Habitat fragmentation effects on biodiversity patterns

We study the effects of habitat fragmentation on biodiversity patterns by means of a simple spatial model which considers selective geographic colonization, diffusion and mutation. In our model, regions of the lattice are characterized by the amount of resources available to populations of species which are going to colonize that regions. We simulate the fragmentation of the habitat by assuming that a proportion p of the sites is not available for colonization, that is, there is no resource availability in those sites. We analyse the patterns of the species-area relationship and the abundance distribution considering two sample methods, in order to simulate the cases in which the habitats are distributed in islands and continents. We have observed that the pattern of the species-area curve is changed when different sample methods are considered. We have also verified that the abundance distribution is bimodal when small mutation probabilities are considered.     

Particle-based modeling of aggregation and fragmentation processes: Fractal-like aggregates

The incorporation of particle inertia into the usual mean field theory for particle aggregation and fragmentation in fluid flows is still an unsolved problem. We therefore suggest an alternative approach that is based on the dynamics of individual inertial particles and apply this to study steady state particle size distributions in a 3D synthetic turbulent flow. We show how a fractal-like structure, typical of aggregates in natural systems, can be incorporated in an approximate way into the aggregation and fragmentation model by introducing effective densities and radii. We apply this model to the special case of marine aggregates in coastal areas and investigate numerically the impact of three different modes of fragmentation: large-scale splitting, where fragments have similar sizes, erosion, where one of the fragments is much smaller than the other and uniform fragmentation, where all sizes of fragments occur with the same probability. We find that the steady state particle size distribution depends strongly on the mode of fragmentation. The resulting size distribution for large-scale fragmentation is exponential. As some aggregate distributions found in published measurements share this latter characteristic, this may indicate that large-scale fragmentation is the primary mode of fragmentation in these cases.     

Ecosystem engineers: from pattern formation to habitat creation

Habitat and species richness in drylands are affected by the dynamics of a few key species, termed "ecosystem engineers." These species modulate the landscape and redistribute the water resources so as to allow the introduction of other species. A mathematical model is developed for a pair of ecosystem engineers commonly found in drylands: plants forming vegetation patterns and cyanobacteria forming soil crusts. The model highlights conditions for habitat creation and for high habitat richness, and suggests a novel mechanism for species loss events as a result of environmental changes.     

Effects of random habitat destruction in a predator–prey model

The influence of habitat destruction on a population of predators and prey is studied. We show, via Monte Carlo simulations of a lattice model, that with growing devastation the oscillations in the densities of both species, as well as cross-correlations between the two densities diminish. As should be expected, predators are more vulnerable and disappear before the prey. Devastation of the habitat is never beneficial and the percentage of coexisting (prey and predators) states decreases with destruction. Because of the high fragmentation of the environment in the case of large devastation, animals’ populations are separated into small sub-populations living in restricted areas. Such small populations become extinct more easily. We have also shown that in the case of large habitat devastation the density of the population of prey depends on its history.     

无序性对脆性材料冲击破碎的影响

脆性材料受冲击荷载作用产生损伤开裂是一个连续介质离散化的过程.采用连续离散耦合方法模拟了一个脆性圆球以不同初始速度与刚性板的冲击,重点研究了无序性对脆性材料冲击破碎的影响,并对其内在机理进行了分析.本文不考虑材料细观结构的无序性,材料的无序仅体现在细观断裂参数的非均质性.数值实验同样揭示了脆性材料在冲击破坏中存在两种破坏模式,即低速时接触区域的局部损伤和高速时的整体碎裂.研究表明,材料无序性对临界冲击速度、破碎模式、碎片形态影响显著.随着无序度增加,材料的临界速度增大,损伤开裂由少量贯穿性裂纹主导转变为全域性的分叉裂纹.高无序度圆球冲击产生的碎片表面更粗糙,体型更为扁平细长.这与细观断裂的主导机制有关,无序度较高时剪切导致开裂的比重更大,碎片内部损伤裂纹面更多.     

