Bayesian Model Averaging in Consumer Demand Systems with Inequality Constraints.

Share equations for the translog and almost ideal demand systems are estimated using Markov Chain Monte Carlo. A common prior on the elasticities and budget shares evaluated at average prices and income is used for both models. It includes equality restrictions (homogeneity, adding up and symmetry) and inequality restrictions (monotonicity and concavity). Posterior densities on the elasticities and shares are obtained; the problem of choosing between the results from the two alternative functional forms is resolved by using Bayesian model averaging. The application is to USDA data for beef, pork and poultry. Estimation of elasticities and shares, evaluated at mean prices and expenditure, is insensitive to model choice. At points away from the means the estimates are sensitive, and model averaging has an impact.conditional prior, Marginal likelihood, Metropolis-Hastings algorithm

Factors affecting the distribution, abundance and diversity of rock-pool fishes on the Cape Peninsula, South Africa

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The Intertidal fish fauna of the west coast of South Africa — species, community and biogeographic patterns

In the first quantitative survey of intertidal fish from the South African west coast 62 intertidal rock pools were sampled at two sites, using the ichthyocide rotenone. A total of 2 022 fish representing 14 species belonging to only two families — the Clinidae (88–98% by number) and the Gobiesocidae (12–2%) — were caught. Clinus superciliosus, C. heterodon and the gobiesocid Chorisochismus dentex were the most abundant species in terms of both numbers and biomass. Vertical zonation of individual species on the shore indicated little separation of the habitat between species, although some species exhibited size-specific partitioning of the shore. Relationships between fish distribution and abundance and rock pool characteristics were elucidated by means of stepwise multiple regression, both at the whole community and individual species levels. The abundances of individual species were best predicted by pool size, although some species also showed an association with weed cover. For the community as a whole, the number of species present, the total number of fish and the total biomass in any pool were all dependent on pool size, height above LWS and amount of available cover. Relative to other South African sites the west coast has a low diversity of intertidal fish, combined with a high degree of dominance and a low level of habitat separation

First record of the sea anemone Metridium senile from South Africa

A sea anemone new to the South African fauna is reported from Table Bay Harbour and is identified as Metridium senile. The population was probably introduced from Europe and although well established, appears to be restricted to the harbour area

Predation by West Coast rock lobsters (Jasus lalandii) on two species of winkle (Oxystele sinensis and Turbo cidaris)

Rock lobsters, Jasus lalandii, may play an important role in structuring the communities on shallow reef ecosystems and have recently increased in density in the area between Cape Hangklip and Danger Point on the southwest coast of South Africa. This has probably resulted in increased predation on natural populations of smooth turban shells (Turbo cidaris) and pink-lipped topshells (Oxystete sinensis), both of which are proposed targets for small-scale commercial fisheries. This study examines the size selectivity, prey species preferences and consumption rates of rock lobsters feeding on these two winkle species. Rock lobsters showed a strong preference for small O. sinensis, and were limited to taking a maximum (or critical) size of prey, which increased linearly with rock-lobster size. By contrast, rock lobsters of all size classes tested were able to crack and consume a full size range of T. cidaris, and no size preferences were evident. When the two gastropods were offered simultaneously, rock lobsters preferentially consumed the thinner shelled O. sinensis.Consumption rates increased linearly with rock-lobster size. Population consumption rates indicate that rock lobsters will have a profound effect on winkle stocks in the area, even if winkles constituted less than 1% of the diet. This in turn suggests that commercial exploitation of these stocks is unlikely to remain sustainable

Sycamore tree lace bug (Corythucha ciliate Say)(Hemiptera: Tingidae) reaches Africa

