Foraging adaptation and the relationship between food-web complexity and stability

Ecological theory suggests that complex food webs should not persist because of their inherent instability. "Real" ecosystems often support a large number of interacting species. A mathematical model shows that fluctuating short-term selection on trophic links, arising from a consumer's adaptive food choice, is a key to the long-term stability of complex communities. Without adaptive foragers, food-web complexity destabilizes community composition; whereas in their presence, complexity may enhance community persistence through facilitation of dynamical food-web reconstruction that buffers environmental fluctuations. The model predicts a linkage pattern consistent with field observations.     

Agent农业土地变化模型研究进展

农业土地变化是全球变化与可持续研究的热点,当前研究虽取得了长足进展,但仍存在诸多不足,集中表现在对农业土地系统复杂性与动态性的认识不够.近年来,基于Agent的农业土地变化研究(农业ABM/LUCC,Agent-based agricultural land change modeling)逐渐兴起,极大的丰富了传统研究的理论与方法,具体表现在:(1)农业ABM/LUCC将微观层面的人类个体行为整合进土地变化研究框架,有助于更加清楚的认识农业土地系统的“人类-自然”综合复杂性问题.(2)农业ABM/LUCC能够动态表达土地系统变化的内生反馈机制,有助于弥补传统的静态土地变化驱动机制分析的不足.(3)基于ABM/LUCC的农业土地利用格局动态研究是整合“人类-自然”综合研究的关键桥梁,农业ABM/LUCC能够与其他生物地球物理模型或经济模型动态嵌套,使多尺度、多维度综合模型研究成为可能.然而,农业ABM/LUCC研究也存在诸多挑战,如理论研究滞后于应用研究,大尺度应用难以开展,以及农户行为的模拟结果很难得到校验等.     

浅谈《有机化学》教学经验和体会

《有机化学》课程内容丰富、复杂且发展迅速,成功讲授此课程并非易事。备课—授课—实验是教学过程中三个相互联系的重要环节,本文从这三个环节分别论述有机化学教学经验和体会。     

Simple systems that exhibit self-directed replication

Biological experience and intuition suggest that self-replication is an inherently complex phenomenon, and early cellular automata models support that conception. More recently, simpler computational models of self-directed replication called sheathed loops have been developed. It is shown here that "unsheathing" these structures and altering certain assumptions about the symmetry of their components leads to a family of nontrivial self-replicating structures, some substantially smaller and simpler than those previously reported. The dependence of replication time and transition function complexity on initial structure size, cell state symmetry, and neighborhood are examined. These results support the view that self-replication is not an inherently complex phenomenon but rather an emergent property arising from local interactions in systems that can be much simpler than is generally believed.     

复杂性科学及其在生态系统研究中的应用

复杂性科学是一门新兴的交叉学科,主要研究复杂系统、复杂性及其方法论.生态系统是一个典型的复杂适应系统,处于混沌的边缘或临界态.内部作用是生态系统复杂化、有序化及自组织的主要推动力.复杂性科学应用于生态系统的研究,旨在更好地了解生物及其环境组分间的相互作用以及生态系统复杂性的动态特征与演化机制.本文综合国内外研究动态,介绍了复杂性的定义、复杂性科学的研究方法及在生态系统研究中的应用,并对一些存在的问题进行了探讨.     

基于蒙特卡洛多重积分的DNA动力学结构参数的计算

依据最新NDB数据库中蛋白质-DNA复合物晶体结构数据,基于修正的DNA结构统计力学模型,利用蒙特卡洛多重积分计算DNA动力学结构的有关参数,并对计算得到的结果进行时间复杂度和精确度分析. Abstract： Based on protein-DNA complex crystal structural data in up-to-date Nucleic Acid Database,the related parameters of DNA Kinetic Structure were investigated by Monte-Carlo Multiple Integrals on the base of modified DNA structure statistical mechanical model,and time complexity and precision were analyzed on the calculated results.     

基于案例推理的森林抚育智能决策算法研究

为帮助林业基层单位管理者摆脱在决策过程中对技术人员经验的过度依赖,实现森林抚育经理小班智能选取以及抚育方式的智能决策,使森林抚育决策过程更具科学性。以黑龙江省森工总局林口林业局为对象,收集2015-2018年度森林抚育作业设计数据为试验数据构建案例库,结合注水分配算法(water-filling assignment,WFA)对案例中各属性进行权重分配;结合基于“原点距”的KML-CB自组织机制优化推理效率,实现森林抚育经理小班的快速选取;采用归一化欧式距离来计算源案例和目标案例之间的相似度,参考“fish-and-shrink”算法思想进行案例推理。进而寻找与目标案例相似的源案例,以源案例的解作为目标案例的满意解,从而实现抚育方式的辅助决策。案例库中共有4 045条案例数据,从中随机抽取80%进行训练,20%的案例数据进行测试。经多次试验,算法的预测精度达到97.16%。研究提出的算法对传统的相似度推理算法进行了改进,提高了推理的精度和速度。与传统算法相比,计算复杂度从O(M×N)降低到O(M+N+4),在降低计算复杂度、优化推理效率方面有一定的意义。     

