Explaining the excess of rare species in natural species abundance distributions

The observation that a few species in ecological communities are exceptionally abundant, whereas most are rare, prompted the development of species abundance models. Nevertheless, despite the large literature on the commonness and rarity of species inspired by these pioneering studies, some widespread empirical patterns of species abundance resist easy explanation. Notable among these is the observation that in large assemblages there are more rare species than the log normal model predicts. Here we use a long-term (21-year) data set, from an estuarine fish community, to show how an ecological community can be separated into two components. Core species, which are persistent, abundant and biologically associated with estuarine habitats, are log normally distributed. Occasional species occur infrequently in the record, are typically low in abundance and have different habitat requirements; they follow a log series distribution. These distributions are overlaid, producing the negative skew that characterizes real data sets.     

Neutral theory and relative species abundance in ecology

The theory of island biogeography asserts that an island or a local community approaches an equilibrium species richness as a result of the interplay between the immigration of species from the much larger metacommunity source area and local extinction of species on the island (local community). Hubbell generalized this neutral theory to explore the expected steady-state distribution of relative species abundance (RSA) in the local community under restricted immigration. Here we present a theoretical framework for the unified neutral theory of biodiversity and an analytical solution for the distribution of the RSA both in the metacommunity (Fisher's log series) and in the local community, where there are fewer rare species. Rare species are more extinction-prone, and once they go locally extinct, they take longer to re-immigrate than do common species. Contrary to recent assertions, we show that the analytical solution provides a better fit, with fewer free parameters, to the RSA distribution of tree species on Barro Colorado Island, Panama, than the lognormal distribution.     

Theoretical biology: comparing models of species abundance

Ecologists are struggling to explain how so many tropical tree species can coexist in tropical forests, and several empirical studies have demonstrated that negative density dependence is an important mechanism of tree-species coexistence. Volkov et al. compare a model incorporating negative density dependence with a dispersal-limited neutral model and claim that each predicts six empirical species-abundance distributions of tropical-tree communities equally well. However, we show here that their main conclusion is premature: when the two models are compared in an improved analysis, we find that the dispersal-limited model outcompetes the density-dependent model in all six cases. Hence, although density dependence is certainly an important diversity-maintaining mechanism, our improved approach indicates that the dispersal-limited model provides a more parsimonious explanation of empirical species-abundance distributions.     

Patterns of relative species abundance in rainforests and coral reefs

A formidable many-body problem in ecology is to understand the complex of factors controlling patterns of relative species abundance (RSA) in communities of interacting species. Unlike many problems in physics, the nature of the interactions in ecological communities is not completely known. Although most contemporary theories in ecology start with the basic premise that species interact, here we show that a theory in which all interspecific interactions are turned off leads to analytical results that are in agreement with RSA data from tropical forests and coral reefs. The assumption of non-interacting species leads to a sampling theory for the RSA that yields a simple approximation at large scales to the exact theory. Our results show that one can make significant theoretical progress in ecology by assuming that the effective interactions among species are weak in the stationary states in species-rich communities such as tropical forests and coral reefs.     

渔船吸鱼装备控制系统设计

在分析国外吸鱼泵样机的基础上,了解吸鱼装置的主要组成部分,分析其工作原理,最后通过结合PLC技术设计出适合本国渔船使用的自动控制电路,来改善现今渔船生产力水平.     

“联合渔法”在汾河二库大水面捕捞中的应用

针对汾河二库水深、库底不平、障碍物较多的特点,通过对围网与＂联合渔法＂不同捕捞方式的比较,最终采用＂联合渔法＂水库捕捞技术。介绍了水库＂联合渔法＂的捕鱼原理、特点、渔具的组成、捕鱼技术及注意事项。     

幂指数方程拟合物种多度分布模型的研究

物种多度分布是物种多样性研究的重要方法之一,首次提出用幂指数方程来拟合物种多度分布模型,实例拟合结果表明,幂指函数应用于物种多度分布研究是理想的,从而丰富了物种多度分布模型理论。     

Density dependence explains tree species abundance and diversity in tropical forests

The recurrent patterns in the commonness and rarity of species in ecological communities--the relative species abundance--have puzzled ecologists for more than half a century. Here we show that the framework of the current neutral theory in ecology can easily be generalized to incorporate symmetric density dependence. We can calculate precisely the strength of the rare-species advantage that is needed to explain a given RSA distribution. Previously, we demonstrated that a mechanism of dispersal limitation also fits RSA data well. Here we compare fits of the dispersal and density-dependence mechanisms for empirical RSA data on tree species in six New and Old World tropical forests and show that both mechanisms offer sufficient and independent explanations. We suggest that RSA data cannot by themselves be used to discriminate among these explanations of RSA patterns--empirical studies will be required to determine whether RSA patterns are due to one or the other mechanism, or to some combination of both.     

