旧大陆视野下的中国旧石器晚期小型两面器溯源

我国北方地区在旧石器晚期偏晚阶段新出现了一类加工复杂且修理精美的石器类型,可称为"小型两面器"。本文对旧大陆东西方晚更新世考古材料进行对比,结果显示这类"小两面器"在旧大陆西侧拥有更为悠久的历史。距今约7万年前南非旧石器时代中期的Still Bay文化已经出现,蕴含热处理技术和压制技术并已作为投射尖状器使用。到了距今4万年前,小型两面器技术在欧洲开始兴起,逐渐形制变的多样化。我国地处旧大陆东侧,发现的小两面器无论是时代还是器形均显示与旧大陆西侧密切关联,应当是旧石器时代晚期旧大陆东西方文化交流的产物。     

Trade-offs in the response of mayflies to low oxygen and fish predation

Summary We examined how mayfly larvae (Ephemeroptera,Callibaetis montanus) balance the conflicting demands of avoiding both benthic hypoxia and fish predators. Using vertical oxygen and temperature gradients typical of ice-covered lakes, we observed the behavior of mayflies in the presence and absence of fish. In the absence of fish and with adequate oxygen, mayflies spent most of the time on the bottom substrate. As benthic oxygen concentration declined, mayflies increased their activity and moved up in the water column. In the presence of fish and with adequate oxygen, mayflies spent even more time associated with the bottom substrate and reduced their activity levels. As benthic oxygen concentrations declined, mayflies increased their activity and moved up in the water column, but to a lesser extent than when fish were absent. Because of this depression in activity and reluctance to leave the bottom substrate, mayflies endured lower oxygen concentrations in the face of predation threat relative to when fish were absent. Despite this trade-off, benthic hypoxia resulted in increased mortality due to fish predation. Because benthic invertebrates vary in their ability to tolerate hypoxia and in their vulnerability to fish predators, periods of benthic hypoxia could lead to selective predation on some taxa and be an important force structuring benthic invertebrate assemblages.     

Electricity Intensity of Internet Data Transmission: Untangling the Estimates

In order to understand the electricity use of Internet services, it is important to have accurate estimates for the average electricity intensity of transmitting data through the Internet (measured as kilowatt‐hours per gigabyte [kWh/GB]). This study identifies representative estimates for the average electricity intensity of fixed‐line Internet transmission networks over time and suggests criteria for making accurate estimates in the future. Differences in system boundary, assumptions used, and year to which the data apply significantly affect such estimates. Surprisingly, methodology used is not a major source of error, as has been suggested in the past. This article derives criteria to identify accurate estimates over time and provides a new estimate of 0.06 kWh/GB for 2015. By retroactively applying our criteria to existing studies, we were able to determine that the electricity intensity of data transmission (core and fixed‐line access networks) has decreased by half approximately every 2 years since 2000 (for developed countries), a rate of change comparable to that found in the efficiency of computing more generally.     

Plant invasions facilitated by suppression of root nutrient acquisition rather than by disruption of mycorrhizal association in the native plant

Invasive species have profound negative impacts on native ranges. Unraveling the mechanisms employed by invasive plant species is crucial to controlling invasions. One important approach that invasive plants use to outcompete native plants is to disrupt mutualistic interactions between native roots and mycorrhizal fungi. However, it remains unclear how differences in the competitive ability of invasive plants affect native plant associations with mycorrhizae. Here, we examined how a native plant, Xanthium strumarium, responds to invasive plants that differed in competitive abilities (i.e., as represented by aboveground plant biomass) by measuring changes in root nitrogen concentration (root nutrient acquisition) and mycorrhizal colonization rate. We found that both root nitrogen concentration and mycorrhizal colonization rate in the native plant were reduced by invasive plants. The change in mycorrhizal colonization rate of the native plant was negatively correlated with both aboveground plant biomass of the invasive plants and the change in aboveground plant biomass of the native plant in monocultures relative to mixed plantings. In contrast, the change in root nitrogen concentration of the native plant was positively correlated with aboveground plant biomass of the invasive plants and the change in aboveground plant biomass of the native plant. When we compared the changes in mycorrhizal colonization rate and root nitrogen concentration in the native plant grown in monocultures with those of native plants grown with invasive plants, we observed a significant tradeoff. Our study shows that invasive plants can suppress native plants by reducing root nutrient acquisition rather than by disrupting symbiotic mycorrhizal associations, a novel finding likely attributable to a low dependence of the native plant on mycorrhizal fungi.     

