The relative importance of environment, human activity and space in explaining species richness of South African bird orders (original) (raw)
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Patterns of bird species richness at two sampling scales in the Karoo biome of South Africa
Journal of Arid Environments, 2019
Species richness has become the common currency of studies of biodiversity. Here we consider measures of species richness for the birds of the arid Karoo region of South Africa. We measured species richness at two scales: at the broad-scale using pentads (5 × 5′); and at the fine scale, using point counts to determine important landscape features. Point counts within randomly selected pentads were conducted throughout the two biomes that comprise the Karoo (Succulent and Nama). Features at points were used to model covariates of species richness at the fine scale, while the total number of unique species from counts was used as the dependent variable at the broad scale. We considered determinants of total species richness; and the subset of ten bird species endemic to the Karoo. Finally, we modelled covariates of presence for 100 of the most common bird species. We found increasing vegetation height and decreasing sand-cover best explain total species richness, while lower Prosopis sp cover and increasing altitude explained endemic species richness at the broad scale. At the finer scale, presence of water and farmsteads were associated with highest general species richness, but with lower numbers of endemics. The presence of water, a 'green' score, sand cover and topography were identified as the most important variables explaining presence of individual species, but often with contrasting effects between species. We conclude that patterns of endemic bird species richness were explained by different variables compared to total species richness. We expect this information will inform landholders, wildlife managers and conservation practitioners in this unique arid zone environment.
2009
Recent research has emphasized the importance of understanding the consequences of species loss, not just for biodiversity per se, but also for ecosystem resilience and functioning. Firstly, a baseline analysis of the effects of a naturally patchy landscape on avian community composition and resilience in a high altitude Afrotemperate forest landscape in South Africa is presented. Bird data from a point count survey of 706 counts at 31 forest sites was used to test whether taxonomic species diversity, functional species richness and density of birds provide insight into community resilience in this historically patchy ecosystem. Bird species richness of forest patches ranged from 17 to 38, with a total species richness of 50. Density was slightly but negatively related to both area and species richness. That density compensation is occurring in these Afrotemperate forests suggests a level of resilience in this system. Following on from this, cumulative species-area and function-area graphs were derived to quantify the loss of forest area or taxonomic bird species richness that this landscape may potentially sustain before ecosystem functioning is negatively affected. The concept that species' patterns of distribution, abundance and coexistence are the result of local ecological processes has recently been challenged by evidence that regionalscale processes are equally instrumental in shaping local community composition. The historically and naturally fragmented Afrotemperate forests of the uKhahlamba-Drakensberg Park, South Africa, offer an interesting test case. In this study the relative effects of local and regional-scale processes on species assemblages in a naturally patchy forest system were investigated. By employing species-area and species-isolation relationships, and nested subset analyses, we showed that isolation (regional-scale process) had a greater effect on bird species richness and composition than area (local-scale process), though the species-area relationship was significant. Using generalized linear models and an information-theoretic approach to model selection, patch area, the size of the regional species pool as well as the distance to the nearest Eastern Mistbelt forest were all influential in determining local bird species richness in these montane forests. Thus, localities are regionally enriched within the constraints on species occupancy provided by the available habitat.
Bird species richness in tropical Africa: Some comparisons
Biological Conservation, 1987
Species richness provides a simple measure of diversity, and high diversity is commonly considered a desirable attribute of an area. To determine factors favouring high species richness, we obtained data for 18 countries in tropical Africa, and for comparison, 12 in tropical America. We also considered data from smaller areas in Africa.
