MINORITY CYTOTYPE EXCLUSION IN LOCAL PLANT POPULATIONS

Summary The outcome of random cross‐pollination and incomplete self‐pollination in populations of two cytotypes not capable of hybridizing is analyzed in a simple model. The reproductive success of a cytotype is frequency‐dependent, the minority being at a disadvantage because it suffers a greater proportion of ineffectual pollinations. The reproductive handicap in a given generation leads to a greater handicap in the next, the minority cytotype being rapidly excluded from the population. Self‐pollination reduces the minority disadvantage and the tempo of the exclusion process as does the immigration of minority type pollen and seeds. It is concluded that unless two cytotypes have disparate ecological requirements, a minority disadvantage will cause the local extinction of one of the cytotypes, even though they may be equally fit in all respects.