12165 research outputs found
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The dilution procedure to manipulate microbial biodiversity in terrestrial systems revisited
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The Exploration and Visualisation of Big Data in the Humanities, Comparing Data Representation of a Large-scale E-infrastructure (CLARIN) and a Dedicated Virtual Research Environment (Soundbites)
No full textFood-web patterns and diversity in tropical fish communities
No full textThe food webs for three Sri Lankan reservoirs, Minneriya (ancient and shallow), Udawalawe (young and shallow) and Victoria (young and deep), were compared. The species richness of the fish communities was highest in Minneriya (30 species), intermediate in Udawalawe (21 species) and lowest in Victoria (18 species). The fish species belonged to 11 families, with Cyprinidae dominating the community in terms of both abundance and species richness. The daily quantity of food consumed per fish species was used to distinguish weak from strong trophic interactions in these food webs. The fish community consumption pattern was characterized by a few strong interactions and many weak ones. The number of major consumers (i.e. contributing >5% of the total fish community consumption) for each reservoir was small and similar for all three reservoirs. Dawkinsia singhala and Amblypharyngodon melettinus were the two major consumers in all three reservoir food webs. Puntius chola was a major consumer in Minneriya and Victoria, although not in Udawalawe, where it fed less on detritus than for the other two food webs. The fish community fed mainly at the bottom of the food web, primarily on algae, macrophytes and detritus in all three reservoirs, with very little piscivory occurring. The average food-web length was measured as the mean trophic index weighted for the consumption rates of the various fish populations that together comprised the fish community. The average food-web length in these three Sri Lankan reservoirs relatively short, compared with most other tropical lake/reservoir food webs in Asia and Africa for which relevant data were available. Furthermore, traditionally unexploited species (Oreochromis mossambicus; O. niloticus), in contrast to species of commercial fisheries interest, are major role players in the trophic dynamics of reservoir ecosystems. Thus, based on this study, the potential of their exploitation should be considered in the management of reservoir fisheries.
The spatial structure of Antarctic biodiversity
No full textPatterns of environmental spatial structure lie at the heart of the most fundamental and familiar patterns of diversity on Earth. Antarctica contains some of the strongest environmental gradients on the planet and therefore provides an ideal study ground to test hypotheses on the relevance of environmental variability for biodiversity. To answer the pivotal question, “How does spatial variation in physical and biological environmental properties across the Antarctic drive biodiversity?” we have synthesized current knowledge on environmental variability across terrestrial, freshwater, and marine Antarctic biomes and related this to the observed biotic patterns. The most important physical driver of Antarctic terrestrial communities is the availability of liquid water, itself driven by solar irradiance intensity. Patterns of biota distribution are further strongly influenced by the historical development of any given location or region, and by geographical barriers. In freshwater ecosystems, free water is also crucial, with further important influences from salinity, nutrient availability, oxygenation, and characteristics of ice cover and extent. In the marine biome there does not appear to be one major driving force, with the exception of the oceanographic boundary of the Polar Front. At smaller spatial scales, ice cover, ice scour, and salinity gradients are clearly important determinants of diversity at habitat and community level. Stochastic and extreme events remain an important driving force in all environments, particularly in the context of local extinction and colonization or recolonization, as well as that of temporal environmental variability. Our synthesis demonstrates that the Antarctic continent and surrounding oceans provide an ideal study ground to develop new biogeographical models, including life history and physiological traits, and to address questions regarding biological responses to environmental variability and change.
