The Relative Influences of Mortality, Nonflowering, and Sex Change on the Sex Ratios of Six Atriplex Species

The relative influence of mortality, nonflowering, and sex change, which may bias sex ratios, was examined in natural populations of Atriplex canescens, A. confertifolia, A. corrugata, A. cuneata, A. lentiformis, and A. tridentata in the Great Basin and Colorado Plateau Deserts. In several cases, sex ratios changed significantly over 4 yr. The relative influence of each factor varied with population and year, but sex change and nonflowering were considerably more important than mortality in biasing sex ratios. Rates of sex change were appreciable for all species. Plants changed from one primary sexual state to another from 1 yr to the next in a plantation of A. canescens over 7 yr. For the population as a whole, 21.2% averaged changing sex expression each year. Plants initially scored as female averaged a change of 20.8% per year; plants initially scored as male, 14.4% per year; plants initially scored as monoecious, 46.2% per year.