Populations of Leavenworthia crassa (Cruciferae) studied for 3 years exhibited among‐ and within‐population genetic variation for a suite of floral and reproductive traits (flower width, petal length, anther position, ability to set seeds in the absence of pollinators, time to first flowering) associated with breeding system. We used electrophoretic markers to show that a population with small, monomorphically colored flowers with introrse anthers had a significantly lower outcrossing rate (t = 0.03) than did a population with larger, polymorphically colored flowers with extrorse anthers (t = 0.33). In the more‐outcrossing population the correlation between higher maternal plant outcrossing rate and the suite of six traits approached significance (P < 0.067), with greater petal size, greater flower width, and reduced ability to set seeds in the absence of pollinators contributing significantly. Plants in selfing populations had a generally higher reproductive success, with a higher number of flowers per plant, a smaller proportion of unfertilized ovules, a smaller proportion of fertilized ovules aborted, a higher rate of fruit set, and overall a larger number of seeds matured than did plants from the more outcrossing populations. Pollen limitation did not appear to account for lower reproductive success in outcrossing populations. Resource limitation did not differ substantially between populations. However, within‐ovary patterns of fertilization, abortion, and seed weight were significantly less random in outcrossing populations than in selfing populations, suggesting that differential gamete and embryo success may be responsible for lower reproductive success in outcrossing populations.
Individual plants of Viola fimbriatula which germinated from buried seed in two tree blowdowns in 1975 were censused for 6 yr. Growth, seed production, and mortality were monitored at fortnightly intervals. Only seedlings of the cohort established immediately following the disturbance grew large enough to produce seed. The performance of individuals within this cohort was highly skewed, and both reproduction and survival were correlated with individual size. After 1977 the conditions in the blowdowns which initially stimulated germination, growth, and reproduction rapidly deteriorated for V. fimbriatula, and the populations declined to extinction. We conclude that individuals of V. fimbriatula, interacting with the habitat conditions of this natural disturbance, display many of the traits characteristic of species commonly associated with disturbance. In this habitat the dynamics of the entire population are determined by the relative performance of individuals immediately following the disturbance.
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