寄生对集团内捕食系统中物种共存的影响

寄生可通过间接效应调节物种间相互作用强度,从而对生态系统中种群动态及物种共存产生重要影响。文章基于生态-传染病模型,考虑寄生对种内竞争的特征调节作用,探讨了物种共存对寄生调节的易感染者和已感染者种内竞争的响应。研究结果表明,不同特征调节下的竞争力对物种共存产生不同影响,其中寄生调节导致易感染者相对较强的种内竞争对物种共存起促进作用,而寄生调节引起的已感染种群相对弱的种内竞争则不利于物种共存。同时,不同特征调节下的共存区域差别明显,强类间竞争时,共存区域最大;弱类间竞争时,共存区域最小。     

一个关于癌转移的数学模型

把癌生长看作癌细胞和正常细胞相互竞争的过程。把生态学中的Ｌｏｔｋａ－Ｖｏｌｔｅｒｒａ模型和我们提出的单竞争因子模型用于癌生长和转移的理论研究。着重分析了癌转移阶段的侵害性和器官特异性。在单竞争因子模型中，“最低资源需求量”是唯一的竞争因子，癌细胞具有低于正常细胞的最低资源需求量，是它在竞争中获胜的原因。由于参与竞争两种群的最低资源需求量不仅由它们本身的细胞性质，而且由它们的相互作用决定，所以癌转移表现出对某些器官的特异性。     

非Allee与Allee竞争种群系统的动力学研究

将Aliee效应引入2-竞争种群系统,建立了具有Aliee效应的2-竞争种群演化动态模型,对非Allee与Aliee竞争种群系统演化进行动力学研究.模拟结果表明:①Allee效应导致两竞争种群系统具有多个平衡态.②Allee效应使竞争共存物种无法续存甚至全部灭绝,最终平衡态值随初始斑块占有率变化而变化.③Allee效应可能使竞争排斥物种共同灭绝,且效应越强,物种存活时间越短;但Allee效应不会增强强物种的竞争优势,反而可能使强物种变弱,弱物种变强,其具有与栖息地破坏类似的影响种群竞争等级排序的作用.④Allee效应对种群续存是极不稳定的干扰因素,微小的变化都将引起系统平衡态的剧变.然而较高的初始斑块占有率也可能使原本濒于灭绝或竞争排斥的物种继续存活.     

依赖个体分布的种间竞争模型的建立

以一个栖息地的2个物种为研究对象,通过假设其个体的分布和个体对同一资源的竞争方式,以实地框架模型为基础,采用自底而上的方式,建立依赖个体分布的种间竞争模型,将个体分布划分为泊松分布、负三项分布和独立负二项分布3种形式,将个体对资源的竞争方式划分为争夺性竞争、竞赛性竞争和兼容性竞争3种类型。在一个物种的竞争方式为争夺性,而另一个为竞赛性或兼容性的情形下,对个体分布服从负三项分布的情况进行了建模,通过对模型的分析,得出争夺性竞争和竞赛性竞争都是兼容性竞争的特殊情况。当个体分布服从泊松分布和独立负二项分布时,可推导出相应的2个物种对同一资源竞争的种群动态模型。     

捕食者追捕与食饵逃逸对共位捕食系统中物种共存的影响

基于元胞自动机模型,探讨捕食者追捕和食饵逃逸两种行为对共位捕食系统中物种共存动态的影响.结果表明:捕食者追捕能够扩大物种共存区域,但食饵逃逸能否提高共位捕食系统中物种的共存取决于两物种竞争与捕食能力的相互权衡关系.在捕食者占绝对优势以及竞争与捕食之间存在弱权衡关系时,食饵逃逸能够促进两物种的共存;而在食饵占有绝对优势以及两物种间强权衡关系时,食饵逃逸则使得物种共存变得更加困难.另外,模拟结果显示,捕食者追捕与食饵逃逸对物种共存与种群密度产生不对称性效应:捕食者追捕对系统产生的影响较食饵逃逸行为更为显著.     

