Faculty of Science
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Item A Partially Articulated Cynodont Encased in a Putative Burrow Structure from the Cynognathus Subzone C(2015-10) Afonso, NadiaA sedimentary structure containing a fossilized therapsid, and bioglyphs on the surface morphology, was found during a field expedition to Cynognathus subzone-C in the Eastern Cape, South Africa. A combination of surface scanning, petrographic thin sections, bone mapping and anatomical comparison were used to determine the deposit type and taxonomic identity of the encased therapsid, and examine the implications for biostratigraphy and faunal assemblage of the Cynognathus Assemblage Zone. The deposit is hypothesized to be a portion of a cynodont burrow (burrow margin) that was constructed in fluvial sediment near a river bank. This is the first account of a burrow in subzone-C. Pattern and directionality analysis of the bioglyphs suggest that the bioglyphs are scratch marks made by the burrower during excavation. The scratch marks are mediolaterally narrow, with some exhibiting indentation marks, indicating that the tracemaker had mediolaterally narrow unguals at the distal phalanx (claws). Anomodonts and cynodonts were common burrowers during the Triassic, however comparisons of Thrinaxodon and Lystrosaurus scratch marks to the bioglyphs on this deposit suggests that the bioglyphs were likely constructed by a cynodont as anomodont unguals are laterally wider, and are unable to create mediolaterally narrow markings. The tracemaker is hypothesized to be closely related to Thrinaxodon based on scratch mark comparison. However, bioglyph published literature is limited, and therefore the tracemaker cannot be identified. The therapsid was identified as Diademodon based on cranial and dental morphology. There is limited published literature on Diademodon constructing and/or exploiting burrows, however the taphonomy suggests that the Diademodon was near the entrance or in the tunnel of burrow nearing/during death. This is the first account of Diademodon encased in a burrow.Item The consequences of replacing wildlife with livestock in Africa(Scientific Reports, 2017-12-01) Hempson, G.P.; Archibald, S.; Bond, W.J.The extirpation of native wildlife species and widespread establishment of livestock farming has dramatically distorted large mammal herbivore communities across the globe. Ecological theory suggests that these shifts in the form and the intensity of herbivory have had substantial impacts on a range of ecosystem processes, but for most ecosystems it is impossible to quantify these changes accurately. We address these challenges using species-level biomass data from sub-Saharan Africa for both present day and reconstructed historical herbivore communities. Our analyses reveal pronounced herbivore biomass losses in wetter areas and substantial biomass increases and functional type turnover in arid regions. Fire prevalence is likely to have been altered over vast areas where grazer biomass has transitioned to above or below the threshold at which grass fuel reduction can suppress fire. Overall, shifts in the functional composition of herbivore communities promote an expansion of woody cover. Total herbivore methane emissions have more than doubled, but lateral nutrient diffusion capacity is below 5% of past levels. The release of fundamental ecological constraints on herbivore communities in arid regions appears to pose greater threats to ecosystem function than do biomass losses in mesic regions, where fire remains the major consumer.Item Comparative studies need to rely both on sound natural history data and on excellent statistical analysis(Royal Society Publishing, 2017-09-20) Schradin, C.No abstract availableItem Carbon lost and carbon gained: a study of vegetation and carbon trade-offs among diverse land uses in Phoenix, Arizona(Ecological Society of America, 2017-03-01) Hall, S.J.; Majumdar, A.; McHale, M.R.; Grimm, N.B.Human modification and management of urban landscapes drastically alters vegetation and soils, thereby altering carbon (C) storage and rates of net primary productivity (NPP). Complex social and ecological processes drive vegetation cover in cities, leading to heterogeneity in C dynamics depending on regional climate, land use, and land cover. Recent work has demonstrated homogenization in ecological processes within human-dominated landscapes (the urban convergence hypothesis) in soils and biotic communities. However, a lack of information on vegetation in arid land cities has hindered an understanding of potential C storage and NPP convergence across a diversity of ecosystem types. We estimated C storage and NPP of trees and shrubs for six different land-use types in the arid metropolis of Phoenix, Arizona, USA, and compared those results to native desert ecosystems, as well as other urban and natural systems around the world. Results from Phoenix do not support the convergence hypothesis. In particular, C storage in urban trees and shrubs was 42% of that found in desert vegetation, while NPP was only 20% of the total NPP estimated for comparable natural ecosystems. Furthermore, the overall estimates of C storage and NPP associated with urban