| 论文/程序题目 | 作者 | 下载 | 主要内容介绍 | Hits |
| Scaling Behaviors of Weighted Food Webs as Energy Transportation Networks |
Jiang Zhang,Liangpeng Guo |  |
Food webs can be regarded as energy transporting networks in which the weight of each edge denotes the energy flux between two species. By investigating 21 empirical weighted food webs as energy flow networks, we found several ubiquitous scaling behaviors. Two random variables Ai and Ci defined for each vertex i, representing the total flux (also called vertex intensity) and total indirect effect or energy store of i, were found to follow power law distributions with the exponents \alpha=1.32 and \beta=1.33, respectively. Another scaling behavior is the power law relationship, Ci~Ai^{\eta}, where \eta=1.02. This is known as the allometric scaling power law relationship because Ai can be treated as metabolism and Ci as the body mass of the subnetwork rooted from the vertex i, according to the algorithm presented in this paper. Finally, a simple relationship among these power law exponents, \eta =(\alpha−1)/(\beta−1), was mathematically derived and tested by the empirical food webs. | 178 |
| Modeling Multi-species Interacting Ecosystem by a Simple Equation |
Jiang Zhang | |
An ecosystem can be viewed as an energy flow system in which various species are connected by energy flows along food web links. To understand the co-evolution of the fast dynamics of energy flows and slow dynamics of food web structure, a simple reaction diffusion equation is presented in this paper. Some statistical indicators such as total system throughflow (TST) and Shannon entropy are designed to describe the macro-level evolution of the system. The positive correlation between time series of TST and Shannon entropy is mainly shown. That means the diversity of the species may accelerate the total energy flows in the system. This conclusion may help us to understand general phenomena of flows and diversity in other complex systems. | 172 |
| Energy Flows in Complex Ecological Systems: A Review |
Jiang Zhang | |
Energy flow drives the complex systems to evolve. The allometric scaling as the universal energy flow pattern has been found in different scales of ecological systems. It reflects the general power law relationship between flow and store. The underlying mechanisms of energy flow patterns are explained as the branching transportation networks which can be regarded as the result of systematic optimization of a biological target under constraints. Energy flows in the ecological system may be modelled by the food web model and population dynamics on the network. This paper reviews the latest progress on the energy flow patterns, explanatory models for the allometric scaling and modelling approach of flow and network evolution dynamics in ecology. Furthermore, the possibility of generalizing these flow patterns, modelling approaches to other complex systems is discussed. | 168 |
| Allometric Scaling of Weighted Food Webs |
Jiang Zhang | |
Allometric scaling is an important universal property of metabolic living systems. It also describes the self-similar branching tree-liked structures in transportation networks. This paper presented a new approach to calculate the allometric scaling power law relations for arbitrary flow networks. This method can not only avoid the shortcoming of losing lots of information in the process of generating spanning trees in the conventional approaches but also can be applied to arbitrary weighted networks. The allometric scaling properties of 20 empirical weighted food webs (weights are energy fluxes) are computed according to the new approach, the power law relationships are derived with the universal exponent \eta = 1.0298 which reflects the transportation efficiency of the food webs. | 118 |
| Intermittent search strategies when losing time becomes efficient |
O. B磂nichou,M. Coppey | |
In this letter, we show that intermittent search strategies, alternating active search phases and non-reactive displacement phases, are universal for a wide class of problems involving search time optimization. More precisely, we address the general question of determining in which cases a searcher should, or should not, interrupt his search activity by 搇osing攖ime in non-reactive phases of mere displacement, and which durations of each phase optimize the search time. Using a representative analytical model, we show that intermittent strategies do optimize the search time as soon as the target is 揹ifficult?to detect, and we explicitly give the optimal search strategies, which depend on the memory skills of the searcher. | 511 |
| Intermittent search strategies when losing time becomes efficient |
O. B磂nichou,M. Coppey | |
In this letter, we show that intermittent search strategies, alternating active search phases and non-reactive displacement phases, are universal for a wide class of problems involving search time optimization. More precisely, we address the general question of determining in which cases a searcher should, or should not, interrupt his search activity by 搇osing攖ime in non-reactive phases of mere displacement, and which durations of each phase optimize the search time. Using a representative analytical model, we show that intermittent strategies do optimize the search time as soon as the target is 揹ifficult?to detect, and we explicitly give the optimal search strategies, which depend on the memory skills of the searcher. | 511 |
| beyond neutrality—ecology finds its niche |
Virginia Gewin | |