Read More: http://www.esajournals.org/doi/abs/10.1890/12-2216.1
Histological Changes of Liver in Overfed Young Nile Tilapia
No full textWe investigated histopathologically liver structural responses of Nile Tilapia Oreochromis niloticus towards overfeeding. Mixed population of O. niloticus with mean weight of 55±3.83 g was acclimated for one week. Then, the fish were separated into control and treatment groups. Glass aquariums with external biofilters and artificial heaters were used. Control and treatment groups were fed commercial Tilapia diet at 3 and 6% of fish body weight, respectively. Fish were dissected at three time intervals. Tissues were fixed, re-fixed, processed, embedded with paraffin and sectioned. Sectioned tissue ribbons were stained with hematoxylin and eosin technique for light microcopy. Hepatosomatic Index (HSI) and Hepatohypertrophic Index (HHI) were calculated. Irregular shaped hepatocytes with circular, conspicuous and centrally located nuclei were found from all control groups. Large hypertrophic hepatocytes with nuclei dislocated to the cell periphery observed after three weeks of overfeeding. Lipid vacuolation and atrophy were found after five weeks of overfeeding. Fish overfed for three weeks showed significantly (p<0.05) higher HSI and HHI values. Whereas, fish which were under third week control group showed the second significantly (p<0.05) higher HSI value. Significant (p<0.05) differences in HSI as well as HHI were not found between zero and fifth week control groups. We conclude that overfeeding may cause liver histological alterations in O. niloticus and in turn lower aquaculture profitability by making the fish susceptible to disease.
Glycoalkaloids of Wild and Cultivated Solanum: Effects on Specialist and Generalist Insect Herbivores.
No full textPlant domestication by selective breeding may reduce plant chemical defense in favor of growth. However, few studies have simultaneously studied the defensive chemistry of cultivated plants and their wild congeners in connection to herbivore susceptibility. We compared the constitutive glycoalkaloids (GAs) of cultivated potato, Solanum tuberosum, and a wild congener, S. commersonii, by liquid chromatography coupled to mass spectrometry. We also determined the major herbivores present on the two species in field plots, and tested their preference for the plants and their isolated GAs in two-choice bioassays. Solanum commersonii had a different GA profile and higher concentrations than S. tuberosum. In the field, S. tuberosum was mostly attacked by the generalist aphids Myzus persicae and Macrosiphum euphorbiae, and by the specialist flea beetle Epitrix argentinensis. In contrast, the most common herbivore on S. commersonii was the specialist sawfly Tequus sp. Defoliation levels were higher on the wild species, probably due to the chewing feeding behavior of Tequus sp. As seen in the field, M. persicae and E. argentinensis preferred leaf disks of the cultivated plant, while Tequus sp. preferred those of the wild one. Congruently, GAs from S. commersonii were avoided by M. persicae and preferred by Tequus sp. The potato aphid performed well on both species and was not deterred by S. commersonii GAs. These observations suggest that different GA profiles explain the feeding preferences of the different herbivores, and that domestication has altered the defensive capacity of S. tuberosum. However, the wild relative is still subject to severe defoliation by a specialist herbivore that may cue on the GAs.
Folivory Affects Composition of Nectar, Floral Odor and Modifies Pollinator Behavior
No full textHerbivory induces changes in plants that influence the associated insect community. The present study addresses the potential trade-off between plant phytochemical responses to insect herbivory and interactions with pollinators. We used a multidisciplinary approach and have combined field and greenhouse experiments to investigate effects of herbivory in plant volatile emission, nectar production, and pollinator behavior, when Pieris brassicae caterpillars were allowed to feed only on the leaves of Brassica nigra plants. Interestingly, volatile emission by flowers changed upon feeding by herbivores on the leaves, whereas, remarkably, volatile emission by leaves did not significantly differ between infested and non-infested flowering plants. The frequency of flower visits by pollinators was generally not influenced by herbivory, but the duration of visits by honeybees and butterflies was negatively affected by herbivore damage to leaves. Shorter duration of pollinator visits could be beneficial for a plant, because it sustains pollen transfer between flowers while reducing nectar consumption per visit. Thus, no trade-off between herbivore-induced plant responses and pollination was evident. The effects of herbivore-induced plant responses on pollinator behavior underpin the importance of including ecological factors, such as herbivore infestation, in studies of the ecology of plant pollination. [KEYWORDS: Brassica nigra (black mustard) Flower visitors Herbivore-induced plant volatiles Herbivory Honeybees Syrphid flies NICOTIANA-ATTENUATA OPTIMAL DEFENSE WILD RADISH ELECTROANTENNOGRAM RESPONSES RAPHANUS-RAPHANISTRUM PIERIS-BRASSICAE PLANT VOLATILES LEAF HERBIVORY DAMAGE VISITATION]