物种累积曲线及其应用

在生物多样性和群落调查中,物种累积曲线被广泛用于抽样量充分性的判断以及物种丰富度估计。然而该方法在国内却很不常见,致使相关研究无法保证科学的抽样。本文介绍了如何运用EstimateS软件计算物种累积曲线,并通过Excel绘图功能绘制曲线,以期提高生物多样性和群落调查中抽样的科学性。     

Molecular biology techniques in parasite ecology

Molecular techniques are increasingly being used to study the ecology of a variety of organisms. These techniques represent important tools for the study of the systematics, population genetics, biogeography and ecology of parasites. Here, we review the techniques that have been employed to study the ecology and systematics of parasites (including bacteria and viruses). Particular emphasis is placed on the techniques of isoenzyme electrophoresis, in situ hybridisation and nucleic acid amplification to characterise parasite/microbial communities. The application of these techniques will be exemplified using ticks, bacterial endosymbionts and parasitic protozoa.     

Species accumulation curves analysed by a class of null models discovered by Arrhenius

Arrhenius is mainly given credit for his discovery of the log-log relationship between number of species and area, but in 1921 he invented the technique of analysing the data with a null model. This achievement, which Arrhenius explicitly stated was more important than the empirical species–area relationship, has been overlooked in the scientific literature. We suggest here that analysis of large communities should be done by a successive addition of predefined subsets of samples. Plotting the resulting accumulation curves in a common diagram usually will reveal heterogeneity between subsamples. We believe that this is a general feature of a counting process, (over space or time), that keeps record of new objects being generated by an unobservable process. We show this by two nonbiological time series: examination scores at the University of Oslo and stock prices on the Oslo stock market. We then apply these ideas to the analysis of the nested accumulation plots obtained from two unusually large community samples, the benthos of the Norwegian continental shelf and of marine areas of Hong Kong. Discontinuities in the accumulation curves can be explained by changes in habitat heterogeneity. These changes may be interpreted as variations in the parameter values in the class of null models discovered by Arrhenius. By selecting appropriate parameter values, the observed accumulation curves (calculated by an analytical expression giving exact values) can be approximated by null curves. This procedure makes it possible to identifying the major factors responsible for the shape of the curves in the accumulation plots.     

Life history, ecology and parasite community structure in Soviet birds

The paper describes an investigation of parasite richness in relation to host life history and ecology using data from an extensive survey of helminth parasites (cestodes, trematodes and nematodes) in Soviet birds. Correlates of parasite richness (number of parasite species per host species) were sought among 13 life-history variables, 13 ecological variables and one non-biological variable (number of host individuals examined) across a sample of 158 species of host. A statistical method to control for the effects of phylogenetic association was adopted throughout. Parasite richness correlates positively with the number of hosts examined (sample size) in all three parasite groups. Positive correlations (after controlling for the effects of sample size) were also found between host body weight and parasite richness for trematodes and nematodes, but not for cestodes.
A number of ecological variables were associated with parasite richness. However, when the effects of sample size and body weight were controlled for, only a single significant correlation (an association between trematode richness and aquatic habitat) remained. Similarly, a number of significant correlates of parasite richness were found among the life-history variables examined. Though several of these were robust to the confounding effects of sample size, all could be explained by the co-variation between life-history traits and body weight among the host species under investigation.     

Molecular ecology of fungal entomopathogens: molecular genetic tools and their applications in population and fate studies

The power of molecular genetic techniques to address ecological research questions has opened a distinct interdisciplinary research area collectively referred to as molecular ecology. Molecular ecology combines aspects of diverse research fields like population and evolutionary genetics, as well as biodiversity, conservation biology, behavioural ecology, or species-habitat interactions. Molecular techniques detect specific DNA sequence characteristics that are used as genetic markers to discriminate individuals or taxonomic groups, for instance in analyses of population and community structures, for elucidation of phylogenetic relationships, or for the characterization and monitoring of specific strains in the environment. Here, we summarize the PCR-based molecular techniques used in molecular ecological research on fungal entomopathogens and discuss novel techniques that may have relevance to the studies of entomopathogenic fungi in the future. We discuss the flow chart of the molecular ecology approaches and we highlight some of the critical steps involved. There are still many unresolved questions in the understanding of the ecology of fungal entomopathogens. These include population characteristics and relations of genotypes and habitats as well as host-pathogen interactions. Molecular tools can provide substantial support for ecological research and offer insight into this far inaccessible systems. Application of molecular ecology approaches will stimulate and accelerate new research in the field of entomophathogen ecology.     

