Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia

Primary Research PaperSpecific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio

BlueGene/L Applications: Parallelism on a Massive Scale

BlueGene/L (BG/L), developed through a partnership between IBM and Lawrence Livermore National Laboratory (LLNL), is currently the world's largest system both in terms of scale with 131,072 processors and absolute performance with a peak rate of 367 TFlop/s. BG/L has led the Top500 list the last four times with a Linpack rate of 280.6 TFlop/s for the full machine installed at LLNL and is expected to remain the fastest computer in the next few editions. However, the real value of a machine like BG/L derives from the scientific breakthroughs that real applications can produce by successfully using its unprecedented scale and computational power. In this paper, we describe our experiences with eight large scale applications on BG/L from several application domains, ranging from molecular dynamics to dislocation dynamics and turbulence simulations to searches in semantic graphs. We also discuss the challenges we faced when scaling these codes and present several successful optimization techniques. All applications show excellent scaling behavior, even at very large processor counts, with one code even achieving a sustained performance of more than 100 TFlop/s, clearly demonstrating the real success of the BG/L design

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TeraScalable Algorithms for Variable-Density Elliptic Hydrodynamics with Spectral Accuracy

We describe Miranda, a massively parallel spectral/compact solver for variabledensity incompressible flow, including viscosity and species diffusivity effects. Miranda utilizes FFTs and band-diagonal matrix solvers to compute spatial derivatives to at least 10th-order accuracy. We have successfully ported this communicationintensive application to BlueGene/L and have explored both direct block parallel and transpose-based parallelization strategies for its implicit solvers. We have discovered a mapping strategy which results in virtually perfect scaling of the transpose method up to 65,536 processors of the BlueGene/L machine. Sustained global communication rates in Miranda typically run at 85 % of the theoretical peak speed of the BlueGene/L torus network, while sustained communication plus computation speeds reach 2.76 TeraFLOPS. This effort represents the first time that a high-order variable-density incompressible flow solver with species diffusion has demonstrated sustained performance in the TeraFLOPS range. (c) 2005 Association for Computing Machinery. ACM acknowledges that this contribution was authored or co-authored by a contractor of affiliate of the U.S. Government. As such, the Government retains a nonexclusive, royalty-free right to publish or reproduce this article, or to allow others to do so, for Government purposes only

Alimentação de Oligosarcus longirostris Menezes & Gèry (Osteichthyes, acestrorhynchinae) do Reservatório de Salto Segredo, Paraná, Brasil Feeding of Oligosarcus longirostris Menezes & Gèry (Osteichthyes, acestrorhynchinae) of the Salto Segredo Reservoir, Paraná, Brazil

<abstract language="eng">In the feeding study of O. longirostris Menezes & Gèry, 1983, 211 stomachs from fish caught between March 1993 and February 1994 were analysed. Diet composition was analysed by the index of relative importance which deals with the numerical and gravimetric occurrence frequency. Results indicated that the species is piscivorous and its preferential food consisted oíAslyanax sp. 2. It was also found that Astyanax sp. 3 became an important food item, depending on the site of capture and its availability. Availability of prey seems to have a strong influence on the diet of O. longirostris. This same tendency has been observed during the different seasons of the year. Ontogenetic changes have also been found in the basic diet