10,088 research outputs found

    Water Resources Review - Fall 2008, Vol 21, No. 1

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    Investigating the foraging ecology and energy requirements of a seabird population increasing in an intensely exploited marine environment

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    Their high energetic demands make seabirds sensitive to changes in prey availability, which is often reflected in their diet and energetic expenditure during breeding. Populations of the three seabirds endemic to southern Africa's Benguela upwelling ecosystem that rely on small pelagic fish have decreased dramatically over the last decade. In contrast, the population of the greater crested tern Thalasseus bergii has increased. To understand these conflicting trends, I investigated the foraging ecology and energy requirements of greater crested tern breeding in the Western Cape, South Africa. Diet was assessed by a novel non-invasive methodology developed in this study, using digital photography. More than 24,000 prey items from at least 51 different prey taxa were identified, with 34 new prey species recorded, revealing a high degree of foraging plasticity for this seabird. Greater crested terns rely mainly on anchovy Engraulis encrasicolus (65%), which averaged 84 mm long. Prey composition differed significantly between breeding stages, with anchovy especially dominant at the onset of the breeding period and the diet becoming more variable as the season progressed. Time-energy models for breeding terns were built based on activity budgets collected from non-invasive video-recordings and focal observations. Foraging trips were significantly longer during incubation than the chick provisioning stages, and feeding rates doubled from early to late chick provisioning. This study illustrated a steady increase in energy needs of adults throughout the breeding season, due to their increased foraging effort to meet chick energy needs. In comparison to other Benguela endemic seabirds that also rely on small pelagic fish, terns displayed substantially lower energy requirements at both individual and population levels. I also explored the benefits underlying interactions within mixed-species aggregations by investigating the costs induced by kleptoparasitism between mixed colonies of greater crested terns and Hartlaub's gulls Chroicocephalus hartlaubii and colonies with greater crested terns alone. Video-recordings coupled with focal observations showed that terns suffer direct costs to chick provisioning rates and indirect costs through energy expenditure in a mixed-species colony, suggesting that these breeding assemblages may be a form of parasitism rather than a mutualistic association. Despite the detrimental effects of interspecific kleptoparasitism, the marked foraging plasticity and low energetic requirements of greater crested terns, described in this study, coupled with specific life history traits such as low fidelity to breeding sites and extended post-fledging care, are key factors that allow this species to cope with changes in the availability and abundance of their main prey. Understanding species-specific behavioural responses to ecosystem variations in the Benguela upwelling system is vital for assessing the impact of commercial fisheries on seabird populations and fish stocks. Finally, the implementation of the method developed in this study, in long-term monitoring programmes, may provide crucial knowledge for conservation plans and key input to realising an ecosystem approach to fisheries management

    Cloud Computing Strategies for Enhancing Smart Grid Performance in Developing Countries

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    In developing countries, the awareness and development of Smart Grids are in the introductory stage and the full realisation needs more time and effort. Besides, the partially introduced Smart Grids are inefficient, unreliable, and environmentally unfriendly. As the global economy crucially depends on energy sustainability, there is a requirement to revamp the existing energy systems. Hence, this research work aims at cost-effective optimisation and communication strategies for enhancing Smart Grid performance on Cloud platforms

    a simple tool for the analysis of periodic cotyledon and leaf movement in Arabidopsis thaliana

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    Background The analysis of circadian leaf movement rhythms is a simple yet effective method to study effects of treatments or gene mutations on the circadian clock of plants. Currently, leaf movements are analysed using time lapse photography and subsequent bioinformatics analyses of leaf movements. Programs that are used for this purpose either are able to perform one function (i.e. leaf tip detection or rhythm analysis) or their function is limited to specific computational environments. We developed a leaf movement analysis tool—PALMA—that works in command line and combines image extraction with rhythm analysis using Fast Fourier transformation and non-linear least squares fitting. Results We validated PALMA in both simulated time series and in experiments using the known short period mutant sensitivity to red light reduced 1 (srr1-1). We compared PALMA with two established leaf movement analysis tools and found it to perform equally well. Finally, we tested the effect of reduced iron conditions on the leaf movement rhythms of wild type plants. Here, we found that PALMA successfully detected period lengthening under reduced iron conditions. Conclusions PALMA correctly estimated the period of both simulated and real-life leaf movement experiments. As a platform-independent console-program that unites both functions needed for the analysis of circadian leaf movements it is a valid alternative to existing leaf movement analysis tools

    Living at the Extremes

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    A preliminary investigation of the potential effects of the invasive Mozambique tilapia Oreochromis mossambicus on the native fish assemblages of Lake MacLeod, Western Australia

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    As one of the major threats to biodiversity in aquatic systems, invasive species can alter the structure and function of a community, often through habitat and resource competition, and/or direct predation. This study aims to determine if invasive tilapia (Oreochromis mossambicus) is likely to have an effect on the native fish communities of Lake MacLeod, a unique and important inland, saline lake system in north-western Western Australia, through competition for key resources, namely habitat and food sources. Seven study sites were selected within the Northern Ponds of Lake MacLeod, from which fish abundances were assessed in three habitats (pneumatophore beds, nearshore and vents) using adapted fyke-nets and unbaited underwater videography. From three of the seven sites, dietary and stable isotope analyses were conducted. The species richness of fish was low, with between 3-4 species caught at each site. Amniataba caudavittata (yellowtail grunters) and Craterocephalus pauciradiatus (hardyheads), the two most prevalent native fish species, were captured in all three habitats. Although observed in every habitat, O. mossambicus was only successfully captured from the vent habitats. The total length of O. mossambicus ranged from 48-385 mm but the cohort at one of the vents, ‘Jack’s vent’, was considerably larger and more abundant than at all other sites. C. pauciradiatus remained consistent in its size structure across sites and habitats, whereas A. caudavittata tended to be slightly smaller in the pneumatophore habitat. Based on stomach contents analysis, O. mossambicus and A. caudavittata consumed many of the same food items, but often in different proportions. Little variation was seen among sites, except for Jack’s, and the diets were more separated by species than by site. A. caudavittata consumed higher percentages of filamentous green algae, amphipods, and seagrasses than O. mossambicus, but O. mossambicus generally consumed a higher percentage of sand and/or sediment, foraminifera, and detritus. A. caudavittata consumed a wider variety of items. From observations on recorded videos, and from the high percentage of sediment in the stomachs of O. mossambicus relative to A. caudavittata, it was concluded that the two species are utilizing different feeding strategies; the former selecting items from the benthos and the latter straight from the water column. A. caudavittata had a higher mean !15N than O. mossambicus, but not high enough to imply they occupy different trophic levels. The mixing models based on stable isotopes that incorporate food assimilated over longer periods than stomach content analysis, suggested a greater similarity in the diets between species within each site. O. mossambicus is occupying some of the same habitats and using some of the same resources as the native fish, particularly A. caudavittata. However, based on behavioural differences, such as feeding strategies, and the observed differences in prey item proportions, along with the observations of high abundances of all species at many sites, it can be hypothesized that the fish species successfully co-exist with the present habitat and food resource availability. It would be prudent to examine other aspects of the ecology of O. mossambicus in this system to determine if they are impacting the system in ways other than its trophic and habitat interactions with other species
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