Foraging preferences of generalist Megachilidae

Abstract

Subalpine ecosystems are home to hundreds of species of wildflowers, many of which are endemic and very vulnerable to climate change. Megachilidae are a family of primarily solitary bees that are very efficient pollinators, making them crucial components of subalpine ecosystems. Some Megachilidae species are generalists, meaning they visit a wide variety of flower species, but their exact foraging preferences remain poorly understood. Since some flowers are more affected by climate change than others, understanding generalists’ flower preferences is necessary in predicting their responses to climate change, and in protecting subalpine ecosystems. In this research project I (1) collected pollen samples from generalist Megachilidae nests and analyzed the pollen composition under a microscope, (2) compared the floral abundance in nests with the floral abundance in intentionally placed transects, (3) analyzed any foraging difference across genera, specifically between Osmia and Hoplitis fulgida, and finally (4) analyzed the relationship between transects and quadrats to see if transects were sufficient in estimating overall floral abundance at a site. I found that abundance in the field has differing effects on nest abundance depending on the flower species, with some species found in nests at disproportionately higher or lower rates than their transect abundance. This indicates that Megachilidae have foraging preferences, selectively choosing which flowers to collect from, and these preferences seem to be the most pronounced at low species abundance. In particular, flowers such as Ipomopsis aggregata, Eriogonum umbellatum, and Lathyrus leucanthus were found in lower abundances in the nest as compared with other flower species. Additionally, Linum lewisii had a significantly larger slope than the average species, indicating a preference for L. lewisii as it grew in abundance. I found no significant differences between the foraging preferences of Osmia and Hoplitis, and the floral abundance described by quadrats vs transects was very consistent, indicating that transects are a good method of estimating general floral abundance at a site. 2

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