Pollination Limitation to Reproductive Success in the Missouri Evening Primrose, Oenothera Macrocarpa (Onagraceae)
Pollination limitation was investigated in three Missouri populations of Oenothera macrocarpa, a hawkmoth-pollinated, perennial herb. The populations represented extremes in size and habitat quality. Fertilization success (proportion of ovules fertilized) increased following supplementation with the mean across populations increasing from 24.3% to 44.8%. Seed set (proportion of ovules that set seed) increased following supplementation with the mean across populations increasing from 14.7% to 27.9%. These increases were statistically significant in two of the three populations. Failure to achieve 100% fertilization and seed set indicates that other factors, in addition to pollination, were limiting to female reproductive success. Fruit set was not apparently pollination limited, as fruits matured with as few as one seed. Length of fruit was significantly correlated with the number of seeds in the fruit indicating that plants may be able to conserve resources by allocating fewer resources to fruits with fewer seeds. The degree of pollination limitation was greatest in the most disturbed population. The largest population located in high quality habitat was not significantly pollination limited. This suggests that pollination limitation is occurring because of reduced pollinator activity in degraded habitats.
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