The evolution of ecological specialization has long puzzled scientists; why would a species evolve a more-restricted niche space? Various hypotheses address the promotion or suppression of ecological specialization. One hypothesis, competitive diversification, states that increased intraspecific competition will cause a population to broaden its niche breadth. With individuals alike in resource use preference, more individuals reduce the availability of preferred resources, thereby granting higher fitness to those which use secondary resources. Recent studies, however, cast doubt on this hypothesis, with increased intraspecific competition reducing niche breadth in some systems. Using the G-function approach, we constructed an evolutionary game-theory model of the evolution of ecological specialization. We fixed the size of a single population and allowed evolution to an equilibrium, repeating this over a gradient of population sizes. We then repeated this over a sweep of parameters governing the diversity of resources, the width of resource utilization, and the trade-off between acquiring preferred versus secondary resources. This was then later compared to a group selection version of the model.
Results/Conclusions
Our model shows greater ecological specialization with weak intraspecific competition in contrast to the competitive diversification hypothesis. Comparison to the group selection version reveals that the competitive advantage an individual gains from specialization drives the population to specialize. When facing weak competition, more specialized individuals acquire more of the preferred resources without greatly sacrificing secondary resources and therefore gain higher fitness. Only when competition is too great for an individual to significantly decrease resource use will intraspecific competition lead to an increased niche breadth. In addition, the parameter sweep shows that a low diversity of resources, wide resource utilization, and a higher magnitude trade-off between acquiring preferred versus secondary resources help to promote ecological specialization in the face of intraspecific competition. By using this game-theoretic approach, we discovered a previously unseen role of intraspecific competition in the evolution of ecological specialization.