Competition for Pollinators as a Stimulus for the Evolution of Flowering Time

Abstract

A study was made of the activities of pollinating insects in relation to the flowering phenology of plants near Banff, Alberta in 1968. From snow-melting time (early May) to the end of May, pollinating insects were abundant and competed actively for relatively scarce pollen and nectar resources. Then, in early June some (Salix spp. and Taraxacum officinale L.) began flowering abundantly offering virtually unlimited supplies of nectar and pollen. Pollinating insects abandoned the spring flowers and were attracted to these cornucopian species. It is postulated that in the presence of cornucopian species natural selection would favour the evolution of earlieror later-flowering populations of all those species that compete with the cornucopians for pollinators. It was found that in the spring, insects competed for flowers but that after the cornucopian species had completed their flowering (throughout the summer), flowers competed for pollinating insects.