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Population biology of a mutualistic association : Yucca glauca and Tegeticula yuccasella
Kingsolver, Robert W.
Kingsolver, Robert W.
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Abstract
Population interactions between Yucca glauca and its coevolved moth Tegeticula yuccasella were subjects of a field investigation. The study emphasizes life history adaptations that stabilize the association over ecological and evolutionary time. Because of the dual role of the moth as Yucca's only pollinator and as a Yucca seed predator in its larval stage, the plant's sexual reproductive success is potentially jeopardized either by scarcity of moths or by abundance of their larvae. Census data and experimental evidence suggest that Yucca is protected from extensive seed damage by the large numbers of flowers, which are more than ten times the number of fruits set in an average year. Large inflorescences saturate female moths with more oviposition sites than they can exploit. Eggs are distributed uniformly among the flowers, and most eggs are lost when superfluous flowers are aborted.
The negative impact of seed crop failure is reduced by the plant's mixed reproductive strategy. Y. glauca reproduces both by seed and by ramets, which arise from the rhizome or from the base of the inflorescence. When fruit set fails, resources are shunted to vegetative reproduction; rosettes that do not set fruit subsequently produce more ramets than fruiting rosettes from the same population. Comparisons of Yucca populations from different regions of the Great Plains reveal geographic variation in the relative importance of sexual versus vegetative reproduction. The contribution of each reproductive mode to maintenance of the Yucca population was measured in a four-year demographic study. A stage transition model based on this information describes the relationship between reproductive strategies, population growth rates, and rosette size distributions. The model is used to test explanations for observed patterns of life history variation and to project the consequences of changes in yucca moth abundance.
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Ph.D. University of Kansas, Systematics and Ecology 1984
Date
1984-05-31
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University of Kansas
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Yucca glauca, Tegeticula yuccasella