Vegetation context influences the strength and targets of pollinator-mediated selection in a deceptive orchid

Abstract

Clarifying the relationship between environmental context and the adaptive significance of floral traits is fundamental for an understanding of spatial and temporal variation in pollinator-mediated selection. We manipulated vegetation height and pollination regime of the orchid Dactylorhiza lapponica in a factorial design to test whether pollinatormediated selection on floral traits is stronger in tall than in short vegetation, and whether this difference is larger for visual traits affecting pollinator attraction than for traits affecting pollination efficiency. In tall vegetation, pollinators mediated strong selection for taller plants (change in selection gradient for pollination, Dbpoll=0.33), more flowers (Dbpoll=0.34), and longer spurs (Dbpoll=0.42). In short vegetation, there was no significant selection on plant height, and pollinator-mediated selection on number of flowers and spur length was reduced by 52% and 25%, respectively. The results demonstrate experimentally that vegetation context can markedly influence the strength of pollinator-mediated selection on visual display traits, and indicate that this effect is weaker for traits affecting pollination efficiency. The study illustrates how crossed manipulations of environmental factors can reveal the causal links between ecological context and selection on floral traits. © 2013 by the Ecological Society of America.