Browsing by Author "Greve, Michelle"
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- ItemAvifaunal responses to environmental conditions and land-use changes in South Africa : diversity, composition and body size(Stellenbosch : Stellenbosch University, 2007-03) Greve, Michelle; Chown, S. L.; Gaston, K. J.; Van Rensburg, B. J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: In macroecology, body sizes in animal assemblages have traditionally been investigated from two perspectives: body size frequency distributions (BSFDs) and geographic variation in body size. Neither of these has been investigated for the South African avifauna; one objective of this study was therefore to explore these. The regional BSFD of South African birds was found to be right-skewed, as is usually found for assemblages at large scales. This suggests that mechanisms driving the shape of BSFDs elsewhere are also acting for the South African avifauna. The Southern African Bird Atlas database was used to calculate median body sizes of avian assemblages in quarter degree grid cells. Median sizes were then used to investigate geographic variation in body size across the country. Of the mechanisms previously proposed to explain geographic variation in body size, only the starvation resistance hypothesis, which states that large size confers starvation resistance during seasonally resource shortages, was supported, though weakly, as median body size decreased with increasing productivity. The ability of null models to predict the variation in body size was subsequently explored, and it was found that much of the variation in median size of assemblages could be predicted by randomly drawing species from the regional BSFD, particularly at high species richness values. This provides empirical support for a continuum between the dominance of niche-based processes (where assemblages are a product of organisms' response to their environment) at low richness and neutral processes (where organisms assemble at random) at higher richness. In addition, it emphasizes the need to consider null expectations in investigations of the geographic variation in size. The importance of the regional BSFD and species richness for body sizes of local assemblages is highlighted. Body size is one of several life history and community characteristics of animals that may be affected by anthropogenic disturbance to the environment. World-wide, landscapes are increasingly being altered by people, though few studies have investigated the effect of such disturbances on the avifauna of South Africa. The consequence of land-use changes on avian assemblages was therefore assessed in three South African regions which experience different environmental conditions and are threatened by different land-use changes. Birds were recorded in transects in undisturbed protected areas and the disturbed landscape outside the protected areas in the three regions. The effect of land-use change on avian assemblages varied between regions, and avian assemblages were most affected where disturbance was most intense. While species richness was not affected in a consistent manner across regions, species composition always changed in response to disturbance. This led to higher regional species richness as natural and disturbed areas supported different avian assemblages, and heterogeneity of assemblages between vegetation types usually became less pronounced in disturbed areas. Functional diversity was also compromised by land-use changes: the relative proportion of feeding guilds was altered, indicating that changes in food availability affect composition of assemblages. In contrast, mean body size of birds did not change in disturbed landscapes, which suggests that habitat architecture has little effect on body size. This study therefore highlights the importance of natural and protected areas for conserving species, assemblages and ecosystem processes.
- ItemExploring South Africa’s southern frontier : a 20-year vision for polar research through the South African National Antarctic Programme(Academy of Science of South Africa, 2017) Ansorge, Isabelle J.; Skelton, Paul; Bekker, Annie; de Bruyn, P.J. Nico; Butterworth, Doug; Cilliers, Pierre; Cooper, John; Cowan, Don A.; Dorrington, Rosemary; Fawcett, Sarah; Fietz, Susanne; Findlay, Ken P.; Froneman, William P.; Grantham, Geoff H.; Greve, Michelle; Hedding, David; Hofmeyr, Greg G. J.; Kosch, Michael; Le Roux, Peter C.; Lucas, Mike; MacHutchon, Keith; Meiklejohn, Ian; Nel, Werner; Pistorius, Pierre; Ryan, Peter G.; Stander, Johan; Swart, Sebastiaan; Treasure, Anne; Vichi, Marcello; Van Vuuren, Bettine J.No abstract available
- ItemSoil nutritional status and biogeography influence rhizosphere microbial communities associated with the invasive tree Acacia dealbata(Nature Research, 2017-07-26) Kamutando, Casper N.; Vikram, Surendra; Kamgan-Nkuekam, Gilbert; Makhalanyane, Thulani P.; Greve, Michelle; Le Roux, Johannes J.; Richardson, David M.; Cowan, Don; Valverde, AngelInvasiveness and the impacts of introduced plants are known to be mediated by plant-microbe interactions. Yet, the microbial communities associated with invasive plants are generally poorly understood. Here we report on the first comprehensive investigation of the bacterial and fungal communities inhabiting the rhizosphere and the surrounding bulk soil of a widespread invasive tree, Acacia dealbata. Amplicon sequencing data indicated that rhizospheric microbial communities differed significantly in structure and composition from those of the bulk soil. Two bacterial (Alphaproteobacteria and Gammaproteobacteria) and two fungal (Pezizomycetes and Agaricomycetes) classes were enriched in the rhizosphere compared with bulk soils. Changes in nutritional status, possibly induced by A. dealbata, primarily shaped rhizosphere soil communities. Despite a high degree of geographic variability in the diversity and composition of microbial communities, invasive A. dealbata populations shared a core of bacterial and fungal taxa, some of which are known to be involved in N and P cycling, while others are regarded as plant pathogens. Shotgun metagenomic analysis also showed that several functional genes related to plant growth promotion were overrepresented in the rhizospheres of A. dealbata. Overall, results suggest that rhizosphere microbes may contribute to the widespread success of this invader in novel environments.