PARENT SESSION
Poster Session #46: Seed Production, Recruitment, and Pollination.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
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Reproductive stochasticity and the reproductive advantages of dioecy versus hermaphroditism.
Wilson, Will1, Harder, Lawrence2, 1 2
ABSTRACT- Interspecific variation in breeding system is generally attributed to differences in the relations of fitness contributions to female and male allocations. Despite the demonstrated importance of these fitness relations, they fail to explain several ecological associations with the occurrence of dioecy or hermaphroditism in flowering plants. We therefore examined the relevance of reproductive stochasticity to the relative advantages of these two breeding systems. Our spatially explicit models consider competition between a dioecious and hermaphroditic species that experience stochasticity in pollen import, ovule fertilization, seed dispersal, seedling establishment. Mating system details affect both the mean and variance of reproductive success. For example, every hermaphroditic plant is a source of pollen, but in a dioecious species with a 1:1 ratio of males and females the pollen donor population is only one-half as large as that of a hermaphroditic species. This difference reduces the variance in hermaphrodite pollen import -- a competitive advantage -- but may be offset by increased pollen production by male plants over hermaphrodites. Our model results provide new explanations for several ecological correlates of breeding system differences in angiosperms.
KEY WORDS: hermaphroditism, dioecy, mating system, theory