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Studies in the Dynamics of Plant Populations: V. Mechanisms Governing the Sex Ratio in Rumex Acetosa and R. Acetosella

P. D. Putwain and John L. Harper
Journal of Ecology
Vol. 60, No. 1 (Mar., 1972), pp. 113-129
DOI: 10.2307/2258045
Stable URL: http://www.jstor.org/stable/2258045
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Studies in the Dynamics of Plant Populations: V. Mechanisms Governing the Sex Ratio in Rumex Acetosa and R. Acetosella
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Abstract

Rumex acetosa and R. acetosella are perennial dioecious species with vegetative reproduction. This gives the opportunity for drifts in the sex ratio from that established at the seedling stage. Natural populations of R. acetosa in North Wales generally show a predominance of females and the sex distribution within them is homogeneous. In contrast populations of R. acetosella are highly heterogeneous but show no definite bias away from equality of the sexes. Populations of both species grown from seed gave sex ratios of 1:1. Biased sex ratios, created by clonal propagation in artificial populations, tended to be restored after a season of growth towards a 2:1 ratio of females to males in R. acetosa and a 1:1 ratio in R. acetosella. This frequency-dependent process was more effective at high density and it is argued that the sexes of each species show such frequency-dependent interaction because they occupy at least partly different ecological niches. A study of the growth cycles, canopy structure and reproductive strategy of the sexes shows that males are precocious in spring growth, senesce earlier than females, and devote a greater proportion of their annual income to vegetative reproduction than the females which are taller and carry a higher, but later developed, canopy. Such ecological sex differentiation is discussed in relation to comparable situations in the animal kingdom.

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