Population biology of Lomatium bradshawii II. Insect interactions, phenology, and breeding systems

Lomatium bradshawii (Bradshaw’s lomatium) is a state and federally listed endangered species that occurs in fragmented native-prairie habitat in western Oregon and southwestern Washington. A U.S. Fish and Wildlife Service recovery plan for the species identifies breeding- system and pollinator-availability research as needed for filling information gaps that could influence recovery efforts. We conducted field experiments and observations to document the importance of these issues to the species’ conservation. A pollinator exclusion experiment showed that insects are required for fruit production in L. bradshawii. Because the species does not reproduce vegetatively or maintain a persistent soil seed bank, reduction or elimination of insect pollinators through destruction of nesting habitat or application of insecticides in or adjacent to critical habitat could result in rapid population decline. A large diversity of insects, including at least 38 species of bees, flies, wasps, beetles, and others visited L. bradshawii flowers throughout the species’ range, so it is unlikely that the management and recovery of the species is vulnerable to failure due to population fluctuations of any one insect taxon. Insects are required for pollination because L. bradshawii has a complex breeding system (protogyny) that inhibits self-fertilization through a temporal separation of the sexual phases of flowers within an inflorescence. Also, the first umbel displayed on a given plant is generally all-male (with no fruit-producing flowers), while the second umbel produces an average of twenty-four hermaphroditic flowers. We hypothesize that L. bradshawii populations have high genetic diversity because of the apparently high outcrossing rate, especially in the west Eugene area where the existing patches may represent fragments of formerly larger and interconnected populations. Also, we recommend that habitat protection and management for L. bradshawii take into account nesting habitat for pollinating insects.