一种新型知识表示在诊断型农业专家系统中的实现

本文通过对目前常用知识表示方法的分析和比较,针对农业知识的复杂性、推理的模糊性,提出了一套适于农业专家系统开发的知识表示方法--"复合知识树法",以期为农业以及相关领域的诊断型专家系统开发提供参考.     

如何在高校图书馆中正确运用激励机制

根据激励机制的作用机理和“复杂人”假设,结合高校图书馆在人事结构以及“人性”方面复杂性的表现,提出在管理中宜采用目标激励、竞争激励和深入调查了解馆员所需等激励措施;并指出在实施过程中应当注意围绕建立一套科学的评价体系,针对馆员的个性化需求和努力营造良好的工作氛围开展工作。     

气-质联用和酶联免疫检测草莓花托中ABA含量

以草莓＂杜克拉＂为试材,分别利用ELISA和GC-MS测定草莓花托中4个时期ABA含量。结果表明,ELISA（ng/g）/GC-MS（ng/g）检测草莓大绿期（大绿）、白色期（纯白）、着色期（始红）和始熟期（片红）花托中ABA含量分别为65.93/72.90,74.49/233.55,69.56/172.11和78.26/225.07。除大绿果期外,其他时期GC-MS检出结果极显著高于ELISA,但二者变化趋势基本相同,即呈N型升-降-升趋势,这表明ABA与草莓果实成熟存在密切关系。通过对造成差异原因、操作程序复杂性和成本比较分析后认为,GC-MS虽然测量精度高,但如果研究ABA的变化趋势,可选择成本低、操作简便、安全的ELISA方法。     

国家安全:从“单一”到“综合”的嬗变

国家安全问题是国际政治领域的重要课题。“国家安全”的内涵具有很大的复杂性、变化性。“国家安全”是时代矛盾的产物。随着时代主题的转换,20世纪70年代以来,传统“单一安全”的主导地位逐渐为“综合安全”所取代,这在理论研究和政治现实中都产生了重大意义。基于这些原因,国家安全的维护也要有新思路。     

怎样当好图书馆中层干部

随着现代图书馆生存环境的变化和职能的拓展,图书馆中层干部工作呈现出复杂、多变、综合性和直接性的新特点.作者结合多年实践,就新形势,中层干部应扮演的"几种角色"进行了阐述,并提出了增强自身理论素养和业务能力的问题.     

Ecology of insect host-parasitoid communities

Although conclusive evidence is lacking for its establishment, the thesis that complexity adds stability to communities is probably accepted by the majority of ecologists. I believe this attitude found its origins in the indisputable fact that there are latitudinal and altitudinal changes in community complexity. As one progresses northward or southward from the equator, or higher in altitude in most parts of the world, one cannot help but notice that communities tend to become simpler, that is, there are fewer species per community. At the same time, these communities appear to become less stable. But perhaps this change in stability is in appearance only; they appear to be less stable because of the relatively greater number of individuals comprising each species population in temperate areas. Each population, because of its greater numbers, is therefore conspicuous, and changes in these numbers are noticed. We are particularly aware of such changes because populations in these areas of the world have been comparatively well studied. Many of the most studied populations include species of economic importance where changes in population numbers are vital to agricultural or forestry practices. Equatorial populations, on the other hand, contain smaller numbers of individuals of each species because of the greater number of species present. Number changes are simply not as noticeable because the population itself is not as obvious among the other populations. It may be that when (if ever) we have as much data on equatorial populations as we have on those of temperate climates, we will find fluctuations of equal relative magnitude (but not of equal numbers, of course). If, on the other hand, we really do find a correlation between complexity and stability, the suggestion by May (12) that stability permits complexity may be well worth investigating. Because of its organization and physical setting, the Rhopalomyia community I have studied might be expected to have considerable stability. In fact, however, it does not. Each of the populations in the community fluctuates greatly and irregularly in both percentages and numbers, and these populations apparently become locally extinct occasionally, because they sometimes cannot be found even in extensive collections. After studying several of the more important parasitoid species, it is evident to me that there is little or nothing about their interactions that might induce greater community stability. Each species seems to have evolved into the community with no higher purpose than simply to usurp what it can from some other member, and it does this by concentrating its energies on better competitive mechanisms rather than higher reproductive capacities. There are never empty niches to be filled by organisms having the "correct specifications" because new niches are created out of parts of older, broader niches which were occupied by other, more r-selected organisms. Thus, perhaps we have read too much into community organization. Perhaps the "ifiling of niches" is essentially nothing more than the haphazard result of competitive jostling among species; and that as communities develop, they are not necessarily programmed for such things as greater stability or better energy utilizationthe species merely become more closely packed.     

