Experimental reduction in interaction intensity strongly affects biotic selection

Abstract

The link between biotic interaction intensity and strength of selection is of fundamental interest for understanding biotically driven diversification and predicting the consequences of environmental change. The strength of selection resulting from biotic interactions is determined by the strength of the interaction and by the covariance between fitness and the trait under selection. When the relationship between trait and absolute fitness is constant, selection strength should be a direct function of mean population interaction intensity. To test this prediction, we excluded pollinators for intervals of different length to induce five levels of pollination intensity within a single plant population. Pollen limitation (PL) increased from 0 to 0.77 across treatments, accompanied by a fivefold increase in the opportunity for selection. Trait-fitness covariance declined with PL for number of flowers, but varied little for other traits. Pollinator-mediated selection on plant height, corolla size, and spur length increased by 91%, 34%, and 330%, respectively, in the most severely pollen-limited treatment compared to open-pollinated plants. The results indicate that realized biotic selection can be predicted from mean population interaction intensity when variation in trait-fitness covariance is limited, and that declines in pollination intensity will strongly increase selection on traits involved in the interaction.

Florivory indirectly decreases the plant reproductive output through changes in pollinator attraction

“…In this context, florivory can decrease fruit and seed set, either directly or indirectly via decreasing pollinator attraction (Krupnick & Weis, ; Mothershead & Marquis, ; Leavitt & Robertson, ; McCall & Irwin, ; Strauss & Whittall, ; Sánchez‐Lafuente, ; Carezza et al., ). Among a wide range of flower traits, flower size has been well studied showing that flower size can alter the strength of flower‐florivore and flower‐pollinator interactions (for florivores: McCall & Irwin, ; Teixido, Mendez, & Valladares, ; McCall & Barr, ; for pollinators: Willson, ; Bell, ; McCall & Irwin, ; Lobo, Ramos, & Braga, ; Sletvold & Agren, ). To examine whether flower size alters the strength of flower‐florivore‐pollinator interactions, we studied the interaction of Eurya japonica plants and its associated pollinators and florivores.…”

A meta‐analysis of the agents of selection on floral traits

“…However, the magnitude of the effect of pollinator declines on selection is unknown. The effect of pollinator declines on selection could depend on the degree to which floral trait variation in contemporary populations has been reduced by past selection (Schluter ) or the degree to which reproduction in contemporary populations is limited by pollen receipt (Benkman ; Sletvold and Ågren ). Whether the effect of pollinator declines on selection on floral traits is relatively large or small has implications for the ability of plant populations to adapt to anthropogenic declines in pollinator populations (de Jong ; Thomann et al.…”

Manipulation of trait expression and pollination regime reveals the adaptive significance of spur length

“…), on available phenotypic variation in flower depth (Conner et al. ), and also on the magnitude of pollen limitation and opportunity for selection (variance in relative fitness; Bartkowska and Johnson ; Sletvold and Ågren ; Trunschke et al. ).…”