The relative importance of natural and human-induced environmental conditions for species richness distribution patterns in South Africa

I studied the spatial distribution of South African avian species richness from the viewpoint that humans are a substantial modifying force on earth, and have also modified the historical spatial distribution of species richness. The main aim of the thesis is to investigate the way in which humans have modified avian species richness patterns in South Africa at the quarter-degree square (QDS) resolution, which is a phenomenon that has been either overlooked, or not completely clarified, in many previous studies of the same region and data at the same resolution. In particular, I investigated hypotheses that were proposed to explain the maintenance of a positive relationship between native species richness and human population density in the face of negative human impacts. Further, I investigated which of the possible anthropogenic and natural environmental factors determine spatial distribution in exotic bird species. Highlighted from these studies are that substantial positive and negative human influences on bird species richness distribution patterns are observable at the QDS resolution, that there are differences between common native birds and rare native birds with regard to their relationships with anthropogenic environmental conditions and exotic bird species, and that the particular combination of environmental covariates that is important for the spatial distributions of exotic species is taxon- and scale-dependent. Even though these results have contributed much towards our understanding on how human modifications have affected species richness patterns, this thesis leaves some unanswered questions. Finer resolution studies and temporal studies are needed to examine many of these questions. Further, an interdisciplinary approach incorporating politics and economics into ecological studies is needed to enhance our understanding of the factors that modify the distribution of humans and their associated threats and benefits to species richness.Dissertation (MSc)--University of Pretoria, 2010.Zoology and Entomologyunrestricte

Are environmental transitions more prone to biological invasions?

Aim To examine whether at a subcontinental-scale ecotonal areas of transition between vegetation communities are at higher risk of plant invasion. Location South Africa and Lesotho. Methods Using plant data on native and established alien species in South Africa, we examined the relationship between plant richness (native and alien) in each grid cell (quarter-degree resolution) in the study area and the distance of the grid cell to the nearest ecotone between vegetation communities. We used a residual analysis to estimate each grid cell's relative invasibility (i.e. susceptibility to invasion) relative to its ecotone distance. We further explored the relative importance of ecotones in relation to large-scale environmental variation, and the importance of ecotonal spatial heterogeneity, in structuring alien species richness patterns. Results Both alien and native richness patterns become higher with declining distance to ecotones, suggesting that transitional environments are more susceptible to invasion than areas located farther away; however, levels of invasibility vary across South Africa. The negative relationship between ecotone distance and alien species richness remained negative and significant for the whole of South Africa, grassland and Nama-Karoo, after controlling for environmental variables. Several sources of environmental heterogeneity, which were shown here to be associated with ecotones, were also found to be important determinants of alien species richness. Main conclusions While most of the current conservation efforts at the regional and global scales are currently directed to distinct ecosystems, our results suggest that much more effort should be directed to the transitions between them, which are small in size and have high native richness, but are also under greater threat from invasive alien species. Understanding how alien species richness and invasibility change across transitions and sharp gradients, where environmental heterogeneity is high, is important for ongoing conservation planning in a biogeographical context

Season and environment modulate aquatic invertebrates’ responses to trout and indigenous fishes in three South African mountain streams

Introduced organisms are seen as one of the greatest threats to resource sustainability worldwide, and aquatic macroinvertebrates are regarded as good indicators of the health of water resources. To explore these two perspectives, the responses of macroinvertebrate faunas to native and introduced fishes in three headwater tributaries of the Keiskamma River system, South Africa, were examined by comparing potential indicator communities in reaches considered to be fishless, reaches invaded by introduced salmonid species, and reaches containing native fishes. Patterns in the macroinvertebrate faunal assemblage data were driven strongly by season and flow rate, and less strongly by the presence of insectivorous fishes and biotope availability, a finding in parallel with several similar studies from the region. This affirms that aquatic macroinvertebrate faunas are responsive indicators of both environmental and biotic factors and leaves room for further studies to resolve the effects of non-native fish in the Keiskamma River system and other similar systems from South Africa

Biogeographical insights from ecotones and phytogeographic regions in southern Africa : case studies on invertebrates and alien plants

This thesis addresses questions within the research fields of invasion biology and spatial ecology, with a focus on species distribution patterns, biogeographical regions and ecological transition zones, or ecotones. More specifically, species distribution patterns in alien plants at large spatial scales using atlas data, and invertebrate patterns making use of field data collected at a smaller scale (total extent ca. 30 km). First I show that alien plants form largescale geographically differentiated species assemblages in southern Africa (i.e. South Africa, Lesotho, Swaziland, Namibia and Botswana). I demonstrated this by mapping and describing several alien phytogeographic regions at a quarter-degree spatial resolution, and further suggest possible environmental and human-caused determinants of each of these regions. Second, at the same spatial resolution (for South Africa and Lesotho combined, and each of the plant biomes), I show that relatively higher levels of alien plant species richness occur at or near to ecotones, compared to areas that are spatially further away from these ecotones and that typically represent the core habitat of the ecoregions examined. This finding remained valid after taking into account the underlying positive relationships between alien plant richness and energy availability. I also suggest that it is the relatively higher environmental heterogeneity at ecotones (represented here by spatial variation in altitude, rainfall and geology) that promote high alien plant richness. Third, at a smaller spatial scale I report several examples of change in beetle and spider species composition across a savannagrassland ecotone in the west of South Africa’s Free State Province, with the ecotone itself supporting comparatively lower levels of species richness and abundance. This contrasts with a popular assumption that ecotones are characterised by high species richness. Data gained from long-term intensive sampling is preferable for ecological studies, but not always available or practical to acquire; however with the three studies in this thesis I show that data from existing species atlases and feasible short-term surveys can be successfully applied to answer a variety of ecological questions.Thesis (PhD)--University of Pretoria, 2012.Zoology and EntomologyUnrestricte

