950 resultados para Hemispheric specialization


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Mutualisms often form networks of interacting species, characterized by the existence of a central core of species that potentially drive the ecology and the evolution of the whole community. Centrality measures allow quantification of how central or peripheral a species is within a network, thus informing about the role of each species in network organization, dynamics, and stability. In the present study we addressed the question whether the structural position of species in the network (i.e. their topological importance) relates to their ecological traits. We studied interactions between cleaner and client reef fishes to identify central and peripheral species within a mutualistic network, and investigated five ecological correlates. We used three measures to estimate the level of centrality of a species for distinct structural patterns, such as the number of interactions and the structural proximity to other species. Through the use of a principal component analysis (PCA) we observed that the centrality measures were highly correlated (92.5%) in the studied network, which indicates that the same species plays a similar role for the different structural patterns. Three cleaner and ten client species had positive values of centrality, which suggests that these species are modulating ecological and evolutionary dynamics within the network. Higher centralities were related to higher abundances and feeding habits for client fishes, but not for cleaners. The high correlation between centrality measures in the present study is likely related to the nested structure of the cleaning network. The cleaner species` set, by having central species that are not necessarily the most abundant ones, bears potentially more vulnerable points for network cohesiveness. Additionally, the present study generalizes previous findings for plant-animal mutualisms, as it shows that the structure of marine mutualisms is also related to a complex interplay between abundance and niche-related features.

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We analyzed the structure of a multispecific network or interacting ants and plants bearing extrafloral nectaries recorded in 1990 and again in 2000 in La Mancha, Veracruz, Mexico. We assessed the replicability of the number of interactions found among species and also whether there had been changes in the network structure associated with appearance of new ant and plant species during. that 10-year period. Our results show that the nested topology of the network was similar between sampling dates, group dissimilarity increased, mean number of interactions for ant species increased, the frequency distribution of standardized degrees reached higher values for plant species, more ant species and fewer plant species constituted the core of the more recent network, and the presence of new ant and plant species increased while their contribution to nestedness remained the same. Generalist species (i.e., those with the most links or interactions) appeared to maintain the stability of the network because the new species incorporated into the communities were linked to this core of generalists. Camponotus planatus was the most extreme generalist ant species (the one with the most links) in both networks, followed by four other ant species; but other species changed either their position along the continuum of generalists relative to specialists or their presence or absence within the network. Even though new species moved into the area during the decade between the surveys, the overall network structure remained unmodified.

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Many generalist populations may actually be composed of relatively specialist individuals. This `individual specialization` may have important ecological and evolutionary implications. Although this phenomenon has been documented in more than one hundred taxa, it is still unclear how individuals within a population actually partition resources. Here we applied several methods based on network theory to investigate the intrapopulation patterns of resource use in the gracile mouse opossum Gracilinanus microtarsus. We found evidence of significant individual specialization in this species and that the diets of specialists are nested within the diets of generalists. This novel pattern is consistent with a recently proposed model of optimal foraging and implies strong asymmetry in the interactions among individuals of a population.

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P>1. Much of the current understanding of ecological systems is based on theory that does not explicitly take into account individual variation within natural populations. However, individuals may show substantial variation in resource use. This variation in turn may be translated into topological properties of networks that depict interactions among individuals and the food resources they consume (individual-resource networks). 2. Different models derived from optimal diet theory (ODT) predict highly distinct patterns of trophic interactions at the individual level that should translate into distinct network topologies. As a consequence, individual-resource networks can be useful tools in revealing the incidence of different patterns of resource use by individuals and suggesting their mechanistic basis. 3. In the present study, using data from several dietary studies, we assembled individual-resource networks of 10 vertebrate species, previously reported to show interindividual diet variation, and used a network-based approach to investigate their structure. 4. We found significant nestedness, but no modularity, in all empirical networks, indicating that (i) these populations are composed of both opportunistic and selective individuals and (ii) the diets of the latter are ordered as predictable subsets of the diets of the more opportunistic individuals. 5. Nested patterns are a common feature of species networks, and our results extend its generality to trophic interactions at the individual level. This pattern is consistent with a recently proposed ODT model, in which individuals show similar rank preferences but differ in their acceptance rate for alternative resources. Our findings therefore suggest a common mechanism underlying interindividual variation in resource use in disparate taxa.

