879 resultados para Extinction Times


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A diversidade de espécies e fenotípica pode variar consideravelmente entre grupos taxonômicos e ao longo do tempo em uma mesma linhagem. O estudo de tais variações tornou-se um dos principais objetivos da biologia evolutiva fornecendo informações importantes a respeito dos possíveis mecanismos que regulam a biodiversidade. Dessa forma, o objetivo geral da presente tese foi investigar os padrões da diversificação de espécies e da morfologia em um grupo cosmopolita de serpentes, a família Viperidae, e os potenciais processos subjacentes. Primeiramente, (1) reconstruímos as relações filogenéticas e estimamos os tempos de divergência entre as linhagens da família Viperidae utilizando uma abordagem Bayesiana. (2) Aplicando um método recentemente desenvolvido (BAMM), exploramos como as taxas de especiação e extinção variaram ao longo da radiação do grupo inferindo os possíveis processos reguladores. Por fim, (3) analisamos se a evolução do tamanho do corpo e as taxas de especiação variam nos diferentes habitats ocupados pelos viperídeos (terrestres vs arborícola). Nesta tese geramos a filogenia molecular de viperídeos mais completa até o momento utilizando sequências para 11 genes mitocondriais e nucleares abrangendo 79% das espécies viventes (264 terminais) e todos com exceção de um gênero. De maneira geral, foi possível obter relações filogenéticas robustas para o grupo com a maioria dos gêneros sendo monofilética. Os tempos de divergência obtidos indicam que os viperídeos começaram a diversificar em meados do Paleoceno tardio/meio do Eoceno inferindo idades um pouco mais tardias que o encontrado em estudos anteriores. Durante a radiação do grupo, um aumento nas taxas de especiação parece ter ocorrido durante a diversificação dos crotalíneos (pit vipers) em decorrência não só da evolução das fossetas loreais mas também como resultado de mudanças geológicas e climáticas na Ásia e da invasão do novo mundo. Após este rápido aumento inicial, as taxas de especiação desaceleraram em direção ao presente. Por fim, os resultados aqui apresentados indicam que apesar dos habitats arborícolas limitarem a evolução morfológica nos viperídeos, a evolução da arborealidade parece não afetar as taxas de especiação que permanecem similares entre linhagens arborícolas e terrestres. Isto sugere dois cenários: (1) a especiação acontece de forma independente das mudanças morfológicas nos viperídeos; ou (2) o isolamento geográfico seria um mecanismo importante na diversificação de linhagens arborícolas contrabalançando decréscimos nas oportunidades de especiação possivelmente relacionados às pressões seletivas impostas pelo ambiente arborícola. A presente tese contribui para entendermos mais sobre como evoluíram os viperídeos ao longo dos seus ∼50 milhões de anos. Além de propor cenários e hipóteses a serem futuramente explorados com os viperídeos, elaboramos uma discussão ampla e conceitual a respeito dos possíveis mecanismos por trás da diversificação de espécies e da morfologia que poderiam também ser contemplados para outros grupos de organismos. Portanto, a presente tese contribui não só para entendermos os mecanismos que geram e mantém a diversidade de serpentes, mas também para enriquecer a discussão dos mecanismos que geram e mantém a biodiversidade como um todo

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In maritime transportation, decisions are made in a dynamic setting where many aspects of the future are uncertain. However, most academic literature on maritime transportation considers static and deterministic routing and scheduling problems. This work addresses a gap in the literature on dynamic and stochastic maritime routing and scheduling problems, by focusing on the scheduling of departure times. Five simple strategies for setting departure times are considered, as well as a more advanced strategy which involves solving a mixed integer mathematical programming problem. The latter strategy is significantly better than the other methods, while adding only a small computational effort.

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This paper deals with a stochastic epidemic model for computer viruses with latent and quarantine periods, and two sources of infection: internal and external. All sojourn times are considered random variables which are assumed to be independent and exponentially distributed. For this model extinction and hazard times are analyzed, giving results for their Laplace transforms and moments. The transient behavior is considered by studying the number of times that computers are susceptible, exposed, infectious and quarantined during a period of time (0, t] and results for their joint and marginal distributions, moments and cross moments are presented. In order to give light this analysis, some numerical examples are showed.

