Sunbirds maintain flower colour diversity

Orange-breasted sunbirds Anthobaphes violacea pollinate at least 67 Erica plant species in the Cape and recent research suggests that these sunbirds have contributed to creating the great diversity of flower colours we see today. This study; by Anina Coetzee, Claire Spottiswoode and Colleen Seymour; tackled the question of why bird-pollinated ericas come in so many different colours. These ericas can have up to eight different flower colours in different geographic locations.

The patterns found in this study indicated that both competition and facilitation between coexisting Erica species shapes their colour. Two co-occurring ericas can evolve the same colour and benefit from collectively attracting more sunbirds. But if their flower size and shape is very similar, then they have the dilemma of the sunbirds mixing their pollen, which results in few seeds being produced. Alternatively, they can evolve different colours and try to keep the birds’ attention on themselves.

Pollination experiments have revealed that these ericas are highly dependent on sunbirds for pollination and, consequently, seed production. This also supports the idea that sunbirds can strongly influence flower colour evolution in these ericas.  The research is published in Functional Ecology and Journal of Plant Research.

Coetzee, A., Seymour, C.L. and Spottiswoode, C.N. 2021. Facilitation and competition shape a geographical mosaic of flower colour polymorphisms. Functional Ecology. https://doi.org/10.1111/1365-2435.13851