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Tackling the great paradox of biodiversity with game theory

In this recent article, scientists at the Champalimaud Centre for the Unknown, in Lisbon, Portugal, presents their theory to explain the “plankton paradox” of biodiversity. The existing paradox pertains to the fact that, while “classical resource competition models predict that each resource will sustain the one species which is best at consuming it, consequently driving all competing species to extinction”, in actuality, the scarce resources are able to sustain multitues of species, even orders of magnitudes larger than predicted.

The scientists have set out to explain the phenomenon using a mathematical model based on game theory – in particular, the Hawk-Dove game, which we have touched upon in lecture. From the textbook, we have that hawks are aggressive, while doves behave passively, and there results in the nash’s equilibria where one species takes the passive stance, while the other takes the aggressive stance. Utilizing this, the study points out that neither hawks nor doves are purely dominant – both species end up coexisting, with the passive species obtaining a lower payoff, but with survival gaurenteed. In this manner, multiple species can play this hawk-dove game over many different kinds of resources simultaneously, with an independent choice of being a hawk or a dove for each resource, which leads to a large number of species who survive instead of driving each other extinct. According to this model, the number of species increases exponentially according to the number of resources – “on one resource, two species can coexist, on two resources, four species, on four resources, 16 species, and on 10 resources, we get to more than 1000 species.” Thus this leads to earth’s current biodiversity. In fact, the inequality between the payoffs of the “hawk” and the “dove” also explains the inequality among the abundance of different species.

This study shows how important game theory is in the natural world, and the fact that the best scenario is achieved by having one side backing down. The natural world tends towards the state of inequality – while monopoly of resources should sound appealing to all species, in the face of strong competition, there will always be “players” who back down and prefer survival, no matter how pathetic, over extinction. In human society, too, the existance of weaker wills is just as important in maintaining the balance of coexistance.


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September 2018