D3292: The pollination and reproductive biology of two endemic cacti of northern Arizona (Pediocactus peeblesianus var. fickeiseniae and P. paradinei)

The conservation of rare plant species may require attention to the disruption of plant-pollinator interactions, as rare plants may be especially vulnerable to pollinator limitation due to their small population sizes and often narrow habitat requirements. In the House Rock Valley and Kaibab Plateau region of northern Arizona, the recovery of two species of endemic cacti may depend on the conservation of their pollinators. The closely related Pediocactus peeblesianus var. fickeiseniae, a federally endangered species, and P. paradinei, a species of concern, have exhibited population declines and likely rely on insect pollination. However, little is yet understood about the cacti’s pollination and reproductive biologies. Meanwhile, low rates of pollinator visitation have already been observed, potentially due to declines in pollinator abundance and diversity in the region. Here, I investigated the cacti’s pollinators, pollination rates, reproductive output, and level of self-compatibility through observational studies, pollination treatment experiments, and collections of pollinators, fruits, and seeds. Unlike many cacti, I found P. paradinei is partially self-compatible with low rates of geitonogamy and autogamy. Flower visitors of both cacti consisted mainly of beetles, ants, and flies, in addition to various species of sweat bees (Halictidae), which may act as the most common pollinator. My ongoing work further investigates the reproductive challenges of the cacti and the quality of pollinator habitat in the region. This work continues to directly address critical research needs for the effective management and conservation of both cacti, which may be missing a crucial component—the conservation of the plants’ pollinators.