Swashed away? Storm impacts on sandy beach macrofaunal communities     

Linda Harris  Ronel Nel  David Schoeman 《Estuarine, Coastal and Shelf Science》2011,94(3):210-221

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The dictionary of human geography, 5th edition – Edited by Derek Gregory,Ron Johnston,Geraldine Pratt,Michael J. Watts and Sarah Whatmore     

Etienne Nel 《New Zealand geographer》2010,66(3):234-236

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Effect of rare disaster risks on crude oil: evidence from El Niño from over 145 years of data     

Demirer  Riza  Gupta  Rangan  Nel  Jacobus  Pierdzioch  Christian 《Theoretical and Applied Climatology》2022,147(1-2):691-699

Theoretical and Applied Climatology - We extend the literature on the effect of rare disaster risks on commodities by examining the effect of the El Niño-Southern Oscillation (ENSO) on crude...  相似文献   

Measuring species richness on sandy beach transects: extrapolative estimators and their implications for sampling effort   总被引：1，自引：0，他引：1  

David S Schoeman  Ronel Nel  & Alexandre Goulart Soares 《Marine Ecology》2008,29(S1):134-149

Species richness is a measure that is fundamental to many studies in ecology, and it is particularly important on sandy beaches, where it underlies patterns described by the broadly accepted swash exclusion hypothesis. However, its estimation in practice is problematic. This has led ecologists in other fields to adopt extrapolative estimators of species richness, which project the total number of species present in a habitat by adjusting upward the number of species observed by an amount related to the number of rare species encountered in the samples. In so doing, the species richness can be estimated, with confidence intervals, at any level of sampling effort. Despite the availability and advantages of these methods, beach ecologists have continued to use the observed species richness as a point estimate of biodiversity for beaches. Here, we employ a Monte Carlo resampling approach over a range of routine transect designs used to sample sandy beaches, and evaluate the performance of seven non-parametric extrapolative estimators for species richness relative to that of the more conventionally used observed species richness. We find that the first-order Jackknife estimator (Jack 1) is the least biased, most accurate and most consistent across sites. Employing this estimator would allow accurate estimation of species richness on short (tens of metres) stretches of beach without exceeding the acceptable levels of sampling effort (4–5 m²). Spreading this effort evenly over three across-shore transects, each with a minimum of 13 equally spaced levels seems appropriately efficient. Although a greater number of research studies is required to ascertain the generality of these results beyond the beaches we sampled, we tentatively recommend the application of our results in biodiversity surveys on sandy beaches.  相似文献   

Society Awards 2015          下载免费PDF全文

Etienne Nel 《New Zealand geographer》2016,72(1):69-69

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A source of bias in rates of surface soil movement as estimated from marked particles     

Nel Caine 《地球表面变化过程与地形》1981,6(1):69-75

When estimated from measurements of introduced tracer particles, the rate of surface soil movement tends to be greater than the natural rate for equivalent particles on the same site. This consistent overestimation is greatest in the period following tracer introduction and leads to a measurement bias that may be as high as 300 per cent. The magnitude of the bias decreases with time, as the tracer is incorporated into the surface material, but remains detectable statistically for more than a year on some low-angle sites.  相似文献   

BEEKEEPING AND LOCAL SELF-RELIANCE IN RURAL SOUTHERN AFRICA*     

Pete M. Illgner  Etienne L. Nel  Mark P. Robertson 《Geographical review》1998,88(3):349-362

ABSTRACT. Beekeeping has the potential to supplement incomes in rural southern Africa. In light of regional economic constraints, self-reliance strategies that draw on local knowledge and skills take on a renewed importance. We consider the advantages and disadvantages of beekeeping and examine appropriate forms of development support. A short case study from Zimbabwe illustrates these issues.  相似文献   

The effect of rock moisture on Schmidt hammer rebound: tests on rock samples from Marion Island and South Africa     