《生态学》教学中几个问题的探讨

对环境因子和生态因子概念的区别和联系、Lotka-Volterra模型中竞争物种获胜条件的推演、种群 Logistic增长实验中K值的计算等三个问题进行了探讨，阐明了其中有疑问的概念和方法，对生态学的学科发展和教学都具有一定的帮助。     

南亚热带4个苗木的生态位

在模糊超体积生态位理论的基础上，研究了南亚热带4个不同演替阶段树种苗木的生态位，探索森林群落演替的规律．以所测定的净光合作用强度值为指标，度量包括pH值、矿物质营养浓度、土壤含水量三个生态因子的三维生态位．结果表明：生态位宽度的大小次序为马尾松（0．4056），荷木（0．3614），藜蒴（0．3108）和黄果厚壳桂（0．3068），正好对应演替不同阶段的优势种；生态位重叠最小值为0．6827，表示总体上物种对资源的竞争较激烈；种间竞争系数介于0．6359和0．7357之间，表示物种问有回避竞争的趋势，这往往有助于物种共存；利用Cody和May的原则会带来生态位重叠的偏差最大为0．1262，最小为0．0361，因此应该避免使用Cody和May的原则．     

湘西北蜡梅的生态位

在模糊超体积生态位理论的基础上，根据样地调查所获得的基本数据，研究了湘西北蜡梅群落中8个物种的生态位．结果表明，生态位宽度从大到小依次为：蜡梅（0．8479）、香叶树（0．5833）、八角枫（0．5761）、黄连木（0．5000）、崖花海桐（0．4500）、鸡仔木（0．4205）、珊瑚朴（0．3135）和樱桃（0．3056），与Simpson指数和Shannow-Wiener公式的结论相同；蜡梅生态位在其他物种的生态位的重叠值都很大，最小的为0．8382，说明其他物种对资源利用受到蜡梅的激烈竞争；其他物种生态位在蜡梅生态位的重叠值都比较小，最大的为0．6278，说明蜡梅对资源利用受到其他物种的竞争并不十分激烈，因而蜡梅是湘西北蜡梅群落中的优势物种．     

水杉自然居群遗传多样性的RAPD研究

用随机扩增多态性方法对四川、湖南、湖北交界处的２７个水杉样本进行了基因组ＤＮＡ多态性分析．１１个随机引物共获得ＲＡＰＤ谱带１２１条,多态性谱带占５３％．聚类分析结果表明：水杉个体间的遗传距离与这些个体的地理分布相关,即相同产地个体间的遗传距离较小,不同产地个体间的遗传距离较大．与松柏目其它类群相比,水杉居群的遗传多样性程度高于银杉（３２％）,而在所处的大类群中则处于中等水平．初步结果表明,尽管孑遗物种水杉的自然种群的目前分布范围和个体数目非常有限,但是它仍然保持着中度的遗传多样性水平．可推测,孑遗植物的遗传多样性水平具有一定的变异范围     

北美CHIHUAHUAN荒漠17种啮齿动物的日耗能动态比较

利用时间序列分析方法，季节性指标和主分量分析比较了北美Ｃｈｉｈｕａｈｕａｎ荒漠１７种啮齿动物的日耗能动态，结果显示：（１）各物种种群日耗能一般随环境改变有相似年变化，但季节变化呈多样化；（２）只有盘尼西拉特斯更格卢鼠有明显的季节性；（３）各物种种群日耗能的对数与体重的对数成正相关关系，与种群密度的对数也成正相关关系，与扩菜距离的对数成负相关关系；（４）１７个物种可划分为４个日耗能类型，即优势型，季     

On the origin of species by sympatric speciation.