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Peponapis bees are considered specialized pollinators of Cucurbita flowers, a genus that presents several species of economic value (squashes and pumpkins). Both genera originated in the Americas, and their diversity dispersion center is in Mexico. Ten species of Peponapis and ten species of Cucurbita (only non-domesticated species) were analyzed considering the similarity of their ecological niche characteristics with respect to climatic conditions of their occurrence areas (abiotic variables) and interactions between species (biotic variables). The similarity of climatic conditions (temperature and precipitation) was estimated through cluster analyses. The areas of potential occurrence of the most similar species were obtained through ecological niche modeling and summed with geographic information system tools. Three main clusters were obtained: one with species that shared potential occurrence areas mainly in deserts (P. pruinosa, P. timberlakei, C. digitata, C. palmata, C. foetidissima), another in moist forests (P. limitaris, P. atrata, C. lundelliana, C. o. martinezii) and a third mainly in dry forests (C. a. sororia, C. radicans, C. pedatifolia, P. azteca, P. smithi, P. crassidentata, P. utahensis). Some species with similar ecological niche presented potential shared areas that are also similar to their geographical distribution, like those occurring predominantly on deserts. However, some clustered species presented larger geographical areas, such as P. pruinosa and C. foetidissima suggesting other drivers than climatic conditions to shape their distributions. The domestication of Cucurbita and also the natural history of both genera were considered also as important factors. (C) 2011 Elsevier B.V. All rights reserved.

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We investigated the evolution of anuran locomotor performance and its morphological correlates as a function of habitat use and lifestyles. We reanalysed a subset of the data reported by Zug (Smithson. Contrib. Zool. 1978; 276: 1-31) employing phylogenetically explicit statistical methods (n = 56 species), and assembled morphological data on the ratio between hind-limb length and snout-vent length (SVL) from the literature and museum specimens for a large subgroup of the species from the original paper (n = 43 species). Analyses using independent contrasts revealed that classifying anurans into terrestrial, semi-aquatic, and arboreal categories cannot distinguish between the effects of phylogeny and ecological diversification in anuran locomotor performance. However, a more refined classification subdividing terrestrial species into `fossorials` and `non-fossorials`, and arboreal species into `open canopy`, `low canopy` and `high canopy`, suggests that part of the variation in locomotor performance and in hind-limb morphology can be attributed to ecological diversification. In particular, fossorial species had significantly lower jumping performances and shorter hind limbs than other species after controlling for SVL, illustrating how the trade-off between burrowing efficiency and jumping performance has resulted in morphological specialization in this group.

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Social organization enables leaf-cutting ants to keep appropriate micro-ecological nest conditions for the fungus garden (their main food), eggs, larvae and adults. To maintain stability while facing changing conditions, individual ants must perceive destabilising factors and produce a proper behavioral response. We investigated behavioral responses to experimental dehydration in leaf-cutting ants to verify if task specialization exists, and to quantify the ability of ant sub-colonies for water management. Our setup consisted of fourteen sub-colonies, ten of which were randomly assigned to different levels of experimental dehydration with silica gel, whereas the remaining four were controls. The ten experimental sub-colonies were split into two groups, so that five of them had access to water. Diverse ant morphs searched for water in dehydrated colonies, but mainly a caste of small ants collected water after sources had been discovered. Size specialization for water collection was replicable in shorter experiments with three additional colonies. Ants of dehydrated colonies accumulated leaf-fragments on the nest entrance, and covering the fungus garden. Behaviors that may enhance humidity within the nests were common to all dehydration treatments. Water availability increased the life span of dehydrated colonies.