Population persistence in weakly-coupled sinks

We consider a single species population obeying a saturated growth model with spatial diffusion taken into account explicitly. Strong spatial heterogeneity is considered, represented by a position dependent reproduction rate. The geometry of the problem is that of two patches where the reproductive rate is positive, surrounded by unfavorable patches where it is negative. We focus on the particular case where the population would not persist in the single patches (sinks). We find by means of an analytical derivation, supplemented by a numerical calculation, the conditions for the persistence of the population in the compound system of weakly connected patches. We show that persistence is possible even if each individual patch is a sink where the population would go extinct. The results are of particular relevance for ecological management at the landscape level, showing that small patches may harbor populations as long as the connectivity with adjacent patches is maintained. Microcosmos experiences with bacteria could be performed for experimental verification of the predictions.     

GC-MS of amaryllidaceous galanthamine-type alkaloids

Galanthamine-type alkaloids produced by plants of the Amaryllidaceae family are potent acetylcholinesterase inhibitors. One of them, galanthamine, has been marketed as a hydrobromide salt for the treatment of Alzheimer's disease. In the present work, gas chromatography with electron impact mass spectrometry (GC-EIMS) fragmentation of 12 reference compounds isolated from various amaryllidaceous plants and identified by spectroscopic methods (1D and 2D nuclear magnetic resonance, circular dichroism, high-resolution MS (HRMS) and EIMS) was studied by tandem mass spectrometry (GC-MS/MS) and accurate mass measurements (GC-HRMS). The studied compounds showed good peak shape and efficient GC separation with a GC-MS fragmentation pattern similar to that obtained by direct insertion probe. With the exception of galanthamine-N-oxide and N-formylnorgalanthamine, the galanthamine-type compounds showed abundant [M](+.) and [M-H](+) ions. A typical fragmentation pattern was also observed, depending on the substituents of the skeleton. Based on the fragmentation pathways of reference compounds, three other galanthamine-type alkaloids, including 3-O-(2'-butenoyl)sanguinine, which possesses a previously unelucidated structure, were identified in Leucojum aestivum ssp. pulchelum, a species endemic to the Balearic islands. GC-MS can be successfully applied to Amaryllidaceae plant samples in the routine screening for potentially new or known bioactive molecules, chemotaxonomy, biodiversity and identification of impurities in pharmaceutical substances. Copyright ? 2012 John Wiley & Sons, Ltd.     

Eigen model version of evolution with directed migration

We consider the two-habitat quasispecies model, which describes evolutionary process with migration on the basis of the Eigen model. In the first habitat there is only one genotype, and here is an influx of the replicators from the first habitat to the second one with the rate h. We solve exactly the case of a single-peak fitness landscape in both habitats, when in the first habitat there are no mutations. The Eigen model version of the model is more adequately describes the real biological experiments than the Crow-Kimura model, as can be related to the serial transfer experiments in chemical reactor.     

Scaling Invariance and Characteristics of the Cloud of Spherical Projectile Fragmentation Products upon High-Velocity Impact on a Thin Mesh Shield

In this paper, we consider the problem of the fragmentation of an aluminum projectile on a thin steel mesh shield at high-velocity impact in a three-dimensional (3D) setting. The numerical simulations are carried out by the smoothed particle hydrodynamics method applied to the equations of mechanics of deformable solids. Quantitative characteristics of the projectile fragmentation are obtained by studying statistics of the cloud of fragments. Considerable attention is given to scaling laws accompanying the fragmentation of the projectile. Scaling is carried out using the parameter K, which defines the number of the mesh cells in the projectile diameter. It is found that the dependence of the critical velocity V_c of fragmentation on the parameter K consists of two branches that correspond to two modes of the projectile fragmentation associated with the “small” and “large” aperture of the mesh cell. We obtain the dependences of the critical velocity V_c on the projectile diameter and the mesh parameters for both modes of the fragmentation. It is shown that the average cumulative mass distributions constructed at V_c exhibit the property of scale invariance, splitting into two groups of distributions corresponding exactly to the modes of the projectile fragmentation. In each group, the average cumulative distributions show good coincidence in the entire mass region; moreover, in the intermediate mass region, each group of distributions has a power-law distribution with an exponent τ different from that in the other group. Conclusions about the dependence of the exponent of the power-law distribution τ on the fragmentation mode are made.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