Building tolerance for bears: A communications experiment

The present study examined the feasibility of experimentally manipulating perceptions of benefit and control via communications to increase public acceptance of bears. We assigned subjects to either a pseudo-control (basic bear biology message) or 1 of 3 treatments adding a benefits message, a perceived control message, or combining messages about both benefits and perceived control. Within-subjects pre–post t-tests showed a significant increase in acceptance among those in the benefits and combined treatments. A between-subjects 1-way analysis of variance (ANOVA) showed a significant difference between the perceived control and combined treatments (where the perceived control message actually decreased acceptance). Our results highlight the importance of including information about benefits stemming from the presence of black bears, as adding this information tended to increase stakeholder acceptance of black bear populations. © 2013 The Wildlife Society.     

Trade-off assessments between environmental and economic indicators in cropping systems of Pampa region (Argentina)

An overall sustainability assessment should include changes in the economic return, the social benefits and the human intervention on the biophysical resources in order to highlight potential trade-off or synergies among them. In this work, we studied the performance of 36 cropping systems (CS) of the Pampa region, Argentina, which include three different crops, three increasing levels of technology adoption in four contrasting site conditions. For each CS, we simultaneously assessed 1) the ecosystem energy flow using the emergy synthesis; 2) the pesticide ecotoxicity using a simple dose-response model; and 3) the economic profit, in order to evaluate the influence of crop identity, technological level, and site location on the indicators values as well as to detect potential trade-offs between indicators. Results revealed that maize crop entailed the most sustainable indicator profile by exhibiting relative high emergy return, low non-renewable emergy use, low pesticide ecotoxicity, and high gross income. In addition, results showed a significant trade-off between economic profit and ecotoxicological risk in the CS studied. Further studies should be conducted for including more contrasting indicators in order to explore the potential trade-off among other ecosystem components as a promising way to identify sustainable crop management regimes for different production zones.     

Internet congestion control using nature population control tactics

In this paper we present a novel bio-inspired approach for congestion control in communication networks. This scheme is based on inspiration by natural population interactions: predator–prey and competition. We show that the relations of those Internet entities that are involved in congestion control mechanisms are similar to predator–prey and competition interactions. In order to apply these population control mechanisms to the Internet congestion control scheme, we combine the mathematical models of these interactions and obtain a hybrid mathematical model. The simulation results show that using appropriately defined parameters, this model leads to a scalable, stable, fair, and high-performance congestion control algorithm.     

Locating spatial variation in the association between road network and forest biomass carbon accumulation

The effects of road network on disturbance regimes of forests are less investigated in biomass carbon accumulation than in landscape pattern. To fills in this knowledge gap, we sought to explore the spatial variations in the relationships between road network and biomass carbon accumulation, taking the upstream area of the Minjiang River, Fujian Province in China, as a case. Our results showed that the biomass carbon density increased gradually as the increase of distances from road in both of the study years 2007 and 2012, with a concentration of the biomass carbon loss within the 1000–1500 m distance zone during the study period. The regression outcomes indicated that the geographically weighted regression models fit better than the ordinary least squares, with all the road network measures being statistically significant at the 1% level for the biomass carbon density in both of the study years. Basing on the sign and size of the coefficients estimated by the geographically weighted regressions for each grid, we found the tradeoff and synergistic relationships between the distribution of road network and biomass carbon density existed simultaneously in the study area. Geographical clusters (i.e., hot spots), where the marginal effects of the road network indictors on biomass carbon sequestration ability varied significantly across locations, were also identified to present spatially explicit and quantitative assessments of the geographic variations in these multiple relationships. Our analysis fills the research gap, which assumes that the road’s impact holds the same everywhere within a given geographical range. Moreover, identified hot spots could facilitate the implement of more elaborate forest management policies (i.e., grid-based) to dialectically deal with the effect of road network construction.     

