Magelonidae (annelida: Polychaeta) de las Seychelles 2: Descripción de cuatro especies más, tres de ellas nuevas para la ciencia

P align=justify>In 2000, the National Museum of Wales mounted a marine biological expedition to the Seychelles as part of the Shoals of Capricorn programme. Following this, three new species of Magelona (M. conversa, M. falcifera and M. gemmata) were described, and published in the Proceedings of the 7th International Polychaete Conference. In this second paper, the authors describe a further three new species (M. symmetrica, M. mahensis and M. cepiceps) and present a new record of M. pygmaea Nateewathana and Hylleberg, 1991 – previously known only from Thailand. The taxonomic affinities of the four species are discussed and a key is provided to all seven recorded from the Seychelles. En el año 2000, dentro del programa Shoals of Capricorn, el Museo Nacional del País de Gales organizó una expedición biológica marina a las Seychelles. Tras ella, se describieron tres nuevas especies de Magelona (M. conversa, M. falcifera, y M. gemmata) que fueron publicadas en los Proceedings of the 7th International Polychaete Conference. En este segundo trabajo, los autores describen tres nuevas especies más (M. symmetrica, M. mahensis y M. cepiceps) y citan nuevamente a M. pygmaea Nateewathana y Hylleberg, 1991 previamente sólo hallada en Tailandia. Se discuten las afinidades taxonómicas de las cuatro especies y se proporciona una clave para las siete especies citadas en las Seychelles. &nbsp

What explains the invading success of the aquatic mud snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)?

The spread of non-native species is one of the most harmful and least reversible disturbances in ecosystems. Species have to overcome several filters to become a pest (transport, establishment, spread and impact). Few studies have checked the traits that confer ability to overcome these steps in the same species. The aim of the present study is to review the available information on the life-history and ecological traits of the mud snail, Potamopyrgus antipodarum Gray (Hydrobiidae, Mollusca), native from New Zealand, in order to explain its invasive success at different aquatic ecosystems around the world. A wide tolerance range to physico-chemical factors has been found to be a key trait for successful transport. A high competitive ability at early stages of succession can explains its establishment success in human-altered ecosystems. A high reproduction rate, high capacity for active and passive dispersal, and the escape from native predators and parasites explains its spread success. The high reproduction and the ability to monopolize invertebrate secondary production explain its high impact in the invaded ecosystems. However, further research is needed to understand how other factors, such as population density or the degree of human perturbation can modify the invasive success of this aquatic snai

Estimation of means in graphical Gaussian models with symmetries

We study the problem of estimability of means in undirected graphical Gaussian models with symmetry restrictions represented by a colored graph. Following on from previous studies, we partition the variables into sets of vertices whose corresponding means are restricted to being identical. We find a necessary and sufficient condition on the partition to ensure equality between the maximum likelihood and least-squares estimators of the mean.Comment: Published in at http://dx.doi.org/10.1214/12-AOS991 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Lattices of Graphical Gaussian Models with Symmetries

In order to make graphical Gaussian models a viable modelling tool when the number of variables outgrows the number of observations, model classes which place equality restrictions on concentrations or partial correlations have previously been introduced in the literature. The models can be represented by vertex and edge coloured graphs. The need for model selection methods makes it imperative to understand the structure of model classes. We identify four model classes that form complete lattices of models with respect to model inclusion, which qualifies them for an Edwards-Havr\'anek model selection procedure. Two classes turn out most suitable for a corresponding model search. We obtain an explicit search algorithm for one of them and provide a model search example for the other.Comment: 29 pages, 18 figures. Restructured Section 5, results unchanged; added references in Section 6; amended example in Section 6.

FOOD CONSUMPTION AND SEASONALITY

Time-series analyses of food demand often add dummy or harmonic variables to shift intercept terms during periods when seasonal effects exist. However, variable coefficients may be influenced by seasonality and the effects may vary by region. In this paper, a cluster analysis of seasonality indices for food products shows that distinct regions exist with similar seasonal patterns. Researchers could use these clusters to test for season-region interactions when other information about seasonality is unavailable.Food Consumption/Nutrition/Food Safety,

The Elasticity of Substitution in Demand for Non-Tradable Goods in Bolivia

This paper uses a CES function to estimate the constant elasticity of substitution in consumption for non-tradables relative to tradables in a dependent economy framework. The methodology for generating data on real consumption of tradable and non-tradable goods, real prices of tradable and non-tradable goods and real absorption is based on the Bolivian Input-Output Matrix, producing quarterly data for the period 1990. 1 to 2002. 4. The data identify Bolivia as a country highly open to trade, with an average ratio of 55 percent in the value of exports and imports relative to GDP, non-tradable production accounting for 52 percent of GDP, and differences in the behavior of the internal and external real exchange rates. The HEGY test is used to identify and separate out seasonal unit roots in the data. A cointegration relationship was found between real absorption, the non-tradable to tradable consumption ratio and the non-tradable to tradable price ratio, suggesting inelasticity of substitution.

Bayesian stochastic model specification search for seasonal and calendar effects

We apply a recent methodology, Bayesian stochastic model specification search (SMSS), for the selection of the unobserved components (level, slope, seasonal cycles, trading days effects) that are stochastically evolving over time. SMSS hinges on two basic ingredients: the non-centered representation of the unobserved components and the reparameterization of the hyperparameters representing standard deviations as regression parameters with unrestricted support. The choice of the prior and the conditional independence structure of the model enable the definition of a very efficient MCMC estimation strategy based on Gibbs sampling. We illustrate that the methodology can be quite successfully applied to discriminate between stochastic and deterministic trends, fixed and evolutive seasonal and trading day effects.Seasonality; Structural time series models; Variable selection.

Modelling Seasonality An Extension of the HEGY Approach in the Presence of Two Structural Breaks

In this paper the HEGY testing procedure (Hylleberg et al. 1990) of analyzing seasonal unit roots is tried to be re-examined by allowing for seasonal mean shifts with exogenous break points. Using some Monte Carlo experiments the distribution of the HEGY and the extended HEGY tests for seasonal unit roots subject to mean shifts and the small sample behavior of the test statistics have been investigated. Based on an empirical analysis upon the conventional money demand relationships in the Turkish economy, our results indicate that seasonal unit roots appear for the GDP deflator, real M2 and the expected inflation variables while seasonal unit roots at annual frequency seem to be disappear for the real M1 balances when the possible structural changes in one or more seasons at 1994 and 2001 crisis years have been taken into account.HEGY Seasonal unit root test, Deterministic seasonality, Structural breaks, Money demand, Turkish economy