A fuzzy classification technique for predicting species' distributions: applications using invasive alien plants and indigenous insects
- Authors: Robertson, Mark P , Villet, Martin H , Palmer, Anthony R
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6897 , http://hdl.handle.net/10962/d1011659 , http://dx.doi.org/10.1111/j.1366-9516.2004.00108.x
- Description: A new predictive modelling technique called the fuzzy envelope model (FEM) is introduced. The technique can be used to predict potential distributions of organisms using presence-only locality records and a set of environmental predictor variables. FEM uses fuzzy logic to classify a set of predictor variable maps based on the values associated with presence records and combines the results to produce a potential distribution map for a target species. This technique represents several refinements of the envelope approach used in the BIOCLIM modelling package. These refinements are related to the way in which FEMs deal with uncertainty, the way in which this uncertainty is represented in the resultant potential distribution maps, and the way that these maps can be interpreted and applied. To illustrate its potential use in biogeographical studies, FEM was applied to predicting the potential distribution of three invasive alien plant species (Lantana camara L., Ricinus communis L. and Solanum mauritianum Scop.), and three native cicada species (Capicada decora Germar, Platypleura deusta Thun. and P. capensis L.) in South Africa, Lesotho and Swaziland. These models were quantitatively compared with models produced by means of the algorithm used in the BIOCLIM modelling package, which is referred to as a crisp envelope model (the CEM design). The average performance of models of the FEM design was consistently higher than those of the CEM design. There were significant differences in model performance among species but there was no significant interaction between model design and species. The average maximum kappa value ranged from 0.70 to 0.90 for FEM design and from 0.57 to 0.89 for the CEM design, which can be described as 'good' to 'excellent' using published ranges of agreement for the kappa statistic. This technique can be used to predict species' potential distributions that could be used for identifying regions at risk from invasion by alien species. These predictions could also be used in conservation planning in the case of native species.
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- Date Issued: 2004
An analysis of automatically scaled F1 layer data over Grahamstown, South Africa
- Authors: Jacobs, Linda , Poole, Allon W V , McKinnell, Lee-Anne
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6808 , http://hdl.handle.net/10962/d1004194
- Description: This paper describes an analysis of automatically scaled F1 layer data over Grahamstown, South Africa (33.3°S, 26.5°E). An application for real time raytracing through the South African ionosphere was identified, and for this application real time evaluation of the electron density profile is essential. Raw real time virtual height data are provided by a Lowell Digisonde (DPS), which employs the automatic scaling software, ARTIST whose output includes the virtual-to-real height data conversion. Experience has shown that there are times when the raytracing performance is degraded because of difficulties surrounding the real time characterisation of the F1 region by ARTIST. The purpose of this investigation is to establish the extent of the problem, the times and conditions under which it occurs, with a view to formulating remedial alternative strategies, such as predictive modelling.
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- Date Issued: 2004
Endothermy in African Platypleurine Cicadas: the influence of body size and habitat (Hemiptera: Cicadidae)
- Authors: Sanborn, Allen F , Villet, Martin H , Phillips, Polly K F
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6925 , http://hdl.handle.net/10962/d1011912
- Description: The platypleurine cicadas have a wide distribution across Africa and southern Asia. We investigate endothermy as a thermoregulatory strategy in 11 South African species from five genera, with comparisons to the lone ectothermic platypleurine we found, in an attempt to ascertain any influence that habitat and/or body size have on the expression of endothermy in the platypleurine cicadas. Field measurements of body temperature (Tb) show that these animals regulate Tb through endogenous heat production. Heat production in the laboratory elevated Tb to the same range as in animals active in the field. Maximum Tb measured during calling activity when there was no access to solar radiation ranged from 13.2° to 22.3°C above ambient temperature in the five species measured. The mean Tb during activity without access to solar radiation did not differ from the mean Tb during diurnal activity. All platypleurines exhibit a unique behavior for cicadas while warming endogenously, a temperature- dependent telescoping pulsation of the abdomen that probably functions in ventilation. Platypleurines generally call from trunks and branches within the canopy and appear to rely on endothermy even when the sun is available to elevate Tb, in contrast to the facultative endothermy exhibited by New World endothermic species. The two exceptions to this generalization we found within the platypleurines are Platypleura wahlbergi and Albanycada albigera, which were the smallest species studied. The small size of P. wahlbergi appears to have altered their thermoregulatory strategy to one of facultative endothermy, whereby they use the sun when it is available to facilitate increases in Tb. Albanycada albigera is the only ectothermic platypleurine we found. The habitat and host plant association of A. albigera appear to have influenced the choice of ectothermy as a thermoregulatory strategy, as the species possesses the metabolic machinery to elevate to the Tb range observed in the endothermic species. Therefore, size and habitat appear to influence the expression of thermoregulatory strategies in African platypleurine cicadas.