高光谱遥感技术在生物多样性保护中的应用研究进展

当今世界物种的减少和栖息地的丧失日益严重,生物多样性保护已经成为最热门的话题之一。遥感这种通过非接触式收集信息的科学,及相应的估算生物多样性、建立物种多样性的关系模型和进行生物多样性指数制图等功能,已在生物多样性保护领域中得到了广泛应用。从遥感传感器和遥感技术两个方面论述了高光谱遥感技术在生物多样性保护中的应用进展,重点列举了光谱遥感在生物多样性保护中的成功应用实例。对生物多样性保护的发展具有一定的参考价值。     

Revisiting Laser-Intensity-Dependent Ionization and Fragmentation of C_(60)

We revisit the laser-intensity-dependent ionization and fragmentation yields of C₆₀ molecules irradiated by 25-fs,798-nm laser pulses based on the approach in which photoions are measured via a velocity map imaging spectrometer working in a time-sliced mode.This approach dramatically improves the signal-to-background ratio compared to those using a simple(traditional) time-of-flight mode(spectrometer),and thus allows us to measure the laser-intensity dependences down to a previously u...     

基于多光谱数据的湿地景观格局变化对越冬候鸟生境影响

安徽升金湖是典型的长江中下游自然通江湖泊湿地,是越冬候鸟尤其是珍稀鹤类的理想越冬地,水利设施的修建改变了升金湖的自然连通状况,使湖泊水位变化受人为控制,继而引起景观格局变化,从而影响越冬候鸟生境.为探究水位波动对越冬候鸟生境影响规律,基于Landsat-8(OLI)多光谱遥感影像对升金湖土地利用类型进行分类,结合水位数...     

Collective escape processes in many-particle systems

We study collective escape phenomena in nonlinear chain models. First we investigate the fragmentation of an overdamped polymer chain due to thermal fluctuations in the absence of an external force. We calculate the activation times of individual bonds in the coupled chain system and compare them with times obtained from Brownian dynamics simulations. We also consider a grafted chain exposed to an external force which monotonically grows as time goes on. In underdamped situations we show that collective localized excitations in a nonlinear force field with absorbing states can cause polymer fragmentation. In a similar fashion, localized modes assist a thermally activated escape of interacting particles in a metastable potential landscape which is additionally subjected to a periodic driving. The latter is necessary to obtain overcritical elongations which create localized modes even in case of stronger damping.     

Landscape structure and the speed of adaptation

The role of fragmentation in the adaptive process is addressed. We investigate how landscape structure affects the speed of adaptation in a spatially structured population model. As models of fragmented landscapes, here we simulate the percolation maps and the fractal landscapes. In the latter the degree of spatial autocorrelation can be suited. We verified that fragmentation can effectively affect the adaptive process. The examination of the fixation rates and speed of adaptation discloses the dichotomy exhibited by percolation maps and fractal landscapes. In the latter, there is a smooth change in the pace of the adaptation process, as the landscapes become more aggregated higher fixation rates and speed of adaptation are obtained. On the other hand, in random percolation the geometry of the percolating cluster matters. Thus, the scenario depends on whether the system is below or above the percolation threshold.     

