Patterns of relative species abundance in rainforests and coral reefs

A formidable many-body problem in ecology is to understand the complex of factors controlling patterns of relative species abundance (RSA) in communities of interacting species. Unlike many problems in physics, the nature of the interactions in ecological communities is not completely known. Although most contemporary theories in ecology start with the basic premise that species interact, here we show that a theory in which all interspecific interactions are turned off leads to analytical results that are in agreement with RSA data from tropical forests and coral reefs. The assumption of non-interacting species leads to a sampling theory for the RSA that yields a simple approximation at large scales to the exact theory. Our results show that one can make significant theoretical progress in ecology by assuming that the effective interactions among species are weak in the stationary states in species-rich communities such as tropical forests and coral reefs.     

Coexistence and relative abundance in forest trees

Contemporary acceleration of biodiversity loss makes increasingly urgent the need to understand the controls of species coexistence. Tree diversity in particular plays a pivotal role in determining terrestrial biodiversity, through maintaining diversity of its dependent species and with them, their predators and parasites. Most theories of coexistence based on the principle of limiting similarity suggest that coexistence of competing species is inherently unstable; coexistence of competitors must be maintained by external forces such as disturbance, immigration or 'patchiness' of resources in space and time. In contrast, storage theory postulates stable coexistence of competing species through temporal alternation of conditions favouring recruitment of one species over the other. Here we use storage theory to develop explicit predictions for relative differences between competitors that allow us to discriminate between coexistence models. Data on tree species from a primary forest on the Mexican Pacific coast support a general dynamic of storage processes determining coexistence of similar tree species in this community, and allow us to reject all other theories of coexistence.     

Explaining the excess of rare species in natural species abundance distributions

The observation that a few species in ecological communities are exceptionally abundant, whereas most are rare, prompted the development of species abundance models. Nevertheless, despite the large literature on the commonness and rarity of species inspired by these pioneering studies, some widespread empirical patterns of species abundance resist easy explanation. Notable among these is the observation that in large assemblages there are more rare species than the log normal model predicts. Here we use a long-term (21-year) data set, from an estuarine fish community, to show how an ecological community can be separated into two components. Core species, which are persistent, abundant and biologically associated with estuarine habitats, are log normally distributed. Occasional species occur infrequently in the record, are typically low in abundance and have different habitat requirements; they follow a log series distribution. These distributions are overlaid, producing the negative skew that characterizes real data sets.     

Two Field Techniques for Estimating Relative Abundance of Galliformes

Galliformes are often difficult to count adequately in their natural habitats due to low detectability of them. In the present study, we confirm availability of feather-count and feces-count as two useful field techniques to estimate the relative abundance of eared-pheasants (Crossoptilon spp. ). The former is suitable to forest environments during the post-incubation period, whereas the latter is best in areas with dry climate conditions during the fall-winter season. With the advantages of reduced survey effort and high repeatability, the two techniques are potentially applicable to other Galliform species in habitat selection studies and long-term population monitoring.     

Neutral theory: the stability of forest biodiversity

The unified neutral theory of biodiversity and biogeography provides a dynamic null hypothesis for the assembly of natural communities. It is also useful for understanding the influence of speciation, extinction, dispersal and ecological drift on patterns of relative species abundance, species-area relationships and phylogeny. Clark and McLachlan argue that neutral drift is inconsistent with the palaeorecord of stability in fossil pollen assemblages of the Holocene forests of southern Canada. We show here that their analysis is based on a partial misunderstanding of neutral theory and that their data alone cannot unambiguously test its validity.     

Fishing elevates variability in the abundance of exploited species

The separation of the effects of environmental variability from the impacts of fishing has been elusive, but is essential for sound fisheries management. We distinguish environmental effects from fishing effects by comparing the temporal variability of exploited versus unexploited fish stocks living in the same environments. Using the unique suite of 50-year-long larval fish surveys from the California Cooperative Oceanic Fisheries Investigations we analyse fishing as a treatment effect in a long-term ecological experiment. Here we present evidence from the marine environment that exploited species exhibit higher temporal variability in abundance than unexploited species. This remains true after accounting for life-history effects, abundance, ecological traits and phylogeny. The increased variability of exploited populations is probably caused by fishery-induced truncation of the age structure, which reduces the capacity of populations to buffer environmental events. Therefore, to avoid collapse, fisheries must be managed not only to sustain the total viable biomass but also to prevent the significant truncation of age structure. The double jeopardy of fishing to potentially deplete stock sizes and, more immediately, to amplify the peaks and valleys of population variability, calls for a precautionary management approach.     

