Human-induced impoverishment of pollinator faunas may affect plant-pollinator interactions and limit pollen availability. Under these conditions, chronic outcross pollen limitation is expected to select for floral characters that maintain seed production, including autonomous selfing. In this study, the impact of anthropogenic disturbances of the pollinator environment of the short-lived Centaurium erythraeaon mating patterns was investigated. First floral traits and the capacity for autonomous selfing were compared between two contrasting pollinator environments. In addition, transplantation experiments were combined with hand-pollination and emasculation treatments to assess the extent of pollen limitation and the contribution of autonomous selfing to total seed production in these pollinator environments. Under severe pollinator impoverishment, C. erythraea produced fewer and smaller flowers that showed no herkogamy and strongly reduced P⁄O ratios. The capacity for autonomous selfing was 36Æ1% higher in these pollinator-limited environments than in more natural, pollinator-rich environments, where plants developed more, larger, and markedly herkogamous flowers. When assigned to the pollinator-rich environments, plants from pollinator-limited populations showed significantly higher outcross pollen limitation compared with the original plants. In contrast, plants from pollinator-rich environments assigned to pollinator-poor populations did not experience higher pollinator-mediated seed production and showed lower total seed production than plants originally occurring in these pollinator-limited environments. These results demonstrate that human-induced pollen limitation selects for selfing as a means of reproductive assurance, whereas in pollinator-rich environments, traits that support outcrossing are favored.