营养元素添加对青藏高原亚高寒草甸物种多度分布格局的影响

以青藏高原亚高寒草甸为研究对象,基于N,P,N+P耦合营养元素添加的控制实验,研究了群落内全部物种、常见种和稀有种的物种多度分布格局以及物种丰富度对N,P,N+P耦合营养元素添加的响应规律,并选取对数正态模型、幂分割模型、几何级数模型、Zipf模型以及中性模型对物种多度数据进行拟合.结果表明:1)P添加对物种丰富度的影响不显著,全部物种、常见种与稀有种的物种多度分布曲线的陡缓程度基本相同.随N,N+P耦合添加量的增大,全部物种与常见种的物种多度分布曲线都越来越陡峭,物种丰富度也都显著下降,表明在青藏高原亚高寒草甸N,N+P耦合添加会导致物种多样性的降低.2)比较CK,N15,P15,N15P15的物种多度分布曲线发现N+P耦合处理的物种多度分布曲线的陡峭度较CK,N15,P15处理的要陡,表明N+P耦合对物种多度分布格局的影响效应要强于单独的N,P的.3)分析施肥对物种多度分布模式的影响发现,全部物种的多度分布符合统计模型的对数正态模型以及基于生态位理论的幂分割模型、几何级数模型与Zipf模型.常见种的多度分布符合几何级数模型与Zipf模型,而稀有种在同时符合这两种基于生态位分化的模型外,呈现出符合中性模型的趋势.说明多种不同模型可以拟合同一生境的物种多度分布,常见种和稀有种通过不同的响应方式共同维持着亚高寒草甸生态系统的物种多样性.     

一类被开发的两种群捕食模型的定性分析

讨论了一类食饵种群被开发的两种群捕食系统.运用定性分析和分支方法给出了该系统极限环的不存在性、存在性和惟一性等结论,并对相应的生态学意义作了说明.     

钓鱼学会换鱼钩

还记得那个一嚼菠菜就变得力大无比的大力水手波比吗?儿时对这部动画片的记忆除了里面的几个主要人物外就是含铁的菠菜了.我有幸听了由中国科学院上海生命科学研究院"百人计划"入选者王福佛研究员主讲的"解密人体锌铁平衡代谢"讲座,从科研角度探讨了锌铁等微量元素在人体内的代谢机制.     

北太平洋中部渔场鱿鱼钓渔具渔法的初步研究

利用舟渔1301鱿鱼钓船,于2000年5月15日～7月8日对北太平洋中部渔场(39°～42°N,180°～171°W)鱿鱼钓渔具渔法进行了初步研究,结果表明:(1)当鱿钓船日产量在4t以下时,手钓产量比例较高;当日产量在4t以上时,机钓就体现了一定的效能。(2)大号钓钩脱钩率最低,小号钓钩脱钩率最高。(3)不同颜色的钓钩脱钩率相差不大,而上钩率则有较大差别,黄色上钩率最佳(20.57%),其余依次为红色(19.43%)、绿色(18.0%)、黄绿色(14.86%)、青色(12.0%)、浅蓝(10.0%)、橙色(5.14%)。(4)设置抖动后,上钩率高于非抖动状态,而脱钩率上升,但总体钓获数还是抖动高于非抖动状态。(5)手线规格大小和新旧,对上钩率影响不大;但钩线的规格大小和新旧对渔获率有较大的影响,从经济效益来分析:一般每隔3～4/d更换钩线一次,并且钩线的材料以PA,直径为0.91mm较好。     

快速凝固技术在新材料开发中的应用及发展

快速凝固技术是当前材料科学与工程中研究比较活跃的领域之一,目前已成为一种挖掘金属材料潜在性能与开发新材料的重要手段,概述了快速凝固技术的原理与方法,及其在新材料开发与研制方面的应用,对快速凝固技术的研究方向进行了探讨.     

