The radiation of Calochortus: generalist flowers moving through a mosaic of potential pollinators

Few studies have surveyed the insects visiting flowers at many sites and for many related species. Calochortus, a genus of about 60 species with its center of diversity in California, has flowers with a wide range of appearances. Insects visiting Calochortus flowers in 25 species were censused at 40 sites. Visitors at coflowering plants were also censused at each site. Calochortus flowers attracted insects in several orders, especially beetles that feed at glands on the petals and bees that often collect pollen. Species in Calochortus section Calochortus had a somewhat narrower spectrum of visitors than species in section Mariposa. The diversity of visitor species at Mariposa flowers was often greater than the diversity at coflowering species. On the whole, Calochortus flowers seem to be generalists in terms of their pollinators. Differences in visitor assemblage were greater between Calochortus populations at different sites than between visitors to Calochortus versus coflowering species at a site. Nevertheless, there were always significant differences in the proportions of various insects at Calochortus versus coflowering plants. In addition, proportions of visitors also differed between species of Calochortus at the same site. Thus, Calochortus flowers have diverged in the visitors they attract, and evidently they have done so without permanently specializing (except to a limited degree at the sectional level). What we know of the radiation of Calochortus lilies is consistent with an interpretation of adaptive wandering through a spatiotemporal mosaic of pollinator communities.