Browsing by Author "Janion, Charlene"

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    Critical thermal limits depend on methodological context
    (Royal Society of Publishing, 2007) Terblanche, John S.; Deere, Jacques A.; Clusella-Trullas, Susana; Janion, Charlene; Chown, Steven L.
    A full-factorial study of the effects of rates of temperature change and start temperatures was undertaken for both upper and lower critical thermal limits (CTLs) using the tsetse fly, Glossina pallidipes. Results show that rates of temperature change and start temperatures have highly significant effects on CTLs, although the duration of the experiment also has a major effect. Contrary to a widely held expectation, slower rates of temperature change (i.e. longer experimental duration) resulted in poorer thermal tolerance at both high and low temperatures. Thus, across treatments, a negative relationship existed between duration and upper CTL while a positive relationship existed between duration and lower CTL. Most importantly, for predicting tsetse distribution, G. pallidipes suffer loss of function at less severe temperatures under the most ecologically relevant experimental conditions for upper (0.06°C min -1; 35°C start temperature) and lower CTL (0.06°C min -1; 24°C start temperature). This suggests that the functional thermal range of G. pallidipes in the wild may be much narrower than previously suspected, approximately 20-40°C, and highlights their sensitivity to even moderate temperature variation. These effects are explained by limited plasticity of CTLs in this species over short time scales. The results of the present study have broad implications for understanding temperature tolerance in these and other terrestrial arthropods. © 2007 The Royal Society.
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    The genus Ectonura Cassagnau, 1980 in South Africa (Collembola, Neanuridae, Neanurinae), with a key to South African Neanurinae
    (Pensoft, 2011-10) Janion, Charlene; Bedos, Anne; Deharveng, Louis
    Two new species of Neanurinae (Collembola) are described from the Western Cape, South Africa: Ectonura monochaeta sp. n. and Ectonura barrai sp. n. E. monochaeta sp. n. differs from other species in the genus by its strongly reduced chaetotaxy, and the lateral shift of dorso-internal chaetae on Abd. V and their integration in the tubercles (De+DL). E. barrai sp. n. is similar to E. natalensis (Womersley, 1934), but differs in chaetotaxic details and chaetal group arrangement. A key to the seven species of Neanurinae recorded from South Africa is given.
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    A new species and first record of the genus Triacanthella Schaffer, 1897 (Collembola, Poduromorpha, Hypogastruridae) for Africa
    (Pensoft, 2012) Janion, Charlene; D'Haese, Cyrille A.; Deharveng, Louis
    The first species of the genus Triacanthella to be recorded from Africa is described. Triacanthella madiba sp. n. belongs to the Southern Hemisphere group of the genus. It is morphologically closely related to T. vogeli Weiner & Najt, 1997 from Chile, and appears to be a gondwanian relict. The new species is also the first Triacanthella recorded from a guano habitat.
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    Springtail diversity in South Africa
    (Academy of Science of South Africa (ASSAf), 2011-11) Janion, Charlene; Bedos, Anne; Bengtsson, Jan; Deharveng, Louis; Janse Van Vuuren, Bettine; Leinaas, Hans Petter; Liu, Amy; Malmstrom, Anna; Porco, David; Chown, Steven L.
    Despite their significance in soil ecosystems and their use for investigations of soil ecosystem functioning and in bioindication elsewhere, springtails (Collembola) have not been well investigated in South Africa. Early recognition of their role in soil systems and sporadic systematic work has essentially characterised knowledge of the southern African fauna for some time. The situation is now changing as a consequence of systematic and ecological work on springtails. To date this research has focused mostly on the Cape Floristic Region and has revealed a much more diverse springtail fauna than previously known (136 identifiable species and an estimated 300 species for the Cape Floristic Region in total), including radiations in genera such as the isotomid Cryptopygus. Quantitative ecological work has shown that alpha diversity can be estimated readily and that the group may be useful for demonstrating land use impacts on soil biodiversity. Moreover, this ecological work has revealed that some disturbed sites, such as those dominated by Galenia africana, may be dominated by invasive springtail species. Investigation of the soil fauna involved in decomposition in Renosterveld and Fynbos has also revealed that biological decomposition has likely been underestimated in these vegetation types, and that the role of fire as the presumed predominant source of nutrient return to the soil may have to be re-examined. Ongoing research on the springtails will provide the information necessary for understanding and conserving soils: one of southern Africa’s major natural assets.