Journal of Biogeography, 2016
Test hypotheses that present biodiversity and endemic species richness are related to climatic stability and/or biome persistence. Location: Africa south of 15° S. Methods: Seventy eight HadCM3 general circulation model palaeoclimate experiments spanning the last 140,000 years, plus a pre-industrial experiment, were used to calculate measures of climatic variability for 0•5° grid cells. Models were fitted relating distributions of the nine biomes of South Africa, Lesotho and Swaziland to present climate. These models were used to simulate potential past biome distribution and extent for the 78 palaeoclimate experiments, and three measures of biome persistence. Climatic response surfaces were fitted for 690 bird species regularly breeding in the region and used to simulate present species richness for cells of the 0•5° grid. Species richness was evaluated for residents, mobile species (nomadic or partially/altitudinally migrant within the region), and intra-African migrants, and also separately for endemic/near-endemic (hereafter 'endemic') species as a whole and those associated with each biome. Our hypotheses were tested by analysing correlations between species richness and climatic variability or biome persistence. Results: The magnitude of climatic variability showed clear spatial patterns. Marked changes in biome distributions and extents were projected, although limited areas of persistence were projected for some biomes. Overall species richness was not correlated with climatic variability, although richness of mobile species showed a weak negative correlation. Endemic species richness was significantly negatively correlated with climatic variability. Strongest correlations, however, were positive correlations between biome persistence and richness of endemics associated with individual biomes. Main Conclusions: Low climatic variability, and especially a degree of stability enabling biome persistence, is strongly correlated with species richness of birds endemic to southern Africa. This probably principally reflects reduced extinction risk for these species where the biome to which they are adapted persisted.
Ostrich, 2021
High human population growth and rapid urbanisation, particularly in Africa, have led to an increased interest in the impacts of this land-use change on bird communities. The African Bird Atlas Project, where species presence lists are collected in pentads, is a valuable source of data with which to explore the extent of these impacts. Here, for the first-time, we test for differences in species richness patterns across 50 matched pentad pairs from sub-Saharan Africa classified as either urban (or semi-urban) and rural. We found that species richness was lowest in pentads classified as urban (mean ± SD: 132 ± 59 species), compared with rural (172 ± 54). However, species richness was similar, compared with rural pentads, when levels of urbanisation were maintained at intermediate levels (semi-urban: 141 ± 69). Surprisingly, we found no significant differences in functional diversity measures between any land-use categories. Across most major dietary guilds (carnivores, herbivores, insectivores, granivores) species richness was lower in urbanised pentads and species were often small. However, the overall biomass of these guilds was similar between urbanised and non-urbanised areas, indicating the presence of common urban exploiter species. This resulted in no differences in functional diversity overall. Pollinators and piscivores showed little difference in metrics between rural and urban pentads. According to a model of the functional traits we consider, an African urban exploiter species is best described by being a scavenger, and less likely to be a habitat specialist, but fill a variety of niches. The urban spatial planning implications are that rare and range-restricted species in proximity to cities, as well as large bird species, will require particular attention and conservation measures as African cities continue to expand. Species richness could be maintained with intermediate levels of urban infrastructure development. Les zones urbanisées sont moins riches en espèces mais conservent une diversité fonctionnelle: un aperçu du projet d'Atlas des oiseaux d'Afrique La forte croissance de la population humaine et l'urbanisation rapide, plus particulièrement en Afrique, ont suscité un intérêt accru sur les impacts de ce changement d'utilisation des terres sur les communautés aviaires. Le projet d'Atlas des oiseaux d'Afrique, qui collecte les données relatives à la présence des espèces au travers de pentades (groupe de cinq unités), est un source précieuse de données permettant d'explorer l'étendue de ces impacts. Au travers de cet article, et pour la première fois, nous testons les différences en termes de richesse d'espèces, au travers de modèles basés sur 50 paires de pentades appariées d'Afrique sub-saharienne et classées comme urbaines (ou semi-urbains) ou rurales. Nous avons estimé que la richesse en espèces était la plus faible dans des pentades de catégorie urbaine (moyenne ± σ: 132 ± 59 espèces) par comparaison aux groupes ruraux (172 ± 54 espèces). Néanmoins, il a été constaté que la richesse en espèces était similaire aux pentades rurales dès lors que le niveau d'urbanisation restait contenu à un niveau intermédiaire (semi-urbain: 141 ± 68). Pour ce qui concerne la diversité fonctionnelle, nous avons été surpris de ne pas trouver de différences significatives entre les catégories d'usage des terres. Quant aux régimes alimentaires des guildes principales (carnivores, herbivores, insectivores, granivores), la richesse en espèces était plus faible dans les pentades urbaines et les espèces étaient souvent de petite taille. Cependant, la biomasse globale de ces guildes était identique entre les zones urbanisées et non-urbanisées, ce qui indique la présence d'espèces communes exploitant ces zones. Ceci induit qu'il n'y a pas de différences dans la diversité fonctionnelle globale. Les pollinisateurs et les piscivores présentaient peu de différence de mesures entre les pentades rurales et urbaines. D'après un modèle des traits fonctionnels, nous considérons qu'une espèce africaine d'exploitation urbaine est mieux décrite comme étant un charognard, remplissant une variété de niches, et moins à même d'être un spécialiste de cet habitat. En matière d'aménagement urbain, cela implique que les espèces rares et à aire de restriction restreinte ainsi que les grandes espèces d'oiseaux se trouvant à proximité des villes, nécessiteront une attention particulière et des mesures de conservation tant que les villes africaines poursuivent leur expansion. La diversité des espèces pourrait être conservée avec des développements d'infrastructures urbaines maintenus à des niveaux intermédiaires.
