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排序方式: 共有178条查询结果,搜索用时 31 毫秒
171.
Jennifer E. Smith Nichole N. Price Craig E. Nelson Andreas F. Haas 《Marine Biology》2013,160(9):2437-2447
Benthic marine primary producers affect the chemistry of their surrounding environment through metabolic processes. Photosynthesis and respiration will elevate or depress the concentration of oxygen in the diffusive boundary layer. Likewise, acid–base regulation and biomineralization/dissolution for calcifying species can alter the relative concentration of inorganic carbon species and thus pH. Here, we measured the relative ability of several common benthic primary producers from coral reef systems of the central Pacific and the Caribbean to simultaneously affect seawater oxygen concentration and pH values. Repeated measurements over a diel cycle confirmed that several primary producers substantially alter surrounding seawater chemistry over time. The majority of fleshy algae exhibited a stoichiometric ratio of oxygen to hydrogen ions not significantly different from one during daylight hours. In contrast, calcifiers exhibited significantly lower oxygen to hydrogen ion ratios that were unique for each species and were inversely correlated with known rates of calcification. These data provide the first quantitative estimates of the simultaneous influence of several species of benthic primary producers on water column oxygen concentrations and pH across different tropical reef systems. Finally, because more productive fleshy taxa have the potential to raise both oxygen and pH during the day to a greater extent than calcified species, our results suggest that some fleshy taxa may provide a buffering capacity to future ocean acidification scenarios. 相似文献
172.
Hypotheses regarding role stress, chronic burden and two forms of vulnerability to mental health symptoms are tested in a longitudinal sample of 590 caregivers working in group homes for the mentally ill. In addition, an organizational exit pressure hypothesis is offered. Measures of exit pressure are identified and incorporated into predictive models of stress and mental health. Exit pressures affect somatization directly and interact with role ambiguity to affect subsequent levels of anxiety and somatization. The results suggest that selection pressures in and out of social settings should be conceptualized as part of models of stress and mental health. 相似文献
173.
The Role of Soil Surface Crusting in Desertification and Strategies to Reduce Crusting 总被引:1,自引:0,他引:1
Soil crusting decreases infiltration, increases erosion, and impedes vegetation establishment, so reducing the impact of crusting
is of major importance in combating desertification. Although surface crusting has been the subject of considerable research
over the past 50 years or more, the practical management of soil crusts remains a challenge for many dryland communities.
Crusting occurs in two steps, an initial aggregate breakdown period that occurs under rainfall and a subsequent hardening
phase during drying. Several factors influence crust development, but the single most important one is soil aggregate stability.
Strategies to reduce crusting can be based either on protecting the surface from raindrop impact or improving aggregate stability,
or a combination of both. However, crust control is labor and/or capital intensive and must be thought out clearly in terms
of the benefits to be achieved. 相似文献
174.
175.
Colin Price 《Environmental management》1981,5(2):161-175
Overuse of recreation sites seems to justify regulation, and the principal tools for this are fee charging or physical exclusion. Both seem equally costly to administer. Both involve equal costs to consumers if recreationists visit from one origin, but if they come from different origins, costs may be greater and consumers' surplus less under either tool, depending on the shape of the demand curve. Which is the more equitable tool depends on the relative representation of rich and poor participants from near and distant origins. Potentially beneficial use of site revenues is an advantage of charging. Neither availability of substitutes nor variation in daily demand seems likely to change these results substantially, but a system of booking admissions before the trip outset might neutralize the advantages of charging. The optimal level of use varies with the regulatory tool chosen. The optimal admissions under exclusion could be fewer than or more than under charging, or may even be equal to unregulated use. 相似文献
176.