Spontaneously broken neutral symmetry in an ecological system

Spontaneous symmetry breaking plays a fundamental role in many areas of condensed matter and particle physics. A fundamental problem in ecology is the elucidation of the mechanisms responsible for biodiversity and stability. Neutral theory, which makes the simplifying assumption that all individuals (such as trees in a tropical forest)-regardless of the species they belong to-have the same prospect of reproduction, death, etc., yields gross patterns that are in accord with empirical data. We explore the possibility of birth and death rates that depend on the population density of species, treating the dynamics in a species-symmetric manner. We demonstrate that dynamical evolution can lead to a stationary state characterized simultaneously by both biodiversity and spontaneously broken neutral symmetry.     

具有列维飞行与布朗运动特征的循环竞争博弈及物种稳定共存条件

循环竞争博弈常被用来研究物种多样性.以前有关循环竞争博弈的研究工作所考虑的相互作用距离模式包括最近邻、取固定距离或一定距离以内的随机值,这与实际情况不相符.考虑到实际生物系统中物种个体做列维飞行与布朗运动的情况广泛存在,综合考虑了最近邻相互作用模式和列维飞行(布朗运动)长程相互作用模式,对循环竞争博弈及保持物种多样性的条件进行了研究.得到了最大飞行距离与选择概率的临界关系(包括Logistic式和指数式关系),进一步得到了幂指数与选择概率的临界关系,以及保持物种共存的条件.     

Does faecal matter reflect location? An initial assessment of isotopic variability between consumed prey remains and faecal matter for wild jaguars*

ABSTRACT

Faecal isotopic analysis may complement other non-invasive wildlife survey tools for monitoring landscape use by carnivores, such as motion-detecting cameras and non-invasive genetic sampling. We analysed carbon, nitrogen, and strontium isotopes in faecal matter produced by jaguars (Panthera onca) as well as bones from consumed prey at the Mountain Pine Ridge Forest Reserve (MPR) in Belize, Central America. The MPR is ideally suited for a spatial isotope study as vegetation and geology both vary considerably. The isotopic composition of faecal matter should reflect the habitat and geology where consumed prey lived. We used bone from consumed prey recovered from jaguar scats as a proxy for diet. Faecal matter and bone showed comparable spatial isotopic trends, suggesting that the isotopic composition of jaguar faeces can be used to detect foraging in different habitats (pine forest versus broadleaf forest) or on different geologies (Mesozoic carbonates; Palaeozoic granite, contact metamorphics, and metasediments). This result is reassuring as bones are not always present in carnivore scats. Studying landscape use by cryptic and wide-ranging carnivore species like jaguars remains challenging. Isotopic analysis of faecal matter complements the existing array of non-invasive spatial monitoring tools.     

Effect of habitat destruction on cooperation in public goods games

We explore the evolution of cooperation in a public goods game where the habitat destruction is taken into account. A model of ordinary differential equations is proposed, in which incorporate the habitat destroyed. And we focus on the impact of different levels of habitat destruction on cooperation. Our results show that the fraction of cooperation receives the biggest boost for moderate habitat destruction, and decreases to zero very quickly for a higher degree of habitat destruction. Similarly, our results suggest that low or moderate habitat degradation can promote the evolution of cooperators, and once habitat degradation is too severe, the fraction of cooperators will decline dramatically. Furthermore, we investigate the cooperation level with different multiplication factor, and results demonstrate that the cooperation increases monotonously with the increasing of the multiplication factor. Our findings may provide many more insights for understanding the emergence and maintenance of cooperation in the complex biological and social systems.     

Fragmentation of shells

We present a theoretical and experimental study of the fragmentation of closed thin shells made of a disordered brittle material. Experiments were performed on brown and white hen egg shells under two different loading conditions: impact with a hard wall and explosion by a combustible mixture. Both give rise to power law fragment size distributions. A three-dimensional discrete element model of shells is worked out. Based on simulations of the model, we give evidence that power law fragment mass distributions arise due to an underlying phase transition which proved to be abrupt for explosion and continuous for impact. We demonstrate that the fragmentation of closed shells defines a new universality class of fragmentation phenomena.