Understanding speciation is a fundamental biological problem. It is believed that many species originated through allopatric divergence, where new species arise from geographically isolated populations of the same ancestral species. In contrast, the possibility of sympatric speciation (in which new species arise without geographical isolation) has often been dismissed, partly because of theoretical difficulties. Most previous models analysing sympatric speciation concentrated on particular aspects of the problem while neglecting others. Here we present a model that integrates a novel combination of different features and show that sympatric speciation is a likely outcome of competition for resources. We use multilocus genetics to describe sexual reproduction in an individual-based model, and we consider the evolution of assortative mating (where individuals mate preferentially with like individuals) depending either on an ecological character affecting resource use or on a selectively neutral marker trait. In both cases, evolution of assortative mating often leads to reproductive isolation between ecologically diverging subpopulations. When assortative mating depends on a marker trait, and is therefore not directly linked to resource competition, speciation occurs when genetic drift breaks the linkage equilibrium between the marker and the ecological trait. Our theory conforms well with mounting empirical evidence for the sympatric origin of many species.     

On-line, voluntary control of human temporal lobe neurons

Daily life continually confronts us with an exuberance of external, sensory stimuli competing with a rich stream of internal deliberations, plans and ruminations. The brain must select one or more of these for further processing. How this competition is resolved across multiple sensory and cognitive regions is not known; nor is it clear how internal thoughts and attention regulate this competition. Recording from single neurons in patients implanted with intracranial electrodes for clinical reasons, here we demonstrate that humans can regulate the activity of their neurons in the medial temporal lobe (MTL) to alter the outcome of the contest between external images and their internal representation. Subjects looked at a hybrid superposition of two images representing familiar individuals, landmarks, objects or animals and had to enhance one image at the expense of the other, competing one. Simultaneously, the spiking activity of their MTL neurons in different subregions and hemispheres was decoded in real time to control the content of the hybrid. Subjects reliably regulated, often on the first trial, the firing rate of their neurons, increasing the rate of some while simultaneously decreasing the rate of others. They did so by focusing onto one image, which gradually became clearer on the computer screen in front of their eyes, and thereby overriding sensory input. On the basis of the firing of these MTL neurons, the dynamics of the competition between visual images in the subject's mind was visualized on an external display.     

Stage-structured cycles promote genetic diversity in a predator-prey system of Daphnia and algae

Competition theory predicts that population fluctuations can promote genetic diversity when combined with density-dependent selection. However, this stabilizing mechanism has rarely been tested, and was recently rejected as an explanation for maintaining diversity in natural populations of the freshwater herbivore Daphnia pulex. The primary limitation of competition theory is its failure to account for the alternative types of population cycles that are caused by size- or stage-dependent population vital rates--even though such structure both explains the fluctuating dynamics of many species and may alter the outcome of competition. Here we provide the first experimental test of whether alternative types of cycles affect natural selection in predator-prey systems. Using competing Daphnia genotypes, we show that internally generated, stage-structured cycles substantially reduce the magnitude of selection (thereby contributing to the maintenance of genetic diversity), whereas externally forced cycles show rapid competitive exclusion. The change in selection is ecologically significant, spanning the observed range in natural populations. We argue that structured cycles reduce selection through a combination of stalled juvenile development and stage-specific mortality. This potentially general fitness-equalizing mechanism may reduce the need for strong stabilizing mechanisms to explain the maintenance of genetic diversity in natural systems.     

Single-species models for many-species food webs

Most species live in species-rich food webs; yet, for a century, most mathematical models for population dynamics have included only one or two species. We ask whether such models are relevant to the real world. Two-species population models of an interacting consumer and resource collapse to one-species dynamics when recruitment to the resource population is unrelated to resource abundance, thereby weakening the coupling between consumer and resource. We predict that, in nature, generalist consumers that feed on many species should similarly show one-species dynamics. We test this prediction using cyclic populations, in which it is easier to infer underlying mechanisms, and which are widespread in nature. Here we show that one-species cycles can be distinguished from consumer resource cycles by their periods. We then analyse a large number of time series from cyclic populations in nature and show that almost all cycling, generalist consumers examined have periods that are consistent with one-species dynamics. Thus generalist consumers indeed behave as if they were one-species populations, and a one-species model is a valid representation for generalist population dynamics in many-species food webs.     