Temperature-mediated coexistence in temperate forest ant communities

Patterns of ant species diversity are well documented and yet the mechanisms promoting species coexistence among communities are often elusive. Two emerging hypotheses that account for coexistence in ant communities are the discovery-dominance tradeoff and the dominance-thermal tolerance tradeoff. Here we used behavioural assays and community-level sampling from ant assemblages in the southern Appalachians, USA to test for the discovery-dominance and dominance-thermal tolerance tradeoffs. Species that were behaviorally dominant during interspecific interactions tended to forage in a narrow window of generally warmer temperatures, whereas subordinate species tended to forage in a wide range of temperatures, including colder temperatures. Species that foraged at lower temperature tended to be behaviourally subordinate, suggesting that a dominance-thermal tolerance tradeoff promotes coexistence in this system. Species richness was positively related to site average annual temperature and within-site variation in ground temperature, suggesting that temperature also shapes the structure of ant communities and regulates diversity. There was no relationship between the ability of a species to discover food resources and its behavioural dominance, contrary to the predictions of the discovery-dominance tradeoff hypothesis. In sum, our results show that temperature plays numerous roles in promoting regional coexistence in this system.     

Brood size and the cost of provisioning nestlings: interpreting Lack's hypothesis

A recent model of parental provisioning (the tradeoff model) suggests that the maximum delivery rate of food to nestlings represents a tradeoff between parental residual reproductive value and nestling survival. In contrast, Lack's hypothesis suggests that maximum provisioning rate determines brood size and therefore delivery rates are limited by shortages of food or foraging time, not by tradeoffs of parental investment. Several authors have examined the shape of the per-nestling feeding curves to test the tradeoff model against Lack's hypothesis. We show that Lack's hypothesis can produce per-nestling feeding curves consistent with the tradeoff model. Therefore, the shape of the per-nestling feeding curve cannot be used to distinguish between the models.     

Impact of mild temperature hardening on thermotolerance, fecundity, and Hsp gene expression in Liriomyza huidobrensis

The pea leafminer, Liriomyza huidobrensis, is one of the most important economic insect pests around the world. Its population fluctuates greatly with seasonal change in China, and temperature was thought to be one of the important reasons. In attempt to further explore the impact of disadvantageous temperature on L. huidobrensis, 1-day-old adults were shocked at various temperatures (10, 25, 32, and 35 degrees C, respectively) for 4h, and the effects on thermotolerance, feeding, and fecundity were studied. Meanwhile the expression of five heat shock genes (hsp90, 70, 60, 40, and 20) was examined by real-time quantitative PCR. Our results showed that both 32 and 35 degrees C hardenings remarkably increased adult heat resistance, whereas cold tolerance was not improved accordingly. No cross resistance in response to cold and heat stresses was observed. Both adult feeding and fecundity were dramatically reduced, but no effect was observed on egg hatching, larval survival, pupal eclosion, or sex ratio. The results indicate that the deleterious effect on fecundity is the result of direct cessation of oviposition during the period of stress. Simultaneously, the mRNA levels of hsp70 and hsp20 significantly increased upon thermal hardening. Taken together, our results suggest that mild heat hardening improves thermotolerance of L. huidobrensis at the cost of impairment on fecundity, and the induced expression of hsp70 and hsp20 may play an important role in balancing the functional tradeoff.     

城市绿地供需的差异与联系研究进展

作为连接城市绿地与居民需求的重要概念,绿地供需是城市绿地研究和规划决策的重要内容。识别城市绿地供给与需求的区别和关联,有助于城市绿地合理配置、人类福祉提升和城市的可持续发展。本文梳理2016—2020年城市绿地供需研究的主要议题和研究模式,探讨不同议题的差异与联系,并对未来城市绿地供需关系研究提出建议。综述发现,多数研究从供给或需求一方面开展研究,较少将城市供给与需求研究结合一起分析。供给方面主要关注绿地时空分布特征与生态系统服务供给,需求方面侧重于研究居民对绿地的主观偏好与行为。绿地供给、需求的研究对象、研究尺度与研究指标存在较大差异,是二者难以建立联系的主要因素。今后的研究应注重绿地供需匹配的情况。基于主观偏好/客观指标的绿地供需整合研究,是城市绿地供需关系研究的重要方向。     

医患通平台在经皮冠状动脉介入治疗术后患者中的应用

目的：探讨医患通平台对经皮冠状动脉介入治疗（PCI）术后患者进行护理的临床效应。方法：选取54例冠心痛行PCI治疗术后患者,随机分为对照组和试验组,各27例。对照组采用常规护理,试验组在对照组的基础上采用医患通平台进行护理干预,比较两组患者血压、血脂、血糖的控制情况,主要不良心脏事件（MACE）的发生情况,并采用汉密尔顿焦虑量表（HAMA）及汉密尔顿抑郁量表（HAMD）对两组患者进行心理状况调查。结果：实施干预后,试验组血压、血脂、血糖的控制率优于对照组（P〈0．05）,MACE的发生率低于对照组（P〈0．05）;两组患者两组干预前HAMA、HAMD评分比较无明显差异（P〉0．05）,干预后试验组患者HAMA评分、HAMD评分有所下降,与干预前及对照组比较差异显著（P〈O．01）,对照组干预前后无变化（P〉0．05）。结论：医患通平台能有效地让PCI术后患者对危险因素进行控制,降低MACE的发生,改善患者的负性情绪,是较好的健康教育方式．     

