Pollination ecology of a threatened lupine from the core to northern edge of its geographic range

Lack of sexual reproduction limits the fitness and long-term viability of many plant populations. This may pose a particular problem for populations at the edges of species’ ranges, which are often small and isolated and therefore may be less likely to attract pollinators. But while many range-edge populations are of significant conservation concern and value, there remain few tests of whether edge populations experience reduced pollination. We address this gap using sundial lupine (Lupinus perennis), a legume that is threatened in much of its range, particularly at its northern range edge in Canada. We first test which visitors are effective pollinators, then assess whether pollination declines from populations in the range core to the northern range edge. Across six populations in the USA and Canada (Ontario), sundial lupine was visited almost exclusively by bees, but only large bees (Bombus, Xylocopa) could be confirmed as effective pollinators in single-visit experiments. While seed production varied significantly among populations, visitation rates did not. Neither pollinator visitation, pollen receipt, nor seed production declined at sundial lupine’s northern range edge. We therefore found no evidence that pollination success constrains either performance of at-risk populations of sundial lupine or the species’ northern range limit.