619 research outputs found
The unknown underworld : understanding soil health in South Africa
No full textCITATION: Louw, S. et al. 2014. The unknown underworld: understanding soil health in South Africa. South African Journal of Science, 110(5/6): 1-4, doi:10.1590/sajs.2014/a0064.The original publication is available at http://www.sajs.co.zaThe 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.http://www.sajs.co.za/unknown-underworld-understanding-soil-health-south-africa/schalk-v-d-m-louw-john-r-u-wilson-charlene-janion-ruan-veldtman-sarah-j-davies-matthew-addisonPublisher's versio
Are managed pollinators ultimately linked to the pollination ecosystem service paradigm?
No full textWei xing ji he qiao na mi jie gou de he cheng yu biao mian deng li ji yuan te xing yan jiu
No full textRuan, Qifeng = 衛星及核殼納米結構的合成與表面等離激元特性研究 / 阮琦鋒.Thesis Ph.D. Chinese University of Hong Kong 2015.Includes bibliographical references.Abstracts also in Chinese.Title from PDF title page (viewed on 16, December, 2016).Ruan, Qifeng = Wei xing ji he qiao na mi jie gou de he cheng yu biao mian deng li ji yuan te xing yan jiu / Ruan Qifeng
Measures, perceptions and scaling patterns of aggregated species distributions
No full textCITATION: Hui, C., Veldtman, R. & McGeoch, M. A. 2010. Measures, perceptions and scaling patterns of aggregated species distributions. Ecography, 33: 95-102, doi:10.1111/j.1600-0587.2009.05997.x.The original publication is available at https://onlinelibrary.wiley.comNon-random (aggregated) species distributions arise from habitat heterogeneity and nonlinear biotic processes. A
comprehensive understanding of the concept of aggregation, as well as its measurement, is pivotal to our understanding of
species distributions and macroecological patterns. Here, using an individual-based model, we analyzed opinions on the
concept of aggregation from the public and experts (trained ecologists), in addition to those calculated from a variety of
aggregation indices. Three forms of scaling patterns (logarithmic, power-law and lognormal) and four groups of scaling
trajectories emerged. The experts showed no significant difference from the public, although with a much lower deviation.
The public opinion was partially influenced by the abundance of individuals in the spatial map, which was not found in
the experts. With the increase of resolution (decrease of grain), aggregation indices showed a general trend from
significantly different to significantly similar to the expert opinion. The over-dispersion index (i.e. the clumping
parameter k in the negative binomial distribution) performed, at certain scales, as the closest index to the expert opinion.
Examining performance of aggregation measures from different groups of scaling patterns was proposed as a practical way
of analyzing spatial structures. The categorization of the scaling patterns of aggregation measures, as well as their over- and
in-sensitivity towards spatial structures, thus not only provides a potential solution to the modifiable areal unit problem,
but also unveils the interrelationship among the concept, measures and perceptions of aggregated species distributions.The authors are grateful to Stuart H.
Hurlbert, Steven L. Chown, Peter C. le Roux, Jesse M. Kalwij,
Lars B. Pettersson, Pedro Peres-Neto, Joaquı´n Hortal and two
anonymous referees for comments and discussions, thankful to
colleagues and other persons who completed the survey. Support
from the DST-NRF Centre of Excellence for Invasion Biology,
Claude Leon Foundation and the NRF Blue Skies Programme is
acknowledged.https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0587.2009.05997.xPublisher's versio
The ecology of southern African wild silk moths (Gonometa species, Lepidoptera: Lasiocampidae): consequences for their sustainable use
No full textThesis (DPhil (Entomology))--University of Pretoria, 2007.The pupal cocoons of two southern African wild silkmoth species, Gonometa postica and G. rufobrunnea (Lepidoptera: Lasiocampidae), are composed of high quality silk and have potential as a commercially viable resource. However, limited ecological research has been done on these species, and their population dynamics is especially poorly known. A steady and predictable supply of cocoons is paramount to the economic sustainability of a wild silk industry. There is thus an urgent need for documenting and understanding the population dynamics of southern Africa’s Gonometa species. Here, the temporal and spatial variation of pupal (and thus cocoon) abundance, as well as associated natural enemies, are described for both Gonometa species for the first time. The larval parasitoid species emerging from parasitised pupae were quantitatively associated with species-specific emergence holes, making field-identification of these species possible. Eleven sites in total were sampled, over four generations, across the region where both species have historically reached high