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671.
PHILLIP S. LEVIN† ELIZABETH E. HOLMES† KEVIN R. PINER† CHRIS J. HARVEY† 《Conservation biology》2006,20(4):1181-1190
Abstract: As in many regions of the world, marine fishes and invertebrates along the Pacific coast of the United States have long been subjected to overexploitation. Despite this history, however, we lack basic information on the current status of many fishes along this coastline. We used data from a quarter century of fishery-independent, coast-wide trawl surveys to study systematically the demersal fish assemblages along the U.S. Pacific coast. We documented fundamental shifts in this fish assemblage. Average fish size, across a diversity of species, has declined 45% in 21 years. There have been major shifts in the constituent species of the assemblage, with some species achieving annual population growth rates of >10% and others declining in excess of 10% per year. Annual rate of change in population size appeared to be a function of life history interacting with fishing pressure. Negative trends in population size were particularly apparent in rockfish ( Sebastes spp.). However, across all taxa examined, trends in population size were associated with size of maturity, maximum size, and growth rate. Trends in population size were associated inversely with harvest levels, but stocks that mature late tended to decline faster than would be predicted by catch rates alone. Our results are disquieting because they raise the possibility that fishing-induced phase shifts in fish communities may affect the recovery of fishes, even after the implementation of severe fishing restrictions. 相似文献
672.
Summary As recognized by Miriam Rothschild as early as the 1960s and repeatedly emphasized in her papers, the use, misuse, or non-use of plant allelochemicals by insects is extremely variable and difficult to predict, at many levels of time, space, and biological organization. Although certain patterns that reoccur have been important in the development of ecological theory, the optimization of cost-benefit equations involving two or three trophic levels, each with large numbers of individuals, populations, and species in erratic and complex interactions, produces unexpected and fascinating scenarios. The development of rapid colorimetric and chromatographic analyses for several types of plant allelochemicals, notably certain groups of alkaloids, cardiac and cyanogenic glycosides, phenolics, terpenes, and glucosinolates, has permitted a detailed investigation of the variation and flow of these substances in natural organisms and ecosystems. The results of these analyses, in our hands mostly for pyrrolizidine alkaloids (PAs), do not suggest a straightforward classical choice by the aposematic insect to simply sequester or synthesize its defences. Rather, they reveal a confusing variety of diffuse and complex patterns that become increasingly closer to chaos as they are multiplied across structures, species, sexes, stages, sites, seasons, and selective regimes. We present a model reflecting results of analyses at this chemoecological interface. Depending upon an initial option, involving the recognition (or not) of a plant allelochemical, the herbivore will face thereafter options to ingest it (or not), and then to tolerate and absorb (or detoxify and excrete), modify (or not), passively, actively or selectively accumulate, turn over (or not), distribute (or concentrate), and use this compound in a variety of growth, defense, or reproductive functions. The herbivore can also quantitatively or qualitatively regulate the intensity or dispersion of its attack on the plant tissues, in order to modify feedback loops of selection on the plant and its chemicals which exist in most of the earlier steps, or those with its predators and parasites that occur in the later ones. Options that lead to mutualism through positive feedback loops will tend to accumulate and become rapidly fixed by natural selection. Additional variations and anomalies such as automimicry, chemical mimicry, sexual dimorphism and communication, selective sequestration and passing-up of allelochemicals, special glands and structures, and synergism effects, are among the secondary complications of this model that have occupied much thought, time, experimental labor, and polemical space in chemical ecology journals and meetings. Examination of the tendencies and results at various points in the model can be used to explain these features and to make further predictions, plan experiments, and devise activity-based bioassays and new chemical analyses. These may lead some day to new and more robust visions of the major patterns of chemical transfer at this widespread and important natural interface. 相似文献
673.
新近发现的安绿玉为利蛇纹石型岫玉,其中铁质的含量、价态及占位与玉石的颜色密切相关.黄色玉的穆斯堡尔谱中出现四组四极双峰,表明Fe~(2+)分布于M1,Fe~(3+)分布于M2、M1及T晶位,Fe~(3+)/Fe~(2+)>4,因而Fe~(3+)d-d跃迁较强,故呈黄色;绿色玉中因含一定量的斜绿泥石,其穆斯堡尔谱表现出M2、M1中均有Fe~(2+)、M2、M1及T中均有Fe~(3+),但Fe~(3+)/Fe~(2+)<1致使Fe~(3+)d-d跃遇减弱以至消失,而Fe~(2+)→Fe~(3+)荷移吸收占优势,故而主要呈现绿色. 相似文献
674.