From physics to ecology, one formidable goal of scientific exploration is determining the forces at work in nature and how these forces organize our world. In trying to uncover simple laws, scientists must balance the accuracy and complexity necessary to describe essential mechanisms. Sir Isaac Newton’s laws of motion were suffi cient for almost 200 years, but Einstein’s addition of a fourth dimension of spacetime was justifi able because it not only increased the accuracy and complexity of understanding but also moved physics past a descriptive stage. Understanding the patterns of biodiversity in a tropical forest or a coral reef, however, has had ecologists mired in the multiple dimensions of natural laws to simply describe how species survive and co-exist. Distilling this complexity to the essential drivers of species assemblages will not only help ecology meet its most daunting conservation challenge—staving biodiversity loss—but also help move the science into a predictive stage. | 339 |
| neutrality versus the niche |
John Whitfield | |
According to some ecologists, you don’t need to invoke adaptation to explain biodiversity. They may sound like nihilists, but their ideas are proving remarkably resilient. John Whitfield reports. | 317 |
Supply–demand balance and metabolic scaling |
Jayanth R. Banavar,John Damuth | |
It is widely accepted that metabolic rates scale across species approximately as the 34 power of mass in most if not all groups of organisms. Metabolic demand per unit mass thus decreases as body mass increases. Metabolic rates reflect both the ability of the organism’s transport system to deliver metabolites to the tissues and the rate at which the tissues use them. We show that the ubiquitous 3/4 power law for interspecific metabolic scaling arises from simple, general geometric properties of transportation networks constrained to function in biological organisms. The 3/4 exponent and other observed scaling relationships follow when mass-specific metabolic demands match the changing delivery capacities of the network at different body sizes. Deviation from the 3/4 exponent suggests either inefficiency or compensating physiological mechanisms. Our conclusions are based on general arguments incorporating the minimum of biological detail and should therefore apply to the widest range of organisms. | 479 |
| Allometric scaling in animals and plants |
Olaf Dreyer,Raymond Puzio | |
In this paper we give a derivation for the allometric scaling relation between the metabolic rate and the mass of animals and plants. We show that the characteristic scaling exponent of 3/4 occurring in this relation is a result of the distribution of sources and sinks within the living organism. We further introduce a principle of least mass and discuss the kind of flows that arise from it. | 444 |
| Allometric Scaling and Central Source Systems |
Olaf Dreyer | |
Allometric scaling relations abound in nature. Examples include the power law relating the metabolic rate of animals and plants to their masses and the power law describing the dependence of the size of the drainage basin of a river on the total amount of water contained in that river. The exponent is of the form D/D+1, where D is the dimension of the system. We show that this scaling exponent is simply a consequence of the source distribution of the systems considered and requires no further assumptions. To demonstrate the wide range of validity of the result we present a simple experiment that shows the predicted behavior in one dimension. | 458 |
| The maximum entropy formalism and the idiosyncratic theory of biodiversity |
Salvador Pueyo,Fangliang He | |
Why does the neutral theory, which is based on unrealistic assumptions, predict diversity patterns so accurately? Answering questions like this requires a radical change in the way we tackle them. The large number of degrees of freedom of ecosystems pose a fundamental obstacle to mechanistic modelling. However, there are tools of statistical physics, such as the maximum entropy formalism (MaxEnt), that allow transcending particular models to simultaneously work with immense families of models with different rules and parameters, sharing only well-established features. We applied MaxEnt allowing species to be ecologically idiosyncratic, instead of constraining them to be equivalent as the neutral theory does. The answer we found is that neutral models are just a subset of the majority of plausible models that lead to the same patterns. Small variations in these patterns naturally lead to the main classical species abundance distributions, which are thus unified in a single framework. | 519 |
| Scaling theory for information networks |
Melanie E. Moses,Stephanie Forrest | |
Networks distribute energy, materials and information to the components of a variety of natural and human-engineered systems, including organisms, brains, the Internet and microprocessors. Distribution networks enable the integrated and coordinated functioning of these systems, and they also constrain their design. The similar hierarchical branching networks observed in organisms and microprocessors are striking, given that the structure of organisms has evolved via natural selection, while microprocessors are designed by engineers. Metabolic scaling theory (MST) shows that the rate at which networks deliver energy to an organism is proportional to its mass raised to the 3/4 power. We show that computational systems are also characterized by nonlinear network scaling and use MST principles to characterize how information networks scale, focusing on how MST predicts properties of clock distribution networks in microprocessors. The MST equations are modified to account for variation in the size and density of transistors and terminal wires in microprocessors. Based on the scaling of the clock distribution network, we predict a set of trade-offs and performance properties that scale with chip size and the number of transistors. However, there are systematic deviations between power requirements on microprocessors and predictions derived directly from MST. These deviations are addressed by augmenting the model to account for decentralized flow in some microprocessor networks (e.g. in logic networks). More generally, we hypothesize a set of constraints between the size, power and performance of networked information systems including transistors on chips, hosts on the Internet and neurons in the brain. | 936 |
