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31.
The ongoing drought in the Sahel region of West Africa highlights the vulnerability of food-producing systems to climate change and variability. Adaptation to climate should therefore increase the sustainability of agriculture under a long-term drought. Progress towards sustainability and adaptation in the the Senegal River Basin is hampered by an existing set of social and ecological relationships that define the control over the means of production and how people interact with their environment. These relationships are sensitive to the technological inputs and the administration of food production, or the factor bias in the different policy alternatives for rural development. One option is based on state-controlled, irrigated plantations to provide rice (Oryza) for the capital, Dakar. This policy emphasizes a top-down management approach, mechanized agriculture and a reliance on external inputs which strengthens the relationships introduced during the colonial period. A time series decomposition of the annual flow in the Senegal River at Bakel in Senegal suggests that water resources availability has been substantially curtailed since 1960, and a review of the water resources budget or availability in the basin suggests that this policy's food production system is not sustainable under the current climate of the basin. Under these conditions, this program is exacerbating existing problems of landscape degradation and desertification, which increases rural poverty. A natural resource management policy offers two adaptation strategies that favour decentralized management and a reduction of external inputs. The first alternative, “Les Perimetres Irrigués”, emphasizes village-scale irrigation, low water consumption cereal crops and traditional socio-political structures. The second alternative emphasizes farm-level irrigation and agro-forestry projects to redress the primary effects of desertification.  相似文献   
32.
Patterns of Genetic Diversity and Its Loss in Mammalian Populations   总被引:3,自引:0,他引:3  
Abstract:  Policy aimed at conserving biodiversity has focused on species diversity. Loss of genetic diversity, however, can affect population persistence, evolutionary potential, and individual fitness. Although mammals are a well-studied taxonomic group, a comprehensive assessment of mammalian genetic diversity based on modern molecular markers is lacking. We examined published microsatellite data from populations of 108 mammalian species to evaluate background patterns of genetic variability across taxa and body masses. We tested for loss of genetic diversity at the population level by asking whether populations that experienced demographic threats exhibited lower levels of genetic diversity. We also evaluated the effect of ascertainment bias (a reduction in variability when microsatellite primers are transferred across species) on our assessment of genetic diversity. Heterozygosity did not vary with body mass across species ranging in size from shrews to whales. Differences across taxonomic groupings were noted at the highest level, between populations of marsupial and placental mammals. We documented consistently lower heterozygosity, however, in populations that had experienced demographic threats across a wide range of mammalian species. We also documented a significant ( p = 0.01) reduction in heterozygosity as a result of ascertainment bias. Our results suggest that populations of both rare and common mammals are currently losing genetic diversity and that conservation efforts focused above the population level may fail to protect the breadth of persisting genetic diversity. Conservation policy makers may need to focus their efforts below the species level to stem further losses of genetic resources.  相似文献   
33.
In a 1989 article, Ben Twight and Fremont Lyden compared the attitudes of national forest managers in the United States in 1981 with those of its major constituents to assess the extent to which the U.S. Forest Service was biased: were the beliefs and values of agency employees concerning resource management more representative of one of two major constituent groups, environmentalists and forest utilizers? The research tested Culhane's (Public Lands Politics: Interest Group Influence on the Forest Service and the Bureau of Land Management. Baltimore, Maryland: John Hopkins University Press. 1981) theory that the Forest Service occupies a middle ground in its attitudes relative to those of its environmental and utilization constituencies. They concluded that the agency did not; ideologically, district rangers were quite close to the Forest Service's utilizer constituency and relatively far from its environmentalist constituency. Given recent changes in the attitudes of Forest Services managers, the present study sought to answer the question: what do these changes reveal about the ideological position of the agency in 1981 vis a vis its position in 1990, and what are their implications for continuing concerns over the agency's representation of all interest groups? The response to survey questions of four groups—1990 district rangers and district rangers, environmentalists and forest utilizers in 1981—were combined for statistical comparison. Discriminant analyses were conducted to clarify the differences in the groups. Although the hypothesized bias of the Forest Service toward the traditional utilizer position was confirmed, the results also suggested that managers' values and attitudes had changed over the decade. The major issue underlying this bias—preservation versus utilization of resources—no longer adequately represented the agency's position, which has been fragmented into concerns with multiple issues.  相似文献   
34.
Since 1987 tree crown condition is surveyed annually in large parts of Europe mainly in terms of defoliation. The plot-wise means of defoliation from 1994 to 2000 were evaluated by General Linear Models (GLM) in order to describe country-specific levels of defoliation and age-trends. Additional runs with estimates for influences of insects and fungi were performed. The amount of variance of defoliation explained by country, age and its interaction was between 35% and 59% for the main tree species, except for Quercus ilex. Additionally, up to 10% could be explained by the inclusion of estimates for infestations by insects and fungi. Residuals of the GLMs were taken as a measure of forest condition not biased by country or age effects and interpreted as preliminarily adjusted defoliation (PAD). PAD values were analysed using geostatistical methods. The modelled spatial autocorrelations were used for kriging. The resulting maps give an overview on regions with elevated defoliation, which may pinpoint regional causes of defoliation. The elimination of methodologically caused variance is a precondition of any cause–effect oriented analyses. The combination of explorative modelling and geostatistics will promote the choice of further promising predictors.  相似文献   
35.
