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Conditions Favourable (condition + favourable)
Selected AbstractsTracing energy flow in stream food webs using stable isotopes of hydrogenFRESHWATER BIOLOGY, Issue 5 2010JACQUES C. FINLAY Summary 1. Use of the natural ratios of carbon and nitrogen stable isotopes as tracers of trophic interactions has some clear advantages over alternative methods for food web analyses, yet is limited to situations where organic materials of interest have adequate isotopic separation between potential sources. This constrains the use of natural abundance stable isotope approaches to a subset of ecosystems with biogeochemical conditions favourable to source separation. 2. Recent studies suggest that stable hydrogen isotopes (,D) could provide a robust tracer to distinguish contributions of aquatic and terrestrial production in food webs, but variation in ,D of consumers and their organic food sources are poorly known. To explore the utility of the stable hydrogen isotope approach, we examined variation in ,D in stream food webs in a forested catchment where variation in ,13C has been described previously. 3. Although algal ,D varied by taxa and, to a small degree, between sites, we found consistent and clear separation (by an average of 67,) from terrestrial carbon sources. Environmental conditions known to affect algal ,13C, such as water velocity and stream productivity did not greatly influence algal ,D, and there was no evidence of seasonal variation. In contrast, algal ,13C was strongly affected by environmental factors both within and across sites, was seasonally variable at all sites, and partially overlapped with terrestrial ,13C in all streams with catchment areas larger than 10 km2. 4. While knowledge of isotopic exchange with water and trophic fractionation of ,D for aquatic consumers is limited, consistent source separation in streams suggests that ,D may provide a complementary food web tracer to ,13C in aquatic food webs. Lack of significant seasonal or spatial variation in ,D is a distinct advantage over ,13C for applications in many aquatic ecosystems. [source] Changes of taxonomic and trophic structure of fish assemblages along an environmental gradient in the Upper Beni watershed (Bolivia)JOURNAL OF FISH BIOLOGY, Issue 1 2006M. Pouilly The distribution and the diet of 28 fish species were evaluated, during the dry season, in 12 streams of the Upper Beni watershed (Amazon basin, Bolivia). The 12 streams were of similar size (stream width and water depth) but situated on a gradient of altitude in the Andean and sub-Andean areas. The environmental conditions in the stream changed in relation to the altitude. As altitude decreased, slope and water velocity also decreased, while temperature, conductivity, pH and the proportion of pools increased. Although the diets of the species were mainly based on two aquatic autochthonous food resources, invertebrates and sediment, species were classified into five trophic guilds: detritivores, algivores, piscivores, invertivores-omnivores and aquatic specialist invertivores. In all streams invertivores dominated or co-dominated with detritivores. The trophic structure of the assemblages, however, changed in relation to the environmental gradient. The fish species richness increased and the trophic composition became more diverse at lower altitudes, when slope decreased and temperature increased. At the same time, the relative number of invertivore species decreased, whereas the relative number of detritivore, algivore and piscivore species increased. Decreasing altitude appeared to play a role similar to increasing stream size along the longitudinal gradient. This could be explained by geomorphological and temperature variations that may generate environmental conditions favourable to an increase of productivity. [source] Interspecific and intraspecific interactions between salt marsh plants: integrating the effects of environmental factors and density on plant performanceOIKOS, Issue 2 2002Jonathan M. Huckle There has been much debate about the role of plant interactions in the structure and function of vegetation communities. Here the results of a pot experiment with controlled environments are described where three environmental variables (nutrients, sediment type and waterlogging) were manipulated factorially to identify their effects on the growth and intensity of interactions occurring between Spartina anglica and Puccinellia maritima. The two species were grown in split-plot planting treatments, representing intraspecific and interspecific addition series experiments, to determine individual and interactive effects of environmental factors and plant interactions on plant biomass. Above-ground growth of both species involved interactions between the environmental and planting treatments, while below-ground, environmental factors affected the biomass irrespective of planting treatments. It was suggested that this difference in growth response is evidence that in our experiment plant interactions between the two species occur primarily at the above-ground level. The intensity of plant interactions varied in a number of ways. First, interactions between Spartina and Puccinellia were distinctly asymmetrical, Puccinellia exerting a competitive effect on Spartina, with no reciprocal effect, and with a facilitative effect of Spartina on Puccinellia in low nutrient conditions. Second, the interactions varied in intensity in different environmental conditions. Interspecific competitive effects of Puccinellia on Spartina were more intense in conditions favourable to growth of Puccinellia and reduced or non-existent in environments with more abiotic stress. Third, intraspecific competition was found to be less intense for both species than interspecific interactions. Finally, the intensity of plant interactions involving both species was more intense above ground than below ground, with a disproportionate reduction in the intensity of interspecific competition below relative to above ground in treatments with less productive sediments and greater immersion. This is interpreted as reflecting a potential mechanism by which Spartina may be able to evade competitive neighbours. [source] The impact of mesoscale convective systems on the surface and boundary-layer structure in West Africa: Case-studies from the AMMA campaign 2006THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 648 2010Juliane Schwendike Abstract Within the framework of the AMMA project, atmospheric, surface and soil observations were performed during the pre-onset phase of the monsoon (Special Observing Period SOP 1) and during the summer monsoon (SOP 2) in 2006. Based on several case-studies the paper investigates the impact of mesoscale convective systems (MCSs) on the surface and boundary layer (PBL), the recovery time of the surface and the PBL after MCS passages, and the differences between the two monsoon phases. In the pre-MCS environment the mean conditional and convective instabilities were higher in SOP 1 than in SOP 2 (e.g. CAPE = 1815 J kg,1 and CAPE = 1295 J kg,1, respectively). In both monsoon phases these instabilities, which were strongly reduced by MCSs, recovered within less than 2 days. Precipitation of the MCSs and the resulting soil moisture increase caused a significant decrease in the surface temperature by up to 10 K and an increase in evapotranspiration by up to 2.5 mm d,1. In both phases of the monsoon, these surface anomalies and, hence, the conditions favourable for triggering MCSs by thermally induced circulation systems, diminished largely within 2 to 3 days. Due to the repeated passage of the first MCSs at intervals of a few days during SOP 1, the surface properties exhibited trends towards higher soil moisture, evapotranspiration and humidity, and lower albedo, temperature and Bowen ratio. After two weeks only, the mean conditions present in the summer monsoon were reached. In SOP 2 no significant trends could be detected. Copyright © 2010 Royal Meteorological Society [source] Evolution of flowering in response to day length: Flipping the CONSTANS switchBIOESSAYS, Issue 9 2003Gordon G. Simpson Day length provides an important environmental cue by signalling conditions favourable for flowering. While Arabidopsis promotes flowering in response to long days, rice promotes flowering in response to short days. Despite this difference, a recent paper reveals that the network controlling this response is highly conserved in these distantly related plants, only the activity of one component is reversed.1 This reveals how an important developmental process can be diversified for adaptation by using the same set of genes, but regulating them differently. BioEssays 25:829,832, 2003. © 2003 Wiley Periodicals, Inc. [source] | |||||||||||||