The visitation rate of bees to spotted knapweed as a function of floral density.

Abstract

Several populations of spotted knapweed were examined in order to determine if pollinator visitation rate varies over density or between species of pollinator. Quadrants were staked out in three densities: high, medium and low. Only bee pollinators were included in the data pool. Visitation rates were calculated by the following equation: visitation rate = (# flowers visited/total # flowers)/(# minutes). Rates of pollinator visitation did increase with floral density though this trend did not meet levels of statistical significance (p=.112). Similarly, bumblebee visitation also increased with floral density, but again did not have statistical significance (p=.108). Solitary bees showed no increase of pollination rate over density (p=.522). While overall visitation rates to spotted knapweed did appear to increase with floral density, a larger sample size is needed in order to verify this statistically. Bumblebees had the highest visitation rate at all densities while solitary bees were less frequent visitors. Furthermore, solitary bees do not appear to use floral density as a measure of flower choice.