The impacts of habitat fragmentation of Tsitsikamma fynbos, South Africa, on avian nectarivore presence, abundance, and pollination
Habitat loss and fragmentation of natural habitat, and other global change drivers resulting from human expansion and development, are putting ecosystems and biodiversity at risk. The Cape Floristic Region (CFR), confined to South Africa and known for its high biodiversity of especially plants, has been subjected to extensive habitat loss and fragmentation through agriculture and other modifying land uses. Habitat loss and fragmentation have the potential to negatively affect pollination systems. A reduction in flowering abundance can result in lower nectar production and availability. This reduction in reliable food, along with a lack of adequate habitat and nesting resources, can reduce the abundance of pollinators which, in turn, may result in reduced seed-set for the plant species that rely on them. This study considers how selected erica and protea plants and the sunbirds and sugarbird that pollinate them are affected by fynbos habitat fragmentation. The study was conducted in an area of fragmented Tsitsikamma Plateau Fynbos in the eastern region of the CFR. In Chapter 2, I described the study area, reported methods used to choose and delineate the 17 study patches, and derived variables that were used in the analyses in subsequent chapters. I identified an expected fragmentation effect using exploratory analyses that investigated patch-similarity based on patch, fragmentation, and focal plant species variables. Large patches with high protea densities and surrounded by indigenous forest were clustered, while small patches with lower protea densities and surrounded by transformed farmland and alien vegetation were clustered separately. In Chapter 3, I explored how these fragmentation patterns affected bird species richness and nectar-feeding birds in fynbos habitat. Based on repeated bird point-counts at 33 locations in the study patches I showed that the surrounding non-habitat matrix contributed to faster species accumulation that led to higher species richness in small patches. Although habitat fragmentation had little direct impact on general bird species richness, it explained differences in nectarivore abundance among patches. The fynbos endemic Cape Sugarbird (Promerops cafer) and Orange-breasted Sunbird (Anthobaphes violacea), as well as the Malachite Sunbird (Nectarinia famosa), were less likely to be recorded at locations surrounded by reduced fynbos habitat, while the habitat-generalist Amethyst (Chalcomitra amethystina), Greater Double-collared (Cinnyris afer), and Southern Double-collared Sunbirds (Cinnyris chalybeus) show the opposite trend. The negative fragmentation impact shown on fynbos specialist bird species presumably resulted from their reliance on fynbos habitat and their exposure to pressures from the surrounding non-habitat matrix. In Chapter 4, I investigated if habitat fragmentation influenced nectar loads in selected erica (Erica discolor and E. densifolia) and protea (Protea neriifolia and P. mundii) flowers through its effect on the abundance of the bird nectarivores that feed on and pollinate these plants. I also considered seasonal protea flowering, nectar availability and Cape Sugarbird abundance in the study area. Although I did not find a marked fragmentation effect on flower nectar load in small patches, total nectar availability per unit area increased with patch size for proteas but decreased for ericas. Orange-breasted Sunbird abundance showed no relationship with erica nectar availability, while numbers of Southern Double-collared Sunbirds and Cape Sugarbirds increased with erica and protea nectar availability, respectively. The number of protea flowers, the amount of nectar available and the number of Cape Sugarbirds per month all showed a strong positive correlation, peaking from around December-June. These findings show the importance of nectar availability in determining nectarivore bird abundance and how fragmentation can affect it between patches. In Chapter 5, I investigated if habitat fragmentation affected seed-set for Erica discolor and Protea neriifolia flowers. I did not find a fragmentation effect on P. neriifolia seed-set, which reflected that Cape Sugarbirds managed to frequent all patches in the study. Erica discolor had higher seed-set in small patches, which might be explained by high sunbird density, thanks mainly to large numbers of Southern Double-collared Sunbirds that visited from the surrounding non-fynbos matrix. As a result, E. discolor seed-set was negatively correlated with Orange-breasted Sunbird abundance because this species was impacted by fragmentation. Protea neriifolia seed-set showed no relationship with Cape Sugarbird abundance. In the summary, Chapter 6, I discuss how habitat fragmentation affected the study system, but note how its impact varies among species. I also consider the limitations of the study and make suggestions for future research. Based on my findings, I suggest that conservation and managing authorities should aim to conserve and expand on remaining fynbos habitat by, for example, clearing the surrounding non-habitat matrix of invasive alien vegetation and/or rehabilitation such as erosion control and reseeding.
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