided we fall — Why harsh environments promote altruism

Snapshots of the spatial distributions

Snapshots of the spatial distributions of different strategies in a 400◊400 lattice. The colour brightness indicates the probabilities that each site is occupied by a co-operator (red) or a defector (green). Black indicates where the site remains empty.

Altruistic behaviour is common in nature. We see cooperation within and between species ranging from microbial interactions to the mutualistic behavior of animals, humans and social organizations. Evidently, cooperative individuals can benefit others at a cost to themselves. However, this devoutness can be easily exploited by selfish individuals that only receive benefit without cost (e.g. free riders). As a result, altruism seems incompatible with the Darwinian natural selection. Even though mutual cooperation can produce higher benefits than costs for both actors, neither side wants to become a victim and make the first move (as the conundrum facing in the current intergovernmental dialogue on climate change). Players are, unfortunately, trapped in a lose-lose situation; this creates a typical social dilemma.

C·I·B post-doc Feng Zhang and core team member Cang Hui explored the key factors that could potentially unlock this dilemma. Besides revealing a rich variety of evolutionary dynamics, they identified two crucial keys to this impasse: (i) assortative interactions and (ii) harsh environment. First, individuals with a similar strategy (like minded) need to prefer to interact (or collaborate) with each other, rather than with individuals of different strategies. It is impossible to unlock this dilemma if players show no preference or discrimination but treat each other as equal. Second, a harsh environment always brings out the good side of the players, and favours mutual collaboration rather than exploitation. More interestingly, the social tendency often forms waves, with each strategy (being either altruistic or selfish) only dominating for a temporal duration.

What are the implications of this theoretical work for invasion biology? Supposing the environmental conditions in introduced ranges are suboptimal compared to those in the native range, results suggests a larger investment of nectars or edible fruits (as tokens for mutualism) in introduced plants when compared with the same investment in the native range. Further empirical verification could lead to a better understanding of how species respond to novel environments and climate change.

Read the paper

Zhang, F. & Hui, C. (2011) Eco-evolutionary feedback and the invasion of cooperation in prisonerís dilemma games. PLoS One, 6(11): e27523.