亚高寒草甸植物群落的中性理论验证

 该文以物种组成较为复杂的青藏高原东部亚高寒草甸为背景,结合最新的群落中性理论,以解释亚高寒草甸草本植物群落的物种分布格局和生物多样性的维持机制。通过对阴坡、阳坡和滩地3个生境进行随机取样调查,用中性模型对所得多样性数据进行拟合,并分别应用置信区间检验、拟合优度检验和多样性指数检验3种方法对拟合效果进行检验。研究结果表明,在拟合优度检验中,3个生境中中性理论预测和实际物种多度分布之间没有显著差异(p>0.05);实际观测值基本全部落入模型预测分布的95%的置信区间之内（仅滩地草本植物群落的63个物种中的1个以及阴坡草本植物群落75个物种中的2个偏离95%的置信区间）;对群落多样性的预测也和实际观测没有显著差异,其中丰富度预测拟合得最好(0.49相似文献   

H. A. GLEASON'S 'INDIVIDUALISTIC CONCEPT' AND THEORY OF ANIMAL COMMUNITIES: A CONTINUING CONTROVERSY

A tradition of natural history and of the lore of early twentieth-century ecology was that organisms lived together and interacted to form natural entities or communities. Before there was a recognizable science of ecology, Mobius (1877) had provided a name ‘biocoenosis’ for such entities. This concept persisted in the early decades of ecological science; at an extreme it was maintained that the community had integrating capabilities and organization like those of an individual organism, hence the term organismic community. In the 1950s- 1970s an alternative individualist concept, derived from the ideas of H. A. Gleason (1939), gained credence which held that communities were largely a coincidence of individualistic species characteristics, continuously varying environments and different probabilities of a species arriving on a given site. During the same period, however, a body of population based theory of animal communities became dominant which perpetuated the idea of patterns in nature based on biotic interactions among species resulting in integrated communities. This theory introduced an extended terminology and mathematical models to explain the organization of species into groups of compatible species governed by rules. In the late 1970s the premises and methods of the theory came under attack and a vigorous debate ensued. The alternatives proposed were, at an extreme, null models of random aggregations of species or stochastic, individualistic aggregations of species, sensu Gleason. Extended research and debate ensued during the 1980s resulting in an explosion of studies of animal communities and a plethora of symposia and volumes of collected works concerning the nature of animal communities. The inherent complexity of communities and the traditional differences among animal ecologists about how they should be defined and delimited, at what scale of taxa, space and time to study them, and appropriate methods of study and analysis have resulted in extended and as yet inconclusive discussions. Recent differences and discussions are considered under five general categories, evolution and community theory, individualistic concept, community definition, questions from community ecology and empirical studies. Communities are seen by some ecologists as entities of coevolving species and, in any case, it is necessary to integrate evolutionary ideas with the varied concepts of community. The individualistic concept of community, as a relative latecomer to discussions of animal community, is sometimes misconstrued as holding that communities are random assemblages of organisms without biotic interactions among species. Nevertheless, it has increasingly been accepted as supported by studies of diverse taxa and habitats. However, many other ecologists continue to argue for integrated, biotically controlled and evolved communities. Among the major difficulties of addressing the problems of community are problems of definition and terminology. One commentator noted that community ecology may be unique in the sciences because there is no consensus definition of community. One consequence of the lack of consensus definition is evident in the varied and diffuse questions posed in studies of community. Some critics of community ecology fault it for posing unanswerable questions. Recent empirical studies include various assessments about community ranging from deterministic, integrated and organismic to individualistic with various suggestions for compromise. The early emphasis on birds in studies of animal communities has expanded to obviate the argument that any position is constrained by the taxon studied. Insects, in general, are more prone to give rise to interpretation of a nonintegrated community. Parasite community studies have given rise to some distinctive categories and terminology. However, consensus is not achieved either within or among taxonomic groups or habitat groups. The extreme heterogeneity and complexity of communities (and of ecologists) has produced extended discussions of how to approach such multidimensional complexity. These discussions often turn on polarized positions of reductionism and experiment versus holism. Proponents of reductionism asserted that natural communities cannot be understood or their structure and organization predicted until experimental communities, or models thereof, are understood. Holists insisted that the inherent complexity and variability of communities cannot be elucidated in simplified experimental communities or in models. A more recent trend has urged pluralism, or, at least, mutual respect and dialogue, which are sometimes lacking, between proponents of these divergent approaches to communities. Recent work perpetuates the original dichotomy between integrated organismic community concept and individualistic non-integrated concept. The hope for a rule-governed community has extended to metarules and a new theory of community as divided into core species and satellite species is called into question. The problems of distinguishing between determinism and chance effects in community organization continue and the lost or fading hope of a general theory of community is revived in a search for rules that govern their assembly.     