| Energy Flows and Maximum Power on an Evolutionary Ecological Community Model |
Jiang Zhang | |
食物网是研究生态群落中多个物种捕食相互作用的有力模型。食物网上的能量流由网络的结构决定，同时长时间的生物进化（物种形成与物种灭绝）又可以改变网络上的结构。为了理解网络结构与能量流的共同演化，本文提出了一个简单的积分偏微分方程模型，并用计算机模拟的方法对模型进行了讨论。最后，本文在此模型简化的特殊情况基础上，证明了最大功率原理——随着食物网演化，总能量流增强。 | 1049 |
| Statistical mechanics unifies different ecological patterns |
Roderick C. Dewar,Annabel Porte | |
Recently there has been growing interest in the use of maximum relative entropy (MaxREnt) as a tool for statistical inference in ecology. In contrast, here we propose MaxREnt as a tool for applying statistical mechanics to ecology. We use MaxREnt to explain and predict species abundance patterns in ecological communities in terms of the most probable behaviour under given environmental constraints, in the same way that statistical mechanics explains and predicts the behaviour of thermodynamic systems. We show that MaxREnt unifies a number of different ecological patterns: (i) at relatively local scales a unimodal biodiversity–productivity relationship is predicted in good agreement with published data on grassland communities, (ii) the predicted relative frequency of rare vs. abundant species is very similar to the empirical lognormal distribution, (iii) both neutral and non-neutral species abundance patterns are explained, (iv) on larger scales a monotonic biodiversity–productivity relationship is predicted in agreement with the species-energy law, (v) energetic equivalence and power law self-thinning behaviour are predicted in resource-rich communities. We identify mathematical similarities between these ecological patterns and the behaviour of thermodynamic systems, and conclude that the explanation of ecological patterns is not unique to ecology but rather reflects the generic statistical behaviour of complex systems with many degrees of freedom under very general types of environmental constraints. | 715 |
| Energy Flows and Organization of Life |
Harold Morowitz,Eric Smith | |
关于生命起源的一种全新研究视角：能量流。作者认为，生命现象只不过是释放能量流的一种更加快速、稳定的途径，因此生命的起源也是不可避免的。 | 1145 |
| Size and form in efficient transportation networks |
Jayanth R. Banavar,Amos Maritan | |
Many biological processes, from cellular metabolism to population dynamics, are characterized by allometric scaling (powerlaw) relationships between size and rate1±10. An outstanding question is whether typical allometric scaling relationships the power-law dependence of a biological rate on body mass can be understood by considering the general features of branching networks serving a particular volume. Distributed networks in nature stem from the need for effective connectivity, and occur both in biological systems such as cardiovascular and respiratory networks and plant vascular and root systems, and in inanimate systems such as the drainage network of river basins. Here we derive a general relationship between size and flow rates in arbitrary networks with local connectivity. Our theory accounts in a general way for the quarter-power allometric scaling of living organisms, recently derived under specific assumptions for particular network geometries. It also predicts scaling relations applicable to all efficient transportation networks, which we verify from observational data on the river drainage basins. Allometric scaling is therefore shown to originate from the general features of networks irrespective of dynamical or geometric assumptions. | 966 |
| Allometry of human fertility and energy use |
Melanie E. Moses,James Brown | |
The flux of energy and materials constrains all organisms, and allometric relationships between rates of energy consumption and other biological rates are manifest at many levels of biological organization. Although human ecology is unusual in many respects, human populations also face energetic constraints. Here we present a model relating fertility rates to per capita energy consumption rates in contemporary human nations. Fertility declines as energy consumption increases with a scaling exponent of )1/3 as predicted by allometric theory. The decline may be explained by parental trade-offs between the number of children and the energetic investment in each child. We hypothesize that the )1/3 exponent results from the scaling properties of the networked infrastructure that delivers energy to consumers. This allometric analysis of human fertility offers a framework for understanding the demographic transition to smaller family sizes, with implications for human population growth, resource use and sustainability. | 1625 |
| Scaling laws in urban supply networks |
Christian Ku¨ hnert,Dirk Helbing | |
In previous work, it has been proposed that urban structures may be understood as a result of self-organization principles. In particular, researchers have identified fractal structures of public transportation networks and land use patterns. Here, we will study spatial distribution systems for energy, fuel, medical, and food supply. It is found that these systems show power-law scaling as well, when the number of ‘‘supply stations’’ is plotted over the population size. Surprisingly, only some supply systems display a linear scaling with population size. Others show sublinear or superlinear scaling. We suggest an interpretation regarding the kind of scaling law that is expected in dependence of the function and constraints of the respective supply system. | 1140 |
| TOWARD A METABOLIC THEORY OF ECOLOGY |
JAMES H. BROWN | |
文章指出生态系统中的很多率，包括出生率、死亡率、繁殖率、能量转换率等等都可以从一个简单的方程异速增长尺度方程R=R0 M^(3/4)中导出，其中R是新陈代谢率，M是生物量。进一步，用新陈代谢的视角可以提出一个统一的理论来研究生态系统，这也暗示了某种复杂系统中流动与转化的普适规律。 | 1362 |
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