Consistent selection for earlier flowering in fireweed (Chamerion angustifolium) is not influenced by pollinators or artificially earlier spring timing

Abstract

Anthropogenic climate change is causing temperatures to increase and seasons to shift, altering the phenology of many plant species. Previous work has measured selection on phenology and found widespread selection for earlier flowering. Pollinator-mediated selection is also common, and plants often flower earlier to secure pollinators and minimize competition within and between species. Experimental warming manipulations which assess responses to higher temperatures, however, are rare and no consensus on common effects on phenology and selection has been reached. I performed both a pollinator-mediated experiment using supplemental pollen to remove pollen limitation as a selective force, and an early spring manipulation to assess agents of selection on phenology and associated floral traits in Chamerion angustifolium. I found that earlier flowering time is selected for independent of both pollinators and earlier spring, which means there is a further underlying mechanism which influences selection on phenology in this species.