Pollinator diversity and floral associations in subarctic sand dunes of Kobuk Valley National Park, Alaska

Abstract

Active sand dunes in Kobuk Valley National Park are a regionally rare and ecologically distinct landscape feature occurring within the northern boreal biome. The sand dunes harbor a rich diversity of plants, including several rare and disjunct species and the endemic Kobuk locoweed (Oxytropis kobukensis). Pollinators associated with these dune plants have not been studied in Kobuk Valley, despite their essential role in transporting pollen which many plants rely on for successful reproduction. In order to gain a better understanding of pollinator diversity and plant-pollinator associations in this unique ecosystem north of the Arctic Circle, we conducted surveys of bees (Hymenoptera: Anthophila) and syrphid flies (Diptera: Syrphidae) in several places along the Kobuk River and in two active dune areas, the Hunt River Dunes and the Great Kobuk Sand Dunes, in late June-early July of 2017 and 2019. We used active and passive collecting methods to sample pollinators at 21 different sites and along five walking transects, and we documented plant associations for net-collected specimens. In all, we collected 326 bees and 256 syrphid flies, representing 27 and 37 taxa, respectively. The most abundant and widespread species collected among syrphid flies were Lapposyrpus lapponicus and Eristalis obscura. For bees, three soil-nesting solitary species, Andrena barbilabris, Megachile circumcincta, and Osmia tarsata made up 60% of the total bee catch. Dryas integrifolia, a widespread plant on the dunes, hosted the highest number of bee and syrphid fly taxa (13 and 20, respectively). Bumble bees (Bombus) and megachilid bees (Megachile, Osmia) favored several plants in the Fabaceae family, while mining bees (Andrena) were abundant on Salix species (willow). A high diversity of syrphid flies were collected on the composite Packera ogotorukensis, and Salix species. Our collections indicate that the endemic Oxytropis kobukensis was primarily visited by the mason bee, Osmia tarsata (44% of all visitors) and the leafcutter bee, Megachile circumcincta (27%). Bumble bees (genus Bombus) made up another 13% of all visitors to this plant. Our study confirms that the active sand dunes in Kobuk Valley provide an ecologically unique habitat both for plants and their associated insect pollinators. For example, many of the solitary bees living in the dunes rely on deep sands for nesting and thus are limited in their distribution across Arctic and boreal landscapes.