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Multilevel Comparative Analysis of the Morphology, Function, and Evolution of Dalechampia Blossoms
- Armbruster, W. Scott
- Ecology 1988 v.69 no.6 pp. 1746-1761
- Apoidea, anthers, breeding, covariance, evolution, fauna, flowers, pollination, pollinators, regression analysis, stigma
- Morphological and ecological data from Dalechampia flowers were subjected to analysis of covariance and component regression analysis, a technique that allows separate estimation of within— and among—group relationships. They yielded results consistent with hypotheses stating that bee—flower relationships are influenced by several morphological parameters of the blossoms (pseudanthial inflorescences). The following correlations emerged: (1) the area of the gland that secretes the pollinator reward (and hence the amount of reward) and the size of the largest bees that visit the flowers; (2) the distance between gland and stigmas and the size of the smallest floral visitor contacting the stigmas; and (3) the distance between gland and anthers and the size of the smallest floral visitor contacting the anthers. Together these variables appear to determine which subset of the bee fauna will be effective in pollination. The distance between the anthers and stigma was correlated with the rate of autopollination and hence probably affects the breeding system. Anther—stigma distance, gland—anther distance, gland—stigma distance, and gland area were correlated with, and may have evolved in response to the size of the principal pollinator. In general, patterns reflecting ecological relationships between plants and pollinators were similar whether comparisons were made among populations within species or among species. However, patterns reflecting the evolution of floral morphology in response to pollinators were generally different at population and species levels; the regressions reflecting the evolutionary response of floral morphology to bee size were consistently steeper in among—species comparisons than in among—population (within—species) comparisons.