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Overriding Influence (overriding + influence)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

Plasma renin in mice with one or two renin genes

ACTA PHYSIOLOGICA, Issue 4 2004
P. B. Hansen
Abstract Aim:, In the present study we have investigated whether the presence of a second renin gene exerts an overriding influence on plasma renin such that mice with two renin genes have consistently higher renin levels than mice with only one renin gene. Methods:, Plasma renin was determined as the rate of angiotensin I generation using a radioimmunoassay (RIA) kit with (plasma renin concentration, PRC) or without (plasma renin activity, PRA) the addition of purified rat angiotensinogen as substrate. Results:, In male 129SvJ, DBA/2 and Swiss Webster mice, strains possessing both Ren-1 and Ren-2, PRC (ng Ang I mL,1 h,1) averaged 178 ± 36, 563 ± 57 and 550 ± 43 while PRA was 2.9 ± 0.5, 3.6 ± 0.8 and 7.8 ± 1.2. In male C57BL/6, C3H and BALB/c mice that express only Ren-1, PRC averaged 426 ± 133, 917 ± 105 and 315 ± 72, and PRA was 3.4 ± 1.0, 6.9 ± 1.7 and 4.5 ± 1.2. In the two renin gene A1AR,/, mice compared with the one renin gene A1AR+/+, PRC averaged 538 ± 321 and 415 ± 159 while PRA averaged 3.2 ± 1.1 and 4.4 ± 1.4 ng Ang I mL,1 h,1. Aldosterone levels showed no significant differences between one renin (C57BL/6, C3H and BALB/c) and two renin (129SvJ, DBA/2 and Swiss Webster) gene mice. Furthermore, by quantitative real-time polymerase chain reaction (RT-PCR) we found no correlation between the number of renin genes and whole kidney renin mRNA levels from one and two renin gene mice. Conclusion:, Our data show that baseline plasma renin is not systematically higher in mice with two renin genes than in one renin gene mice. Thus, the presence of a second renin gene does not seem to be a major determinant of differences in PRC between different mouse strains. [source]

Weedbeds and big bugs: the importance of scale in detecting the influence of nutrients and predation on macroinvertebrates in plant-dominated shallow lakes

FRESHWATER BIOLOGY, Issue 3 2010
ANGELA L. BERESFORD
Summary 1. The scale of investigations influences the interpretation of results. Here, we investigate the influence of fish and nutrients on biotic communities in shallow lakes, using studies at two different scales: (i) within-lake experimental manipulation and (ii) comparative, among-lake relationships. 2. At both scales, fish predation had an overriding influence on macroinvertebrates; fish reduced macroinvertebrate biomass and altered community composition. Prey selection appeared to be size based. Fish influenced zooplankton abundance and light penetration through the water column also, but there was no indication that fish caused increased resuspension of sediment. 3. There were effects of nutrients at both scales, but these effects differed with the scale of the investigation. Nutrients increased phytoplankton and periphyton at the within-lake scale, and were associated with increased periphyton at the among-lake scale. No significant effect of nutrients on macroinvertebrates was observed at the within-lake scale. However, at the among-lake scale, nutrients positively influenced the biomass and density of macroinvertebrates, and ameliorated the effect of fish on macroinvertebrates. 4. Increased prey availability at higher nutrient concentrations would be expected to cause changes in the fish community. However, at the among-lake scale, differences were not apparent in fish biomass among lakes with different nutrient conditions, suggesting that stochastic events influence the fish community in these small and relatively isolated shallow lakes. 5. The intensity of predation by fish significantly influences macroinvertebrate community structure of shallow lakes, but nutrients also play a role. The scale of investigation influences the ability to detect the influence of nutrients on the different components of shallow lake communities, particularly for longer lived organisms such as macroinvertebrates, where the response takes longer to manifest. [source]

Not seeing the ocean for the islands: the mediating influence of matrix-based processes on forest fragmentation effects