population densities. Apparent spatial synchrony in pupal abundance found between sites suggests that climate is responsible for observed population size fluctuations. As predicted from their life history traits, temporal variability was lower than expected for classically eruptive species. Gonometa species thus have an intermediate position on the population dynamics gradient. In turn, the responses of natural enemies were not predictable from Gonometa species defensive traits, but appear to be mediated by between-species cocoon strength differences. Using data on the number of G. postica pupae per tree and associated parasitism at several sites, the importance of the degree of spatial explicitness in the quantification of aggregation and the detection of density dependence was illustrated. The spatially explicit method gave different results and more information regarding the spatial pattern of pupal abundance and parasitism than non- and semi-explicit methods. Similarly, the detection of density dependence in parasitism rates was affected by the use of spatially explicit data, with the spatial explicit approach giving different and more biologically informative results than traditional, non-spatially explicit methods. This has marked implications for previous insect-host - parasitoid studies aimed at detecting density dependence. The variability in cocoon size, a surrogate for larval performance, adult fecundity and silk yield, revealed that gender, followed by species, contributed most to observed size differences, with no clear differences between generations or localities. Finally, the between-host plant and withinhost plant distribution ofG. postica and G. rufobrunnea pupae was quantified, chiefly investigating the deterministic nature of the choice of pupation site. The distribution of both species at these scales was found to be markedly non-random, with pupae generally preferring specific tree characteristics and micro-sites. These results now provide the basis for recommending an appropriate utilisation strategy for southern Africa’s wild silk moths. Based on the spatial and temporal variability in pupal abundance observed, a constant and predictable cocoon supply for natural harvesting is unlikely. Long-term, broad-scale documentation of Gonometa species population cycles may make it possible to predict cocoon availability in the future. Until such research is done, it is recommended that the current practise of only collecting cocoons from which moths have emerged be continued. Simultaneously, artificial rearing and seeding as alternative utilisation strategies should be experimentally explored based on the information gathered and patterns identified here.Zoology and Entomologyunrestricte
CUHK electronic theses & dissertations collection
No full textRuan, Pengfei.Thesis M.Phil. Chinese University of Hong Kong 2015.Includes bibliographical references (leaves 33-35).Abstracts also in Chinese.Title from PDF title page (viewed on 18, November, 2016)
On the distribution and ecology of the African wild silk moth, Gonometa
No full textDissertation (MSc (Plant Ecology))--University of Pretoria, 2015.The African wild silk moths, Gonometa postica and G. rufobrunnea are a valuable natural resource in southern and East Africa because of the high quality silk fibre derived from their cocoons. However, using these species for commercial silk production has proven problematic because of the sporadic and unpredictable nature of Gonometa outbreaks. Moreover, little is known about the ecology and distribution of the Gonometa species.
The first part of this study focussed on the importance of moth-host plant interactions, in addition to climatic variables, in determining the species’ current regional distributions, using species distribution modelling (SDM). Based on recent studies which have documented the importance of biotic interactions in shaping broad-scale species distributions, I expected moth-host plant interactions to be an important predictor of Gonometa species distributions because of the species’ dependencies on host plants for survival. Contrary to expectation, my results showed that models’ predictive power did not improve following the inclusion of moth-host plant interactions. Biotic and abiotic models predicting G. postica distribution performed fairly well, but all models predicting G. rufobrunnea distribution performed poorly. Nonetheless, host plant distributions contributed significantly to SDMs of large-scale Gonometa distributions, along with annual mean temperature, annual precipitation and precipitation seasonality. Host plant distribution also appeared to limit Gonometa species distributions, suggesting that the effect of host tree occurrence patterns on Gonometa species distributions should not be ignored. The idea that climate drives large-scale species distributions was supported, but host plant occurrence also had an effect on Gonometa species distributions.