Alien and native birds in South Africa: patterns, processes and conservation

The spatial distribution of alien species richness often correlates positively with native species richness, and reflects the role of human density and activity, and primary productivity and habitat heterogeneity, in facilitating the establishment and spread of alien species. Here, we investigate the relationship between the spatial distribution of alien bird species, human density, and anthropogenic and natural environmental conditions. Next, we examined the relationship between the spatial distribution of alien bird species and native bird species richness. We examined alien species richness as a response variable, using correlative analyses that take spatial autocorrelation into account. Further, each alien bird species was examined as a response variable, using logistic regression procedures based on binary presence–absence data. A combination of human density and natural habitat heterogeneity best explained the spatial distribution of alien species richness. This contrasts with the results for individual alien species and with previous studies on other non-native taxa showing the importance of primary productivity and anthropogenic habitat modification as explanatory variables. In general, native species richness is an important correlate of the spatial distribution of alien species richness and individual alien species, with alien species being more similar to common species than to rare species

The percentage of grid cells of each phytogeographic region that has been assigned to each particular biome [37] (see the Methods section for more details).

<p>The percentage of grid cells of each phytogeographic region that has been assigned to each particular biome <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036269#pone.0036269-Mucina1" target="_blank">[37]</a> (see the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036269#s2" target="_blank">Methods</a> section for more details).</p

The main spatial features of the study area, focusing on South Africa, Lesotho and Swaziland.

<p>Here we represent the political boundaries of the general study area (i.e. including Namibia and Botswana) and the spatial distributions of seven of the biomes in South Africa, Lesotho and Swaziland, as based on the biome classifications of Mucina & Rutherford <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036269#pone.0036269-Mucina1" target="_blank">[37]</a>. The forest and desert biomes occupy very little of South Africa’s surface area, and are not shown here. The approximate position of the Great Escarpment in South Africa is represented by the dashed line. The numbers indicate the following political regions: 1. Limpopo Province, 2. North West Province, 3. Gauteng Province, 4. Mpumalanga Province, 5. Swaziland, 6. Northern Cape Province, 7. Free State Province, 8. Lesotho, 9. KwaZulu-Natal Province, 10. Western Cape Province, 11. Eastern Cape Province. The insert shows the countries 12. Namibia, 13. Botswana, and 14. South Africa.</p

The dendrogram of the TWINSPAN classification analysis showing two levels of division.

<p>The initial TWINSPAN results was a dendrogram, which is represented here in a simplified form showing only the ecologically meaningful clusters (i.e. phytogeographic regions) from two levels of division (– – – – higher level; ▪▪▪▪▪ lower level). These phytogeographic regions were: 1. the Greater Arid Region, which includes the 1.1 Arid, and 1.2 Orange River regions; and 2. the Multiclimate Region, which includes the 2.1 Escarpment, 2.2 Northern, 2.3 Agricultural, 2.4 Western Cape, 2.5 Grassland, and 2.6 Savanna Regions.</p

Rapid recovery of macroinvertebrates in a South African stream treated with rotenone:

South Africa’s Cape Fold Ecoregion supports a unique freshwater fish assemblage with many endemics. To mitigate impacts of alien invasive fishes on this unique assemblage, nature conservation authority CapeNature used rotenone to remove smallmouth bass (Micropterus dolomieu) from the Rondegat River. We investigated whether the rotenone treatments had an adverse impact on the aquatic macroinvertebrate community over the long-term, the first study of its kind in Africa. We monitored macroinvertebrates within treated and untreated (control) sites on multiple sampling events for 2 years before and 2 years after two rotenone treatments. We analysed the difference in invertebrate abundance between treatment and control sites before and after treatment, using generalised linear mixed models with sampling event as a random factor to partition out natural fluctuations in abundances over time

Spatial distributions of the lower level phytogeographic regions.

<p>As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036269#pone-0036269-g003" target="_blank">Figure 3</a>, the grid cells comprising the lower level phytogeographic regions as derived from the cluster analysis (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036269#pone-0036269-g002" target="_blank">Figure 2</a>) are depicted: the 1.1 Arid and the 1.2 Orange River phytogeographic regions were subdivided from the Greater Arid region, and the 2.1 Escarpment, 2.2 Northern, 2.3 Agricultural, 2.4 Western Cape, 2.5 Grassland and 2.6 Savanna regions were subdivided from the Multiclimate region.</p