Density dependence explains tree species abundance and diversity in tropical forests

The recurrent patterns in the commonness and rarity of species in ecological communities--the relative species abundance--have puzzled ecologists for more than half a century. Here we show that the framework of the current neutral theory in ecology can easily be generalized to incorporate symmetric density dependence. We can calculate precisely the strength of the rare-species advantage that is needed to explain a given RSA distribution. Previously, we demonstrated that a mechanism of dispersal limitation also fits RSA data well. Here we compare fits of the dispersal and density-dependence mechanisms for empirical RSA data on tree species in six New and Old World tropical forests and show that both mechanisms offer sufficient and independent explanations. We suggest that RSA data cannot by themselves be used to discriminate among these explanations of RSA patterns--empirical studies will be required to determine whether RSA patterns are due to one or the other mechanism, or to some combination of both.     

Theoretical biology: comparing models of species abundance

Ecologists are struggling to explain how so many tropical tree species can coexist in tropical forests, and several empirical studies have demonstrated that negative density dependence is an important mechanism of tree-species coexistence. Volkov et al. compare a model incorporating negative density dependence with a dispersal-limited neutral model and claim that each predicts six empirical species-abundance distributions of tropical-tree communities equally well. However, we show here that their main conclusion is premature: when the two models are compared in an improved analysis, we find that the dispersal-limited model outcompetes the density-dependent model in all six cases. Hence, although density dependence is certainly an important diversity-maintaining mechanism, our improved approach indicates that the dispersal-limited model provides a more parsimonious explanation of empirical species-abundance distributions.     

鱼类生态学的教学应注重理论与实践相结合

阐明了鱼类生态学理论与实践相结合教学的必要性;介绍了鱼类生态学课程中与实践密切联系的几个理论体系;总结了笔者在教学过程中所采取的一些易于实行的实践尝试.     

分光光度法测定溪黄草及其近缘种中总黄酮含量

采用微波辅助萃取法提取溪黄草及其近缘种中的黄酮类化合物,以芦丁为对照品,以亚硝酸钠-硝酸铝-氢氧化钠作为显色体系,用可见分光光度法测定了溪黄草及其近缘种中总黄酮的含量.该方法在0.00～1.25 mg范围内吸光度与含量呈良好的线性关系,加标回收率为97.43 ％～103.0％,相对标准偏差（n=6）为1.83％.结果表明：溪黄草及其近缘种中总黄酮含量差异不大.该方法操作简便、结果稳定、重复性好,可用于溪黄草及其近缘种中总黄酮含量检测,实验结果为溪黄草及其近缘种的开发和利用奠定了基础.     

幂指数方程拟合物种多度分布模型的研究

物种多度分布是物种多样性研究的重要方法之一,首次提出用幂指数方程来拟合物种多度分布模型,实例拟合结果表明,幂指函数应用于物种多度分布研究是理想的,从而丰富了物种多度分布模型理论。     

基于教育生态学原理的高职英语教学思考

运用教育生态学的基本原理,对影响高职英语教学的各种因素进行深层的、系统的分析,并为高职英语教学目标、教学内容、教学方法、教学评价等方面的改革提供新的理论依据和途径。     

Relationship between climatic conditions and the relative abundance of modern C3 and C4 plants in three regions around the North Pacific

Using −24‰ and −14‰ as the endpoints of stable carbon isotopic composition of total organic carbon (δ¹³C_TOC) of surface soil under pure C₃ and C₄ vegetation, and surface soil δ¹³C_TOC data from eastern China, Australia and the Great Plains of North Amer- ica, we estimate the relative abundance of C₃/C₄ plants (i.e., the ratio of C₃ or C₄ biomass to local primary production) in modern vegetation for each region. The relative abundance of modern C₃/C₄ vegetation from each region is compared to the corresponding climatic parameters (mean annual temperature and precipitation) to explore the relationship between relative C₄ abundance and climate. The results indicate that temperature controls the growth of C₄ plants. However, even where temperature is high enough for the growth of C₄ plants, they will only dominate the landscape when precipitation declines as temperatures increase. Our results are consistent with those of other investigations of the geographic distribution of modern C₄ plant species. Therefore, our results provide an important reference for interpretation of past C₃/C₄ relative abundance records in these three regions.     

