The functional role of birds as pollinators in southern Cape fynbos.
Whitehead, Kellyn Jean.
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Nectarivorous birds, particularly sunbirds, are important pollinators of plants in the Cape Flora of South Africa, being responsible for pollinating approximately 5% of plant species. However, interactions between plants and nectarivorous birds in the eastern part of the Cape Floristic Region have not received much attention. This study focussed on two putatively bird-pollinated plant species found within the Nature’s Valley area, namely Kniphofia uvaria and Chasmanthe aethiopica. The breeding systems were determined for each species and, due to their patchy population distribution, potential Allee effects on plant fecundity were also tested for. Flowering phenology in the area was also examined to test for associations between flowering of bird-pollinated plant species and the temporal presence of nectarivorous birds. Selective exclusion experiments showed that sunbirds were the main pollinators of K. uvaria and C. aethiopica – fruit set and the number of viable seeds were much higher for untreated (open control) individuals where birds could visit flowers freely, compared to caged individuals which only allowed for insect visitation. Very few seeds developed when plants of the two species were bagged to exclude all pollinators, indicating that the species are not capable of autonomous self-fertilization. Fruit and seed set were determined for patches of K. uvaria and C. aethiopica in order to test for potential Allee effects. There was a significant relation between the percentage of flowers that set fruit and the number of plants per patch for both K. uvaria and C. aethiopica. However, the number of seeds set per flower of K. uvaria and C. aethiopica had no significant relation with the number of plants per patch. Flowering phenology for the area was determined by bi-weekly walks along the two study sites to document plants in flower. Bird presence was determined using data collected from bi-weekly mist netting sessions at the two sites. We then compared the presence of birds with the flowering data of bird-pollinated plant species. For the Kalander Kloof site there were ten bird-pollinated plant species found and eight for the Salt River site. A comparison of the flowering data with bird presence data, indicated that nectar feeding birds were more likely to be present when accessible nectar availability is high. A total of 135 plant species across both sites were documented during the period of this study of which 14 were bird pollinated.