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The endangered Rio Grande silvery minnow (Hybognathus amarus; RGSM) is nearing extinction and requires immediate recovery actions. In a draft report to the Middle Rio Grande Program, a Program Advisory Panel (PAP) recommended 34 short-term recovery measures to be implemented within the next five years, and 21 long-term recovery actions. However, these recommendations need further analysis to determine if and how the actions could be implemented. This project evaluated short-term recommendations provided by the PAP to identify the most effective and rank the relative importance of the actions. These recommendations were divided into 7 recovery categories: population augmentation (5 recommendations); hydrologic regimen (4 recommendations); physical habitat (3 recommendations); biological component of habitat (2 recommendations); population monitoring (6 recommendations); monitoring, analysis, and modeling (12 recommendations); and information and planning (2 recommendations). Each recommendation was evaluated for its potential to produce anticipated recovery progress for the RGSM based on assessments of the degree of feasibility, cost effectiveness, and associated potential consequences if fully implemented. In addition, other alternatives in a range of options were also considered where applicable. In each case, recommendations were evaluated from on-site visits, interviews with researchers and resource managers, and literature review. Based on the research findings, three major groupings of the recovery categories were identified: natural aspects of recovery, program aspects of recovery, and emergency measures. At least one recovery category within each major grouping was considered important by the respondents, which indicates that each grouping is of high importance in relation to the situation at hand. However, actions within each grouping have varying priorities given constraints on available resources, time, and budget. An integrated approach that accounts for the complexity of the river system and the species itself was considered the best approach to avoid extinction while ensuring long-term sustainability. Results of these analyses were provided directly to the PAP for their review, and it is anticipated that project results could advance implementation of the most appropriate immediate recovery actions needed to prevent extinction of the RGSM.

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Using information from two recently published atlases of threatened invertebrate species in peninsular Spain, we examined the climatic, land use and geographic characteristics of the 100 km2 UTM cells with most likelihood of suffering extinctions (extinction cells), as well as the attributes of the species prone to population extinctions. Extinction cells have had significantly (1) lower precipitation values, (2) higher temperatures, (3) higher percentages of anthropic land uses or (4) higher rates of anthropization during the last 20 years than the remaining cells. Nevertheless, probable extinctions may occur under a wide range of climatic and anthropization change rates and these variables can only explain a low proportion (~5 %) of variability in the occurrence or number of extinction cells. Aquatic species seem to suffer higher local extinction rates than terrestrial species. Interestingly, many invertebrate species with approximately 25 or less occurrence cells are on a clear trajectory towards extinction. These results outline the difficulties and uncertainties in relating probable population extinctions with climatic and land use changes in the case of invertebrate data. However, they also suggest that a third of the considered Spanish threatened species could have lost some of their populations, and that current conservation efforts are insufficient to reverse this tendency.

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Koninckinids are a suitable group to shed light on the biotic crisis suffered by brachiopod fauna in the Early Jurassic. Koninckinid fauna recorded in the late Pliensbachian–early Toarcian from the easternmost Subbetic basin is analyzed and identified as a precursor signal for one of the most conspicuous mass extinction events of the Phylum Brachiopoda, a multi-phased interval with episodes of changing environmental conditions, whose onset can be detected from the Elisa–Mirabile subzones up to the early Toarcian extinction boundary in the lowermost Serpentinum Zone (T-OAE). The koninckinid fauna had a previously well-established migration pattern from the intra-Tethyan to the NW-European basins but a first phase with a progressive warming episode in the Pliensbachian–Toarcian transition triggered a koninckinid fauna exodus from the eastern/central Tethys toward the westernmost Mediterranean margins. A second stage shows an adaptive response to more adverse conditions in the westernmost Tethyan margins and finally, an escape and extinction phase is detected in the Atlantic areas from the mid-Polymorphum Zone onwards up to their global extinction in the lowermost Serpentinum Zone. This migration pattern is independent of the paleogeographic bioprovinciality and is unrelated to a facies-controlled pattern. The anoxic/suboxic environmental conditions should only be considered as a minor factor of partial control since well-oxygenated habitats are noted in the intra-Tethyan basins and this factor is noticeable only in the second westward migratory stage (with dwarf taxa and oligotypical assemblages). The analysis of cold-seep proxies in the Subbetic deposits suggests a radiation that is independent of methane releases in the Subbetic basin.

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Current economic crisis together with the Internet revolution has had direct impacts on the franchise sector of Spain: in particular on its unique communication network. The aim of this research is to analyse how Spanish franchise companies have adapted to these changes through its corporate communications management. We want to determine whether the management of communications is ideal to the growth and consolidation of companies in the market. Corporate communications plans and organizational structures were analyzed to verify whether or not information technology (i.e. the use of the Internet) is maximized: the communications aspect being a critical area of company growth. We found that most franchise companies surveyed had adapted well to the changes in information technology, despite economic challenges. The Internet as a communications tool has been limited to its utility as a “bulletin board” for information. The marketing advantage of Internet communication, or its use as an avenue for customer exchange and exchange of goods and services has yet to be maximized. Future research may look into the details of how companies are able to maximize the communications-marketing advantage that Online/Internet can contribute to the franchise sector.

