Repository logo

Ecology

Permanent URI for this communityhttps://hdl.handle.net/10413/7482

Browse

Browsing Ecology by Author "Bitani, Nasiphi."

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Effects of landscape and forest structural characteristics on the avian communities in Southern Mistbelt Forests, Midlands of KwaZulu-Natal, South Africa.
    (2023) Bitani, Nasiphi.; Downs, Colleen Thelma.; Ehlers Smith, David Alan.; Ehlers Smith, Yvette Cathrine.
    Globally forest ecosystems are under threat from land-use changes threatening biodiversity. Biodiversity conservation in forest systems has become a major concern as these impacts affect ecosystem functioning. Habitat destruction results in highly fragmented forest patches with reduced habitat quality. Therefore, it is essential to assess species' responses to these changes for conservation. Like other parts of the world, South African forests are threatened by destruction, mainly habitat conversion to exotic commercial tree plantations. Forest bird species within this system have been reported to be declining. Considering these impacts, it is important to understand the main drivers at different spatial scales. This study aimed to assess local and landscape drivers of avian communities in the Southern Mistbelt Forests in the Midlands of KwaZulu-Natal, South Africa. The objectives were to assess (1) the local scale drivers and influences on bird species richness, use and functional diversity, (2) microhabitat requirements and occupancy of understorey forest specialist bird species using camera traps, and (3) landscape attributes influencing bird species richness, habitat use and functional groups. Firstly, the influence of forest structure and composition on bird species richness, habitat use and functional diversity in 14 selected Southern Mistbelt Forest patches of KwaZulu-Natal were assessed. The bird species were surveyed using point count surveys. Functional diversity for each surveyed patch was quantified using three indices: functional richness, functional evenness and functional divergence. Species-specific responses were assessed by focusing on three forest specialists, orange ground-thrush Geokichla gurneyi, forest canary Crithagra scotops, and Cape parrot Poicephalus robustus. Bird community and forest bird specialists' responses to forest structure and tree species diversity varied. Forest structural complexity, canopy cover, and tree species richness were the main structural characteristics influencing bird functional diversity. Also, forest composition and structure are important for bird species and functional richness. Secondly, the microhabitat requirements of forest specialist bird species using camera surveys in the selected 14 Southern Mistbelt Forests were assessed. The results showed that the microhabitat requirements of the understorey forest specialist species are specific. Occupancy models showed that forest specialist understorey birds are mainly influenced by tree species richness, understorey cover of leaf litter and water. Lastly, the bird species richness, habitat use and functional groups’responses to selective logging history, livestock grazing and adjacent matrix type were assessed. The bird communities were surveyed using point-counts. Functional diversity was quantified using functional richness, functional divergence and functional evenness estimated using bird functional traits. The disturbance did not affect bird species richness. Forest specialists' responses to disturbance were species-specific depending on the type of disturbance and intensity. The orange ground-thrush and forest canary were affected by livestock grazing, while the Cape parrot was influenced by forest logging history. Functional richness for all functional groups was high in disturbed forests, while functional evenness for forest specialists and insectivores was low in disturbed sites. The results of this study provide insight into the local and landscape drivers of avian species richness and diversity. Forest patches with high tree species diversity and structural complexity should be maintained to conserve forest specialists, bird species richness and functional richness. Also, to maintain the persistence of the understorey forest specialists, forest structures within 5 m of the forest floor should be maintained. It is recommended to use functional diversity indices with taxonomic indices to understand bird species responses to disturbance better.
  • Thumbnail Image
    Item
    Fleshy-fruited invasive plant species in KwaZulu-Natal, South Africa: native avian seed dispersal and impact assessment.
    (2019) Bitani, Nasiphi.; Downs, Colleen Thelma.
    Globally, alien plant species have been recognised as a major threat to biodiversity. The increased global trade and travel have resulted in the increased introduction of new species. Direct or indirect introductions of alien invasive plant species result in altered ecosystem functioning, negatively affect economies, human health and wellbeing. In forest systems, habitat fragmentation has major impacts on biodiversity including the facilitation of alien invasions. Habitat alteration creates disturbance zones that are associated with increased invasion success. South Africa, like other parts of the world, is severely affected by alien plant species. Fleshy-fruited invasive species are amongst the most damaging invasive species with major environmental, social and economic impacts. Fleshy-fruited invasive plant species integrate into local seed dispersal networks and form mutual relationships with local avian seed dispersers leading to increased invasion potential. The success of avian mediated seed dispersal is influenced by the functional traits of both the plant and avian seed dispersers. Considering the negative impacts of fleshy-fruited alien invasive species it is important to understand ecological processes leading to their successful spread and if high priority species are being targeted for management to guide policy and conservation. Understanding avian mediated dispersal is important as it gives insights into the species that could promote alien plant invasion. The aim of the present study was to assess avian seed dispersal, and ecological and socio-economic impacts of fleshy-fruited alien invasive plant species. The objectives were to (1) predict avian seed dispersers of fleshy-fruited alien invasive plant species; (2) determine the assemblage of native avian species potentially dispersing the seeds of Lantana camara; and (3) determine the socio-economic and ecological impacts of fleshy-fruited alien invasive plant species. Firstly, we predicted the avian seed dispersers of fleshy-fruited invasive plant species in the Indian Coastal Belt Forest of KwaZulu-Natal Province, South Africa using functional traits of avian species (body mass, gape width, bill length, degree of frugivory, foraging strategy, abundance and habitat specificity) and fleshy-fruited invasive plants (crop size, fruit size, seed size, number of seeds, plant height, plant habitat, fruiting period and derived invasiveness score). The results showed that small, abundant forest generalist avian species were potentially effective dispersers of fleshy-fruited invasive species. Fleshy-fruited invasive plant species that were more likely to persist in the disturbed Indian Coastal Belt Forest through avian-mediated seed dispersal were small-seeded, open habitat plants with relatively longer fruiting duration. Secondly, we assessed the role of native avian species in the potential dispersal of a highly invasive shrub Lantana camara of the family Verbenaceae in Pietermatzburg, KwaZulu-Natal, South Africa. Avian species visiting L. camara were observed and potential dispersal distances estimated. The results showed that native avian species were potential seed dispersers of L. camara were mostly relatively small, moderately frugivorous avian species. The dark-capped bulbul (Pycnonotus tricolor) showed relatively high visitation frequencies to L. camara and was more likely the main effective dispersers of the plant. Potential seed dispersal distances were shown to range from 9 to 45 km and long distance seed dispersal distances were shown to be rare and only limited by rarely large avian frugivores. Lastly, we assessed the ecological and socio-economic impacts of fleshy-fruited invasive species using the generic impact scoring system. The results showed that fleshy-fruited invasive plant species have both socio-economic and environmental impacts. The highest environmental impacts were shown to be on ecosystem and vegetation, or plant and the highest socioeconomic impacts were on agriculture, forest production and human health. The results presented in this thesis provide essential insights into the importance of avian mediated seed dispersal in the invasion of fleshy-fruited invasive plant species. The findings of the study also highlight the importance of predictive approaches in informing the management of invasions and showed fleshy-fruited invasive plant species with high socio-economic and ecological impacts. Knowledge of species with high impacts will help in guiding resource allocation and preventing the introduction of high-risk species. Also, ecologists and other decision-makers should consider ecological processes that are leading to the spread of invasive plant species in management practices or plans.