STRUCTURAL EVIDENCE FOR A THEORY OF VEIN LOADING OF TRANSLOCATE

The ultrastructure of minor veins of Beta vulgaris was examined with reference to possible models for vein loading of translocate. Structural evidence was reviewed in the light of recent physiological observations as a basis for proposed mechanisms. Features which appeared to be of significance in formulating a model included the open, differentiated sieve plates, the predominance of organelle-rich parenchyma cells, and the branched plasmodesmata connecting sieve tubes and parenchyma cells. The resulting model views cell to cell movement of photosynthate via the symplast to the specialized parenchyma cells. The actively accumulated sucrose appears to move from the specialized parenchyma cells into the sieve tubes via plasmodesmata in the lateral and end walls.     

A MODEL APPROACH FOR SIZE-SELECTIVE COMPETITION OF MARINE PHYTOPLANKTON FOR FLUCTUATING NITRATE AND AMMONIUM1

Phytoplankton size-selective competition for fluctuating nutrients was studied with the use of a numerical model, which describes nitrate and ammonium uptake, nitrate reduction to ammonium, and growth as a function of cell she under fluctuating nitrogen limitation. The only size-dependent parameter in the model was the cell nutrient quota. Related to this, the cell surface area per biomass was negatively correlated to cell volume, and the vacuole volume per biomass ratio was positively correlated to cell volume. Simulations showed an inverse correlation between the maximum specific growth rate and cell size under steady-state conditions. With nitrate as the limiting nitrogen source, nitrogen quotas were always higher than with ammonium at the same specific growth rate. Net passive transport of ammonium due to unspecific diffusion of ammonia across the plasma membrane decreased the affinity for ammonium, whereas the affinity for nitrate was not influenced. Transient state-specific ammonium uptake was not dependent on cell size. However, small algae always have the highest specific growth rate in ammonium-controlled systems according to our model. Transient state nitrate uptake rate was positively correlated to cell size because larger algae have a higher vacuole volume per biomass, in which nitrate can be stored. Despite their lower maximum growth rate, larger algae became dominant during simulations under fluctuating nitrate supply when amplitude of and the period between nitrate pulses were high enough. Results from model simulations were qualitatively validated by earlier observations that large diatoms become dominant under fluctuating conditions when nitrate is the main nitrogen source.     

草地植物群落地上生物量非破坏性估测方法的探讨

 羊草群落的高度和盖度与地上生物量存在良好的复相关关系(R=0.9316),所获多元回归方程可用于该群落地上生物量的估测。通过对羊草群落、羊草+杂类草群落和贝加尔针茅群落植冠红光(0.63—0.69μm)和近红外辐射(0.76—0.90μm)反射率实测数据的分析,表明这些群落的光谱反射率比IR、IR/R和VI与地上生物量呈高度的指数相关关系,其中由VI和IR/R所获各群落不同生长时期地上生物量回归模型的估测效果较好。     

植物群落种群分布格局研究的新方法

本文给出一种研究植物群落种群分布格局的新方法。该方法与英国著名生态学家Greig-Smith提出的“邻接格子样方法”相比较,具有如下优点: 1.用计算机算出的结果,具有令人满意的精度。当计算完毕后,机器能打印输出植物种群斑块大小、斑块在样地平面上分布的状况,样地上某种植物斑块的总面积,种群个体的总数等有关信息。 2.适用于天然植物群落种群分布格局的研究。 本文讨论了处理数据时采用的计算公式,所依据的数学原理以及如何确定输出界限(舍入界限)等问题。 此外,文中还叙述了用该法对随机相嵌几何斑块图形,人工模拟草地样方进行处理的过程和计算结果分析。 源程序是用BASIC语言编制的。     

SPERM COMPETITION GAMES: A GENERAL MODEL FOR PRECOPULATORY MALE–MALE COMPETITION

Reproductive males face a trade‐off between expenditure on precopulatory male–male competition—increasing the number of females that they secure as mates—and sperm competition—increasing their fertilization success with those females. Previous sperm allocation models have focused on scramble competition in which males compete by searching for mates and the number of matings rises linearly with precopulatory expenditure. However, recent studies have emphasized contest competition involving precopulatory expenditure on armaments, where winning contests may be highly dependent on marginal increases in relative armament level. Here, we develop a general model of sperm allocation that allows us to examine the effect of all forms of precopulatory competition on sperm allocation patterns. The model predicts that sperm allocation decreases if either the “mate‐competition loading,”a, or the number of males competing for each mating, M, increases. Other predictions remain unchanged from previous models: (i) expenditure per ejaculate should increase and then decrease, and (ii) total postcopulatory expenditure should increase, as the level of sperm competition increases. A negative correlation between a and M is biologically plausible, and may buffer deviations from the previous models. There is some support for our predictions from comparative analyses across dung beetle species and frog populations.     

