Measuring pollinator-mediated selection on morphometric floral traits: bumblebees and the alpine sky pilot, Polemonium viscosum

Abstract

Sweet-flowered plants of Polemonium viscosum in Colorado are visited by a fly-dominated pollinator fauna at timberline (krummholz), but almost exclusively by bumblebees in higher-elevation tundra habitats. Significant increases in flower size and height are associated with increasing elevation along this habitat gradient. This paper presents the results of an experiment designed to test whether bumblebees exert sufficient selection on morphometric floral phenotypes to account for the clinal shifts seen in natural populations. Results support the hypothesis that pollinator-mediated selection can bring about changes in floral form, and can explain shifts in floral morphology of P. viscosum along natural habitat gradients. -Author