994 resultados para Marinetti, Filippo Tommaso
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Spatial patterns in assemblage structures are generated by ecological processes that occur on multiple scales. Identifying these processes is important for the prediction of impact, for restoration and for conservation of biodiversity. This study used a hierarchical sampling design to quantify variations in assemblage structures of Brazilian estuarine fish across 2 spatial scales and to reveal the ecological processes underlying the patterns observed. Eight areas separated by 0.7 to 25 km (local scale) were sampled in 5 estuaries separated by 970 to 6000 km (regional scale) along the coast, encompassing both tropical and subtropical regions. The assemblage structure varied significantly in terms of relative biomass and presence/absence of species on both scales, but the regional variation was greater than the local variation for either dataset. However, the 5 estuaries sampled segregated into 2 major groups largely congruent with the Brazilian and Argentinian biogeographic provinces. Three environmental variables (mean temperature of the coldest month, mangrove area and mean annual precipitation) and distance between estuaries explained 44.8 and 16.3%, respectively, of the regional-scale variability in the species relative biomass. At the local scale, the importance of environmental predictors for the spatial structure of the assemblages differed between estuarine systems. Overall, these results support the idea that on a regional scale, the composition of fish assemblages is simultaneously determined by environmental filters and species dispersal capacity, while on a local scale, the effect of environmental factors should vary depending on estuary-specific physical and hydrological characteristics © 2013 Inter-Research.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Se sugieren algunos elementos de juicio tendientes a justificar la necesidad de desarrollar un enmarcamiento historico del tema de la investigacion comparativa. Deberia establecerse un vinculo organico entre el comportamiento de aquellos factores de largo plazo y los que se consideran mas especificamente en el estudio durante su periodo de cobertura. En sintesis, la localizacion de las actividades urbanas del complejo exportador, el caracter de la propiedad de los recursos naturales exportables, la localizacion del gobierno central y su capacidad para captar ingresos de exportacion y crear empleos urbanos, la modificacion de las formas precapitalistas de relacionamiento social en areas rurales y la magnitud y orientacion de las grandes migraciones ultramarinas del siglo pasado y comienzos de este, son algunas de las "pistas" plausibles a considerar en la pesquisa de los factores historicos que promovieron una fuerte tendencia primacial en el perfil urbano de los principales paises de America Latina.