营养元素添加对青藏高原亚高寒草甸物种多度分布格局的影响

以青藏高原亚高寒草甸为研究对象,基于N,P,N+P耦合营养元素添加的控制实验,研究了群落内全部物种、常见种和稀有种的物种多度分布格局以及物种丰富度对N,P,N+P耦合营养元素添加的响应规律,并选取对数正态模型、幂分割模型、几何级数模型、Zipf模型以及中性模型对物种多度数据进行拟合.结果表明:1)P添加对物种丰富度的影响不显著,全部物种、常见种与稀有种的物种多度分布曲线的陡缓程度基本相同.随N,N+P耦合添加量的增大,全部物种与常见种的物种多度分布曲线都越来越陡峭,物种丰富度也都显著下降,表明在青藏高原亚高寒草甸N,N+P耦合添加会导致物种多样性的降低.2)比较CK,N15,P15,N15P15的物种多度分布曲线发现N+P耦合处理的物种多度分布曲线的陡峭度较CK,N15,P15处理的要陡,表明N+P耦合对物种多度分布格局的影响效应要强于单独的N,P的.3)分析施肥对物种多度分布模式的影响发现,全部物种的多度分布符合统计模型的对数正态模型以及基于生态位理论的幂分割模型、几何级数模型与Zipf模型.常见种的多度分布符合几何级数模型与Zipf模型,而稀有种在同时符合这两种基于生态位分化的模型外,呈现出符合中性模型的趋势.说明多种不同模型可以拟合同一生境的物种多度分布,常见种和稀有种通过不同的响应方式共同维持着亚高寒草甸生态系统的物种多样性.     

Spatial and temporal variations of C3/C4 relative abundance in global terrestrial ecosystem since the Last Glacial and its possible driving mechanisms

The primary factor controlling C 3 /C 4 relative abundance in terrestrial ecosystem since the Last Glacial has been widely debated. Now more and more researchers recognize that climate, rather than atmospheric CO 2 concentration, is the dominant factor. However, for a specific area, conflicting viewpoints regarding the more influential one between temperature and precipitation still exist. As temperature and precipitation in a specific area usually not only vary within limited ranges, but also covary with each other, it is difficult to get a clear understanding of the mechanism driving C 3 /C4 relative abundance. Therefore, systematic analysis on greater spatial scales may promote our understanding of the driving force. In this paper, records of C3/C4 relative abundance since the Last Glacial on a global scale have been reviewed, and we conclude that: except the Mediterranean climate zone, C3 plants predominated the high latitudes during both the Last Glacial and the Holocene; from the Last Glacial to the Holocene, C4 relative abundances increased in the middle latitudes, but decreased in the low latitudes. Combining with studies of modern process, we propose a simplified model to explain the variations of C3 /C4 relative abundance in global ecosystem since the Last Glacial. On the background of atmospheric CO2 concentration since the Last Glacial, temperature is the primary factor controlling C3/C4 relative abundance; when temperature is high enough, precipitation then exerts more influence. In detail, in low latitudes, temperature was high enough for the growth of C4 plants during both the Last Glacial and the Holocene; but increased precipitation in the Holocene inhibited the growth of C4 plants. In middle latitudes, rising temperature in the Holocene promoted the C4 expansion. In high latitudes, temperature was too low to favor the growth of C4 plants and the biomass was predominated by C3 plants since the Last Glacial. Our review would benefit interpretation of newly gained records of C3/C4 relative abundance from different areas and different periods, and has its significance in the understanding of the driving mechanisms of C3/C4 variations on longer timescales (e.g., since the late Miocene) with reliable records of temperature and atmospheric CO2 concentration.     

关于相对遗传模及相对余遗传模

简要回顾了相对遗传模、相对余遗传模等有关概念和性质,讨论了当Ｍ为内射模时,Ｍ－投射模的等价刻画,及其对偶问题,Ｍ为投射模时,Ｍ－内射模的等价条件,从而给出在相应条件的Ｍ－遗传模、Ｍ－余遗传模的一些性质。     

中立型时滞差分方程的振动性

得到了中立型时滞差分方程的所有解都振动的充分条件。