Some evolutionary properties of parental investment per offspring in a heterogeneous environment

The possibility of protected polymorphisms and of monomorphic evolutionarily stable strategies for parental investment per offspring in a heterogeneous environment is theoretically analysed. A high density two-niche model of the classical soft selection kind is used, although it incorporates the possibility of rare strategies invading an empty niche the contribution of which is not constant. Protected polymorphisms can be found whether or not both strategies included produce surviving offspring in both niches. However, a monomorphic evolutionarily stable strategy exists unless offspring of the optimal size in one of the niches cannot survive in the other. The robustness of the model is graphically illustrated under a variety of circumstances, and some evolutionary consequences are briefly discussed.