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- Date Issued: 2004
In situ feeding rates of the copepods, Pseudodiaptomus hessei and Acartia longipatella, in a temperate, temporarily open/closed Eastern Cape estuary
- Authors: Froneman, P William
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6901 , http://hdl.handle.net/10962/d1011754
- Description: Size-fractionated chlorophyll-a (chl-a) concentrations and the in situ grazing rates of the copepods, Pseudodiaptomus hessei and Acartia longipatella, were assessed seasonally at the temporarily open/closed Kasouga estuary situated along the southeast coast of southern Africa. Total integrated chl-a concentration ranged between 1.17 and 12.18 mg chl-a m^(–3) and was always dominated by small phytoplankton cells (<20 μm), which comprised up to 86% (range 64–86%) of the total pigment. Total zooplankton abundance ranged between 2676 and 62 043 individuals m^(–3). These copepods numerically dominated the zooplankton counts, accounting for between 79% and 91% of the total. Gut pigment concentrations of the two species at night were significantly higher than the daytime values (P<0.05 in all cases). The observed pattern could be related to the marked diurnal vertical migration patterns exhibited by the copepods. Gut evacuation rates of P. hessei during the study ranged between 0.29 and 0.77 h^(–1) and between 0.39 and 0.58 h^(–1) for A. longipatella. The rate of gut pigment destruction for P. hessei and A. longipatella ranged between 55% and 81% and between 88% and 92% of the total chl-a ingested, respectively. The combined grazing impact of the two copepods ranged between 0.65 and 4.37 mg chl-a m^(–3), or between 4.3% and 35.9% of the available chl-a in the water column. Variations in the grazing activity of the two species could be attributed largely to seasonality in water temperature and shifts in the phytoplankton community structure and zooplankton abundance.
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- Date Issued: 2004
Making sense of science through two languages: a South African case study
- Authors: Probyn, Margie J
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:7025 , http://hdl.handle.net/10962/d1007209
- Description: Mzamo Senior Secondary School (not its real name) looks like any typical township school in South Africa: modern face-brick classroom blocks which conceal a serious lack of resources, material and human. Under apartheid the disparities in spending on white and African students meant hugely different teaching and learning contexts - including infrastructure, teacher training, pupil: teacher ratios and teaching materials. Today, 10 years into the new democracy and despite government’s efforts to equalize spending, the historic inequalities persist. The school is surrounded by township houses and shacks that reflect the high poverty levels in the Eastern Cape Province. Students at schools like this face an additional but less obvious problem – that of the language medium. Although in the Eastern Cape, Xhosa is the home language of 83,8% of the population and English speakers comprise only 3.7%, the official language medium in schools is English from the beginning of Grade 4 in the majority of schools. South Africa is a multilingual country with 11 official languages recognized in the Constitution of 1996 – 9 indigenous languages and the two colonial languages, English and Afrikaans.