Species accumulation curves and incidence-based species richness estimators to appraise the diversity of cultivable yeasts from beech forest soils

Background

Yeast-like fungi inhabit soils throughout all climatic zones in a great abundance. While recent estimations predicted a plethora of prokaryotic taxa in one gram of soil, similar data are lacking for fungi, especially yeasts.

Methodology/Principal Findings

We assessed the diversity of soil yeasts in different forests of central Germany using cultivation-based techniques with subsequent identification based on rDNA sequence data. Based on experiments using various pre-cultivation sample treatment and different cultivation media we obtained the highest number of yeasts by analysing mixed soil samples with a single nutrient-rich medium. Additionally, several species richness estimators were applied to incidence-based data of 165 samples. All of them predicted a similar range of yeast diversity, namely 14 to 16 species. Randomized species richness curves reached saturation in all applied estimators, thus indicating that the majority of species is detected after approximately 30 to 50 samples analysed.

Conclusions/Significance

In this study we demonstrate that robust species identification as well as mathematical approaches are essential to reliably estimate the sampling effort needed to describe soil yeast communities. This approach has great potential for optimisation of cultivation techniques and allows high throughput analysis in the future.     

Exploratory path analysis with applications in ecology and evolution

In this article, I first describe some recent developments in the identification of the structure of dependencies among variables in multivariate data relevant to exploratory path analysis. I then introduce a bootstrap modification of one important method (the SGS algorithm) that is designed to improve error rates of exploratory path analysis in the small data sets that are typical of studies in ecology and evolution. Monte Carlo results indicate that this modified technique can find path models that are close to the true model even in very small data sets. The bootstrapped SGS algorithm is then applied to a previously published data set involving attributes affecting seed dispersal in St. Lucie's cherry.     

Helminth parasite populations in newts and their tadpoles

Five species of helminth parasites were found in adults and tadpoles of the newts Triturus helveticus, T. vulgaris, and T. cristatus, caught at eight different localities in Somerset. These parasites were Acanthocephalus anthuris, A. ranae, Megalobatra-chonema terdentatum, Thominx filiformis and Oswaldocruzia molgeta. Mean worm burdens did not change through the year, and egg-producing females of Acantho-cephalus anthuris and Megalobatrachonema terdentatum were found throughout. There was no difference in the level of infection of male and female newts.     

Host ecology and life-history traits associated with blood parasite species richness in birds

Identifying host traits associated with the number of different parasite species or strains harboured by a particular host species can have important implications for understanding the impact of parasitism on hosts. We investigated associations between host ecology and life history, and parasite richness and prevalence of the four major avian blood parasite genera. We used an extensive data on blood parasite infections and host ecology in 263 bird species from the Western Palearctic, combining species-specific data with a comparative approach to control for similarity in phenotype among host species due to the effects of common phylogenetic descent. Adult survival rate negatively correlated with the number of parasite species infecting a host species when controlling for similarity due to common descent and body mass. In addition, the prevalence of Haemoproteus, Plasmodium and Leucocytozoon was higher in species harbouring a richer parasite assemblage. These results suggest that the impact on host fitness caused by avian haematozoa may be underestimated in natural populations if the exacerbated virulence associated with exposure to multiple parasites is not taken into account.     

Selenium accumulation in plants--phytotechnological applications and ecological implications

Selenium (Se) is an essential trace element for many organisms including humans, yet toxic at higher levels. Both Se deficiency and toxicity are problems worldwide. Since plants readily accumulate and volatilize Se, they may be used both as a source of dietary Se and for removing excess Se from the environment. Plant species differ in their capacity to metabolize and accumulate Se, from non-Se accumulators (< 100 mg Se/kg DW), to Se-accumulators (100-1000 mg Se/kg DW) to Se hyperaccumulators (> 1,000 mg Se/kg DW). Here we review plant mechanisms of Se metabolism in these various plant types. We also summarize results from genetic engineering that have led to enhanced plant Se accumulation, volatilization, and/or tolerance, including field studies. Before using Se-accumulating plants at a large scale we need to evaluate the ecological implications. Research so far indicates that plant Se accumulation significantly affects the plant's ecological interactions below and above ground. Selenium canprotect plants from fungal pathogens and from a variety of invertebrate and vertebrate herbivores, due to both deterrence and toxicity. However, specialist (Se-tolerant herbivores), detritivores and endophytes appear to utilize Se hyperaccumulator plants as a resource. These findings are relevant for managing phytoremediation of Se and similar elements.     

