Evolutionarily Stable Strategy (ESS)

Definition

An Evolutionarily Stable Strategy (ESS) is a strategy that, if adopted by a population, cannot be invaded by any alternative strategy that is initially rare. This concept arises from game theory and is essential for understanding how certain behaviors or traits become stable within a population over time. An ESS ensures that once a particular strategy is established, any deviation from it will not lead to a greater fitness compared to the established strategy, making it resistant to changes and maintaining its presence in the population.

5 Must Know Facts For Your Next Test

1. An ESS can be thought of as a Nash Equilibrium that is specifically applied to biological contexts, ensuring that a stable strategy is favored in the face of competing strategies.
2. If a small number of individuals in a population adopt a different strategy from the ESS, they will not succeed in spreading that alternative strategy due to the fitness advantage held by the ESS.
3. ESS can help explain behaviors in nature such as altruism or aggression, showing how these traits can evolve and persist despite potential disadvantages.
4. The concept of ESS was popularized by John Maynard Smith in the context of evolutionary biology, providing insights into how evolutionary pressures shape strategic behavior.
5. In order for a strategy to be considered an ESS, it must meet certain criteria: it must outperform any alternative strategy when played against itself, and when faced with a rare mutant strategy, it must also perform well.

Review Questions

• How does an Evolutionarily Stable Strategy (ESS) relate to the concept of Nash Equilibrium in game theory?
  • An ESS is similar to a Nash Equilibrium but focuses specifically on biological scenarios. While both concepts describe situations where individuals have chosen optimal strategies based on others' choices, an ESS must also withstand invasion by alternative strategies. This means that when a population adopts an ESS, it ensures that any mutant strategy cannot outperform it, thereby maintaining stability within the population.
• What role does fitness play in determining whether a strategy can be classified as an ESS?
  • Fitness is crucial in determining if a strategy qualifies as an ESS because it measures the reproductive success of individuals adopting that strategy. If an alternative strategy provides lower fitness when competing against the established ESS, then that ESS remains stable. Essentially, for a strategy to be considered an ESS, it must ensure higher reproductive success than any invading strategies under various scenarios.
• Analyze how the concept of mutualism might illustrate the principles of ESS in evolutionary strategies.
  • Mutualism exemplifies the principles of ESS by showcasing how two species can evolve strategies that benefit both parties involved. In such relationships, each species adopts behaviors that enhance their own fitness while also supporting their partner's survival and reproduction. Over time, these mutualistic behaviors can become an ESS as they provide consistent advantages in terms of fitness, making it unlikely for alternative strategies to invade since cooperation enhances both species' reproductive success.

Related terms

Nash Equilibrium: A situation in which each player's strategy is optimal given the strategies of all other players, and no player has anything to gain by changing only their own strategy.

Fitness: The reproductive success of an individual or genotype, which determines its contribution to the next generation's gene pool.

Mutualism: A type of symbiotic relationship between two species in which both parties benefit, often influencing their evolutionary strategies.