The identification of major selective agents and their variation across environmental gradients is fundamental to advance our understanding of adaptive evolution, but despite a sustained interest in quantifying phenotypic selection in natural populations, we know surprisingly little about the ecological causes of selection. This significantly limits our ability to link micro- and macroevolution, and predict evolutionary effects of environmental change. We use field experiments and demographic monitoring to examine the degree of pollen limitation and the strength, form and mechanism of pollinator-mediated selection on floral traits. In a couple of systems, we have documented that
-pollinators are major selective agents on traits affecting pollinator attraction and pollination efficiency
-spatio-temporal variation in pollinator-mediated selection explains much of the variation in net selection on floral traits
-pollinator-mediated selection is consistently stronger in populations of the severely pollen-limited deceptive species Dactylorhiza lapponica compared to the rewarding species Gymnadenia conopsea
-variation in pollen limitation does not explain spatio-temporal variation in pollinator-mediated selection within species
We now intend to estimate selection on life-time fitness, by combining selection gradients with demographic data. We will also further explore to what degree spatio-temporal variation in the strength of biotic selection is explained by variation in interaction intensity versus variation in the trait-fitness function. This research significantly improves our understanding of the mechanisms of natural selection in the wild, as well as our ability to predict the evolutionary outcome of changing biotic interactions.
Selected publications
Sletvold N., J. M. Grindeland and J. Ågren. 2013. Vegetation context influences the strength and targets of pollinator-mediated selection in a deceptive orchid. Ecology 94: 1236-1242.
Sletvold N., J. Trunschke, C. Wimmergren and J. Ågren. 2012. Separating selection by diurnal and nocturnal pollinators on floral display and spur length in Gymnadenia conopsea. Ecology 93: 1880-1891.
Sletvold N. and J. Ågren. 2011. Nonadditive effects of floral display and spur length on reproductive success in a deceptive orchid. Ecology 92: 2167-2174.
Sletvold N., J. M. Grindeland and J. Ågren. 2010. Pollinator-mediated selection on floral traits and flowering phenology in the deceptive orchid Dactylorhiza lapponica. New Phytologist 188: 385-392.