Herbivory reduces the strength of pollinator-mediated selection in the Mediterranean herb Erysimum mediohispanicum: consequences for plant specialization.

In this study, I tested whether selection occurring on several morphological and floral traits in Erysimum mediohispanicum (Cruciferae) is modified by the effects of herbivores. Six plots were established in 1997 in the Sierra Nevada, Spain; three were fenced to exclude native ungulates, and the remaining were open to ungulates. I determined pollinator and ungulate preferences for plant traits and their effect on plant fecundity. Then I compared the selection regimes between plants excluded from herbivores and plants open to them. When ungulates were absent, I found significant selection on flower number, reproductive stalk height, basal diameter of the stalks, petal length, and inner diameter of the flowers. When ungulates were present, selection on floral traits completely disappeared, and selection strength on flower number and morphological traits decreased. This effect was due to the ungulate preference for larger plants and the phenotypic correlations between plant size and floral traits. Results suggest that pollinator-mediated selection can be disrupted by conflicting effects of plant enemies acting during or subsequent to pollination. An accurate picture of the pollinator role as selective pressure requires the consideration of the entire life cycle of the plant as well as the ecological scenario in which the interactions occur.