Paul Sumner  Werner Nel 《地球表面变化过程与地形》2002,27(10):1137-1142

In an assessment of the influence of internal rock moisture content on Schmidt hammer readings, rebound (R) values are found to decrease with increasing moisture content. For samples of basalt, sandstone and dolerite the maximum decrease in R‐values is found between oven dry values and saturated rock rebound values, the magnitude of which varies from 2 to 10 points on the R‐scale. A quartzite block has the greatest decline of 6 points at 60 per cent saturation. For certain rock types under differing site‐to‐site field moisture conditions the moisture effect can be a significant factor in the interpretation of the relative state of weathering from rebound values. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Effects of kelp Ecklonia maxima inclusion in formulated feed on the growth,feed utilisation and gut microbiota of South African abalone Haliotis midae     

A Nel  BI Pletschke  CLW Jones  J Kemp  G Robinson  PJ Britz 《African Journal of Marine Science》2017,39(2):183-192

The effect of kelp Ecklonia maxima inclusion in formulated feeds on abalone growth and gut bacterial communities has not been previously investigated in South Africa. An eight-month on-farm growth trial was conducted with sub-adult Haliotis midae (～43 mm shell length) fed graded levels of kelp in formulated feeds. Kelp inclusion (0.44–3.54% of pellet dry mass) promoted faster growth (65.7–74.5% total mass gain), with better feed and protein conversions (apparent feed conversion ratio [FCR] 1.4–1.8, apparent protein efficiency ratio [PER] 2.3–2.7), as compared with the non-supplemented feed (52.3% total mass gain, FCR 2.1, PER 1.9; p < 0.001). Abalone-gut bacterial DNA was sequenced using 16S rRNA gene pyrosequencing and the sequences were clustered into operational taxonomic units (OTUs) at a 97% similarity level. A supplementary 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) analysis was employed. The dominant OTUs differed in terms of their relative abundances, with an autochthonous Mycoplasma strain being significantly more abundant (p = 0.03) in the gut of abalone fed a kelp-supplemented feed. The DGGE band patterns displayed higher within-group variability for abalone fed the control diet, suggesting that dietary kelp inclusion promotes gut-bacteria homeostasis. This may contribute to better feed utilisation and growth in abalone fed kelp-supplemented feeds.  相似文献   

Effect of graded levels of dietary carbohydrate on growth,feed utilisation and intestinal microbial community structure in dusky kob Argyrosomus japonicus fed a pelleted diet     

NC Mabasa  PJ Britz  CLW Jones  A Nel 《African Journal of Marine Science》2018,40(3):267-277

The ability to utilise carbohydrates is limited for many predatory marine fishes. Graded levels of dietary carbohydrate (4.1–24.6%) were formulated using pregelatinised maize starch, to determine optimal levels for dusky kob Argyrosomus japonicus, an emerging mariculture finfish for which pelleted feeds are being developed. Specific growth rate increased with an increase in the carbohydrate level up to 16.72%, after which it declined. Feed utilisation followed a similar trend, with the best feed conversion ratio (1.28) and protein efficiency ratio (1.76) recorded at 16.4% carbohydrate. Lipid vacuolisation of the hepatocytes was evident in all livers examined, with melano-macrophage aggregates in those of fish fed 24.6% carbohydrate suggesting starvation. Gut bacterial community profiles were variable but were not influenced by dietary carbohydrate level and differed mostly between fish fed trout feed prior to the trial and those fed experimental diets containing starch. The dusky kob were able to clear glucose from their blood when fed up to 16.4% carbohydrate, but glucose removal was not achieved at 24.6% carbohydrate. In conclusion, dusky kob has a limited ability to utilise cooked starch as a carbohydrate source, which may be included in pelleted feed at 16.4% without adverse effects. For this species, levels of dietary carbohydrate above this may result in symptoms consistent with physiological breakdown, including reduced growth, reduced feed intake and feed conversion efficiency, prolonged hyperglycaemia, liver pathology and altered microbial communities in the foregut.  相似文献