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- Date Issued: 2004
Pre-emigration reflections : Afrikaans speakers moving to New Zealand
- Authors: De Klerk, Vivian A , Barkhuizen, Gary
- Date: 2004
- Language: English
- Type: Article , text
- Identifier: vital:6138 , http://hdl.handle.net/10962/d1011590
- Description: This article reports on the pre-emigration reflections of 15 Afrikaans speakers, all of whom were in the final stages of preparing to emigrate to New Zealand. The study explores the linguistic histories of the participants, their attitudes to their mother tongue (Afrikaans) and to English, and their views on South Africa's language policy and how it has influenced their decisions to leave the country. The paper also offers a view on possible long-term linguistic outcomes for these families.
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- Date Issued: 2004
Recent African derivation of Chrysomya putoria from C. chloropyga and mitochondrial DNA paraphyly of cytochrome oxidase subunit one in blowflies of forensic importance
- Authors: Wells, J D , Lunt, N , Villet, Martin H
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6888 , http://hdl.handle.net/10962/d1011648
- Description: Chrysomya chloropyga (Wiedemann) and C. putoria (Wiedemann) (Diptera: Calliphoridae) are closely related Afrotropical blowflies that breed in carrion and latrines, reaching high density in association with humans and spreading to other continents. In some cases of human death, Chyrsomya specimens provide forensic clues. Because the immature stages of such flies are often difficult to identify taxonomically, it is useful to develop DNA-based tests for specimen identification. Therefore we attempted to distinguish between C. chloropyga and C. putoria using mitochondrial DNA (mtDNA) sequence data from a 593-bp region of the gene for cytochrome oxidase subunit one (COI). Twelve specimens from each species yielded a total of five haplotypes, none being unique to C. putoria. Therefore it was not possible to distinguish between the two species using this locus. Maximum parsimony analysis indicated paraphyletic C. chloropyga mtDNA with C. putoria nested therein. Based on these and previously published data, we infer that C. putoria diverged very recently from C. chloropyga.
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- Date Issued: 2004
Science after a century at Rhodes University
- Authors: Woods, D R
- Date: 2004
- Language: English
- Type: Article , text
- Identifier: vital:7123 , http://hdl.handle.net/10962/d1006584
- Description: Rhodes Centenary issue , The small University of Rhodes (6142 students), in the rural city of Grahamstown, was established in 1904 as a result of a £50 000 grant from the Rhodes Trust in Oxford. It grew out of St Andrew’s College, which provided the first four professors and 41 students. The first paper from Rhodes in the South African Journal of Science (then called the Report of the South African Association for the Advancement of Science) was by Selmar Schonland, one of the university’s founding fathers. Entitled: ‘Biological and ethnological observations on a trip to the N.E. Kalahari’, it appeared in 1904. The following pages provide a glimpse into the growth and achievements of various departments in the faculties of Science and Pharmacy and associated institutes a century after the university was born.
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- Date Issued: 2004
The development of a toxicity database using freshwater macroinvertebrates, and its application to the protection of South African water resources
- Authors: Palmer, Carolyn G , Muller, Wilhelmine J , Gordon, Andrew K , Scherman, Patricia A , Davies-Coleman, Heather D , Pakhomova, L , de Kock, E
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:7073 , http://hdl.handle.net/10962/d1009528
- Description: There is a growing international trend towards the protection of freshwater resources from pollution by imposing instream guidelines and specified waste-discharge conditions. Current methods for devising freshwater quality guidelines are based on species sensitivity distributions (SSDs) that are used to identify pollutant concentrations, ensuring the protection of a modelled percentage of species (95% protection is a common goal). SSDs are derived from the toxicity test results of as many taxa as possible for each polluting substance. Waste-discharge licences can be for single substances, specified in terms of chemical concentrations, and derived in conjunction with instream guidelines; or for complex mixtures, specified in terms of toxic units. In both cases toxicity test results are the core data used. The emphasis on SSDs calls into question the species constituting the test populations. It is likely that SSDs based in part on the responses of local organisms will achieve superior site-specific ecological protection. Until the early 1990s, there were very few data on the tolerances of South African freshwater organisms. In the intervening decade, the Unilever Centre for Environmental Water Quality at Rhodes University has developed a toxicity database that, to date, records the responses of 21 South African freshwater taxa to 26 single-substance pollutants or mixtures. This is the most comprehensive database of South African toxicity responses available and has been used in the drawing up of methods and guidelines to protect water resources. This paper aims to make these data available and to describe applications of the data using selected case studies.