ENVIRONMENTAL MODELS FOR PALEOZOIC COMMUNITIES

Nearshore communities in Paleozoic epeiric seas occur in two distinct lateral patterns which parallel shorelines — an expanded pattern of five and a compressed pattern of three laterally adjacent communities. The two community patterns are correlated with two distinct environmental models which are a product of local tectonics. Model 1 (tectonically stable) develops in low slope transgressing epeiric seas. Model 2 (tectonically active) develops in high slope prograding epeiric seas commonly with abundant terrigenous clastic influx. Environmental variables and organic evolution change community constituents, but the broad community patterns recur at least through the early and middle Paleozoic.     

HISTORY OF NEOGENE MICROMAMMAL FAUNAL REGIONS OF CHINA

EaistenceofcertainhigherendeIinctaxainanecogeograPhiccategoryisthesolecriteri0nfordifferentiatingafaunalregion'ThepalaearcticRegion,forexamPle,possessesaseriesofpeculiarbolies,suchasDipwhdae,SeleviniidaeandSiphneidae'HtoPadri,however,wasawide-ranging(eurytopic)g0nusanditswideoccurreneeinthelateNeogenedepositsofthecountrydoesnotindicateasinglezoogeographicwhtinChina'Smallmammalsseemtomorereliablydefinefaunalregionsthan1argermanunals;theirstrictercorrespondencetoenvironmelltresultsmainlyfrom…     

EVOLUTION OF CENOZOIC MAMMALIAN FAUNAL REGIONS OF CHINA

SincetheCenozoic,changesofmammalsintaxonomiccompositionanddistributionhavetakenplaceinChina,mainlyduetocollisionofplates,changesoftopographyandclimate.ThepaperdiscussessomeproblemsofecologyandbiogeographyinvolvingtheChneseCenozoicmammals,aftertherecognitionofthe18manunalagesbasedonnatureandmagnitudeofthefaunalchanges(Tongetal.,1995).BiogeOgraPhicProvincesandec0l0gyChinaisvastinterritoryandtheclimatebetweenthenorthernahds0uthernpartsdiffers'Thepresentmammaliandistributionindicatesdistinctpr…     

单种群非自治缀块扩散的竞争模型的概周期解

本文考虑单种群非自治缀块扩散的竞争系统,利用微分不等式,证明了系统存在唯一的正概周期解,它在壳的扰动下是稳定的．     

POLLEN AND GENE DISPERSAL: THE INFLUENCES OF COMPETITION FOR POLLINATION

Pollinators that forage indiscriminately can transfer pollen from one species to another, reducing the amount that reaches conspecific flowers. I present evidence that the presence of another plant species visited by the same pollinators can also reduce pollen dispersal distances and outcrossing. This has the potential to influence gene flow and reproductive success. Pollen carryover and movement patterns were measured for the shared insect pollinators of Stellaria pubera and Claytonia virginica in North Carolina. Bee flies deposited similar amounts of Stellaria pollen on a series of pistillate Claytonia flowers as on a series of pistillate Stellaria flowers. In arrays of potted plants, flies and solitary bees visited most flowers on a plant before leaving and then flew to a nearby plant chosen independently of species; 95% of moves were to one of 12 nearest neighbors. These measures of pollen carryover and movement patterns were used in a set of computer simulations to predict pollen dispersal distances. The simulations suggested that C. virginica substantially reduces outcrossing and pollen flow in S. pubera. These predictions were tested by tracking dye movement from anthers in populations of potted plants. Addition of C. virginica reduced the mean squared distance moved by dye to receptive S. pubera flowers by 23% and reduced the amount of dye moved by 51%. The estimated pollen component of gene flow was also much lower in a natural population of 5. pubera mixed with C. virginica than in the synthetic single-species populations.     

四川非雀形目鸟类区系的结构分析

通观种的繁殖区资料后,将文献报导的253种四川非雀形目鸟类分为11个分布类型：极地型,北半球北部型,欧亚北部型,中亚型,青藏高地型,横断-喜马拉雅山地型,中国东北及其邻区型,中国季风区型,南亚及东南亚型,东半球热带亚热带型,环球热带亚热带型;进而对有关分布型的划分作了研讨。文东对此区系的结构特点作了叙述。     

四海非雀形目鸟类区系的结构分析

通观种的繁殖区资料后,将文献报导的２５３种四川非雀形目鸟类分为１１个分布类型：极地型,北半球北部型,欧亚北部型,中亚型,青藏高地型,横断－喜马拉雅山地型,中国东北及其邻区型,中国季风区型,南亚及东南亚型,东半球热带亚热带型,环球热带亚热带型;进而对有关分布型的划分作了研讨。文末对此区系的结构特点作了叙述。     

距离计算法在化石群对比中的运用

分析前人的几种化石群对比方法，指出其中存在的问题，提出了经过改进后的距离计算法。这一方法的特点是：１）采用半定量取值法，准确地反映出化石群对比思想；２）在进行世界范围对比时，采用对地方性分子逐步加权的方法，以降低世界性分子在对比过程中所产生的干扰。另外，还选取了全球１２个赛诺曼期的钙质超微化石群，运用距离计算法进行对比。