Chown S


Recent Submissions

Now showing 1 - 5 of 33
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    Land-use change promotes avian diversity at the expense of species with unique traits
    (John Wiley & Sons Ltd, 2016) Coetzee, B.W.T.; Chown, S.L.
    Land-use change may alter both species diversity and species functional diversity patterns. To test the idea that species diversity and functional diversity changes respond in differing ways to land-use changes, we characterize the form of the change in bird assemblages and species functional traits along an intensifying gradient of land use in the savanna biome in a historically homogeneous vegetation type in Phalaborwa, South Africa. A section of this vegetation type has been untransformed, and the remainder is now mainly characterized by urban and subsistence agricultural areas. Using morphometric, foraging and breeding functional traits of birds, we estimate functional diversity changes. Bird species richness and abundance are generally higher in urban and subsistence agricultural land uses, as well as in the habitat matrix connecting these regions, than in the untransformed area, a pattern mainly driven through species replacement. Functionally unique species, particularly ground nesters of large body size, were, however, less abundant in more utilized land uses. For a previously homogenous vegetation type, declines in the seasonality of energy availability under land-use change have led to an increase in local avian diversity, promoting the turnover of species, but reduced the abundance of functionally unique species. Although there is no simple relationship between land-use and diversity change, land-use change may suit some species, but such change may also involve functional homogenization.
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    Conservation biogeography of the Antarctic
    (Blackwell Publishing, 2012) Terauds, A.; Chown, S.L.; Morgan, F.; Peat, H.J.; Watts, D.J.; Keys, H.; Convey, P.; Bergstrom, D.M.
    Aim To present a synthesis of past biogeographic analyses and a new approach based on spatially explicit biodiversity information for the Antarctic region to identify biologically distinct areas in need of representation in a protected area network. Location Antarctica and the sub-Antarctic. Methods We reviewed and summarized published biogeographic studies of the Antarctic. We then developed a biogeographic classification for terrestrial conservation planning in Antarctica by combining the most comprehensive source of Antarctic biodiversity data available with three spatial frameworks: (1) a 200-km grid, (2) a set of areas based on physical parameters known as the environmental domains of Antarctica and (3) expert-defined bioregions. We used these frameworks, or combinations thereof, together with multivariate techniques to identify biologically distinct areas. Results Early studies of continental Antarctica typically described broad bioregions, with the Antarctic Peninsula usually identified as biologically distinct from continental Antarctica; later studies suggested a more complex biogeography. Increasing complexity also characterizes the sub-Antarctic and marine realms, with differences among studies often attributable to the focal taxa. Using the most comprehensive terrestrial data available and by combining the groups formed by the environmental domains and expert-defined bioregions, we were able to identify 15 biologically distinct, ice-free, Antarctic Conservation Biogeographic Regions (ACBRs), encompassing the continent and close lying islands. Main conclusions Ice-free terrestrial Antarctica comprises several distinct bioregions that are not fully represented in the current Antarctic Specially Protected Area network. Biosecurity measures between these ACBRs should also be developed to prevent biotic homogenization in the region.
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    A new specific plant host for the agave snout weevil, Scyphophorus acupunctatus Gyllenhal, 1838 (Coleoptera: Curculionidae) in South Africa: A destructive pest of species of Agave L. (Agavaceae)
    (2012) Smith, G.F.; Figueiredo, E.; Klopper, R.R.; Crouch, N.R.; Janion, C.; Chown, S.L.
    The widely distributed agave snout weevil, Scyphophorus acupunctatus Gyllenhal, is for the first time recorded from Agave salmiana Otto ex Salm-Dyck subsp. salmiana in South Africa. In its native habitat in Mexico, this new host plant species is one of the most important sources of pulque, a fermented alcoholic beverage. With efforts underway at Bothaville in the Free State Province, South Africa, to establish an agave nectar industry, commercial farmers should be made aware of the destruction that the agave weevil can cause, especially in concentrated populations and plantations of Agave L. species.
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    Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica
    (2012) Chown, S.L.; Huiskes, A.H.L.; Gremmen, N.J.M.; Lee, J.E.; Terauds, A.; Crosbie, K.; Frenot, Y.; Hughes, K.A.; Imura, S.; Kiefer, K.; Lebouvier, M.; Raymond, B.; Tsujimoto, M.; Ware, C.; van de Vijver, B.; Bergstrom, D.M.
    Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Year’s first season (2007–2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarctica’s climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios Scenario A1B [Nakic´enovic´ N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (∼33,054) are higher than those of scientists (∼7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides themeans tomitigate this threat now and into the future as the continent’s climate changes.
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    Variation in decomposition rates in the fynbos biome, South Africa: the role of plant species and plant stoichiometry
    (Springer Science+Business Media B.V., 2011) Bengtsson, J.; Janion, C.; Chown, S.L.; Leinaas, H.P.
    Previous studies in the fynbos biome of the Western Cape, South Africa, have suggested that biological decomposition rates in the fynbos vegetation type, on poor soils, may be so low that fire is the main factor contributing to litter breakdown and nutrient release. However, the fynbos biome also comprises vegetation types on more fertile soils, such as the renosterveld. The latter is defined by the shrub Elytropappus rhinocerotis, while the shrub Galenia africana may become dominant in overgrazed areas. We examined decomposition of litter of these two species and the geophyte Watsonia borbonica in patches of renosterveld in an agricultural landscape. In particular, we sought to understand how plant species identity affects litter decomposition rates, especially through variation in litter stoichiometry. Decomposition (organic matter mass loss) varied greatly among the species, and was related to litter N and P content. G. africana, with highest nutrient content, lost 65% of its original mass after 180 days, while E. rhinocerotis had lost ca. 30%, and the very nutrient poor W. borbonica \10%. Litter placed under G. africana decomposed slightly faster than when placed under E. rhinocerotis. Over the course of the experiment, G. africana and E. rhinocerotis lost N and P, while W. borbonica showed strong accumulation of these elements. Decomposition rates of G. africana and E. rhinocerotis were substantially higher than those previously reported from fynbos vegetation, and variation among the species investigated was considerable. Our results suggest that fire may not always be the main factor contributing to litter breakdown and nutrient release in the fynbos biome. Thus, biological decomposition has likely been underestimated and, along with small-scale variation in ecosystem processes, would repay further study.