| I investigated the effects of population size and isolation on reproductive output in Aquilegia canadensis on the St. Lawrence Islands and adjacent mainland areas in eastern Ontario, Canada. A survey of reproductive output in 29 island and 20 mainland populations, ranging in size from 3-750 flowering individuals, revealed a positive correlation between population size and reproductive output in both island and mainland populations. However, no correlation was found between isolation and reproductive output in island populations. Reduced reproductive output in small populations may partially be explained by data from detailed studies of the reproductive ecology and mating system of A. canadensis. Although the large, showy flowers of this species suggest a strong-reliance on outcrossing via hummingbird pollination, A. canadensis is self-compatible and highly autofertile, with plants isolated from pollinators producing almost as many seeds as those supplied with excess outcross pollen. Although the flowers were initially described as protogynous, data from pollen loads, pollen tube growth, nectar production and components of flower size across floral development do not indicate temporal separation of stigma receptivity and anther dehiscence. Functionally, then, A. canadensis is adichogamous. Mating system estimates from two populations indicate mixed mating, with an average outcrossing rate of 0.56. Genetic estimates of inbreeding depression suggest that selfed offspring are half as fit as outcrossed progeny. Together with results from a concurrent study showing that small populations self-fertilize more than large populations, my results suggest that variation in selfing among populations may ultimately translate into variation in plant vigour. (Abstract shortened by UMI.)... |
