The relative importance of color signaling for plant generalization in pollination networks

Plant strategies frequently vary from opportunistic pollination to specialization to single pollinators within the same community. Unraveling the proximate mechanisms that determine the degree of plant generalization to pollinators has become a primary goal of pollination ecology. Color signaling is a potentially important mechanism because it is well established that many pollinators use color stimuli to locate food items. Until now, studies on the importance of color signaling in structuring pollination networks have not considered floral coloration as it is perceived by pollinators. Here, we use a framework recently developed for network analyses to compare the relative importance of color matching (i.e. the degree of phenotypic matching between flower coloration and pollinators' visual system) and other variables (phylogeny, co-abundance and spatiotemporal overlap between plants and pollinators) for plant generalization. We analyzed 25 000 visits in three temperate regions. We show that color matching in combination with spatiotemporal overlap or co-abundance significantly influences plant generalization in one of the three regions. We suggest that intense human activities in two regions have decreased the mean level of color matching, potentially disrupting the communication between plants and pollinators. This study illuminates how the sensory ecology of pollinators contributes to structure a highly diversified pollination network.