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- Date Issued: 2004
The wing coupling apparatus and the morphometric analysis of honeybee populations
- Authors: Hepburn, H Randall , Radloff, Sarah E
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:6904 , http://hdl.handle.net/10962/d1011760
- Description: Significant differences between countries were found in the distribution of the number of hamuli within Apis andreniformis, A. florea, A. cerana and A. koschevnikovi. The mean hamuli numbers for Apis mellifera intermissa differed significantly among localities in Algeria. Significant differences in intercolonial variability between countries were found within A. cerana. There was no significant infraspecific variability within A. andreniformis, A. florea, A. koschevnikovi and A. m. intermissa. Significant differences in the mean number of hamuli occur between A. m. intermissa and A. andreniformis, A. florea and A. cerana; also between A. cerana/A. koschevnikovi and A. andreniformis and A. florea. Significant differences were found in the distribution and variability of the number of hamuli between species (populations). The mean numbers of hamuli for A. andreniformis differed from those of A. florea. Both these population means differed from those of A. cerana, A. koschevnikovi and A. m. intermissa. No significant differences were found between A. cerana and A. koschevnikovi. When the analysis included data for A. dorsata, A. nigrocincta, A. m. carnica, A. m. caucasica and A. m. ligustica, the results showed significant differences in hamuli numbers between A. andreniformis/A. florea and A. cerana/A. koschevnikovi/A. nigrocincta and A. m. intermissa/A. m. carnica/A. m. caucasica/A. m. ligustica. Hamuli numbers in A. dorsata significantly differed from those of other populations except A. m. intermissa. These results show that hamuli numbers are useful in the classification of honeybee populations. Whether hamuli would be useful in multivariate analysis depends on the correlation between the number of hamuli and the other characters used.
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- Date Issued: 2004
Three decades of hydrological modelling research in South Africa
- Authors: Hughes, Denis A
- Date: 2004
- Language: English
- Type: text , Article
- Identifier: vital:7072 , http://hdl.handle.net/10962/d1009526
- Description: This paper presents a review of the research undertaken in the field of hydrological modelling over roughly the last three decades, concentrating primarily on South African work in an international context. The focus is on deterministic, rainfall-runoff models and addresses issues related to model design as well as to the application of models in practice. I provide a brief description of what hydrological models are and what they are used for and discuss also the following issues: • Developments in understanding hydrological process and the extent to which these have filtered down into models. • Model calibration and parameter estimation. • Trends in data availability and how these have affected model development. • Trends in computer technology and their impacts on model development. I suggest that there have been substantial developments in the science and practice of hydrological modelling, but that there remain many problems that need to be addressed to improve the ability of models to contribute to the solution of problems of water resource management. Southern African scientists have contributed to the body of knowledge on hydrological modelling, despite the limited resources available compared to resources elsewhere. Internationally, the focus has not always been on the practical issues of model application and has commonly tended towards the more theoretical and mathematical issues of model calibration. This is not a trend that has found much favour in southern Africa (particularly amongst research funding agencies), where there are many problems of water resource management that have the potential to be resolved with existing models, applied in an appropriate way. The paper concludes by suggesting that further research needs to focus on the integration of the best in international developments with the tried and tested models that have been developed locally. The context of this research should be the search for more reliable estimations of water resource availability.
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- Date Issued: 2004