McGeoch M


Recent Submissions

Now showing 1 - 5 of 6
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    Fine scale variability in soil frost dynamics surrounding cushions of the dominant vascular plant species (Azorella Selago) on Sub-Antarctic Marion Island
    (Swedish Society for Anthropology and Geography, 2009) Haussmann, N.S.; Boelhouwers, J.C.; McGeoch, M.A.
    Through changing soil thermal regimes, soil moisture and affecting weathering and erosion processes plants can have an important effect on the physical properties and structure of soils. Such physical soil changes can in turn lead to biological facilitation, such as vegetation-banked terrace formation or differential seedling establishment. We studied the fine scale variability in soil temperature and moisture parameters, specifically focusing on frost cycle characteristics around cushions of the dominant, vascular plant species, Azorella selago, on sub-Antarctic Marion Island. The frost season was characterised by numerous low intensity and very shallow frost cycles. Soils on eastern cushion sides were found to have lower mean and maximum temperatures in winter than soils on western cushion sides. In addition, lower variability in temperature was found on eastern cushion sides in winter than on western cushion sides, probably as a result of higher wind speeds on western cushion sides and/or eastern, leeside snow accumulation. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms at temperatures above –2°C. Our results demonstrate the effectiveness of frost pull as a heave mechanism under shallow frost conditions. The results highlight the importance of Azorella cushions in modifying site microclimates and of understanding the consequences of these modifications, such as potentially providing microhabitats. Such potential microhabitats are particularly important in light of current climate change trends on the island, as continued warming and drying will undoubtedly increase the need for thermal and moisture refugia.
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    A biodiversity monitoring framework for South Africa: progress and directions
    (SAEON Reviews, 2007) Reyers, B.; McGeoch, M.A.
    Global declines in biodiversity, and the associated impacts on human wellbeing, have triggered national and international agreements to reduce or halt these trends. The Convention on Biological Diversity’s 2002 commitment, ‘to achieve, by 2010, a significant reduction in the current rate of biodiversity loss....’, is an often cited example and has caused a flurry of activity in the development of biodiversity monitoring systems. At a national scale, South Africa’s National Environmental Management: Biodiversity Act and associated legislation have highlighted the need for a national biodiversity monitoring framework. The National Biodiversity Strategy and Action Plan makes a significant contribution to the development of this framework. As South Africa begins to implement the action plan, a review of existing national monitoring programmes in terms of global and national biodiversity monitoring requirements is important. This paper presents the results of a review of these national programmes, to provide a broad overview, assess alignment with national and global requirements, evaluate gaps and discuss a way forward in the devising of a national biodiversity monitoring framework. We find that the National Biodiversity Strategy and Action Plan aligns well with the Convention on Biological Diversity’s 2010 target objectives, but differs in terms of the indicators proposed. Existing national biodiversity monitoring programmes also exhibit these indicator differences and show several gaps in indicator development and data collation. These gaps raise concern around the country’s ability to report on the Convention on Biological Diversity’s 2010 target, but together with the sound platform provided by the National Biodiversity Strategy and Action Plan, provide a good indication of national priorities and a way forward through a combination of short-term achievable tasks and longer-term development of programmes.
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    Fine-scale temporal and spatial dynamics of epigaeic ants in Fynbos: sampling implications
    (Entomological Society of Southern Africa, 2007) Boonzaaier, C.; McGeoch, M.A.; Parr, C.L.
    Conservation and management strategies are dependent on reliable species richness information. Accurate species richness counts, especially for invertebrates, are almost impossible to obtain from sampling alone, due to the high costs and effort involved. Therefore, there is a great need to optimize sampling effort to gain maximum information from minimum sampling duration and intensity. Reliable species richness information is particularly critical for under-studied, high diversity regions, such as the Cape Floristic Region (CFR), where biodiversity is threatened by agricultural practices and urbanization. Ants (Formicidae) form an important part of the fauna of the CFR, especially as seed dispersers. This study investigated sampling effort options for maximizing ant species representivity in the region. The specific aims were to determine (i) whether a doubling in the sample duration significantly increased the number of species captured (ii) the effect of increased spatial versus temporal sampling effort on diversity estimates and (iii) the effect of adding an additional trapping method. Sampling was conducted at Elandsberg, Western Cape Province, from 20 February to 1 March 2004. Pitfall trapping was conducted in two five-day sessions and tuna-baits were used once. Species rarefaction curves were drawn and compared using EstimateS. A total of 42 species were captured and asymptotes to species richness were reached. Doubling of sample duration yielded no significant increase in species richness and was equally affected in terms of number of species as was doubling the sampling intensity. However, increasing the number of spatial replicates yielded a higher turnover in species. Baiting added no additional species to pitfall catches. Therefore, when sampling ant diversity in theCFR, investing sampling effort within seasons in spatial replication is likely to be more effective than increasing sampling duration.
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    Extrapolating population size from the occupancy–abundance relationship and the scaling pattern of occupancy
    (2009) Hui, C.; McGeoch, M.A.; Reyers, B.; le Roux, P.C.; Greve, M.; Chown, S.L.
    The estimation of species abundances at regional scales requires a cost-efficient method that can be applied to existing broadscale data. We compared the performance of eight models for estimating species abundance and community structure from presence– absence maps of the southern African avifauna. Six models were based on the intraspecific occupancy–abundance relationship (OAR); the other two on the scaling pattern of species occupancy (SPO), which quantifies the decline in species range size when measured across progressively finer scales. The performance of these models was examined using five tests: the first three compared the predicted community structure against well-documented macroecological patterns; the final two compared published abundance estimates for rare species and the total regional abundance estimate against predicted abundances. Approximately two billion birds were estimated as occurring in South Africa, Lesotho, and Swaziland. SPO models outperformed the OAR models, due to OAR models assuming environmental homogeneity and yielding scale-dependent estimates. Therefore, OAR models should only be applied across small, homogenous areas. By contrast, SPO models are suitable for data at larger spatial scales because they are based on the scale dependence of species range size and incorporate environmental heterogeneity (assuming fractal habitat structure or performing a Bayesian estimate of occupancy). Therefore, SPO models are recommended for assemblagescale regional abundance estimation based on spatially explicit presence–absence data.
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    Modeling species distributions by breaking the assumption of self-similarity
    (2007) Hui, Cang; McGeoch, Melodie A.
    Species distributions are commonly measured as the number of sites, or geographic grid cells occupied. These data may then be used to model species distributions and to examine patterns in both intraspecific and interspecific distributions. Harte et al. (1999) used a model based on a bisection rule and assuming self-similarity in species distributions to do so. However, this approach has also been criticized for several reasons. Here we show that the self-similarity in species distributions breaks down according to a power relationship with spatial scales, and we therefore adopt a power-scaling assumption for modeling species occupancy distributions. The outcomes of models based on these two assumptions (self-similar and power-scaling) have not previously been compared. Based on Harte’s bisection method and an occupancy probability transition model under these two assumptions (self-similar and power-scaling), we compared the scaling pattern of occupancy (also known as the area-of-occupancy) and the spatial distribution of species. The two assumptions of species distribution lead to a relatively similar interspecific occupancy frequency distribution pattern, although the spatial distribution of individual species and the scaling pattern of occupancy differ significantly. The bimodality in occupancy frequency distributions that is common in species communities, is confirmed to a result for certain mathematical and statistical properties of the probability distribution of occupancy. The results thus demonstrate that the use of the bisection method in combination with a power-scaling assumption is more appropriate for modeling species distributions than the use of a self-similarity assumption, particularly at fine scales.