Determinants of fruit and seed set in Pavonia dasypetala (Malvaceae).

Female reproductive success (fruit and seed set) in Pavonia dasypetala (Malvaceae) was only weakly related to pollinator attentiveness (number of pollinator visits and number of pollen grains deposited on stigmas). This result has implications for field studies of pollination: observational measures of pollinator attentiveness do not necessarily provide an, accurate basis for inferring reproductive success. Further, these results indicate that, although pollination is essential for seed set in this species, reproduction is not limited by pollination. Many flowers that were visited numerous times by hummingbirds and that received pollen in excess of the number of ovules per flower failed to produce fruits. If pollen is limiting, it is pollen quality rather than quantity that is inadequate. Patterns of reproduction in this species were as predicted if resource availability limits seed set (Stephenson 1981): (1) among mature fruits there was an excess of fruits with full seed set (4 or 5 seeds) and (2) probability of fruit, set decreased over the reproductive season. However, resource availability was not the only determinant of seed set in this species: there was also variation among individuals that seems unrelated to either pollen or resource availability. Reproductive success thus appears to be determined by several factors and cannot be described as simply pollen or resource limited.