A general model for food web structure

A central problem in ecology is determining the processes that shape the complex networks known as food webs formed by species and their feeding relationships. The topology of these networks is a major determinant of ecosystems' dynamics and is ultimately responsible for their responses to human impacts. Several simple models have been proposed for the intricate food webs observed in nature. We show that the three main models proposed so far fail to fully replicate the empirical data, and we develop a likelihood-based approach for the direct comparison of alternative models based on the full structure of the network. Results drive a new model that is able to generate all the empirical data sets and to do so with the highest likelihood.     

Direct and indirect effects of resource quality on food web structure

The diversity and complexity of food webs (the networks of feeding relationships within an ecological community) are considered to be important factors determining ecosystem function and stability. However, the biological processes driving these factors are poorly understood. Resource quality affects species interactions by limiting energy transfer to consumers and their predators, affecting life history and morphological traits. We show that differences in plant traits affect the structure of an entire food web through a series of direct and indirect effects. Three trophic levels of consumers were influenced by plant quality, as shown by quantitative herbivore-parasitoid-secondary parasitoid food webs. We conclude, on the basis of our data, that changes in the food web are dependent on both trait- and density-mediated interactions among species.     

Scale invariance in food web properties

The robustness of five common food web properties is examined by varying the resolution of the data through aggregation of trophic groupings. A surprising constancy in each of these properties is revealed as webs are collapsed down to approximately half their original size. This analysis of 60 invertebrate-dominated community food webs confirms the existence of all but one of these properties in such webs and addresses a common concern held by critics of food web theory that observed food web properties may be sensitive to trophic aggregation. The food web statistics (chain length; predator/prey ratio; fraction of top, intermediate, and bottom species; and rigid circuits) are scaling in the sense that they remain roughly invariant over a wide range of data resolution. As such, within present standards of reporting food web data, these statistics may be used to compare systems whose trophic data are resolved differently within a factor of 2.     

Growing local food: scale and local food systems governance

“Scaling-up” is the next hurdle facing the local food movement. In order to effect broader systemic impacts, local food systems (LFS) will have to grow, and engage either more or larger consumers and producers. Encouraging the involvement of mid-sized farms looks to be an elegant solution, by broadening the accessibility of local food while providing alternative revenue streams for troubled family farms. Logistical, structural and regulatory barriers to increased scale in LFS are well known. Less is understood about the way in which scale developments affect the perception and legitimacy of LFS. This value-added opportunity begs the question: Is the value that adheres to local food scalable? Many familiar with local food discourse might suggest that important pieces of added value within LFS are generated by the reconnection of producer and consumer, the direct exchange through which this occurs, and the shared goals and values that provide the basis for reconnection. However, these assertions are based on tenuous assumptions about how interactions within the direct exchange produce value, and how LFS are governed. Examination shows that existing assumptions do not properly acknowledge the hybridity, diversity, and flexibility inherent in LFS. A clear analysis of the potential of scale in LFS will depend on understanding both how value is determined within LFS, and the processes through which these systems are governed. Such an analysis shows that, while scaled-up LFS will be challenged to maintain legitimacy and an identity as “alternative”, the establishment of an open governance process—based on a “negotiation of accommodations”—is likely to enhance their viability.     

群落水平食物网能流季节演替特征

稳定碳、氮同位素比值分析技术是研究生态系统中物质循环与能量流动的有效技术。δ¹³C可以用来判断食物网中不同生物的能量来源;δ¹⁵N主要用于确定生物在食物网中所处的营养位置。通常用δ¹³C-δ¹⁵N图来表征某一特定时间或空间的食物网结构,但是这种方法在比较不同时间和空间食物网结构中功效较差。同时这种定性描述食物网结构也无法满足食物网复杂变化下的假说验证。应用环形统计方法,以太湖梅梁湾鱼类群落为例,定量评价了群落水平食物网能流季节演替特征。结果表明太湖梅梁湾鱼类营养生态位移动的季节特征明显。进一步物种水平分析结果表明,各种鱼类角度和幅度随季节均有变化。Rayleigh检验结果表明,群落中不同种类在秋冬、冬春和夏秋均有显著的一致的方向变化;而春夏期间不显著。Watson-William检验结果表明,群落水平的鱼类营养生态位移动在秋冬和冬春季节转换中有显著差异。引起鱼类群落水平营养生态位在食物网空间中季节性移动的主要因素为可利用资源稳定同位素的季节变化和不同鱼类种群自身的食性季节性转变。同时,由于梅梁湾食物网鱼类群落杂食性水平高,季节性浮游初级生产力成为食物网能量流动的重要驱动作用。因此,在富营养化生态系统中,食物网群落水平营养生态位季节波动也暗示了系统稳定性的下降。定量评价食物网变化有助于认识和理解食物网结构与功能在生态学和生态系统管理等方面的重要。     

