GeologyRocks

Where different morphs of an organism exploit different resources. Sometimes maintained by frequency-dependent selection, e.g. scale eating fish. Two morphs exist, one with the mouth on the left-hand side, the other with the mouth on the right-hand side. The side on which they approach their prey depends upon the side on which their mouth is located. As the prey become used to attacks from the right-hand side by left-hand side mouthed scale-eaters, the right-hand side mouthed fish become more successful at securing prey and the left side morph becomes less so. At some point the prey starts to anticipate attacks from the left. Then the right side morph starts to decrease in frequency and the frequency of the left side morph starts to increase again. This pattern continues such that one morph is always predominant over the other.