特有濒危植物长柄双花木濒危原因及其保护对策

长柄双花木为我国特有二级重点保护濒危植物,主要分布于江西、湖南、浙江和广东等省的部分区域。本研究综合分析了长柄双花木的自然地理分布特征、群落学特征、生物学特性、繁殖生态学特征及其濒危的可能原因。导致长柄双花木濒危的原因主要有：（1）在有性生殖过程中,由于花粉和资源限制、花粉竞争、传粉昆虫缺乏以及有机养分积累不足等,导致其有性繁殖能力差,结实率和结籽率低。（2）自然条件下种子萌发困难,萌发率、成苗率。（3）克隆繁殖能力有限,自然种群中克隆个体稀少。（4）生境片段化导致种群缩小,更新困难。（5）严重人为干扰直接导致种群锐减。此外,本研究还从强化科学研究和和保护途径等方面探讨了其保护对策。     

Mobility promotes and jeopardizes biodiversity in rock-paper-scissors games

Biodiversity is essential to the viability of ecological systems. Species diversity in ecosystems is promoted by cyclic, non-hierarchical interactions among competing populations. Central features of such non-transitive relations are represented by the 'rock-paper-scissors' game, in which rock crushes scissors, scissors cut paper, and paper wraps rock. In combination with spatial dispersal of static populations, this type of competition results in the stable coexistence of all species and the long-term maintenance of biodiversity. However, population mobility is a central feature of real ecosystems: animals migrate, bacteria run and tumble. Here, we observe a critical influence of mobility on species diversity. When mobility exceeds a certain value, biodiversity is jeopardized and lost. In contrast, below this critical threshold all subpopulations coexist and an entanglement of travelling spiral waves forms in the course of time. We establish that this phenomenon is robust; it does not depend on the details of cyclic competition or spatial environment. These findings have important implications for maintenance and temporal development of ecological systems and are relevant for the formation and propagation of patterns in microbial populations or excitable media.     

Local dispersal promotes biodiversity in a real-life game of rock-paper-scissors

One of the central aims of ecology is to identify mechanisms that maintain biodiversity. Numerous theoretical models have shown that competing species can coexist if ecological processes such as dispersal, movement, and interaction occur over small spatial scales. In particular, this may be the case for non-transitive communities, that is, those without strict competitive hierarchies. The classic non-transitive system involves a community of three competing species satisfying a relationship similar to the children's game rock-paper-scissors, where rock crushes scissors, scissors cuts paper, and paper covers rock. Such relationships have been demonstrated in several natural systems. Some models predict that local interaction and dispersal are sufficient to ensure coexistence of all three species in such a community, whereas diversity is lost when ecological processes occur over larger scales. Here, we test these predictions empirically using a non-transitive model community containing three populations of Escherichia coli. We find that diversity is rapidly lost in our experimental community when dispersal and interaction occur over relatively large spatial scales, whereas all populations coexist when ecological processes are localized.     

The effects of competition and predation on diversification in a model adaptive radiation

Much of life's diversity is thought to have arisen through successive rounds of adaptive radiation-the rapid diversification of a lineage into a range of ecologically and phenotypically distinct species. Both resource competition and predation have been suggested as mechanisms driving this process, although the former is better studied than the latter. Here we show experimentally how predation by a protist, Tetrahymena thermophila, affects diversification in a model adaptive radiation of the bacterial prey, Pseudomonas fluorescens. We estimate the frequency-dependent fitness functions of competing niche-specialist prey in the presence and absence of predation, and use these to test hypotheses about the extent (measured as the number of new genotypes) and rate of diversification. Competition and predation independently generated diversifying selection that we show is capable of driving prey diversification to similar extents but at different rates, diversification being markedly delayed in the presence of predators. The cause of this delay stems from weaker diversifying selection due to the reduction in prey density caused by predation. Our results suggest that predation may play an under-appreciated role in driving adaptive radiations.