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Background: The immigrant population living in Spain grew exponentially in the early 2000s but has been particularly affected by the economic crisis. This study aims to analyse health inequalities between immigrants born in middle- or low-income countries and natives in Spain, in 2006 and 2012, taking into account gender, year of arrival and socioeconomic exposures. Methods: Study of trends using two cross-sections, the 2006 and 2012 editions of the Spanish National Health Survey, including residents in Spain aged 15–64 years (20 810 natives and 2950 immigrants in 2006, 14 291 natives and 2448 immigrants in 2012). Fair/poor self-rated health, poor mental health (GHQ-12 > 2), chronic activity limitation and use of psychotropic drugs were compared between natives and immigrants who arrived in Spain before 2006, adjusting robust Poisson regression models for age and socioeconomic variables to obtain prevalence ratios (PR) and 95% confidence interval (CI). Results: Inequalities in poor self-rated health between immigrants and natives tend to increase among women (age-adjusted PR2006 = 1.39; 95% CI: 1.24–1.56, PR2012 = 1.56; 95% CI: 1.33–1.82). Among men, there is a new onset of inequalities in poor mental health (PR2006 = 1.10; 95% CI: 0.86–1.40, PR2012 = 1.34; 95% CI: 1.06–1.69) and an equalization of the previously lower use of psychotropic drugs (PR2006 = 0.22; 95% CI: 0.11–0.43, PR2012 = 1.20; 95% CI: 0.73–2.01). Conclusions: Between 2006 and 2012, immigrants who arrived in Spain before 2006 appeared to worsen their health status when compared with natives. The loss of the healthy immigrant effect in the context of a worse impact of the economic crisis on immigrants appears as potential explanation. Employment, social protection and re-universalization of healthcare would prevent further deterioration of immigrants’ health status.

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by Sarah Harvey Porter.

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[From the Introduction]. European lawyers, at least those dealing predominantly with institutional matters, are living particularly interesting times since the setting-up of the “European Convention on the Future of Europe” in December 2001.1 As the Convention’s mandate, spelled out in rather broad terms in the European Council’s declaration of Laeken,2 is potentially unlimited, and as the future constitution of the European Union (EU) will be ultimately adopted by the subsequent Intergovernmental Conference (IGC), there appears to be a great possibility to clarify, to simplify and also to reform many of the more controversial elements in the European legal construction. The present debate on the future of the European constitution also highlights the relationship between the pouvoir constituant3 and the European Courts, the Court of Justice (ECJ) and its Court of First Instance (CFI), who have to interpret the basic rules and principles of the EU.4 In that light, the present article will focus on a classic theme of the Court’s case law: the relationship between judges and pouvoir constituant. In the EU, this relationship has traditionally been marked by the ECJ’s role as driving force in the “constitutionalisation” of the EC Treaties – which has, to a large extent, been accepted and even codified by the Member States in subsequent treaty revisions. However, since 1994, the ECJ appears to be more reluctant to act as a “law-maker.”5 The recent judgment in Unión de Pequeños Agricultores (UPA)6 – an important decision by which the ECJ refused to liberalize individuals’ access to the Community Courts – is also interesting in this context. UPA may be seen as another proof of judicial restraint - or even as indicator of the beginning of a new phase in the “constitutional dialogue” between the ECJ and the “Masters of the Treaties.”

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The article describes and assesses the role of national parliaments in EU legislation considering the reforms introduced by the Lisbon Treaty. This is closely connected with the understanding and (political) application of the principle of subsidiarity. After an analysis of the possibilities and limitations of the relevant legal regulations in the post-Lisbon age, alternative ways for participation of national legislators on the European level are being scrutinized and proposed. The issue of democratic legitimization is also interconnected with the current political reforms being discussed in order to overcome the Euro Crisis. Finally, the authors argue that it does not make sense to include national parliaments in the existing legislative triangle of the EU, but instead to promote the creation of a new kind of supervisory body.

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The current debate taking place in continental Europe on the need to reform labour law to reduce the duality between labour market insiders and outsiders, thus giving new employment opportunities to young people seems to be, at its best, a consequence of the crisis, or at its worst, an excuse. The considerable emphasis placed on the power of legislation to reduce youth unemployment prevents real labour market problems from being clearly identified, thus reducing the scope to adopt more effective measures. Action is certainly required to help young people during the current crisis, yet interventions should not be exclusively directed towards increased flexibility and deregulation. This paper questions the “thaumaturgic power” wrongly attributed to legislative interventions and put forward a more holistic approach to solve the problem of youth employment, by focusing on the education systems, school-to-work transition and industrial relations. As a comparative analysis demonstrates, in order to effectively tackle the issue of youth employment, it is not enough to reform labour law. High quality education systems, apprenticeship schemes, efficient placement and employment services, cooperative industrial relations and flexible wage determination mechanisms are the key to success when it comes to youth employment, not only in times of recession.