trees in the CAP ecosystem were much lower (8-63%) than the other cities included in this analysis. We also found that C storage (175.25-388.94 g/m2) and NPP (8.07-15.99 g·m-2·yr-1) were dominated by trees in the urban residential land uses, while in the desert, shrubs were the primary source for pools (183.65 g/m2) and fluxes (6.51 g·m-2·yr-1). These results indicate a trade-off between shrubs and trees in arid ecosystems, with shrubs playing a major role in overall C storage and NPP in deserts and trees serving as the dominant C pool in cities. Our research supports current literature that calls for the development of spatially explicit and standardized methods for analyzing C dynamics associated with vegetation in urbanizing areas.Item Variation by Geographic Scale in the Migration-Environment Association: Evidence from Rural South Africa(Federal Institute for Population Research, 2017) Hunter, L.M.; Leyk, S.; Maclaurin, G.J.; Nawrotzki, R.; Twine, W.; Erasmus, B.F.N.; Collinson, M.Scholarly understanding of human migration’s environmental dimensions has greatly advanced in the past several years, motivated in large part by public and policy dialogue around “climate migrants”. The research presented here advances current demographic scholarship both through its substantive interpretations and conclusions, as well as its methodological approach. We examine temporary rural South African outmigration as related to household-level availability of proximate natural resources. Such “natural capital” is central to livelihoods in the region, both for sustenance and as materials for market-bound products. The results demonstrate that the association between local environmental resource availability and outmigration is, in general, positive: households with higher levels of proximate natural capital are more likely to engage in temporary migration. In this way, the general findings support the “environmental surplus” hypothesis that resource security provides a foundation from which households can invest in migration as a livelihood strategy. Such insight stands in contrast to popular dialogue, which tends to view migration as a last resort undertaken only by the most vulnerable households. As another important insight, our findings demonstrate important spatial variation, complicating attempts to generalize migration-environment findings across spatial scales. In our rural South African study site, the positive association between migration and proximate resources is actually highly localized, varying from strongly positive in some villages to strongly negative in others. We explore the socio-demographic factors underlying this “operational scale sensitivity”. The cross-scale methodologies applied here offer nuance unavailable within more commonly used global regression models, although also introducing complexity that complicates story-telling and inhibits generalizability.Item Notes on the flowering and pollination of the endemic grassland Aloe reitzii var. reitzii (Asphodelaceae)(AOSIS (pty) Ltd, 2017) Symes, C.T.Aloe reitzii var. reitzii is a succulent with a restricted distribution in the montane grassland of eastern South Africa. It is a summer (late January-March) flowering succulent that grows on rocky outcrops at 1000 m-1600 m, and the conspicuous inflorescences suggest a pollination system focused towards birds. Objectives: To understand more about the pollination biology of A. reitzii var. reitzii. Methods: Nectar standing crop (flower volume and concentration) and the proportion of plants flowering were recorded. Camera traps and observations were used to record visitors to A. reitzii var. reitzii inflorescences. Results: Nectar volume was 36 μL ± 27 μL per flower (range 6 μL-93 μL; n = 27) and concentration was 16.5% ± 1.7% (range 13.5% - 19.5%). Camera trap observations, where 18.9% of all plants were observed flowering, recorded the three bird species Cape Weaver, Ploceus capensis, Malachite Sunbird, Nectarinia famosa and Greater Double-collared Sunbird, Cinnyris afer (60.4%, 27.1% and 12.5% of plant visits, respectively) visiting inflorescences. Conclusion: Because birds are important pollinators for many Aloe species, it is assumed that the bird species detected visiting A. reitzii var. reitzii are similarly important pollinators. At least 10 invertebrate species and sengi (Elephantulus sp.) were also recorded as visitors to flowers, but they may be less important pollinators than specialist and generalist avian nectarivores. This study provides further insight into the pollination biology of a diverse, and ecologically important, succulent genus in Africa.Item The sixth World Flora Online Council meeting held in South Africa(AOSIS (pty) Ltd, 2017) le Roux, M.; Klopper, R.; Jackson, P.S.W.; Loizeau, P.; Victor, J.E.; Sebola, J.R.Biannual Council meetings are held with the aim of developing a World Flora Online (WFO) in response to Target 1 of the Global Strategy for Plant Conservation (2011-2020). Objectives: To report on the sixth WFO Council meeting held in Pretoria, South Africa, on November 2016. Method: A WFO Council meeting (preceded by Taxonomic and Technical Working Group meetings) was hosted by the South African National Biodiversity Institute