Department of Botany and Zoology

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Browsing Department of Botany and Zoology by browse.metadata.advisor "Barnard, Phoebe"

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    Nectar distribution and nectarivorous bird foraging behaviour at different spatial scales
    (Stellenbosch : Stellenbosch University, 2016-03) Coetzee, Anina; Pauw, Anton; Barnard, Phoebe; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: While foraging strategies of animals may be shaped by the distribution of their food resources, these strategies in turn also affect the ecology and evolution of their resources. In this regard, African systems, of all the different bird-pollination systems worldwide, have been least studied. I investigated the relationships between these aspects at population, community and landscape levels in the bird-pollination systems of the Cape Floristic Region. This biodiversity hotspot in the southwest of South Africa contains an unusually high number of bird-pollinated plant species relative to the number of pollinating bird species. Chapter 2 describes how I experimentally tested which nectar resource traits affect sunbird foraging behaviour at the small scale within populations. Sunbirds’ behaviour was largely determined by visual signals and distances between nectar resources. The birds showed flower colour preferences, but no flower constancy (selective foraging only on one flower type). The foraging behaviour of pollinators seems to influence plant community assembly. With the use of null models, I show in Chapter 3 that communities of Proteaceae, a diverse and dominant plant family in the Cape Floristic Region, are structured both by competition for and facilitation of pollination. This was deduced from the non-random structure of the plant communities with respect to pollination syndromes and style lengths, which are proxies of the degree of pollinator sharing and of interspecific pollen transfer. While species traits were important driving forces of community assembly in natural habitat, I show in Chapter 4 that species and habitat traits may also be important factors structuring bird communities in novel environments such as human settlements. Through a questionnaire, I determined how well different species of nectarivorous birds are adjusting to urban environments and which traits facilitate and prevent this adjustment. Nectar-generalist birds were successful exploiters of urban resources and were most abundant in gardens with large vegetated areas, bird baths and feeders. Nectar-specialist birds were less successful at adjusting, due to their high dependence on nectar. The presence of sugar water feeders and the number of indigenous bird-pollinated plants in gardens best predicted the communities of nectar-specialist birds. All nectarivorous birds were negatively affected by dispersal barriers. Lastly, in Chapter 5, I use biome-wide atlas databases for birds and proteas to show how nectar distribution affects bird abundances at a landscape scale. The non-significantly different flowering phenology patterns throughout the biome suggest that nectarivorous birds would not need to migrate seasonally. Instead, birds may be sustained within mountain ranges all year round by the complementary flowering of species of different genera. Low floral abundances in the dry months of the year may still produce resource bottlenecks and this may encourage birds to forage in areas of human settlement. Though we have gained insight into some of the relationships between African nectarivorous birds and their nectar resource distributions in space and time, there is still much to learn. There is also an urgent need to understand the effects of land-use change on the long-term persistence of nectar-feeding birds of the Cape Floristic Region.