Morphological variability and genetic diversity in five species of Skeletonema （Bacillariophyta）

Twelve strains of Skeletonema from Chinese coastal waters and another strain from the West Sea of Korea were examined using light microscopy （LM）, scanning and transmission electron microscopy （SEM, TEM）, and small subunit （SSU） rDNA sequence analysis. We identified four species of Skeletonema： S. marinoi Sarno et Zingone, S. subsalsum （A.Cleve） Bethge, S. dohrnii Sarno et Kooistra, S. trop- icum Cleve, as well as a Skeletonerna-like species. These are the first records of S. rnarinoi, S. dohrnii and S. subsalsurn in China. The Skeletonema-like species, MMDLS067, was isolated from the estuary of the Changjiang River. The morphologic and phylogenetic characteristics of this species are not correspond to those of any previously published Skeletonerna species. The intercalary fultoportula pro- cesses （IFPPs） has long open tubes, and the intercalary rimoportula process （IRP） is short and located inside the rim of the IFPPs. Phylogenetic analysis revealed that MMDL5630 clustered with S. tropicurn in the NJ and MP trees, but its IRPs differed from those of previously described specimens of S. tropicum. The IRP is partially open, with an elongated opening at the base of the tube, and is longer than the IFPPs. Some specimens of S. marinoi and S. dohrnii also have longer tubular IRPs than the IFPPs. Compared to pre- viously described specimens of S. rnar＆oi and S. dohrnii, these two specimens we identified have shorter IRPs. Our results reflect the ambiguity and diversity of Skeletonema taxonomy. They are also significant for the future identification and management of red tides caused by Skeletonerna in the seas around China.     

休渔的建模与分析

通过建立数学模型,分析了休渔措施下水生生物种群的动态.一年中生产积累大于捕捞积累时,种群持续生存;反之,种群趋向灭绝.休渔期越长,种群规模越大.     

Rapid assessment and explanation of tree species abundance along the elevation gradient in Gaoligong Mountains,Yunnan, China

This article presents an analysis of tree species abundance and its association with climatic variables along elevation gradient in the Gaoligong Mountains in west Yunnan, China. Data from scientific papers and books in the Gaoligong Mountains area were collected and extrapolated to elucidate a mechanistic understanding of elevation patterns and the relationship between the elevation range and elevation mid-point of tree species along the gradient by examining climatic variables. Tree species abundance showed a unimodal pattern with a peak at mid-elevation (about 2000 m) and species with a narrow elevation range occurred at higher or lower elevation, while a wider elevation range was found at the middle of the gradient. Tree species abundance was the highest where both temperature and water availability were moderate. The relationship between the climatic variables affecting species appear to be due to both direct and indirect factors, and the effect of these effects varied at different gradients.

     

透空式防波堤在渔船避风港中的综合研究

采用波浪断面物理模型测定中咀湾渔船避风港透空堤断面透浪系数及堤后不同距离有效波高,分析挡浪板入水深度与透浪系数及有效波高的关系,提出了合理的透空堤断面尺寸。采用MIKE21 BW模块数值计算透空堤堤后水域波高分布和渔船泊稳面积,论证透空堤口门大小与泊稳面积之间的关系,探讨透空堤整体防浪掩护效果。     

信息系统脆弱性被利用概率计算方法

针对现有信息系统风险评估工作中对脆弱性的评估未考虑各脆弱性间的相关性,评估结果受到较多人为主观因素的影响,提出"被利用难易程度"和"被选择概率"两个指标将现有对脆弱性的"被利用难易程度"评价转换为更为科学的"被利用概率"评价,并用贝叶斯网络的正向推理计算脆弱性节点的累积"被选择概率"。通过理论和实验分析,与相关的研究成果相比,提出的脆弱性被利用概率计算方法更准确、合理。     

一类被开发的捕食系统的定性分析

对一类被开发的捕食系统在较一般的情况下进行了较为详细的定性分析 ,得到了系统奇点的全局渐进稳定性、闭轨的不存在性以及极限环的存在惟一性等一系列充分条件 ,为进一步深入研究被开发的两种群生态系统的动力学行为提供了理论依据