共查询到20条相似文献，搜索用时 15 毫秒
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Several cases of high species diversity, for example in tropical rain forests, imply that speciation has been frequent or rapid. However, how speciation could proceed so frequently as to generate extraordinary diversity still remains unsolved, despite recent advancements of diverse theories of allopatric and sympatric speciation. This paper presents a theoretical model that demonstrates the process of frequent speciation by means of geographical fragmentation. We focus on allopatric speciation and explore the evolutionary effect of fragmentation and extinction of demes (subpopulations) in a widespread species or species group. After a large contagious population of a single species is fragmented into demes, extinction of some demes could result in isolation of multiple demes. Thus, several demes could become good species simultaneously through the process of allopatric speciation. We apply the random extinction method to this fragmentation process where demes become randomly extinct. The present model illustrates that frequent speciation could occur in communities where large environmental changes frequently take place. 相似文献
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Christopher A. Hamm James A. Fordyce 《Evolution; international journal of organic evolution》2015,69(3):589-601
Herbivorous insects represent one of the most successful animal radiations known. They occupy a wide range of niches, feed on a great variety of plants, and are species rich; yet the factors that influence their diversification are poorly understood. Host breadth is often cited as a major factor influencing diversification, and, according to the Oscillation Hypothesis, shifts from generalist to specialist feeding states increase the diversification rate for a clade. We explored the relationship between host breadth and diversification within the Nymphalidae (Lepidoptera) and explicitly tested predictions of the Oscillation Hypothesis. We found strong evidence of diversification rate heterogeneity, but no difference in host breadth between clades with a higher diversification rate compared to their sisters. We also found some clades exhibited phylogenetic nonindependence in host breadth and these clades had lower host plant turnover than expected by chance, suggesting host breadth is evolutionarily constrained. Finally, we found that transitions among host breadth categories varied, but the likelihood of reductions in host breadth was greater than that of increases. Our results indicate host breadth is decoupled from diversification rate within the Nymphalidae, and that constraints on diet breadth might play an important role in the evolution of herbivorous insects. 相似文献
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我国西北地区内陆分布着近20万km~2的黑戈壁,由于其环境的特殊性,使其具有独特的生态系统,境内分布着多样的植被,蕴藏着大量特有的自然资源。但由于自然环境苛刻与交通条件不便,目前我国关于黑戈壁区系统的植被与物种多样性的研究还很缺乏。针对黑戈壁区植物多样性组成与分布特点,基于遥感及实地调查,采用DCCA排序和半变异函数模型等分析方法,对黑戈壁区植物群落组成,植物多样性特点及影响因素进行分析。研究结果表明:研究区植物以藜科和蒺藜科灌木或半灌木为主,群落物种生活型具有逐渐趋于简单甚至单一的特性,重要值0.1的植物主要有梭梭、红砂、白刺等13种;群落物种多样性呈现区域性的斑块化分布,结构性因子引起的物种多样性空间异质性占主导地位;作为极端干旱区,该区植物群落类型具有贫乏化及单一化的趋势,群落结构简单,植被覆盖度低,植物生长随环境的变化具有明显的可塑性,群落空间分异明显,群落空间演变具有明显的水分及土壤结构梯度;DCCA结果显示气候、土壤、地形是群落物种及类型变化的主要原因,海拔、坡位、土壤机械组成、降水、温度等环境因子对群落有着显著的影响,水土条件的空间异质性是戈壁植物多样性维持的关键因素。 相似文献
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近年研究表明养分异质促进植物多样性与群落生产力的正相关性。然而,相关的促进机制还很不清楚。以农田生态系统下作物多样性群体(玉米马铃薯间作体系)为例,在盆栽条件下采用控释性氮肥构建养分异质性,通过目标植物法设计根间作用处理,探讨根系的觅养行为,植株个体生长和总生产力对土壤氮空间分布和根间作用的响应特征。结果表明:根间作用提高作物的觅养精确度(F=3.017,P=0.094),在异质性条件下马铃薯的根冠比增加(P=0.001),而玉米的根冠比则不论在均质性还是异质性条件下均显著降低(F=4.781,P=0.039);氮异质性显著地提高在根间作用下两作物的生物量生产(P=0.021),明显增加总生产力LER(Land equivalent ratio)(F=4.171,P=0.064),显著地降低相对关系指数RII(Relative interaction index)值(F=5.636,P=0.026),显著降低玉米的根冠比(F=4.273,P=0.049),增加根间作用下马铃薯的根冠比,而在无竞争下则降低。上述结果说明,非资源性的根间作用激发玉米和马铃薯对异质性氮的觅养能力,这可能是为什么异质性养分环境促进植物多样性与群体生产力正向关系的重要原因;结果还表明觅养能力的激发主要来自非资源性的根间作用机制,因此本研究验证了植物对异质性养分和竞争者的协同响应理论。而有关的非资源性根间作用机制,例如种间识别作用等值得进一步深入探讨。 相似文献
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The likely future extinction of various species will result in a decline of two quantities: species richness and phylogenetic diversity (PD, or ‘evolutionary history’). Under a simple stochastic model of extinction, we can estimate the expected loss of these quantities under two conservation strategies: An ‘egalitarian’ approach, which reduces the extinction risk of all species, and a ‘targeted’ approach that concentrates conservation effort on the most endangered taxa. For two such strategies that are constrained to experience the same expected loss of species richness, we ask which strategy results in a greater expected loss of PD. Using mathematical analysis and simulation, we describe how the strategy (egalitarian versus targeted) that minimizes the expected loss of PD depends on the distribution of endangered status across the tips of the tree, and the interaction of this status with the branch lengths. For a particular data set consisting of a phylogenetic tree of 62 lemur species, with extinction risks estimated from the IUCN ‘Red List’, we show that both strategies are virtually equivalent, though randomizing these extinction risks across the tip taxa can cause either strategy to outperform the other. In the second part of the paper, we describe an algorithm to determine how extreme the loss of PD for a given decline in species richness can be. We illustrate the use of this algorithm on the lemur tree. 相似文献
