COS 95-4 - Quantifying the nectar resource landscape available to pollinators

Background/Question/Methods

Floral nectar is a vital energy resource for pollinators. Although nectar volumes and sugar concentrations have been quantified for many species of flowering plants, few datasets exist to understand nectar resources available within an ecosystem. Additionally, many questions remain regarding sources of intraspecific and interspecific variation, including the effects of abiotic factors, such as soil moisture. To help address this knowledge gap, we quantified nectar resources, floral abundance, and soil moisture for the pollinator-visited flowering species making up the majority of flowers available in subalpine meadows in the southern Rocky Mountains. This allowed us to examine: (1) interspecific variation in nectar traits (volume, sugar concentration, and total sugar content) for 50 pollinator visited plants, (2) how nectar traits vary with soil moisture, (3) how interspecific variation contributes to landscape level patterns of nectar availability across time and space, and (4) intraspecific variation in nectar traits across four years for six plant species.

Results/Conclusions

We observed considerable variation in nectar traits. Nectar volume ranged from 0 μl to 55 μl per flower; nectar sugar concentration ranged from 0.056 mg/μl to 1.2 mg/μl; and total sugar content per flower ranged from 0.0043 mg to 49 mg. Most species showed no correlation between soil moisture and any nectar trait, although a few showed either positive or negative correlations. We observed a discrepancy between the floral resource landscape as quantified using flower counts alone versus using the total sugar contained within those flowers. Wet and dry meadow habitats contributed the most to the floral nectar landscape, compared to aspen forest. However, the relative contribution of these habitat types varied across the growing season. Sugar concentration, but not volume or total sugar content, varied across the four years for six high-volume species. Taken together, this research fills an important knowledge gap in our quantitative understanding of the floral resources exchanged among plants and pollinators, and begins to consider how those resources may be impacted by environmental change.