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    Springtail diversity in the Cape floristic region
    (Stellenbosch : Stellenbosch University, 2013-03) Janion, Charlene; Scheepers, Charlene; Chown, Steven L.; Bengtsson, Jan; Deharveng, Louis; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Understanding the distribution, abundance and diversity of species and the mechanisms causing these patterns has been the interest of ecologists and taxonomists for decades. The exceptionally high plant diversity in the Fynbos biome has been well studied. Whilst early arguments suggested that the high plant diversity is not reflected in the arthropod diversity and that insect species richness is low compared to other comparable areas, these observations might have been hampered by the taxonomic impediment. Despite global recognition of the significance of this below-ground component of diversity for ecosystem functioning, soil is one of the most poorly studied habitats of terrestrial ecosystems. Although knowledge is increasing for epigaeic groups, other significant groups such as the Collembola remain especially poorly understood. This thesis starts addressing this serious gap in knowledge concerning the below-ground component of biodiversity in the Fynbos biome and the effects of landscape transformation thereon. As part of the work, considerable attention was given to resolving the taxonomic impediment for the springtail fauna of the Fynbos biome using modern morphological and DNA barcoding methods, while also examining the correlates of soil animal diversity in the biome, by using Collembola (springtails) as exemplars. First, using a combination of published records of Collembola from South Africa, various sampling methods and DNA barcoding, a species list is compiled for the Western Cape. Currently 213 species are known to exist from the Western Cape. A high level of cryptic diversity was also found in several genera, together with several potential species radiations in the Ectonura, Seira, Parisotoma and Cryptopygus. A start is a made at addressing the lack of taxonomic knowledge by describing five new species. Two Ectonura Cassagnau 1980 species are described from Betty’s Bay and Grootvadersbosch respectively and a key to the Neanurinae of South Africa is provided. The first record of the genus Triacanthella Schäffer, 1897 is described from a cave in Table Mountain, while two new species of Delamarephorura are described and the genera Spicatella Thibaud 2002 and Delamarephorura Weiner & Najt 1999 are synonymized. Although fire is thought to be the main form of decomposition in the Fynbos biome, recent work has shown that biological decomposition may be more important than previously thought. I examine the resilience of Collembola after a large-scale fire in Jonkershoek Nature Reserve using quantitative sampling which is temporally replicated. The resilience of invertebrate fauna in the fynbos is not well understood, thus I investigate the diversity of Collembola before and after a major fire. Results show Collembola species richness and abundance recovered surprisingly quickly after the fire. On a larger scale, litterbags were deployed at six sites across the Western Cape using different litter types. Here, a total of 113 morphospecies species was found. Local richness was found to be highest in Kogelberg (32 species), while the turnover between sites was also high. Thus, the degradation of local habitat patches will be as much of a threat to Collembola as to the endemic plants in this region.
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    The unknown underworld : understanding soil health in South Africa
    (Academy of Science of South Africa, 2014-05) Louw, Schalk v. d. M.; Wilson, John R. U.; Janion, Charlene; Veldtman, Ruan; Davies, Sarah J.; Addison, Matthew
    The need to provide food security to a growing human population in the face of global threats such as climate change, land transformation, invasive species and pollution is placing increasing pressure on South African soils. South Africa is losing an estimated 300–400 million tonnes of soil annually, while soil degradation is a major threat to agricultural sustainability. In spite of these problems, treatment of soil health in biodiversity assessment and planning in South Africa has been rudimentary to date.