16 research outputs found
Untangling associations between chironomid taxa in Neotropical streams using local and landscape filters
1. Analyses of species association have major implications for selecting indicators for freshwater biomonitoring and conservation, because they allow for the elimination of redundant information and focus on taxa that can be easily handled and identified. These analyses are particularly relevant in the debate about using speciose groups (such as the Chironomidae) as indicators in the tropics, because they require difficult and time-consuming analysis, and their responses to environmental gradients, including anthropogenic stressors, are poorly known. 2. Our objective was to show whether chironomid assemblages in Neotropical streams include clear associations of taxa and, if so, how well these associations could be explained by a set of models containing information from different spatial scales. For this, we formulated a priori models that allowed for the influence of local, landscape and spatial factors on chironomid taxon associations (CTA). These models represented biological hypotheses capable of explaining associations between chironomid taxa. For instance, CTA could be best explained by local variables (e.g. pH, conductivity and water temperature) or by processes acting at wider landscape scales (e.g. percentage of forest cover). 3. Biological data were taken from 61 streams in Southeastern Brazil, 47 of which were in well-preserved regions, and 14 of which drained areas severely affected by anthropogenic activities. We adopted a model selection procedure using Akaike`s information criterion to determine the most parsimonious models for explaining CTA. 4. Applying Kendall`s coefficient of concordance, seven genera (Tanytarsus/Caladomyia, Ablabesmyia, Parametriocnemus, Pentaneura, Nanocladius, Polypedilum and Rheotanytarsus) were identified as associated taxa. The best-supported model explained 42.6% of the total variance in the abundance of associated taxa. This model combined local and landscape environmental filters and spatial variables (which were derived from eigenfunction analysis). However, the model with local filters and spatial variables also had a good chance of being selected as the best model. 5. Standardised partial regression coefficients of local and landscape filters, including spatial variables, derived from model averaging allowed an estimation of which variables were best correlated with the abundance of associated taxa. In general, the abundance of the associated genera tended to be lower in streams characterised by a high percentage of forest cover (landscape scale), lower proportion of muddy substrata and high values of pH and conductivity (local scale). 6. Overall, our main result adds to the increasing number of studies that have indicated the importance of local and landscape variables, as well as the spatial relationships among sampling sites, for explaining aquatic insect community patterns in streams. Furthermore, our findings open new possibilities for the elimination of redundant data in the assessment of anthropogenic impacts on tropical streams.FAPESP Sao Paulo state Research FoundationFundação de Amparo Ă Pesquisa do Estado de SĂŁo Paulo (FAPESP)Conselho Nacional de Desenvolvimento CientĂfico e TecnolĂłgico (CNPq)CNP
Ăreas de inundação no trecho paulista da bacia do Rio ParaĂba do Sul e nascentes do Cadastro Ambiental Rural
The effect of asymmetric information risk on returns of stocks traded on the BM&FBOVESPA
A quem se dirigem os editoriais? Um estudo acerca de personagens e instituiçÔes mencionadas pelos jornais O Estado de S. Paulo e Folha de S. Paulo
A literatura sobre jornalismo polĂtico indica que aqueles agentes ocupando cargos de maior hierarquia tendem a dispor de maior cota de visibilidade no noticiĂĄrio. A fim de esclarecer as relaçÔes entre o cargo ocupado pelo agente polĂtico ou o fato de tratar-se de uma instituição e o grau de visibilidade do qual se dispĂ”e, este artigo busca compreender como funcionam os parĂĄâmetros de escolha editorial, por meio de mapeamento das personagens e instituiçÔes mencionadas por 185 editoriais dos jornais O Estado de S. Paulo e Folha de S. Paulo sobre o Congresso Nacional. O trabalho propĂ”e trĂȘs hipĂłteses: H1 ââ hĂĄ correlação positiva entre tratar-se de uma instituição e a quantidade de mençÔes recebidas nos editoriais; H2 ââ hĂĄ correlação positiva entre ocupar cargo nos campos polĂtico e econoĂâmico ou no JudiciĂĄrio e a quantidade de mençÔes recebidas nos editoriais; e H3 ââ uma vez que os editoriais compondo o corpus tratam do Congresso Nacional, as duas Casas (CĂĄâmara e Senado) e os agentes integrantes do Legislativo sĂŁo os mais mencionados pelas peças. Para testar as hipĂłteses, utilizou-se estatĂstica descritiva. TambĂ©m se aplicou um teste-t, uma regressĂŁo mĂșltipla e observou-se o valor-p para os dados. Apenas a primeira hipĂłtese foi confirmada por completo, enquanto a segunda foi refutada e a terceira foi confirmada em parte. Os dados contradizem a literatura sobre jornalismo polĂtico. Apenas agentes polĂticos muito poderosos, a exemplo do presidente da RepĂșblica, obtĂȘm visibilidade nos editoriais, pois se priorizam mençÔes a instituiçÔes. Assim, o jornalismo polĂtico praticado nos editoriais dirige-seĂ a agentes polĂticos detentores de poder de decisĂŁo ou a instituiçÔes significativas para a democracia e para o sistema polĂtico do paĂs, tornando o acesso Ă esfera de visibilidade pĂșblica ainda mais restrito