Effects of experimental seaweed deposition on lizard and ant predation in an island food web

The effect of environmental change on ecosystems is mediated by species interactions. Environmental change may remove or add species and shift life-history events, altering which species interact at a given time. However, environmental change may also reconfigure multispecies interactions when both species composition and phenology remain intact. In a Caribbean island system, a major manifestation of environmental change is seaweed deposition, which has been linked to eutrophication, overfishing, and hurricanes. Here, we show in a whole-island field experiment that without seaweed two predators--lizards and ants--had a substantially greater-than-additive effect on herbivory. When seaweed was added to mimic deposition by hurricanes, no interactive predator effect occurred. Thus environmental change can substantially restructure food-web interactions, complicating efforts to predict anthropogenic changes in ecosystem processes.     

依靠科技进步促进粮食结构调整

党中央国务院明确指出:我国农业已进入新阶段,实施战略性结构调整是当前和整个新阶段农业的中心任务.长期以来,由于粮食生产受传统计划经济增长方式的约束,一方面农业资源配置对粮食增长造成不利影响;另一方面,政府在粮食市场化改革过程中制定的保障粮食安全措施难以落实实施.因此,当前农业结构调整中不能放松粮食生产,要切实保护粮食综合生产能力和农民种粮积极性,要以市场需求为导向,以科技进步为先导,以提高粮食品质为重点,加大农业科技的支持力度,要重点关注粮食生产潜力的增长和安全规则的制定,增强对粮食生产宏观调控能力.     

海洋食物网结构稳定性及干扰响应研究综述

针对当前全球环境急剧变化的背景,本文归纳了海洋食物网结构复杂性常用的量化指标,梳理了食物网稳定性不同维度的概念并深入探究其与复杂性之间的内在联系。根据海洋生态系统的不同干扰类型,分析了各种类型干扰的发生方式以及食物网在应对干扰时的适应机理,最后总结了海洋生态系统数据获取分析以及食物网构建时有待解决的问题,并指出开展初级生产者与消费者之间的相互作用研究能更利于解析全球变化对海洋食物网结构和功能的影响。     

热带东太平洋中上层食物网结构指数分析

根据2017年6月—2019年2月在热带太平洋东部海域(14°03′N～30°22′S, 179°36′E～114°29′W)开展的6个航次金枪鱼延绳钓渔获采样资料及胃含物组成数据,运用12个食物网网络分析指数,研究热带东太平洋中上层食物网结构特征。结果显示,本食物网物种(类群)数为83,连接数为542,食物网的平均营养级为2.4,顶级物种、中间物种、基础物种的比例分别为10.85%、83.13%、6.02%。食物网不同营养级物种的比例、杂食性指数(omnivorous,O=92.77%)、连接复杂性指数(connection complexity index,C_SC=13.22)和特征路径长度(characteristic path length,P=1.85)的分析表明,该食物网结构处于较稳定状态;聚类系数(clustering coefficient,C_C=0.242)表明食物网物种间可形成几个连接性较密切的子网络结构;由连接密度(linkage density,D=6.53)和连通度指标(connectance,C_l     

东平湖食物网关键种鲫鱼体中氨基酸分析

运用化学衍生化和GC-MS分析技术,测定了东平湖生态系统中的关键种鲫鱼体中的氨基酸含量,比较了鲫鱼体中各类氨基酸的组成水平,为进一步进行东平湖生态系统的能量流动稳定性研究提供了理论依据。     

The role of ammonites in the Mesozoic marine food web revealed by jaw preservation

Ammonites are prominent in macroevolutionary studies because of their abundance and diversity in the fossil record, but their paleobiology and position in the marine food web are not well understood due to the lack of preserved soft tissue. We present three-dimensional reconstructions of the buccal apparatus in the Mesozoic ammonite Baculites with the use of synchrotron x-ray microtomography. Buccal mass morphology, combined with the coexistence of food remains found in the buccal mass, suggests that these ammonites fed on plankton. This diet may have extended to all aptychophoran ammonites, which share the same buccal mass morphology. Understanding the role of these ammonites in the Mesozoic food web provides insights into their radiation in the Early Jurassic, as well as their extinction at the end of the Cretaceous/early Paleogene.     

