Reproductive ecology of a rare serpentine endemic, Vancouveria chrysantha (Berberidaceae)

Thesis (M.S.)--Humboldt State University, Biology, 2014This study examined how pollinator visitation and local neighborhood density may affect pollen limitation (PL) of reproductive success for Vancouveria chrysantha Greene (Berberidaceae), a rare plant, strictly endemic to serpentine substrates in northwestern California and southwestern Oregon. Previous to this study nothing was known about its pollination biology. V. chrysantha is protandrous, self-incompatible, and presents pollen and nectar attractive to pollinators. Although infrequently seen, bumblebees were the most common floral visitor, and were the only visitor observed contacting receptive stigmas. The majority of individual plants studied experienced PL, and average supplemental-pollination seed set was nearly double that of natural open-pollination. Surprisingly, bumblebee visitation did not predict the degree of PL, suggesting that the amount or quality of pollen carried by bumblebees is more important than their rate of visitation. Increases is the number of neighbors at the largest spatial scale measured (25 m) significantly decreased PL, but the smallest scale (1 m) had no effect, indicating that near neighbors may not donate quality pollen, and larger spatial scales are more likely to encompass suitable pollen donors. The dependence of V. chrysantha on bumblebees and local neighborhoods large enough to harbor compatible mates has implications for the conservation and management of this rare plant; decreases in plant or bee abundance could negatively affect population persistence