Spatiotemporal variation in pollinator taxa on the Santa Ana River woolly star Eriastrum densifolium ssp. sanctorum (Milliken) Mason (Polemoniaceae)

Flood control, via the construction of the Seven Oaks Dam in the Santa Ana River in Southern California, has led to the alteration and destruction of habitat in the downstream alluvial wash community and jeopardized the persistence of pioneer plant species that have evolved to rely on periodic flood-scouring and sand recharge. One species, Eriastrum densifolium ssp. sanctorum (Eds), Santa Ana River Woolly Star, an endangered perennial sub-shrub, has been greatly impacted and persists in spatially-separated populations on successional vegetation terraces. This study employed "dawn to dusk" pollination observations in three phenological stages at four sites, representing young and old seral stages to identify primary pollinators and to elicit daily, site, and seasonal patterns of visitors. Data were compared to previous observations and correlated with annual rainfall to elicit long-term trends. Results indicate shifts in taxa have occurred, with some consistency through time and space during nine years of data collection. The sites with the highest pollinator abundance (older sites) are least suited to Eds. Two taxa are consistent across years: hummingbirds (prevalent in early season) and the giant flower-loving fly (prevalent in late season), whereas other taxa have varied. A shift from native bees, including bumble bees, to non-native bees has occurred, although bees in the Halictidae, Micranthophora, and Melissodes remain important. Eds appears to be to be a generalist able to take advantage of the behavior, cycling and availability of diverse pollinators daily, seasonally, and annually. Successful management should include the varying habitat needs of the pollinators.