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Johnson KP Adler FR Cherry JL 《Evolution; international journal of organic evolution》2000,54(2):387-396
Abstract.— Island biogeography theory predicts that the number of species on an island should increase with island size and decrease with island distance to the mainland. These predictions are generally well supported in comparative and experimental studies. These ecological, equilibrium predictions arise as a result of colonization and extinction processes. Because colonization and extinction are also important processes in evolution, we develop methods to test evolutionary predictions of island biogeography. We derive a population genetic model of island biogeography that incorporates island colonization, migration of individuals from the mainland, and extinction of island populations. The model provides a means of estimating the rates of migration and extinction from population genetic data. This model predicts that within an island population the distribution of genetic divergences with respect to the mainland source population should be bimodal, with much of the divergence dating to the colonization event. Across islands, this model predicts that populations on large islands should be on average more genetically divergent from mainland source populations than those on small islands. Likewise, populations on distant islands should be more divergent than those on close islands. Published observations of a larger proportion of endemic species on large and distant islands support these predictions. 相似文献
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Bokma F 《Evolution; international journal of organic evolution》2003,57(11):2469-2474
Taxa differ widely in numbers of species, which may be due either to chance alone or to factors that cause differences in speciation and extinction rates between taxa. To test whether an observed distribution of species over taxa differs from the distribution expected from chance alone, one must take into account that neither speciation nor extinction rates are known. This paper introduces a way to estimate speciation and extinction probabilities from the distribution of extant species over families and to test whether the observed distribution is different from expected. Application of this procedure to the distributions of bird, hexapod, primate, and angiosperm species over taxa provides statistical evidence of differences in rates of cladogenesis between taxa. 相似文献
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Grant Vernham;Joseph J. Bailey;Richard Field;Franziska Schrodt; 《Global Ecology and Biogeography》2024,33(11):e13904
Heterogeneity of the Earth's abiotic surface and subsurface (geodiversity) is increasingly recognised as an important driver of biodiversity. Theoretically, species' traits should match to abiotic conditions in the local environment. Here, we test this for the first time at a continental extent by analysing the relationships between geodiversity and plant trait diversity in forested vegetation plots across Europe, at three plot sizes (100, 400 and 1000 m2). 相似文献
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James S. Rogers 《Evolution; international journal of organic evolution》1994,48(6):2026-2036
The great increase in the number of phylogenetic studies of a wide variety of organisms in recent decades has focused considerable attention on the balance of phylogenetic trees—the degree to which sister clades within a tree tend to be of equal size—for at least two reasons: (1) the degree of balance of a tree may affect the accuracy of estimates of it; (2) the degree of balance, or imbalance, of a tree may reveal something about the macroevolutionary processes that produced it. In particular, variation among lineages in rates of speciation or extinction is expected to produce trees that are less balanced than those that result from phylogenetic evolution in which each extant species of a group has the same probability of speciation or extinction. Several coefficients for measuring the balance or imbalance of phylogenetic trees have been proposed. I focused on Colless's coefficient of imbalance (7) for its mathematical tractability and ease of interpretation. Earlier work on this statistic produced exact methods only for calculating the expected value. In those studies, the variance and confidence