国际30年来土壤食物网的研究历程与热点分析

利用文献计量学方法,研究1989—2018年来土壤食物网研究领域的热点内容,概括土壤食物网的研究脉络及国际土壤食物网未来的研究方向。结果显示:土壤生物多样性、食物网的碳氮循环功能及管理方式对土壤食物网结构的干扰是现在研究热点,而土壤食物网功能多样性、系统稳定性、及土壤食物网对全球变化的响应则是新兴的研究方向。     

餐厨废弃物复合酶解预处理-厌氧发酵中试工程研究

为获得复合酶解预处理-厌氧发酵二步法工艺稳定性工程数据,在中温（35±2）℃条件下,采用自行设计的1 m³太阳能辅热连续搅拌式（CSTR）厌氧反应器,进行了180 d的连续式餐厨废弃物中试厌氧发酵效果研究,结果表明：餐厨废弃物复合酶解预处理-厌氧发酵二步法工艺具有良好的运行稳定性及较高的发酵效率,中试工程有机负荷可达约3.5 kgVS·m^-3·d^-1,单位总固体（TS）及挥发性固体（VS）产气率、产气平均甲烷（CH₄）含量、容积产气率等指标可分别达到645.19 L·kg^-1、685.06 L·kg^-1、75.54%和2.37 m³·d^-1,折合餐厨废弃物原料产气量158 m³·t^-1。     

Scale and structure in natural food webs

The degree to which widely accepted generalizations about food web structure apply to natural communities was determined through examination of 50 pelagic webs sampled consistently with even taxonomic resolution of all trophic levels. The fraction of species in various trophic categories showed no significant overall trends as the number of species varied from 10 to 74. In contrast, the number of links per species increased fourfold over the range of species number, suggesting that the link-species scaling law, defined on the basis of aggregated webs, does not reflect a real ecological trend.     

A major food web component in the orinoco river channel: evidence from planktivorous electric fishes

Deep-water sampling of the Orinoco River main channel resulted in the collection of an unexpectedly high abundance and diversity of specialized fishes. Twenty-eight of the more than 60 species collected belong to the Gymnotiformes(New World electric or knife fishes). One of the more numerous of these, a recently described species of the genus Rhabdolichops, consumes large numbers of very small planktonic Crustacea and insect larvae. These items are captured in the very swift, turbid, and deep waters of the Orinoco. Although the strong dependence of the river food web on terrestrial and floodplain food sources is well known, the specialized capabilities of Rhabdolichops and of other fishes that occur with it indicate a significant extension of the river food web into the main channel.     

Web数据库技术综述

一、引言今年来Internet/Intranet的蓬勃发展对数据库技术产生了巨大的影响。Internet的核心应用Web上信息量大、面广,难以管理;数据库技术则比较成熟,机构严谨,但是灵活性不足。这两种技术的天然互补性决定了相互融合是其发展的必然趋势,将Web技术和数据库相结合,不仅把Web与数据库的所有优点集中在一起,而且充分利用了大量的已有的数据库信息资源。总的思路是采用中间件将两者结合起来,而对于Web和数据库服务器的变动都不大。所以Web数据库访问技术是Internet和数据库共同的发展方向,也是Internet应用中的关键技术。二、Web数据库的…     

改革开放以来广东粮食生产结构变化分析

从粮食作物总产量、单产、种植结构、区域布局、产值结构以及粮食生产在全国所处地位6个方面分析了改革开放以来广东粮食生产结构变化的特征。广东粮食作物总播种面积逐年下调，单产总体上不断增长，总产表现出周期性波动特征；粮食生产的品种结构趋向优质化、多样化；粮食生产比较效益低下的矛盾加剧；广东粮食生产在全国的地位趋于弱化。