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Plants Have the Best Strategies When It Comes to Evolutionary Game Theory

http://phys.org/news/2015-12-theory-smart-evolution-global-ecosystems.html

Normally, when someone thinks of an ecosystem, they don’t think of flora and fauna; they only think of fauna. This is because animals are active: they move around and change their environment, and therefore influence the habitat they live in. But who says plants don’t affect their environment? Researchers and Princeton University used evolutionary game theory to study plants, specifically ones that use nitrogen from the soil as a natural fertilizer. Originally, what brought this experiment on, was that legume plants heavily rely on nitrogen from the soil to get fertilized. The bacteria rhizobia infects the roots of the plant and convert nitrogen into a fertilizer the plant can use. In return, the plant provides the bacteria with a supply of carbohydrates. However, researchers realized that legumes mainly lived in very nitrogen-rich soil, and not in nitrogen-poor soil. This didn’t make sense to them: if a plant could use nitrogen to create soil, shouldn’t they adapt to do that in places that don’t have much nitrogen, so they can create more fertilizer for themselves and beat out any competition that can’t do the same?

Researchers took the evolutionary game theory model and analyzed these plant’s behaviors in tropical and non-tropical forests to see how they survived. In tropical forests, where there was a big supply of nitrogen, plants that could convert nitrogen to fertilizers (nitrogen-fixers), would use it as a kickstart to their growth and save the energy for converting for the rest of the season. In non-tropical habitats, the nitrogen-fixers would have to constantly keep generating since there was no reservoir of nitrogen it could use. This behavior hurt them, and hence the population of nitrogen-fixers were scarce there. Plants were smart, and knew when to apply this skill they have in order to maximize the efficiency of their use of energy.

This relates to the topic of evolutionary game theory from class. We had an example with a hawk and a dove, with their passive-aggressive behaviors and what benefitted who. However, this article shows that this theory can be applied to plants as well. When plants are in a nitrogen-rich soil, the nash equilibrium can be seen as being that both should be nitrogen-fixers. If one species was and the other wasn’t, the one that wasn’t would eventually go extinct. However, even if both were nitrogen fixers, they would still have high payoffs, making nitrogen-fixing an evolutionarily stable trait, where as not being able to convert nitrogen to fertilizer is not stable. But if looking at both environments together, both traits are not evolutionarily stable given the fact that it could lead to extinction depending on the ecosystem.

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