Maize root complexity analysis using a Support Vector Machine method

Root complexity is an important factor in the growth and survivability of maize plants under biotic and abiotic stress conditions. To genetically improve root structure in the future, there is a need to identify the genes that govern root complexity. Root complexity itself is ill defined, but indicators derived from images of the root system such as Fractal Dimension can be used as proxies. A disadvantage of using Fractal Dimension as a complexity indicator is that the complexity of the root as seen in the images is captured into a single parameter.This paper describes an alternative method, which translates a root image into a set of parameters. The method consists of computing the intercepts of circles drawn around the centre of the root image with the root branches. This led to characteristic curves from which parameters can be extracted using curve fitting. In addition to the parameters obtained by curve fitting, the density of the root images was included. All parameters were evaluated on their ability to classify the roots among their original genotypes using a method from the realm of Artificial Intelligence, the Support Vector Machine (SVM).The results showed that whilst using merely three parameters originating from the characteristic curves, the SVM algorithm was capable of correctly classifying 99.95% of roots among 235 original genotypes.     

The socio-cultural context and practical implications of ethnoveterinary medical pluralism in western Kenya

This article discusses ethnoveterinary medical pluralism in Western Kenya. Qualitative methods of data collection such as key informant interviews, open-ended in-depth interviews, focus group discussions (FGDs), narratives, and participant and direct observations were applied. The study shows that farmers in Nyang’oma seek both curative and preventive medical services for their animals from the broad range of health care providers available to them within a pluralistic medical system. Kleinman’s model of medical pluralism, which describes the professional, folk, and popular sectors, informs this discussion because of its relevance and appropriateness to the study. It is, however, important to note the overlap in the three sectors and to point out that livestock farmers engage in multiple “consultations” based on a combination of their own characteristics and the cost, availability and specialization of health care providers. The study concludes by recognizing the complexity of ethnoveterinary medical pluralism and calls for the integration of a pluralistic perspective into the planning and implementation of animal health care interventions and services.

综合农协“三位一体”多中心公共行动分析——基于多中心治理框架理论

立足于多中心治理理论分析框架,从主体、手段和角色分析了瑞安综合农协"三位一体"模式的多中心公共行动体系,在此基础上根据综合农协运作实践来讨论多中心公共行动体系进一步发展的取向,即对制度供给的监督、反思理性的复杂和重构政府角色并整合社会资源。     

浅谈国土资源执法监察中的问题及应对措施——以湖南省长沙市为例

基层国土资源执法监察工作作为国土资源管理的一个重要组成部分,曾对保护国土资源和维护社会稳定起着支撑和保障作用。然而近几年来,随着土地违法现象的复杂化,基层土地执法出现"瓶颈"效应,遇到不少难题。结合长沙市实际情况浅析了当前国土资源违法状况,在此基础上,提出一些完善措施。     

Geographic variation in the molluscan recovery from the end-cretaceous extinction

Biotic recovery patterns after the end-Cretaceous mass extinction differ among the molluscan faunas of the North American Gulf Coast, northern Europe, northern Africa, and Pakistan and northern India. In contrast to the Gulf Coast, the other three regions lack a rapid expansion and decline of "bloom taxa" and have lower proportions of invaders early in the recovery phase. The anomalous Gulf Coast patterns, distinct from extratropical Europe and the tropical regions, provide evidence for the biogeographic and macroevolutionary complexity of biotic recoveries and may have implications for present-day biotas.     

土地资源系列图研究

本文把土地视为自然——经济复合体。通过对土地学科所需图种、图的作用、图的内容、基本要素的研究,提出了综合地、微观地、形象地描述土地资源的自然特性和经济特性的有效方法。     

Bottom-up synthetic biology: engineering in a tinkerer's world

How synthetic can "synthetic biology" be? A literal interpretation of the name of this new life science discipline invokes expectations of the systematic construction of biological systems with cells being built module by module--from the bottom up. But can this possibly be achieved, taking into account the enormous complexity and redundancy of living systems, which distinguish them quite remarkably from design features that characterize human inventions? There are several recent developments in biology, in tight conjunction with quantitative disciplines, that may bring this literal perspective into the realm of the possible. However, such bottom-up engineering requires tools that were originally designed by nature's greatest tinkerer: evolution.