limits, which are necessary for testing the departure of observed values of I from the expected, were estimated by Monte Carlo simulation. I developed recursion equations that allow exact calculation of the mean, variance, skewness, and complete probability distribution of I for two different probability-generating models for bifurcating tree shapes. The Equal-Rates Markov (ERM) model assumes that trees grow by the random speciation and extinction of extant species, with all species that are extant at a given time having the same probability of speciation or extinction. The Equal Probability (EP) model assumes that all possible labeled trees for a given number of terminal taxa have the same probability of occurring. Examples illustrate how these theoretically derived probabilities and parameters may be used to test whether the evolution of a monophyletic group or set of monophyletic groups has proceeded according to a Markov model with equal rates of speciation and extinction among species, that is, whether there has been significant variation among lineages in expected rates of speciation or extinction. 相似文献
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The comment by Gamisch (2020) draws the attention of users of the R‐package RPANDA (Methods Ecol. Evol., 7, 2016, 589) on situations when properly interpreting the results of linear diversification dependencies requires caution. Here we provide clarifications to help users interpreting their results when using any type of functional diversification dependencies with time or the environment. 相似文献
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Borja Jiménez‐Alfaro Milan Chytrý Ladislav Mucina James B. Grace Marcel Rejmánek 《Ecology and evolution》2016,6(5):1515-1526
Broad‐scale animal diversity patterns have been traditionally explained by hypotheses focused on climate–energy and habitat heterogeneity, without considering the direct influence of vegetation structure and composition. However, integrating these factors when considering plant–animal correlates still poses a major challenge because plant communities are controlled by abiotic factors that may, at the same time, influence animal distributions. By testing whether the number and variation of plant community types in Europe explain country‐level diversity in six animal groups, we propose a conceptual framework in which vegetation diversity represents a bridge between abiotic factors and animal diversity. We show that vegetation diversity explains variation in animal richness not accounted for by altitudinal range or potential evapotranspiration, being the best predictor for butterflies, beetles, and amphibians. Moreover, the dissimilarity of plant community types explains the highest proportion of variation in animal assemblages across the studied regions, an effect that outperforms the effect of climate and their shared contribution with pure spatial variation. Our results at the country level suggest that vegetation diversity, as estimated from broad‐scale classifications of plant communities, may contribute to our understanding of animal richness and may be disentangled, at least to a degree, from climate–energy and abiotic habitat heterogeneity. 相似文献
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农业景观是人类生活所需资料的最主要来源地和生物多样性保护的重要区域之一。黄河中下游地区是我国最重要的农业区之一,在区域农业景观中,非农生境中各群落植物物种多样性组成特征有何差异?在不同尺度上,景观异质性特征与生境特征对植物物种多样性特征有何影响?在黄河中下游典型区域布点,对区内主要非农生境(次生林、次生灌丛、人工林和农田边缘等)中的植物群落物种多样性进行调查。结果显示:(1)次生灌丛中的物种丰富度和多样性显著高于其他生境,而农田边缘也保育有较多的物种;(2)从物种组成来看,景观尺度上样点间物种多样性差异(β_2)是所有生境中物种丰富度的最主要组成部分,而次生灌丛与次生林两类自然生境中小尺度(α和β1)物种丰富度的贡献相对较高。(3)景观异质性特征指标对物种多样性的影响主要体现在样方尺度上(α_(样方)),而β和γ多样性与之的关系并不甚密切。表征生境特征的群落高度和盖度指标能更好的预测物种多样性的特征。研究发现,常用的表征景观异质性的指数在各尺度上对植物群落物种多样性特征的影响也并不显著,局地群落特征的影响更为直接和重要。在探讨景观异质性特征与生物多样性关系时,常用的多样性指数(Shannon多样性指数、均匀度指数和Simpson指数等)并不合适,而拆分后的物种丰富度会更有效。但景观异质性对生物多样性的影响也不容忽视,它的改变会是影响群落物种多样性及其组成结构的重要潜在因素,在更大尺度上景观异质性会通过对景观组成要素特征(生境组成和构型)的影响进而影响到区域植物物种丰富度的变化。 相似文献
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物种多样性的地理分布格局及其机制是宏生态学和生物地理学的核心问题之一。区域尺度与局域尺度的影响因素, 如温度、降水、海拔变化、生境过滤、捕食、竞争与互惠等, 共同影响昆虫物种多样性的分布格局。然而, 迄今为止少有研究同时讨论不同尺度驱动因子对昆虫多样性地理分布格局的影响。本文基于内蒙古自治区86个旗县的昆虫多样性数据, 结合各地年平均气温、年降水量、古气候变化、海拔变化及植物多样性, 探讨昆虫物种多样性分布格局及其主要驱动因子。结果发现内蒙古昆虫多样性主要受到植物多样性与海拔变化的影响, 而气候因子对昆虫物种多样性的影响并不大。这一结果表明种间关系(食物多样性)与生境异质性可能对内蒙古昆虫多样性的分布格局起着主导作用。 相似文献
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Richard G. Davies C. David L. Orme rea J. Webster Kate E. Jones Tim M. Blackburn Kevin J. Gaston 《Global Ecology and Biogeography》2007,16(2):220-233
