Easy technique for assessing pollination rates in the genus Erica reveals road impact on bird pollination in the Cape fynbos, South Africa

Road traffic is one of the most pervasive forms of anthropogenic disturbance, but its impact on pollination, a potentially sensitive ecosystem process, has not been investigated. Such an assessment is needed in order to evaluate the potential for roadside verges to act as biodiversity refugia and corridors in otherwise transformed landscapes. Here, we document the impact of a two-lane tar road on pollination by birds in the Cape fynbos of South Africa. To do so, we developed a quick and widely applicable method of determining pollination rates in bird-pollinated members of the large genus Erica. Experiments with caged birds showed that the status of the anther ring (broken/perfect) indicated a sunbird visit with 92% accuracy, while field surveys confirmed anther ring status also serves as a proxy for pollen receipt to stigmas. Using this technique we determined pollination rate in Erica perspicua at three distances from the road (0-10, 20-30 and 40-50 m). After controlling for flower colour, robbing rate and plant density, significantly fewer anther rings were disturbed in close proximity to the road. The documented twofold decline in pollination along roadsides could have important implications for the way we view and manage road verges as refugia for species and ecological processes.