GLOBAL ECOLOGY, Issue 1 2006
John A. Kupfer
ABSTRACT The pervasive influence of island biogeography theory on forest fragmentation research has often led to a misleading conceptualization of landscapes as areas of forest/habitat and ,non-forest/non-habitat' and an overriding focus on processes within forest remnants at the expense of research in the human-modified matrix. The matrix, however, may be neither uniformly unsuitable as habitat nor serve as a fully,absorbing barrier to the dispersal of forest taxa. In this paper, we present a conceptual model that addresses how forest habitat loss and fragmentation affect biodiversity through reduction of the resource base, subdivision of populations, alterations of species interactions and disturbance regimes, modifications of microclimate and increases in the presence of invasive species and human pressures on remnants. While we acknowledge the importance of changes associated with the forest remnants themselves (e.g. decreased forest area and increased isolation of forest patches), we stress that the extent, intensity and permanence of alterations to the matrix will have an overriding influence on area and isolation effects and emphasize the potential roles of the matrix as not only a barrier but also as habitat, source and conduit. Our intention is to argue for shifting the examination of forest fragmentation effects away from a patch-based perspective focused on factors such as patch area and distance metrics to a landscape mosaic perspective that recognizes the importance of gradients in habitat conditions. [source]

Classification of hydrological regimes of northern floodplain basins (Peace,Athabasca Delta, Canada) from analysis of stable isotopes (,18O, ,2H) and water chemistry

HYDROLOGICAL PROCESSES, Issue 2 2007
Brent B. Wolfe
Abstract We used stable isotopes (,18O and ,2H) and water chemistry to characterize the water balance and hydrolimnological relationships of 57 shallow aquatic basins in the Peace-Athabasca Delta (PAD), northern Alberta, Canada, based on sampling at the end of the 2000 thaw season. Evaporation-to-inflow ratios (E/I) were estimated using an isotope mass-balance model tailored to accommodate basin-specific input water compositions, which provided an effective, first-order, quantitative framework for identifying water balances and associated limnological characteristics spanning three main, previously identified drainage types. Open-drainage basins (E/I < 0·4; n = 5), characterized by low alkalinity, low concentrations of nitrogen, dissolved organic carbon (DOC) and ions, and high minerogenic turbidity, include large, shallow basins that dominate the interior of the PAD and experience frequent or continuous river channel connection. Closed-drainage basins (E/I , 1·0; n = 16), in contrast, possess high alkalinity and high concentrations of nitrogen, DOC, and ions, and low minerogenic turbidity, and are located primarily in the relict and infrequently flooded landscape of the northern Peace sector of the delta. Several basins fall into the restricted-drainage category (0·4 # E/I < 1·0; n = 26) with intermediate water chemistries and are predominant in the southern Athabasca sector, which is subject to active fluviodeltaic processes, including intermittent flooding from riverbank overflow. Integration of isotopic and limnological data also revealed evidence for a new fourth drainage type, mainly located near the large open-drainage lakes that occupy the central portion of the delta but within the Athabasca sector (n = 10). These basins were very shallow (<50 cm deep) at the time of sampling and isotopically depleted, corresponding to E/I characteristic of restricted- and open-drainage conditions. However, they are limnologically similar to closed-drainage basins except for higher conductivity and higher concentrations of Ca2+ and Na+, and lower concentrations of SiO2 and chlorophyll c. These distinct features are due to the overriding influence of recent summer rainfall on the basin water balance and chemistry. The close relationships evident between water balances and limnological conditions suggest that past and future changes in hydrology are likely to be coupled with marked alterations in water chemistry and, hence, the ecology of aquatic environments in the PAD. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Oil industry, wild meat trade and roads: indirect effects of oil extraction activities in a protected area in north-eastern Ecuador

ANIMAL CONSERVATION, Issue 4 2009
E. Suárez
Abstract Starting in 1994, a wholesale wild meat market developed in north-eastern Ecuador, involving Waorani and Kichwa people in the area of influence of a road built to facilitate oil extraction within Yasuní National Park. Between 2005 and 2007, we recorded the trade of 11 717 kg of wild meat in this market, with pacas Cuniculus paca, white-lipped peccaries Tayassu pecari, collared peccaries Pecari tajacu and woolly monkeys Lagothrix poeppiggi accounting for 80% of the total biomass. Almost half of the wild meat brought to the market was transported by dealers for resale at restaurants in Tena, a medium-sized town 234 km west of the market. Prices of wild meat were 1.3,2 times higher than the price of meat of domestic animals, suggesting that it is a different commodity and not a supplementary protein source in the urban areas where it is consumed. The actual price of transportation between the local communities and the market was a significant predictor of the amount of meat sold in Pompeya. Based on this relationship the Waorani hunters sold exceptionally larger amounts of wild meat than would be expected if they would not have the transportation subsidies provided by the oil companies. Although the scale of this wild meat wholesale market is still relatively small, its dynamic reflects the complex interactions that emerge as the overriding influence of oil companies or other private industries modify the culture and subsistence patterns of marginalized indigenous groups, increasing their potential impacts on wildlife and natural ecosystems. [source]