Unusually cold winters, a slowing in upward global temperatures, or an increase in Arctic sea ice extent are often falsely cast as here-and-now disconfirmation of the scientific consensus on climate change. Such conclusions are examples of “end point bias,” the well documented psychological tendency to interpret a recent short-term fluctuation as a reversal of a long-term trend. End point bias poses a challenge to those trying to communicate cross-decade climate warming trends. In this study, we demonstrate that exposure to misleading scientific information on FoxNews.com that evokes end point bias can affect the beliefs of liberals and moderates as well as conservatives. We also show that the leveraging-involving-visualizing-analogizing communication model can reduce the effects of endpoint bias among moderates and liberals at the same time as it dampens both the ideological and endpoint biasing of conservatives.  相似文献   
36.
The present research contributes to a growing literature on observer reactions to injustice experienced by others. In particular, we separated two variables that have previously been confounded in prior research, namely perpetrator intent to cause harm and victim perception of harm. We expected that injustice intent and injustice perceptions would have both unique and joint effects on observer reactions. The results of three experiments in which we manipulated perpetrator injustice intent and victim injustice perceptions supported our predictions. First, we found that observers had more negative reactions toward superiors who intended to inflict high versus low levels of interpersonal injustice toward a subordinate. Second, the injustice intent of the superior influenced observers' reactions more than did victim perceptions of injustice. Third, most novel, we found that the mere intent to cause injustice generated negative reactions in observers, even in the absence of a “true” victim—that is, when the subordinate perceptions of injustice were low. Together, our results emphasize the importance of examining observers' reactions to injustice and incorporating perpetrator intentions into the study of organizational justice. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
37.
For more than 40 years, scholars have been investigating psychological and communicative implications for the concept of place. During that time, a variety of methods have been employed, yet often without an obvious concern for the extent to which investigative conclusions match perceptions held by respondents who originally generate data the analyses rely upon. Although this distinction between actors’ and informants’ meanings for place is a subject most in the field of environmental communication encounter in their formative education, the actual practice of place-based research sometimes fails to adequately address the issue. Thus, the following commentary explores various threats to representational validity and suggests a number of areas we researchers should consider when conducting our place-based studies. In urging ourselves to rise to the challenge of self-skepticism, I hope my analysis provides a modestly novel take on empiricism regarding what places mean to those we study.  相似文献   
38.
建筑结构的半主动控制系统中的传感器,在强震作用下可能因出现故障而影响控制效果。以磁流变阻尼器为例,研究半主动容错控制系统的设计方法。首先,研究了基于状态观测器的半主动H∞控制器设计方法,并将之应用到建筑结构采用磁流变阻尼器的减振控制中;运用改进Bouc-Wen模型,计算磁流变阻尼器的阻尼力,通过求解一个代数Riccati方程和一个状态观测方程,得出了基于状态观测器的H∞主动控制律;再对其采用Clipped-optimal方法实施半主动控制策略。然后,针对传感器故障,利用观测器组的输出残差对故障进行在线诊断,并通过几个观测器状态值的比较得到故障的大小,并据此对传感器的测量值进行修正,从而消除故障对闭环系统的影响,最终实现半主动H∞容错控制。仿真结果表明,该方法具有很好的容错控制效果。  相似文献   
39.
采用固相萃取-液相色谱法,通过统计全国多家实验室的测定数据,对水中微囊藻毒素测试的平行样测定相对偏差、空白加标回收率、实际样品加标回收率、空白加标回收率平行样相对偏差以及样品加标回收率平行样相对偏差5个质控指标进行了研究,并给出了质控指标评价标准,提出在概率P和γ均为0.90时,其平行样测定允许最大相对偏差应控制在7.3%;空白加标质量浓度为0.005~20 μg/L时,回收率的控制范围为61%~125%;样品测定浓度为未检出、加标质量浓度在0.2~3.6 μg/L时,实际样品加标回收率控制范围为66%~108%;空白加标、样品加标回收率平行样最大相对偏差应分别控制在3.9%和8.9%。在概率P和γ均为0.95时,其平行样测定允许最大相对偏差应控制在8.3%;空白加标质量浓度为0.005~20 μg/L时,回收率的控制范围为49%~137%;样品测定浓度为未检出、加标质量浓度在0.2~3.6 μg/L时,实际样品加标回收率控制范围为60%~114%;空白加标、样品加标回收率平行样最大相对偏差应分别控制在5.2% 和14.8%。  相似文献   
40.
● Emotional responses to visibility-reducing haze was assessed in a controlled lab. ● Valence and arousal have non-linear responses to pollution-caused low visibility. ● Repetitive exposure aggravates negative emotions in severely polluted conditions. ● Emotional bias to pollution relates with gender, decisiveness, attitude to clean air. A growing number of studies have shown that impaired visibility caused by particulate matter pollution influences emotional wellbeing. However, evidence is still scant on how this effect varies across individuals and over repetitive visual exposure in a controlled environment. Herein, we designed a lab-based experiment (41 subjects, 6 blocks) where participants were presented with real-scene images of 12 different PM2.5 concentrations in each block. Emotional valence (negative to positive) and arousal (calm to excited) were self-rated by participants per image, and the response time for each rating was recorded. We find that as pollution level increases from 10 to 260 µg/m3, valence scores decrease, whereas arousal scores decline first and then bounce back, following a U-shaped trend. When air quality deteriorates, individual variability decreases in hedonic valence but increases in arousal. Over blocks, repetitive visual exposure increases valence at a moderate pollution level but aggravates negative emotions in severely polluted conditions (> 150 µg/m3). Finally, we find females, people who are slow in making responses, and those who are highly aroused by clean air tend to express more negative responses (so-called negativity bias) to ambient pollution than their respective counterparts. These results provide deeper insights into individual-level emotional responses to dirty air in a controlled environment. Although the findings in our pilot study should only be directly applied to the conditions assessed herein, we introduce a framework that can be replicated in different regions to assess the impact of air pollution on local emotional wellbeing.  相似文献   
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