Biological Conservation, 2001
Multivariate analyses and complementarity-based reserve selection algorithms were used as tools for delimiting representative conservation areas in KwaZulu-Natal, South Africa, based on environmental variables and records for 566 breeding and nonbreeding birds. The relationships between species assemblages and 20 environmental variables were investigated; including climate, topography, vegetation, landscape attributes, and land-use. Detrended correspondence analysis, canonical correspondence analysis, and hierarchical classi®cation suggested that the major gradients of bird species variation are primarily related to climatic variables such as growing season temperature and seasonality of precipitation, re¯ecting the strong east±west gradient in oceanicity in KwaZulu-Natal, and water balance, re¯ecting a strong north±south gradient in aridity. Hierarchical classi®cation was applied to the ordination data and revealed ®ve representative types of bird communities. Four of the ®ve bird communities and 37 species are under-represented in the existing reserve system, and the environmental processes required for long-term maintenance of birds have not been adequately sampled, showing that additional reserves are needed to ensure a more functional representative system. As an alternative, the inclusion of species spatial turnover structure together with associated environmental gradients were employed in both rarity and richness-based complementary reserve selection algorithms to provide a better representation of birds and environmental processes. Improvements on the current generation of reserve selection techniques derived by including ordination analysis and spatial structure are discussed. #
Drivers of Bird Species Richness within Moist High-Altitude Grasslands in Eastern South Africa
PLOS ONE, 2016
Moist high-altitude grasslands in South Africa are renowned for high avifaunal diversity and are priority areas for conservation. Conservation management of these areas conflicts with management for other uses, such as intensive livestock agriculture, which requires annual burning and leads to heavy grazing. Recently the area has become target for water storage schemes and renewable electricity energy projects. There is therefore an urgent need to investigate environmental factors and habitat factors that affect bird species richness in order to optimise management of those areas set aside for conservation. A particularly good opportunity to study these issues arose at Ingula in the eastern South African highaltitude grasslands. An area that had been subject to intense grazing was bought by the national power utility that constructed a pumped storage scheme on part of the land and set aside the rest for bird conservation. Since the new management took over in 2005 the area has been mostly annually burned with relatively little grazing. The new management seeks scientific advice on how to maintain avian species richness of the study area. We collected bird occurrence and vegetation data along random transects between 2006 and 2010 to monitor the impact of the new management, and to study the effect of the habitat changes on bird species richness. To achieve these, we convert bird transect data to presence only data to investigate how bird species richness were related to key transect vegetation attributes under this new grassland management. First we used generalised linear mixed models, to examine changes in vegetation grass height and cover and between burned and unburned habitats. Secondly, we examined how total bird species richness varied across seasons and years. And finally we investigated which habitat vegetation attributes were correlated with species richness of a group of grassland depended bird species only. Transects that were burned showed a larger decrease in vegetation cover compared to transects that were not burned. Grass height increased over time. Bird species richness was highest in summer compared to other seasons and increased over time. Overall bird