Empirical likelihood confidence intervals for adaptive cluster sampling

Adaptive cluster sampling (ACS) is an efficient sampling design for estimating parameters of rare and clustered populations. It is widely used in ecological research. The modified Hansen-Hurwitz (HH) and Horvitz-Thompson (HT) estimators based on small samples under ACS have often highly skewed distributions. In such situations, confidence intervals based on traditional normal approximation can lead to unsatisfactory results, with poor coverage properties. Christman and Pontius (Biometrics 56:503–510, 2000) showed that bootstrap percentile methods are appropriate for constructing confidence intervals from the HH estimator. But Perez and Pontius (J Stat Comput Simul 76:755–764, 2006) showed that bootstrap confidence intervals from the HT estimator are even worse than the normal approximation confidence intervals. In this article, we consider two pseudo empirical likelihood functions under the ACS design. One leads to the HH estimator and the other leads to a HT type estimator known as the Hájek estimator. Based on these two empirical likelihood functions, we derive confidence intervals for the population mean. Using a simulation study, we show that the confidence intervals obtained from the first EL function perform as good as the bootstrap confidence intervals from the HH estimator but the confidence intervals obtained from the second EL function perform much better than the bootstrap confidence intervals from the HT estimator, in terms of coverage rate.     

Small queens in the ant Ectatomma tuberculatum: a new case of social parasitism

Social parasites exploit the worker force of colonies of other social insects to rear their own young. Social parasitism occurs in several Hymenoptera and is particularly common in several tribes of the ant subfamilies Myrmicinae and Formicinae. Here, we document the occurrence of miniaturized queens (microgynes) in colonies of Ectatomma tuberculatum, an ant belonging to the subfamily Ectatomminae. Behavioral observations and genetic analyses show that microgynes concentrate their reproductive efforts almost exclusively on the production of sexual offspring (microgynes and males), whereas the regular, large queens (macrogynes) produce workers in addition to sexuals. According to mitochondrial and nuclear markers, gene flow between microgynes and macrogynes is extremely limited. Whereas the co-occurrence of microgynes and macrogynes in the related species Ectatomma ruidum constitutes an intraspecific polymorphism associated with alternative dispersal tactics, microgynes found in colonies of E. tuberculatum appear to be a distinct species and to represent the first case of social parasitism in the poneromorph subfamilies of ants.     

Life history costs of olfactory status signalling in mice

Large body size confers a competitive advantage in animal contests but does not always determine the outcome. Here we explore the trade-off between short-term achievement of high social status and longer-term life history costs in animals which vary in competitive ability. Using laboratory mice, Mus musculus, as a model system, we show that small competitors can initially maintain dominance over larger males by increasing investment in olfactory status signalling (scent-marking), but only at the cost of reduced growth rate and body size. As a result they become more vulnerable to dominance reversals later in life. Our results also provide the first empirical information about life history costs of olfactory status signals. Received: 15 December 1999 / Revised: 6 June 2000 / Accepted: 24 June 2000     

Green technology for sustainable surface protection of steel from corrosion: a review

Plants contain substances that inhibit corrosion. Here we review biomass-based corrosion inhibitors from plant leaves, nuts, and fruit peels, after treatment with acids, bases or saline solutions. The mechanism of corrosion inhibition involves a monolayer coverage, according to isotherm and Langmuir models. Plant extract-based corrosion inhibitors contain heteroatoms whose electrons pair in the p-electron level in multiple bonds and the vacant d-orbitals of iron. Corrosion inhibition under marine conditions involves various chemical interactions between metals and dissolved ionic components.

     

Nano-structured dynamic Schiff base cues as robust self-healing polymers for biomedical and tissue engineering applications: a review

Polymer materials are vulnerable to damages, failures, and degradations, making them economically unreliable. Self-healing polymers, on the other hand, are multifunctional materials with superior properties of autonomic recovery from physical damages. These materials are suitable for biomedical and tissue engineering in terms of cost and durability. Schiff base linkages-based polymer materials are one of the robust techniques owing to their simple self-healing mechanism. These are dynamic reversible covalent bonds, easy to fabricate at mild conditions, and can self-reintegrate after network disruption at physiological conditions making them distinguished. Here we review self-healing polymer materials based on Schiff base bonds. We discuss the Schiff base bond formation between polymeric networks, which explains the self-healing phenomenon. These bonds have induced 100% recovery in optimal cases.

