Effects of Population Size and Density on Pollinator Visitation, Pollinator Behavior, and Pollen Tube Abundance in Lupinus perennis

Both the number and the density of flowering plants in a population can be important determinants of pollinator abundance and behavior. We report the joint effects of population size and density on pollinator visitation and pollination success for Lupinus perennis (Fabaceae). Focusing on five pairs of populations, we matched one small population (125–800 flowering plants) with one distinctly larger population (1000–3000 flowering plants). In these pairs, population size did not affect pollinator communities or pollination success. All measures of pollination success increased significantly with density. Only bee behavior (number of flowers probed per inflorescence) exhibited a significant interaction of size and density. Testing whether population sizes smaller than those in the paired populations might affect pollination, we gathered pollen tube samples from 14 unpaired populations (16–215 flowering plants). Combining these data with those from the paired populations revealed a significant decrease in po...