Abstract

The distribution of dioecious species among forty-four plant communities of western United States was examined. The dioecious habit is most prevalent in harsh environments. In many communities, over 20 percent of the species and 40 percent of the individuals are dioecious. Dioecy is most common among woody species which are pollinated by wind. It is concluded that inbreeding depression alone is insufficient to account for all known facts concerning dioecy. Disruptive selection acting upon differential success of gametes produced on sites of differing quality appears to have played a major role in producing separate sexed individuals. Dioecious species reported to exhibit sex reversal and factors believed to promote such reversals are tabulated. It is concluded that for dioecious species which exhibit differential resource utilization by the sexes, individuals which produce offspring capable of sex reversal have a selective advantage. Sex reversal provides a strategy that permits dioecious species to reproduce optimally in patchy environments.

Degree

PhD

College and Department

Life Sciences; Plant and Wildlife Sciences

Rights

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