An investigation of temporal flowering segregation in species-rich grasslands

Processes such as competition and facilitation are believed to be important in defining pollination niches in species-rich plant communities. Species with similar floral phenotypes are expected to flower together where this facilitates pollination, while differences in floral phenology are expected if such flowers compete for pollinators. These expectations were tested at seven sites by comparing the observed co-flowering of plants with similar floral phenotypes with null model outcomes. Phenotypic classifications were evaluated using observations of plant–pollinator interactions. Pollinator guilds differed in the number of visits made to flowers in different floral colour and shape categories, indicating that such categories were ecologically relevant. For species with complex flowers, each floral category contained few species, so that the observed low occurrence of co-flowering could be explained by chance. In contrast, within phenotypic categories species with simple flowers bloomed together more than expected at three sites, but these overlaps could be explained by family membership. Most species with complex flowers could be segregated into unique pollination niches by broad floral colour and shape categories, so that there was little opportunity for competition between flowers within such categories. Species with simple floral phenotypes were less well defined by floral phenotype and phenology. Historical sorting may explain differences between complex flowers, while co-flowering between species with simple flowers requires further investigation. Differences found between species with simple and complex flowers suggest that levels of phenotypic specialisation should be taken into account in community level studies of pollination systems.