Floral biology and breeding systems of geoflorous Protea species (Proteaceae)

Information about breeding systems and pollinator effectiveness is critical for establishing the ecological dependence of plants on particular pollinators. Previous studies using remote camera footage and qualitative floral trait classification have suggested that the geoflorous Cape shrubs Protea cordata, P. decurrens, P. scabra, and P. subulifolia are pollinated by small mammals. This study investigates the floral traits and breeding systems of these species and their reliance on small mammals for seed production. The floral traits of these Protea species - including yeasty-scented, cryptic inflorescences with a short (14-19 mm) distance between nectar and pollen presenter - suggested that small mammals are the likely pollinators of these species. Results from controlled hand-pollination experiments indicated that P. cordata and P. scabra are self-incompatible, and thus rely on external vectors for seed production, and that P. decurrens is self-compatible. Selective exclosure experiments suggested that insects contribute to the pollination of P. cordata and P. scabra since the exclusion of vertebrates lowered but did not significantly reduce seed set. However, hand cross-pollination did not increase seed set in either species, indicative of resource limitation. We conclude that mammals and insects contribute to reproductive success in these largely self-incompatible species.