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Leaves comprise most of the vegetative body of tank bromeliads and are usually subjected to strong longitudinal gradients. For instance, while the leaf base is in contact with the water accumulated in the tank, the more light-exposed middle and upper leaf sections have no direct access to this water reservoir. Therefore, the present study attempted to investigate whether different leaf portions of Guzmania monostachia, a tank-forming C(3)-CAM bromeliad, play distinct physiological roles in response to water shortage, which is a major abiotic constraint in the epiphytic habitat. Internal and external morphological features, relative water content, pigment composition and the degree of CAM expression were evaluated in basal, middle and apical leaf portions in order to allow the establishment of correlations between the structure and the functional importance of each leaf region. Results indicated that besides marked structural differences, a high level of functional specialization is also present along the leaves of this bromeliad. When the tank water was depleted, the abundant hydrenchyma of basal leaf portions was the main reservoir for maintaining a stable water status in the photosynthetic tissues of the apical region. In contrast, the CAM pathway was intensified specifically in the upper leaf section, which is in agreement with the presence of features more suitable for the occurrence of photosynthesis at this portion. Gas exchange data indicated that internal recycling of respiratory CO(2) accounted for virtually all nighttime acid accumulation, characterizing a typical CAM-idling pathway in the drought-exposed plants. Altogether, these data reveal a remarkable physiological complexity along the leaves of G. monostachia, which might be a key adaptation to the intermittent water supply of the epiphytic niche. (C) 2009 Elsevier GmbH. All rights reserved.

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There is evidence that automatic visual attention favors the right side. This study investigated whether this lateral asymmetry interacts with the right hemisphere dominance for visual location processing and left hemisphere dominance for visual shape processing. Volunteers were tested in a location discrimination task and a shape discrimination task. The target stimuli (S2) could occur in the left or right hemifield. They were preceded by an ipsilateral, contralateral or bilateral prime stimulus (S1). The attentional effect produced by the right S1 was larger than that produced by the left S1. This lateral asymmetry was similar between the two tasks suggesting that the hemispheric asymmetries of visual mechanisms do not contribute to it. The finding that it was basically due to a longer reaction time to the left S2 than to the right S2 for the contralateral S1 condition suggests that the inhibitory component of attention is laterally asymmetric.

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Divorces and separations: the impact of role specialisation and equality At the same time as women made their large scale entrance on the labour market divorce rates increased in most western societies. This combination of societal trends was widely understood from the perspective of the specialization and trading model, which implies undermined marital stability through decreasing interdependency between husband and wife. We argue the need to acknowledge the new roles, and perceptions of these roles, men and women have in order to explain differences in separation and stability among couples. When both partners are expecting to be in paid labour and share housework responsibilities, specialisation could actually be a risk factor for cohabitational dissolution. This article uses a ten year longitudinal database of all Swedish cohabiting first time parents in 1993. The analyses generally support what could be labelled a role balance model on separation rather than the specialization model. Looking at the father’s participation in childcare this was quite clear, where the man’s outtake of parental leave for the first child was shown to be related to reduced hazards of separation. In the same way equal distribution of the household labour market incomes between the partners was related to lower hazards of separation.

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In 1982, Greek shipping plunged into a severe crisis: the size of the fleet declined dramatically and over 30% of the fleet was laid-up. catapulting many shipping companies into bankruptcy. The causes of the crisis were: The world recession, leading to regulation, protectionism, subsidization. and the growth of new competition in the tramp shipping market. The erosion of the cost differential between Greek shipping and other maritime nations of the world. The specialization and containerization of the world fleet. The old age and other characteristics of the Greek fleet, which exacerbated the crisis. Greek shipping, with its long history and the expertise, diligence, and supreme opportunism of its dynamic shipowners, will survive the crisis.

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In this paper we analyze the optimality of allowing firms to observe signals of workers’ characteristics in an optimal taxation framework. We show that it is always optimal to prohibit signals that disclose information about differences in the intrinsic productivities of workers like mandatory health exams and IQ tests, for example. On the other hand, it is never optimal to forbid signals that reveal information about the comparative advantages of workers like their specialization and profession. When signals are mixed (they disclose both types of information), there is a trade-off between efficiency and equity. It is optimal to prohibit signals with sufficiently low comparative advantage content.