In February 2014 colonies of a large and conspicuous lacebug (Fig. 1A) were collected from the undersides of the leaves of London plane trees (Platanus x acerifolia) in the suburb of Newlands, Cape Town, South Africa. Infected leaves could easily be identified by their characteristic bronzed appearance (Fig. 1B). The lace bugs were subsequently identified as Corythucha ciliata (Say) using keys to North American Corythucha species (Mead 1989) and economically important tingids of the world (Stonedahl et al. 1992). Corythucha species have high host-specificity, whilst C. ciliata is the only lace bug known to feed on Platanus species (sycamores) - this association is thus considered to be diagnostic for the species (CABI 2014). C. ciliata has a broad native range across the eastern parts of North America and Canada, where it is largely monophagous on Platanus (sycamore) trees, with P. occidentalis being its main host. However, it also occurs on Platanus hybrids, and in invasive parts of its range feeds on P. orientalis and P. x acerifolia (the hybrid between P. occidentalis and P. orientalis (CABI 1984).Our thanks to the DST-NRF Centre of Excellence for Invasion Biology for funding support for this study and to A. Wright and R. Griffiths for assistance with the field surveys. The source of the shapefile for the distribution map was Naude et al. (2007). The two reviewers are thanked for their useful comments

Four notable additions to the South African echinoid fauna (Echinodermata, Echinoidea)

Although a comprehensive guide to the South African echinoid fauna was published as recently as 2017, four notable additions to the fauna have emerged since that time and are reported on here. The first South African records for Histocidaris purpurata (Thomson, 1872), Echinothrix diadema (Linnaeus, 1758), Microcyphus rousseaui L. Agassiz, in Agassiz and Desor 1846, and Pseudoboletia maculata Troschel, 1869 are presented. All four species have previously been recorded from the Atlantic and/or Indian Oceans and their ranges are thus extended southwards here. These additions increase the total number of echinoid species known from South Africa to 74

Resilience and elasticity of intertidal communities in response to harvesting of the alien mussel Mytilus galloprovincialis

Besides the direct impacts of exploitation on target species, indirect effects on non-target species are unavoidable and find expression in changes in community structure. We quantified the effects of experimental harvesting of Mytilus galloprovincialis on intertidal communities on the South African west coast. In the mid- and low-shore, four months of harvesting at intensities greater than F=0.3 and F=0.6 respectively, resulted in significant changes in community composition. These changes were driven by progressively greater spatial dominance by the macroalgae Cladophora flagelliformis, Porphyra capensis and Ulva species as harvesting intensity increased. Four months after cessation of harvesting, community structure had not recovered and even areas subjected to as little as F=0.3 supported significantly altered communities in both zones. The fact that substantial community changes were induced by even low-intensity exploitation is indicative of low resilience to harvesting. The densities and cover of the dominant taxa returned to a pre-harvest state 16 months after the cessation of harvesting, but multivariate analyses indicated that the overall community composition required 32 months for Cover Letter full recovery. Although these communities displayed elasticity within three years, it is recommended that should a M. galloprovincialis fishery be established in the region, harvesting be implemented at a maximum intensity of F=0.3. This approach would maximise yields and protect associated intertidal communities.Centre of Excellence for Invasion Biolog

Quasi-1D dynamics and nematic phases in the 2D Emery model

We consider the Emery model of a Cu-O plane of the high temperature superconductors. We show that in a strong-coupling limit, with strong Coulomb repulsions between electrons on nearest-neighbor O sites, the electron-dynamics is strictly one dimensional, and consequently a number of asymptotically exact results can be obtained concerning the electronic structure. In particular, we show that a nematic phase, which spontaneously breaks the point- group symmetry of the square lattice, is stable at low enough temperatures and strong enough coupling.Comment: 8 pages, 5 eps figures; revised manuscript with more detailed discussions; two new figures and three edited figuresedited figures; 14 references; new appendix with a detailed proof of the one-dimensional dynamics of the system in the strong coupling limi

Lost in translation? Standardising the terminology used in marine invasion biology and updating South African alien species lists

Confusion between terms and ambiguities among definitions have long plagued the field of invasion biology. One result is disruption in flow of information from researchers to policy-makers and managers who rely on science to inform regulatory frameworks and management actions. We reviewed the South African marine biology literature to quantify the current usage of terminology describing marine invasions and found a variety of terms in use, few of which are defined when used. In response, we propose standard terminology that aligns with international practice. We then interpreted the Blackburn unified framework for biological invasions within the marine context and used this as a transparent way to apply the standardised terms to an updated list of marine alien species for the country. This resulted in the recognition of 36 alien and 53 invasive species within South Africa. Most notably, follow-up research is required to confirm the status of at least 11 listed species, the majority of which have been recorded only once, or not in the past 25 years. It is hoped that by standardising terminology, marine science in South Africa will better support authorities charged with managing the threat posed by marine alien species