The second focus of this study was the potential ecosystem engineering effect created by G. postica (via its cocoons) for other invertebrates. Arboreal ants are known to use a wide variety of plant structures as potential nesting sites, including structures created by arboreal ecosystem engineers. However, ant nest site selection in arboreal systems is poorly understood. I observed, for the first time, ants using empty G. postica cocoons as shelter and nesting sites on the myrmecophilic tree Vachellia erioloba. I examined cocoon selection by these ants and tested whether selection was based on cocoon characteristics. Cocoons were predominantly occupied by one dominant ant species, but in some cases simultaneously by two ant species. Ant abundance and occurrence were positively related to cocoon size, the presence of scale insects on branches of the trees and cocoon entrance hole type (i.e. cocoons containing only small parasite holes), and negatively influenced by cocoon occupancy by other invertebrates. This suggested that ants select G. postica cocoons based on specific cocoon characteristics, and revealed a novel ecological role of the moth-host plant interaction at alocal-scale, where the product of this interaction (i.e. cocoon production) appeared to benefit arboreal invertebrates. Empty G. postica cocoons probably create a new, favourable habitat for ants. Thus, G. postica acts as autogenic ecosystem engineer in arboreal habitats.
This study highlighted the importance of Gonometa-host plant interactions in shaping large-scale Gonometa species distributions, but also showed that these interactions may play a role in the abundance and distribution of arboreal species at local scales.Plant ScienceMSc (Plant Ecology)Unrestricte
Behavioural response of honeybees (Apis mellifera scutellata Lep.) to wild pollinators on sunflowers (Helianthus annuus L.)
No full textDissertation (MScAgric)--University of Pretoria, 2010.Pollination is an essential ecosystem service, increasing reproductive success of many crops, which can be provided by managed pollinators, wild bees (including honeybees) and other insect pollinators. However, the pollination services and the economic value of wild pollinators are often underestimated. Better understanding of the factors that influence honeybee foraging behaviour and pollination efficiency can contribute to the improvement of management practices that aim to enhance crop pollination and ecosystem services. The objectives of this study were to investigate the importance of managed honeybees and wild honeybees to sunflower pollination as well as to evaluate the response of honeybees to different levels of floral rewards and to behavioural interactions with wild flower visitors. The study was conducted in 16 commercial sunflower farms and one experimental farm of South Africa during the 2009 sunflower flowering season. The results showed that insects, particularly honeybees, were efficient pollinators, improving sunflower production in all self-fertile sunflower cultivars used in this study. Furthermore, wild honeybee colonies were found to be as efficient as managed honeybee colonies in sunflower pollination near to natural habitat. Both sunflower yield and the abundance of pollinators decreased with distance from natural habitat, suggesting that sunflower yield is directly correlated with the abundance of pollinators. The amount of nectar present in the florets of sunflower significantly affected pollinator behaviour, influencing honeybee visitation length and foraging rate which prefer to exploit floral rewards from the same source if they find the higher amount per foraging trip, possibly having a negative impact on cross-pollination. Moreover, the concentration of nectar collected from honeybees was significantly lower than the nectar concentration from florets, suggesting that honeybees diluted highly concentrated sunflower nectar with their saliva to their optimum concentration level. Interspecific exploitative competition between honeybees and wild pollinators (wild bees, butterflies and moths) significantly increased the movement of honeybees among sunflower heads, which enhances cross-pollination. Furthermore, behavioural interactions influenced the length of foraging time spent by individual honeybees per sunflower head. Butterflies were the most influential in enhancing honeybee foraging movement, followed by wild bees and then moths. The importance of a given flower visitor species to honeybee movement is likely related to the size of the visitor, as the bigger size of butterflies and movement of their wings increases the chance of disturbing a neighbouring honeybee. Conservation of natural habitat is important to maintain the diversity of flower visitors which indirectly contribute to crop production by enhancing honeybee foraging activity and consequent direct pollination service. Furthermore, the pollination effectiveness of wild pollinators, density of wild honeybees surrounding sunflower fields and effects of human activities on pollination disruption are suggested as topics for future research.Zoology and Entomologyunrestricte
Witten's D4 Integrable Hierarchies Conjecture
No full textThe authors prove that the total descendant potential functions of the theory of Fan-Jarvis-Ruan-Witten for D-4 with symmetry group < J > and for D-4(T) with symmetry group G(max), respectively, are both tau-functions of the D-4 Kac-Wakimoto/Drinfeld-Sokolov hierarchy. This completes the proof, begun in the article by Fan-Jarvis-Ruan (2013), of the Witten Integrable Hierarchies Conjecture for all simple (ADE) singularities.the National Natural Science Foundation of China; the National Security Agency of USA; the Doctoral Fund of the Ministry of Education of ChinaSCI(E)中国科技核心期刊(ISTIC)中国科学引文数据库(CSCD)[email protected]; [email protected]; [email protected]; [email protected]; [email protected]
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