Nickolas M. Waser Mary V. Price Daniel T. Blumstein S. Reneé Arózqueta Betsabé D. Castro Escobar Richard Pickens Alessandra Pistoia 《Die Naturwissenschaften》2014,101(5):427-436
Spatial gradients in human activity, coyote activity, deer activity, and deer herbivory provide an unusual type of evidence for a trophic cascade. Activity of coyotes, which eat young mule deer (fawns), decreased with proximity to a remote biological field station, indicating that these predators avoided an area of high human activity. In contrast, activity of adult female deer (does) and intensity of herbivory on palatable plant species both increased with proximity to the station and were positively correlated with each other. The gradient in deer activity was not explained by availabilities of preferred habitats or plant species because these did not vary with distance from the station. Does spent less time feeding when they encountered coyote urine next to a feed block, indicating that increased vigilance may contribute, along with avoidance of areas with coyotes, to lower herbivory away from the station. Judging from two palatable wildflower species whose seed crop and seedling recruitment were greatly reduced near the field station, the coyote–deer–wildflower trophic cascade has the potential to influence plant community composition. Our study illustrates the value of a case-history approach, in which different forms of ecological data about a single system are used to develop conceptual models of complex ecological phenomena. Such an iterative model-building process is a common, but underappreciated, way of understanding how ecological systems work. 相似文献
177.
C. Price Y. Yair A. Mugnai K. Lagouvardos M.C. Llasat S. Michaelides U. Dayan S. Dietrich E. Galanti L. Garrote N. Harats D. Katsanos M. Kohn V. Kotroni M. Llasat-Botija B. Lynn L. Mediero E. Morin K. Nicolaides S. Rozalis K. Savvidou B. Ziv 《Environmental Science & Policy》2011,14(7):898-911
The FLASH project was implemented from 2006 to 2010 under the EU FP6 framework. The project focused on using lightning observations to better understand and predict convective storms that result in flash floods. As part of the project 23 case studies of flash floods in the Mediterranean region were examined. For the analysis of these storms lightning data from the ZEUS network were used together with satellite derived rainfall estimates in order to understand the storm development and electrification. In addition, these case studies were simulated using mesoscale meteorological models to better understand the meteorological and synoptic conditions leading up to these intense storms. As part of this project tools for short term predictions (nowcasts) of intense convection across the Mediterranean and Europe, and long term forecasts (a few days) of the likelihood of intense convection were developed. The project also focused on educational outreach through our website http://flashproject.org supplying real time lightning observations, real time experimental nowcasts, forecasts and educational materials. While flash floods and intense thunderstorms cannot be prevented as the climate changes, long-range regional lightning networks can supply valuable data, in real time, for warning end-users and stakeholders of imminent intense rainfall and possible flash floods. 相似文献
178.
Single Species as Indicators of Species Richness and Composition in California Coastal Sage Scrub Birds and Small Mammals 总被引:6,自引:0,他引:6
Mary K. Chase William B. Kristan III Anthony J. Lynam† Mary V. Price John T. Rotenberry 《Conservation biology》2000,14(2):474-487
Abstract: Individual species may be useful as indicators of biodiversity if an association exists between the presence of a species and another component of biodiversity. We evaluated 40 species of birds and small mammals, including 11 species of conservation concern, as potential indicators of species richness and species composition in southern California coastal sage scrub habitats. This habitat, which is the target of large-scale conservation planning, has been greatly reduced by human development and supports many plants and animals of conservation concern. We asked whether there is an association between the presence of a potential indicator species and the species richness and composition of the bird or small-mammal community in which it is found. We used point counts and live-trapping to quantify the distribution of birds and small mammals, respectively, at 155 points in 16 sites located in three counties. Of the few species we found associated with species richness, some were associated with higher species richness and others with lower richness, and species of conservation concern were not more frequently associated with species richness than were common species. Ordination analysis revealed a geographic gradient in coastal sage scrub bird and small-mammal species composition across southern California, and 18 of the species we evaluated were associated with the composition of the bird and small-mammal community in which they were found. Our results suggest that efforts to conserve bird and small-mammal biodiversity in coastal sage scrub should not focus exclusively on rare species or on locations with the highest species richness, but instead should focus on a diverse suite of species that are representative of the range of variation in communities found in coastal sage scrub habitats. 相似文献