医患通平台在经皮冠状动脉介入治疗术后患者中的应用

目的:探讨医患通平台对经皮冠状动脉介入治疗(PCI)术后患者进行护理的临床效应。方法:选取54例冠心病行PCI治疗术后患者,随机分为对照组和试验组,各27例。对照组采用常规护理,试验组在对照组的基础上采用医患通平台进行护理干预,比较两组患者血压、血脂、血糖的控制情况,主要不良心脏事件(MACE)的发生情况,并采用汉密尔顿焦虑量表(HAMA)及汉密尔顿抑郁量表(HAMD)对两组患者进行心理状况调查。结果:实施干预后,试验组血压、血脂、血糖的控制率优于对照组(P0.05),MACE的发生率低于对照组(P0.05);两组患者两组干预前HAMA、HAMD评分比较无明显差异(P0.05),干预后试验组患者HAMA评分、HAMD评分有所下降,与干预前及对照组比较差异显著(P0.01),对照组干预前后无变化(P0.05)。结论:医患通平台能有效地让PCI术后患者对危险因素进行控制,降低MACE的发生,改善患者的负性情绪,是较好的健康教育方式。     

A model for the evolutionary dynamics of cross-feeding polymorphisms in microorganisms

 Understanding mechanisms of evolutionary diversification is central to evolutionary biology. Microbes constitute promising model systems for observing processes of diversification directly in the laboratory. One of the main existing paradigms for microbial diversification is the evolution of cross-feeding polymorphisms, in which a strain specializing on a primary resource coexists with a cross-feeding strain that specializes on a waste product resulting from consumption of the primary resource. Here I propose a theoretical model for the evolutionary dynamics through which cross-feeding polymorphisms can gradually emerge from a single ancestral strain. The model is based on the framework of adaptive dynamics, which has proved to be very useful for studying adaptive processes of divergence under sympatric conditions. In particular, the phenomenon of evolutionary branching serves as a general paradigm for diversification. I show that evolutionary branching naturally occurs in evolutionary models of cross-feeding if (1) there is a trade-off between uptake efficiencies on the primary and secondary resources, and (2) this trade-off has positive curvature. The model also suggests that the evolution of cross-feeding should be more likely in chemostat cultures than in serial batch cultures, which conforms with empirical observations. Overall, the model provides a theoretical metaphor for the evolution of cross-feeding polymorphisms. Received: February 19, 2002 / Accepted: May 8, 2002     

Experimental tests of trophic dynamics: taking a closer look

The relative importance of bottom-up versus top-down forces, and the effect of productivity on community dynamics continue to be of much interest to ecologists. Trophic dynamic theories are difficult to test, as they require explicit knowledge of the many organisms involved, as well as the nature of the interactions between them. The Oksanen-Fretwell (OF) theory, which suggests that the relative roles of top-down and bottom-up factors vary with primary productivity, is well known in the literature, but is difficult to test rigorously. Recently, two experimental studies have tried to test OF theory. In this paper we discuss methodological problems associated with these studies that may weaken the conclusions drawn by the authors. Received: 21 April 1998 / Accepted: 30 July 1998     

植物挥发性物质及其代谢工程

植物挥发性物质在植物之间和植物与昆虫间的化学通讯中起着重要作用.有关这些次生物质的生物合成、代谢调控、生理功能以及与环境相互作用的研究近十多年来取得了重要进展.迄今为止,已经有3 0多种植物挥发性物质的合成酶基因被克隆.这些基因调控着植物萜类、芳香化合物、脂肪酸衍生物这三大类主要挥发性物质的生物合成.由于潜在的应用价值,近几年该领域颇受注目,特别是应用基因工程技术设计植物释放特殊气味物质,诸如特定的驱避剂或者其它控制植物或昆虫行为的特殊气味乃至与人类健康相关的药用气味物质.该文就植物挥发性物质的生物合成、生理和生态功能以及基因工程方面的研究进展作一概述.