     

Numbers,biomass, and caloric content of the echinoderm fauna of the rocky shores of Barbados

The high-energy windward coasts with narrow rocky intertidal regions (Oistens, River Bay) at Barbados, West Indies, had abundant macroscopic algae (mainly Sargassum sp.) and populations of Holothuria glaberrima Selenka and Echinometra lucunter (Linnaeus), while protected ones with a wide rocky intertidal had sparse macroscopic algae and populations of E. lucunter only. The low-energy leeward coasts with wide rocky intertidal regions (Six Men's Bay, Payne's Bay) had no macroscopic algae in the surf zone and populations of E. lucunter only. Numerical densities of E. lucunter were high in all localities; the highest level of 144 m^-2 was found at Six Men's Bay; numerical densities of H. glaberrima were high at both Oistens and River Bay, the highest level of 36 m^-2 being recorded at River Bay. The caloric density of H. glaberrima at River Bay was 412 kcal m^-2. The highest combined density of H. glaberrima and E. lucunter was at Oistens (632 kcal m^-2, with 254 kcal m^-2 being due to E. lucunter). The highest caloric density of E. lucunter at Six Men's Bay was 482 kcal m^-2. Dependence on suspended food probably restricts H. glaberrima to high-energy environments while E. lucunter has an additional food source through its ability to scrape the rock substratum. E. lucunter may be more efficient in catching drift food. Mortality is suggested to be the basis of the failure of E. lucunter to displace H. glaberrima from the high-energy location.     

Seaweed sex pheromones and their degradation products frequently suppress amphipod feeding but rarely suppress sea urchin feeding

Summary. A diverse group of brown seaweeds produce bouquets of C₁₁ metabolites, some of which act as pheromones that cue gamete release or attract sperm to eggs following release. We demonstrate that these C₁₁ metabolites and their degradation products also frequently and strongly deter feeding by the herbivorous amphipod Ampithoe longimana, but rarely by the herbivorous sea urchin Arbacia punctulata. Across the range of concentrations tested, seven of twelve C₁₁ metabolites or mixtures that we tested deterred feeding by the amphipod, but only two of eleven deterred the sea urchin. For those compounds where we could rigorously contrast the magnitude of deterrence against the amphipod with the magnitude of deterrence against the urchin, the amphipod was deterred significantly more than the urchin by five of six metabolites. Thus, C₁₁ compounds were more frequently and more strongly deterrent to the amphipod than to the sea urchin. These findings for C₁₁ metabolites conflict with previous investigations, where other classes of seaweed chemical defenses have been shown to deter feeding by large mobile herbivores like urchins and fishes but to be relatively ineffective against mesograzers, especially the species of amphipod that we used here. Our results suggest that C₁₁ metabolites are unusual among the known seaweed chemical defenses in that they are especially effective against mesograzers, which often consume seaweed spores, zygotes, and juveniles. The high concentrations of C₁₁ metabolites in brown algal eggs could allow these defenses to be especially important in defending gametes, zygotes, or young sporelings from herbivorous mesograzers. Received 26 February 1998; accepted 9 April 1998.     

Sloughed mucus and drag-reduction in a school of Atlantic silversides,Menidia menidia

Atlantic silversides, Menidia menidia, were collected by seine-net from the Newport River estuary, North Carolina, USA and maintained in the laboratory. Direct measurement showed that the amount of mucus sloughed off individual silversides was 567 g h^-1 at a swimming speed of 50 cm s^-1. Individual M. menidia were also allowed to swim in a flowtank filled with 0, 1, and 10 ppm of the synthetic drag-reducer Polyox to determine if any changes in tailbeat frequency or amplitude could be correlated with the level of this sloughed material. Tailbeat measurements between seawater controls and either Polyox concentration did not differ significantly. Calculations based on this evidence indicate that the amount of solubilized mucus sloughed off a school of 10 000 M. menidia would be at least two orders of magnitude less than the highest concentration of Polyox tested. We conclude that solubilized mucus in the water column does not confer drag-reduction to schooling M. menidia.     

Esterase heterogeneity and an investigation into racial differences in the cirripede Balanus balanoides using acrylamide gel electrophoresis

Four groups of bands showing esterase activity were found after electrophoretic separation of extracts of Balanus balanoides (L.) prosoma on polyacrylamide gels. Each group was distinguishable from other groups by mobility, reaction with specific substrates, and susceptibility to various inhibitors. Groups designated BbEII and BbEIII showed cholinesterase activity, BbEIV showed carboxylesterase activity, and BbEI possible arylesterase activity. Polymorphisms were found within Groups BbEIII and BbEI. The frequency distribution of BbEIV polymorphs in a sample from the Menai Straits, UK, fitted the Hardy-Weinberg predicted values for 4 co-dominant alleles. A sample from St. Andrews, New Brunswick, Canada, however, did not fit the Hardy-Weinberg prediction. No variation between individuals was found when malate dehydrogenase (MDH) and lactate dehydrogenase (LDH) isozymes were examined. Hence, these systems are unsuitable for testing racial differences. The results for the cholinesterase and arylesterase isozymes substantiate the view, originally based on differences in reproductive phenology and egg size, that genetically separate races exist on either side of the Atlantic Ocean.