Aim Spatial patterns of phylogenetic diversity (PD) aid our ability to discern diversification rate mechanisms underlying hypotheses for the large‐scale distribution of biodiversity. We develop a predictive framework for the way in which spatial patterns of PD vary with those of species richness, depending on the balance between speciation and extinction rates. Within this framework, diversification processes thought to underlie the productive energy, ambient energy, topographic variability and habitat variety hypotheses predict that gradients of increase in species richness will be associated with: (1) decreasing extinction rates where driven by productive energy, hence increasing relative PD (i.e. PD controlling for species richness, or PDrel); (2) a similar positive relationship between ambient energy and PDrel; (3) increasing speciation rates where driven by topographic variability, hence decreasing PDrel; and (4) no consistent relationship between PDrel and habitat variety when driven by the latter. We test these predictions using distributional data on parrots. Location Neotropical, Afrotropical, Indo‐Malayan and Australasian realms. Methods Spatial models were used to test the predictions. Results Globally, a positive association between productive energy and PDrel confirms prediction (1). However, within realms, hump‐shaped relationships suggest the importance of decreasing extinction rates up to a threshold level of productive energy, and the increasing importance of speciation rates thereafter. Ambient energy is positively associated with PDrel in Australasia, Indo‐Malaya, and globally, supporting prediction (2). However, this is driven by the coincidence of highest PDrel in areas of high ambient energy and intermediate productive energy (i.e. in seasonal tropical environments), which may be characterized by relatively low speciation and extinction rates. In the Neotropics, increasing topographic variability is associated with decreasing PDrel and increasing species richness, suggesting an increasing gradient of speciation, supporting prediction (3). Elsewhere, the signal of this mechanism may be obscured by collinearities with energy gradients. The lack of an overall relationship between habitat diversity and PDrel confirms prediction (4). Main conclusions Spatial patterns of PDrel in relation to environmental gradients may be sensitive to collinearities among those gradients. Nevertheless, patterns emerge which have implications for the relative importance of speciation and extinction processes in generating latitudinal diversity gradients. 相似文献
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Abstract Grasslands are often considered as two‐dimensional habitats rather than complex, multilayered habitats. However, native grasslands are complex habitats, with multiple layers of annual and perennial grasses, sedges, shrubs and mosses. Vegetation complexity, including plant type, quality and three‐dimensional structure is important for providing a variety of food and habitat resources for insects. Grazing by domestic livestock can affect these processes through the loss or fragmentation of habitats, as well as altering the vertical and horizontal vegetation structure. This study aimed to investigate the role of host plants and microhabitat architecture for determining foliage invertebrate assemblages. Different plant species supported distinct invertebrate assemblages and less complex host plants supported fewer invertebrate individuals and species. Manipulations of plant architecture changed the species composition of invertebrates, with most species found in more complex vegetation. This study illustrates the importance of host diversity and pasture complexity for invertebrate communities. Management practices that encourage a heterogeneous environment with diverse and structurally complex pastures should also sustain a more diverse and functional invertebrate assemblage. 相似文献
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Extinction,turnover and species diversity in an experimentally fragmented California annual grassland 总被引：2，自引：0，他引：2
Summary Many natural populations are subdivided among partially isolated habitat patches, but the influence of habitat patchiness per se on species immigration, extinction, and the resulting patterns of species diversity, has received virtually no experimental study. In an experiment designed to test the effects of habitat subdivision on local community structure, we compare the diversity and annual turnover of flowering plant species in 3 treatments of the same total area, but subdivided to different degrees. We experimentally fragmented a California winter annual grassland into isolated plots, two of 32 m2, eight of 8 m2, and 32 of 2 m2, each treatment representing a combined area of 64 m2. Insularization of the experimental habitat fragments is provided by grazing sheep. The effects of plot area on species diversity, extinction, and turnover are consistent with the MacArthur-Wilson model. Species richness increases with the degree of habitat subdivision. Extinction, immigration, and turnover, however, are relatively independent of the degree of subdivision. These experimental results contrast with predictions that habitat subdivision necessarily results in greater rates of extinction accompanied by reduced species diversity. 相似文献