美国1961～2000年氮使用量的变化及未来趋势预测

从1961～1997年,因人类活动而输入到美国的氮翻了一番,特别是在上个世纪60年代和70年代,其增长量最大.尽管无机氮肥的使用量增长最大,但矿物燃料燃烧所造成的NOx排放,也有明显的增加.1961年,美国农业生产系统中的生物固氮量是活性氮的最大来源;到了1997年,尽管生物固氮量也有增加,但相比而言,无机氮肥的使用和NOx的排放增加得更快,成为两个最大的氮源.1961～1997年,在输入到美国的活性氯中,有2/3发生了脱氮反应或者是被贮存在土壤与生物群落之中,有1/3输出到境外.在输出到境外的这部分氮中,通过河流流到海洋中的分量最大,其次是通过粮食和饲料出口而到其它国家以及通过大气平流传输到了海洋中.动物性蛋白的消费是美国农业系统中氮使用的主要驱动因子,如果饮食方式或农业生产方式不发生改变,在未来30年的时间里,美国肥料的使用量将继续增长,流向海洋中的氮通量将可能再增长30%,但也有可能出现下降.     

Temporal overlap of female kin in Columbian ground squirrels (Spermophilus columbianus)

Summary Columbian ground squirrels (Spermophilus columbianus) were live-trapped from 5 to 7 years at three sites in southwestern Alberta, Canada. The two most common adult matrilineal relatives for 2-year-old females were the mother and a 1 year older non-littermate sister. Co-occurrence of female kin depended firstly on size and sexual composition of litters and secondly on age-specific survival and recruitment rates. Adult matrilineal kin frequently coexisted among breeding females of this species, leading us to predict a social system strorgly influenced by nepotism. However, the life history traits of S. columbianus suggest an adult female kin cluster unlike that found for other species of Spermophilus in which littermate sisters are common. If availability of adult female kin influences kin-differential behaviour, then female S. columbianus should favour mothers, daughters and non-ittermate sisters.     

Resources from another place and time: responses to pulses in a spatially subsidized system

As the theoretical bases for the dynamics of spatially subsidized communities emerge, ecologists question whether spatially subsidized communities exhibit similar structure or dynamics to communities that receive strongly pulsed resources. In both cases, communities may be structured by responses to resources that are potentially absent at any given point in time (pulsed communities) or space (subsidized communities), even if pulsed resources are part of the in situ productivity of the system or the subsidies arrive as a relatively constant input from a nearby system. The potential for significant spatial or temporal resource limitation, therefore, may be a key factor influencing in similar ways the persistence of populations, the structure and dynamics of communities, and the evolution of specific life history traits. In most complex systems, however, multiple resources may arrive for various trophic entities at various points in time and from various points in space, and thus it may be difficult to separate or compare the dynamics of spatially subsidized and pulsed systems. In this paper, we explore the effects of interactions between pulses and subsidies in plant and animal populations and communities on highly pulsed and variably subsidized islands in the Gulf of California. While many of the plant and animal communities on the unsubsidized islands in this system respond to pulses of rain in classic ways, responses to these rain pulses on islands subsidized by seabird guano or other marine resources are quite different and variable, and depend on a combination of life history characteristics, physiology, competitive interactions, and trophic relationships. These variable responses to rain pulses then translate into large differences in dynamics and community structure of subsidized vs. unsubsidized islands. Indeed, most systems experience both temporal pulses and spatial subsidies. When considered in tandem, complementary or synergistic effects of the multiple, temporally and spatially variable resources may emerge that help explain complex food web structure and dynamics.     

How does spouse career support relate to employee turnover? Work interfering with family and job satisfaction as mediators

Employee turnover is a major concern because of its cost to organizations. Although theory supports the influence of nonwork factors on turnover, our understanding of the degree to which nonwork factors relate to actual turnover behavior is not well developed. Using a sample of 5505 U.S. Army officers, we assessed the extent to which spouse career support related to reduced turnover four years later through work interfering with family (WIF) and job satisfaction as mechanisms. Results revealed that spouse career support decreased the odds of turnover, and WIF and job satisfaction sequentially mediated this relationship, with lower WIF and higher job satisfaction reducing the odds of turnover. Practical implications of using family support systems as retention interventions are discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Differential treatment within sports teams,leader–member (coach–player) exchange quality,team atmosphere,and team performance

Using the leader–member exchange (LMX) theory as a theoretical framework, the present study focused on the occurrence of differential treatment by leaders on social and task‐related issues within teams. It was investigated whether team members' perceptions of the frequency and degree of social and task‐related differential treatment by the leader were associated with their evaluation of team atmosphere and team performance, in addition to the effects of the quality of their own working relationship with the leader (LMX quality). The context of this study consisted of interdependent sports teams. The participants were 605 players belonging to 69 amateur sports teams playing various team sports such as soccer, hockey, and basketball. Social differential treatment was negatively associated with team atmosphere and unrelated to team performance. In addition, it was found that the two forms of task‐related differential treatment included in this study were unrelated to team atmosphere and were differently associated with team performance. The results are discussed with reference to the existing leadership literature. Copyright © 2010 John Wiley & Sons, Ltd.     

Maternal investment in sons and daughters: problems of methodology

Summary The prediction that mothers should invest more in sons than daughters was briefly examined in American bison (Bison bison) by Wolff (1988). He concluded that (a) male calves suckle more than females, (b) cows that had previously produced sons were more likely to be barren, and (c) cows that had male calves became estrous later in the year than other cows. In this paper we present data from two long term studies at different sites to show that Wolff's conclusions are equivocal at best and difficult to reconcile with predictions of the hypothesis because of questionable methods and assumptions. Offprint requests to: W.C.H. Green