Types Of Ecological Interactions Research Articles

Evolutionary Branching and Sympatric Speciation Caused by Different Types of Ecological Interactions

Evolutionary branching occurs when frequency‐dependent selection splits a phenotypically monomorphic population into two distinct phenotypic clusters. A prerequisite for evolutionary branching is that directional selection drives the population toward a fitness minimum in phenotype space. This article demonstrates that selection regimes leading to evolutionary branching readily arise from a wide variety of different ecological interactions within and between species. We use classical ecological models for symmetric and asymmetric competition, for mutualism, and for predator‐prey interactions to describe evolving populations with continuously varying characters. For these models, we investigate the ecological and evolutionary conditions that allow for evolutionary branching and establish that branching is a generic and robust phenomenon. Evolutionary branching becomes a model for sympatric speciation when population genetics and mating mechanisms are incorporated into ecological models. In sexual populations with random mating, the continual production of intermediate phenotypes from two incipient branches prevents evolutionary branching. In contrast, when mating is assortative for the ecological characters under study, evolutionary branching is possible in sexual populations and can lead to speciation. Therefore, we also study the evolution of assortative mating as a quantitative character. We show that evolution under branching conditions selects for assortativeness and thus allows sexual populations to escape from fitness minima. We conclude that evolutionary branching offers a general basis for understanding adaptive speciation and radiation under a wide range of different ecological conditions.

Models of Coevolution

Various aspects of genetic models of coevolution are reviewed and discussed. The emphasis is on the assumptions made in coevolutionary models and the questions addressed. In the first part of the review, general results from models of single species or of interacting species are summarized. In a number of cases, there are useful maximization and equilibration principles that can be applied to particular coevolutionary problems. Such principles can sometimes be used without making explicit genetic assumptions. The second part of the review summarizes various models of particular types of ecological interactions: generalized competition, character displacement, predator-prey and host-parasite interactions, and mutualism. When possible, the principles available from the general theory are applied. There is also some discussion of the role of different time scales of genetic and ecological change and of the role of assumptions concerning genetic variability in each species. The current emphasis in theoretical studies is on the equilibrium properties of panmictic species under constant conditions. Even under those restrictive conditions, a wide variety of results can be obtained, but it does not seem that there is a consistent effect of coevolution on community stability.