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Male biased sex ratios in the cycad macrozamia riedlei zamiaceae



Male biased sex ratios in the cycad macrozamia riedlei zamiaceae



Bulletin of the Torrey Botanical Club 112(4): 393-397



Most populations of the Western Australian cycad Macrozamia riedlei that were sampled for individuals with cones were characterized by an excess of male plants (66%-79%). Less than 32% of the apparently mature plants produced cones in most populations examined. It is suggested that the deficiency of females in cone is a consequence of the greater energic effort required to produce female cones as compared to male cones. As a result of these differences in energetic costs, sexually mature female plants probably produce cones less frequently than do male plants. The high energetic costs of cone production may not only influence the sex ratio, but they may also account for the low frequency of reproductive individuals of either sex. The depletion of starch reserves associated with cone production requires several years for restoration, during which time cones are not produced. Age structure may also affect the incidence of non-coning individuals, but in most populations sampled most individuals were judged to be mature, and immature individuals were omitted from sampling. The role of fire in the reproductive ecology of M. riedlei has been considered by some authors to stimulate cone production, but there is evidence that under certain circumstances cone production is inhibited by fire.

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Accession: 005846385

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DOI: 10.2307/2996040


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