Spalding-Fecher Randall Thorne Steve Wamukonya Njeri 《Mitigation and Adaptation Strategies for Global Change》2002,7(2):135-153
A community-based Clean Development Mechanism (CDM) project – asolar water heating project in a low-income community in South Africa –is analysed to illustrate the methodological and policy challenges that faceimplementation of the Kyoto Protocol to the United Nations FrameworkConvention on Climate Change. We evaluate four baseline options, andthree potential CDM interventions. The emissions reductions range from –670 to +5 929 Mg CO2 per year, with all option but oneshowing positive emission reductions. Using metered solar water heatingwith liquefied petroleum gas back-up as the CDM intervention, and electricstorage geysers as the baseline, the annual emissions reductions are 5686 Mg CO2. The cost-effectiveness from the national perspective,which is the incremental life cycle costs divided by the lifetime emissionsreductions, is –$18 per Mg CO2 From the perspective of theCDM investor, however, the cost-effectiveness is $5.2 per mgCO2, assuming that the investor receives all of the carbon credits forproviding the incremental capital investment. From our analysis, weconclude that using the current technology (kerosene stoves) as a baselineis probably not appropriate because it does not reflect likely future trendsand also penalises the community for their poverty and current lack ofinfrastructure. We also highlight the importance of credit sharing, and howit affects the cost-effectiveness of the project from the CDM investor'sperspective. The lessons from this analysis are important for the currentinternational policy debate on how to preferentially treat small-scale CDMprojects. 相似文献
675.
采用开放式悬浮型光催化反应器,以太阳能中紫外光替代紫外灯,激发染料污水悬浮液中TiO2产生OH自由基将染料催化氧化脱色,探讨了催化剂用量,催化剂活性,曝气,污水流速,反应器受辐射面积,Fe3+离子等对染料污水脱色率的影响,实验结果表明:在一般晴天的条件下,经过2小时太阳能辐射后,阳离子蓝X-GRRL染料脱色率在80%-93%之间,说明太阳能是非均相光催化氧化染料污水脱色处理的有效紫外光源,太阳能非均相光催化氧化染料污水脱色处理是经济实用,效率高,很有发展前景的污水脱色处理技术 相似文献
676.
BAI Yu |bo SHI Guang |yu {* } Koichi Tamura Takashi Shibata Yasunobu Iwasaka Kaneta Shin′ichi Takamura Tamio 《环境科学学报(英文版)》2000,(4)
IntroductionAerosolshavethepotentialtochangetheglobalclimatebecauseoftheirdirectradiativeeffectsandtheirindirecteffectsascloudcondensationnuclei.Aerosolsarealsoimportantcomponentsinbiogeochemicalcyclesandinheterogeneouschemistry ,whichcanaffecttrace ga… 相似文献
677.
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679.
An inventory of the severity and spatial distribution of wilderness campsite impacts in Sequoia and Kings Canyon National
Parks identified a total of 273 distinct nodes of campsites or “management areas.” A campsite impact matrix was developed
to evaluate management areas based on total impacts (correlated to the total area of campsite development) and the density,
or concentration, of impacts relative to each area's potentially campable area. The matrix is used to quantify potential recreational
opportunities for wilderness visitors in a spectrum from areas offering low impact-dispersed camping to those areas offering
high impact-concentrated camping. Wilderness managers can use this type of information to evaluate use distribution patterns,
identify areas to increase or decrease use, and to identify areas needing site-specific regulations (e.g., one-night camping
limits) to preserve wilderness resources and guarantee outstanding opportunities for solitude. 相似文献
680.
目前,我国直接和间接参与设备作业的人数,达二亿多人。因此,职业作业安全十分重要。本文介绍了应用FFT谱分析技术进行职业作业事故预测分析,能在潜在性故障尚未转变成功能性故障前,即发生事故前给出预告,便于人们实施措施对策。从而从根本上杜绝事故的发生,确保生产安全。 相似文献