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Este relatório intitulado “Pesquisa sobre o ECR na Relação Fornecedor X Atacadista no Brasil”, foi desenvolvido pelo Professor Manoel de Andrade e Silva Reis, para o Núcleo de Pesquisas e Projetos (NPP) da Fundação Getúlio Vargas de São Paulo. Inicialmente apresenta alguns conceitos importantes para o entendimento do texto e faz considerações gerais sobre o ECR no Brasil e seu histórico. A principal parte do trabalho é a pesquisa realizada com 10 FORNECEDORES e 20 ATACADISTAS, sendo que 60% dos FORNECEDORES e 40% dos ATACADISTAS responderam aos questionários. As principais conclusões da pesquisa são: 1) Existem sérios obstáculos a transpor para a implantação abrangente do ECR na relação FORNECEDOR X ATACADISTA no Brasil, como: a) O setor ATACADISTA tem um forte preconceito com relação ao ECR, pelo receio de perda de mercado com a implantação de uma nova forma de fazer negócio. Isso evita que seus membros aprofundem o conhecimento das suas estratégias e ferramentas; b) Empresas ATACADISTAS tendem a ser muito fechadas, dificilmente abrindo suas informações para fornecedores, um dos requisitos básicos para a implantação bem sucedida do ECR. Têm também grande rivalidade com seus pares ATACADISTAS. c) O setor ATACADISTA desconfia das verdadeiras intenções dos FORNECEDORES. Há ATACADISTAS que chegaram a implantar uma ferramenta do ECR para teste e desistiram, por sentirem que os FORNECEDORES fogem aos acordos estabelecidos, visando, em especial, preencher as cotas de venda. 2) Na opinião das empresas ATACADISTAS, a sobrevivência setor depende de fatores como: a) Necessidade de uma radical mudança cultural das empresas, de forma a adotar os conceitos de compra e venda necessários no ECR; b) Necessidade de especialização em canais escolhidos e nos produtos característicos dos mesmos, visando tornar-se especialista na sua comercialização; c) Gestão mais adequada dos níveis de estoque; d) Maior agilidade no acesso ao pequeno varejo. 3) Fatores que podem aumentar a atratividade do setor ATACADISTA para os FORNECEDORES: a) Redução do número de transações; b) Redução dos custos pelos elevados volumes; c) Prestação de serviços ao pequeno varejo (devoluções, trocas, promoções, treinamento e incentivos); d) Pulverização das vendas.

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This research was as principal interest to verify the motives the prominence of crescent outstanding of distance education in brazilian higher education. To make real the study were used the bibliographical and field researches. The bibliographical informations permitted to conclude that the total success of distance education in Brazil strikes against two obstacles: the digital exclusion and illiteracy. These, in turn, have created another problem called today digital illiteracy. Although there are those limitations, by the data about distance education in the country, it is patent that this modality of education is gaining more and more space in brazilian educational process. It has to detach that the greatest concentration of distance courses accredited in Brazil occurs in higher education. Today, distance courses at this level in the country are authorized in sequential, graduation, specialization, master and doctorate areas. The field research led to confirm practically all suppositions about the increase of distance education in higher education, proposed in anticipation. The flexibility that makes possible the transmission of knowledge at any place and time and the new technologies, chiefly the Internet, were the factors that more impelled the increase of distance education in brazilian higher teaching. Meanwhile, the quality improving of the courses was the less significative in respect to the growth of distance education it the higher level in Brazil. But, this fact does not signify that the distance higher courses have not quality. On the contrary, the courses are ministered by professionals of confirmed competence. What can still legitimize the presence of quality in distance higher teaching is its exponential growth in the country. Moreover, the importance attributed to the pedagogical project well planned in distance higher courses demonstrates the interest by excellence in the distance learning. Certainly, when a pedagogical project is well delineated, at any level of distance teaching, the trend of quality is perfect itself.

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O mercado exige cada vez mais o aperfeiçoamento das organizações, inclusive às de pequeno porte, haja visto que as empresas de pequeno porte estão aumentando sua área de atingimento e consequêntemente necessitam de maiores controles gerenciais. No que tange ao controle econômico-financeiro, não basta o administrador apenas prestar atenção nos valores movimentados, mas sim ter cuidado especial em sua base de dados que gera as informações para as decisões, isso recai sobre o sistema de custos na empresa. O sistema de custos é formado pelos princípios e métodos que auxiliarão na formação de preços, que também além do mercado, sofre influência do fluxo de caixa que por sua vez decorre em função do ciclo operacional realizado. Por isso da necessidade do aperfeiçoamento do administrado da empresa de pequeno porte, para poder implementar uma Gestão Financeira eficaz que possua controle sobre todas essas nunces citadas. O presente trablho buscou discernir de forma objetiva a parte teórica e tembém através de um modelo a parte prática dessa integração de informações criando um modelo de Gestão Financeira.