in Pretoria. Results: Significant progress with the development of the WFO portal was made. Conclusion: The WFO portal will be launched at the International Botanical Congress in China in 2017.Item Both thyroid hormone levels and resting metabolic rate decrease in African striped mice when food availability decreases(Company of Biologists Ltd, 2017-03) Rimbach, R.; Pillay, N.; Schradin, C.In response to variation in food availability and ambient temperature (Ta), many animals show seasonal adaptations in their physiology. Laboratory studies showed that thyroid hormones are involved in the regulation of metabolism, and their regulatory function is especially important when the energy balance of an individual is compromised. However, little is known about the relationship between thyroid hormones and metabolism in free-living animals and animals inhabiting seasonal environments. Here, we studied seasonal changes in triiodothyronine (T3) levels, resting metabolic rate (RMR) and two physiological markers of energy balance (blood glucose and ketone bodies) in 61 free-living African striped mice (Rhabdomys pumilio) that live in an semi-arid environment with food shortage during the dry season. We predicted a positive relationship between T3 levels and RMR. Further, we predicted higher T3 levels, blood glucose levels and RMR, but lower ketone body concentrations, during the moist season when food availability is high compared with summer when food availability is low. RMR and T3 levels were negatively related in the moist season but not in the dry season. Both RMR and T3 levels were higher in the moist than in the dry season, and T3 levels increased with increasing food availability. In the dry season, blood glucose levels were lower but ketone body concentrations were higher, indicating a change in substrate use. Seasonal adjustments in RMR and T3 levels permit a reduction of energy expenditure when food is scarce, and reflect an adaptive response to reduced food availability in the dry season.Item First limits on the very-high energy gamma-ray afterglow emission of a fast radio burst HESS observations of FRB 150418(EDP Sciences, 2017-01-01) Colafrancesco, S.; Jingo, M.; Shafi, N.; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Andersson, T.; Angüner, E. O.; Arakawa, M.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Chen, A.; Jingo, M.; Komin, N.; Shafi, N.Aims. Following the detection of the fast radio burst FRB150418 by the SUPERB project at the Parkes radio telescope, we aim to search for very-high energy gamma-ray afterglow emission. Methods. Follow-up observations in the very-high energy gamma-ray domain were obtained with the H.E.S.S. imaging atmospheric Cherenkov telescope system within 14.5 h of the radio burst. Results. The obtained 1.4 h of gamma-ray observations are presented and discussed. At the 99% C.L. we obtained an integral upper limit on the gamma-ray flux of Φγ(E > 350 GeV) < 1.33 × 10-8 m-2 s-1. Differential flux upper limits as function of the photon energy were derived and used to constrain the intrinsic high-energy afterglow emission of FRB 150418. Conclusions. No hints for high-energy afterglow emission of FRB 150418 were found. Taking absorption on the extragalactic background light into account and assuming a distance of z = 0.492 based on radio and optical counterpart studies and consistent with the FRB dispersion, we constrain the gamma-ray luminosity at 1 TeV to L < 5.1 × 1047 erg/s at 99% C.L.Item Characterizing the gamma-ray long-term variability of PKS2155 304 with HESS and Fermi-LAT(EDP Sciences, 2017-02) Chen, A.; Colafrancesco, S.; Jingo, M.; Collaboration, H.E.S.S.; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A.G.; Andersson, T.; Angüner, E.O.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Becker Tjus, J.; Berge, D.; Bernhard, S.; Komin, Nu.Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To this end, the long-term variability of the BL Lac object PKS 2155-304 is analyzed in the high (HE, 100 MeV < E < 300 GeV) and very high energy (VHE, E > 200 GeV) γ-ray domain. Over the course of ∼9 yr of H.E.S.S. observations the VHE light curve in the quiescent state is consistent with a log-normal behavior. The VHE variability in this state is well described by flicker noise (power-spectral-density index βVHE = 1.10-0.13 +0.10) on timescales larger than one day. An analysis of ∼5.5 yr of HE Fermi-LAT data gives consistent results (βHE = 1.20-0.23 +0.21), on timescales larger than 10 days) compatible with the VHE findings. The HE and VHE power spectral densities show a scale invariance across the probed time ranges. A direct linear correlation between the VHE and HE fluxes could neither be excluded nor firmly established. These long-term-variability properties are discussed and compared to the red noise behavior (β ∼ 2) seen on shorter timescales during VHE-flaring states. The difference in power spectral noise behavior at VHE energies during quiescent and flaring states provides evidence that these states are influenced by different physical processes, while the compatibility of the HE and VHE long-term results is suggestive of a common physical link as it might be introduced by an underlying jet-disk connection.