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1. Population dynamics and interactions that vary over a species' range are of particular importance in the context of latitudinal clines in biological diversity. Winter moth (Operophtera brumata) and autumnal moth (Epirrita autumnata) are two species of eruptive geometrids that vary widely in outbreak tendency over their range, which generally increases from south to north and with elevation. 2. The predation pressure on geometrid larvae and pupae over an elevational gradient was tested. The effects of background larval density and bird occupancy of monitoring nest boxes on predation rates were also tested. Predation on larvae was tested through exclusion treatments at 20 replicate stations over four elevations at one site, while pupae were set out to measure predation at two elevations at three sites. 3. Larval densities were reduced by bird predation at three lower elevations, but not at the highest elevation, and predation rates were 1.9 times higher at the lowest elevation than at the highest elevation. The rate of predation on larvae was not related to background larval density or nest box occupancy, although there were more eggs and chicks at the lowest elevation. There were no consistent differences in predation on pupae by elevation. 4. These results suggest that elevational variation in avian predation pressure on larvae may help to drive elevational differences in outbreak tendency, and that birds may play a more important role in geometrid population dynamics than the focus on invertebrate and soil predators of previous work would suggest.  相似文献   
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Evidence suggests that global maize yield declines with a warming climate, particularly with extreme heat events. However, the degree to which important maize processes such as biomass growth rate, growing season length (GSL) and grain formation are impacted by an increase in temperature is uncertain. Such knowledge is necessary to understand yield responses and develop crop adaptation strategies under warmer climate. Here crop models, satellite observations, survey, and field data were integrated to investigate how high temperature stress influences maize yield in the U.S. Midwest. We showed that both observational evidence and crop model ensemble mean (MEM) suggests the nonlinear sensitivity in yield was driven by the intensified sensitivity of harvest index (HI), but MEM underestimated the warming effects through HI and overstated the effects through GSL. Further analysis showed that the intensified sensitivity in HI mainly results from a greater sensitivity of yield to high temperature stress during the grain filling period, which explained more than half of the yield reduction. When warming effects were decomposed into direct heat stress and indirect water stress (WS), observational data suggest that yield is more reduced by direct heat stress (?4.6 ± 1.0%/°C) than by WS (?1.7 ± 0.65%/°C), whereas MEM gives opposite results. This discrepancy implies that yield reduction by heat stress is underestimated, whereas the yield benefit of increasing atmospheric CO2 might be overestimated in crop models, because elevated CO2 brings yield benefit through water conservation effect but produces limited benefit over heat stress. Our analysis through integrating data and crop models suggests that future adaptation strategies should be targeted at the heat stress during grain formation and changes in agricultural management need to be better accounted for to adequately estimate the effects of heat stress.  相似文献   
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The use of crop residues for bioenergy production needs to be carefully assessed because of the potential negative impact on the level of soil organic carbon (SOC) stocks. The impact varies with environmental conditions and crop management practices and needs to be considered when harvesting the residue for bioenergy productions. Here, we defined the sustainable harvest limits as the maximum rates that do not diminish SOC and quantified sustainable harvest limits for wheat residue across Australia's agricultural lands. We divided the study area into 9432 climate‐soil (CS) units and simulated the dynamics of SOC in a continuous wheat cropping system over 122 years (1889 – 2010) using the Agricultural Production Systems sIMulator (APSIM). We simulated management practices including six fertilization rates (0, 25, 50, 75, 100, and 200 kg N ha?1) and five residue harvest rates (0, 25, 50, 75, and 100%). We mapped the sustainable limits for each fertilization rate and assessed the effects of fertilization and three key environmental variables – initial SOC, temperature, and precipitation – on sustainable residue harvest rates. We found that, with up to 75 kg N ha?1 fertilization, up to 75% and 50% of crop residue could be sustainably harvested in south‐western and south‐eastern Australia, respectively. Higher fertilization rates achieved little further increase in sustainable residue harvest rates. Sustainable residue harvest rates were principally determined by climate and soil conditions, especially the initial SOC content and temperature. We conclude that environmental conditions and management practices should be considered to guide the harvest of crop residue for bioenergy production and thereby reduce greenhouse gas emissions during the life cycle of bioenergy production.  相似文献   
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We have no standard computer algorithm for the reconstruction of parental genotypes from the data generated by molecular studies of progeny arrays. Here I present a computer program that uses the multilocus genotypes of parents and offspring to reconstruct the genotypes of unknown parents contributing gametes to a progeny array for which one parent is known a priori. A second program performs simulations to assess the reliability of the algorithm under various scenarios. These programs will aid scientists engaged in parentage analyses, particularly in species with large clutches.  相似文献   
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构建生物量预估模型,探究生物量在各器官中的分配策略和异速生长关系及其对环境因子的响应,对理解植物群落结构、功能、碳储存和分配机制具有重要意义。本研究以内蒙古荒漠草原常见种茵陈蒿(Artemisia capillaris Thunb.)为对象,在不同水分处理下,利用易测指标,如株高、基径、分枝数、冠幅和生物量等参数建立生物量模型,采用标准化主轴分析法分析其异速生长关系。结果表明:在不同水分处理下,茵陈蒿的最佳生物量预估模型的变量选择不同;不同水分处理下茵陈蒿各器官间、各器官与地上生物量间的异速生长关系不同,但相对于自然降水量,增水和减水50%下均为等速生长,这说明在不同水分条件下茵陈蒿对各器官间的资源配置存在权衡策略,符合最优分配假说;而在极端气候条件下,各器官对资源的竞争会变弱;在荒漠草原中,对草本植物进行生物量模拟,选择预测变量和方程模型时,应考虑生长季降水量。本研究可为荒漠草原草本植物生物量预估模型的建立和异速生长关系对环境因子适应的理解等提供方法支持及理论依据。  相似文献   
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Mitigating the impacts of climate change and ensuring energy supply security has compelled China’s policy makers to maximise the use of alternative and low carbon fuels. Use and production of natural gas (an energy source with low carbon emissions) has experienced remarkable growth in China during the last decade, making China the third largest consumer and importer in the world. This study applied a powerful system-oriented ecological network analysis (ENA) technique to study China’s natural gas policies as they pertain to guarantee supply security. Several indicators based on the ENA were measured to analyse the degree of connectivity, the contributions of different compartments, resource utilisation (aggradation), development (ascendancy) and sustainability of China’s natural gas supply system. It was found that China’s source and route diversification policy have caused the natural gas supply system to exhibit considerable network complexity, demonstrating the high level of development, flexibility and diversity of China’s natural gas supply system. However, the policy also has caused a decrease in the aggradation and sustainability from the perspective of an ecological system network. The most important compartments in terms of their contribution to China’s natural gas supply system were found to be domestic natural gas production and transit compartments.  相似文献   
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