Quantifying chaos for ecological stoichiometry

The theory of ecological stoichiometry considers ecological interactions among species with different chemical compositions. Both experimental and theoretical investigations have shown the importance of species composition in the outcome of the population dynamics. A recent study of a theoretical three-species food chain model considering stoichiometry [B. Deng and I. Loladze, Chaos 17, 033108 (2007)] shows that coexistence between two consumers predating on the same prey is possible via chaos. In this work we study the topological and dynamical measures of the chaotic attractors found in such a model under ecological relevant parameters. By using the theory of symbolic dynamics, we first compute the topological entropy associated with unimodal Poincareacute return maps obtained by Deng and Loladze from a dimension reduction. With this measure we numerically prove chaotic competitive coexistence, which is characterized by positive topological entropy and positive Lyapunov exponents, achieved when the first predator reduces its maximum growth rate, as happens at increasing delta(1). However, for higher values of delta(1) the dynamics become again stable due to an asymmetric bubble-like bifurcation scenario. We also show that a decrease in the efficiency of the predator sensitive to prey's quality (increasing parameter zeta) stabilizes the dynamics. Finally, we estimate the fractal dimension of the chaotic attractors for the stoichiometric ecological model.

Changes in the influence of board characterisitcs on corporate results due to the recent global financial crisis

The main purpose of this study is to analyse the changes caused by the global financial crisis on the influence of board characteristics on corporate results, in terms of corporate performance, corporate risk-taking, and earnings management. Sample comprises S&P 500 listed firms during 2002-2008. This study reveals that the environmental conditions call for different behaviour from directors to fulfil their responsibilities and suggests changes in normative and voluntary guidelines for improving good practices in the boardroom.

Ecological footprint as an indicator of sustainability at Lisbon School of Health Technology, Portugal

Higher education institutions, has an active role in the development of a sustainable future and for this reason, it is essential that they became environmentally sustainable institutions, applying methods such as the Ecological Footprint analysis. This study intent is to strengthen the potential of the ecological footprint as an indicator of the sustainability of students of Lisbon School of Health Technology, and identify the relationship between the ecological footprint and the different socio-demographic variables.

On chaos, transient chaos and ghosts in single populations models with allee effects

Density-dependent effects, both positive or negative, can have an important impact on the population dynamics of species by modifying their population per-capita growth rates. An important type of such density-dependent factors is given by the so-called Allee effects, widely studied in theoretical and field population biology. In this study, we analyze two discrete single population models with overcompensating density-dependence and Allee effects due to predator saturation and mating limitation using symbolic dynamics theory. We focus on the scenarios of persistence and bistability, in which the species dynamics can be chaotic. For the chaotic regimes, we compute the topological entropy as well as the Lyapunov exponent under ecological key parameters and different initial conditions. We also provide co-dimension two bifurcation diagrams for both systems computing the periods of the orbits, also characterizing the period-ordering routes toward the boundary crisis responsible for species extinction via transient chaos. Our results show that the topological entropy increases as we approach to the parametric regions involving transient chaos, being maximum when the full shift R(L)(infinity) occurs, and the system enters into the essential extinction regime. Finally, we characterize analytically, using a complex variable approach, and numerically the inverse square-root scaling law arising in the vicinity of a saddle-node bifurcation responsible for the extinction scenario in the two studied models. The results are discussed in the context of species fragility under differential Allee effects. (C) 2011 Elsevier Ltd. All rights reserved.

100 Años de desarrollo de la teoría financiera : situación actual y previsible evolución tras la crisis : resumen de la ponencia

"Las Finanzas, como disciplina académica, nacen a caballo entre los siglos XIX y XX. Sin duda el importante desarrollo industrial de la época y la necesidad de empresas de mayores dimensiones llevaron a un creciente interés por las concentraciones empresariales como fusiones y adquisiciones. También aumentó el interés por los mercados donde se financiaban estas empresas cada vez mayores. Y esto, aunque sucedía en diversas partes del mundo, estaba ocurriendo de forma especial en Estados Unidos, de manera que allí fue donde nacieron las finanzas, y donde se han seguido desarrollando. De esta manera, desde un comienzo, las finanzas tienen un claro sello anglosajón." [introdução]