The ecology of the parasite population in micro-mammals in the Italian peninsula and islands

The importance of micro mammals from many points of view, mainly with an ecological approach was stressed. The study of the spatial-temporal distribution of parasites in their hosts may be carried out in several ways. Tests done in collaboration with the Parasitology Laboratory in the Faculty of Chemistry at the University of Barcelona, the NRCS and the Department of Ecological Studies in Cosenza, have contributed to an understanding of the Helminth communities as relating to several intrinsic variables of microteriofauna as well as extrinsic ones, particularly those concerning environment, climate and season. These comparisons were made using statistical means which compared the categorical and dichotomic variables which would highlight risk differences and their effects on the system. Quantitative dependent variables were also considered in relation to the aforementioned qualitative variables. One of the models studied is that of logistic regression, which estimates the function of regression, connecting the probability of the presence of Helminth as a dependent variable, with biological and ecological parameters (independent variables) such as: gender, age, season of capture, bioclimate, biotope and trapping section.     

Phytoflagellates and their ecology in Finnish brown-water lakes

The ecology of phytoflagellates in Finnish brown-water lakes is discussed using results from three studies. The data allow analysis of both phytoflagellate community relationships and the autecology of dominant species.Humic matter imparts a brown colour to most Finnish lakes. The consequent rapid warming of the water, shallow epilimnion and nutritional differences between epilimnion and hypolimnion are related to the migrations and nutritional pathways of flagellates in such systems. In large lakes migrations are not of such fundamental significance as in small forest lakes, where both illumination and the nutritional relationships may induce phytoflagellate migrations. The occurence of flagellates is more frequent and their dominance in the phytoplanktonic biomass is strongest in the most brown lakes, where independent motility is a particular advantage for the survival and competition of flagellates against other species.     

Phyloflagellates and their ecology in Tasmanian polyhumic lakes

Tasmania has many polyhumic lakes with a wealth of phytoflagellates, especially chromophytes. Dystrophic coastal lagoons, such as Lake Garcia, are rich habitats of the Chrysophyta and Dinophyta, containing a number of new or rare species. In meromictic Lake Fidler and Sulphide Pool flagellates and prokaryotes are permanently zoned in a finely structured array astride the redoxcline. In the mixolimnetic waters phytoflagellates are zoned and probably perform regular migrations. Chaoborus larvae migrate daily. In monomictic, polyhumic Lake Chisholm there is probably a permanent zonation of flagellates and prokaryotes about the long-lasting thermocline, with diel migrations of other species in the epilimnion. With its numerous new or rare species Tasmania is a phytoflagellate haven.     

最大熵原理及其在生态学研究中的应用

最大熵原理(the principle of maximum entropy)起源于信息论和统计力学,是基于有限的已知信息对未知分布进行无偏推断的一种数学方法.这一方法在很多领域都有成功应用,但只是近几年才被应用到生态学研究中,并且还存在很多争论.我们从基本概念和方法出发,用掷骰子的例子阐明了最大熵原理的概念,并提出运用最大熵原理解决问题需要遵从的步骤.最大熵原理在生态学中的应用主要包括以下方面:(1)用群落水平功能性状的平均值作为约束条件来预测群落物种相对多度的模型;(2)基于气候、海拔、植被等环境因子构建物种地理分布的生态位模型;(3)对物种多度分布、种一面积关系等宏生态学格局的推断;(4)对物种相互作用的推断;(5)对食物网度分布的研究等等.最后我们综合分析了最大熵原理在生态学应用中所存在的争议,包括相应模型的有效性、可靠性等方面,介绍了一些对最大熵原理预测能力及其局限性的检验结果,强调了生态学家应用最大熵原理需要注意的问题,比如先验分布的选择、约束条件的设置等等.在物种相互作用、宏生态学格局等方面对最大熵原理更广泛的讨论与应用可能会给生态学带来新的发展机会.