When the exception becomes the rule: The disappearance of limiting similarity in the Lotka-Volterra model

We investigate the transition between limiting similarity and coexistence of a continuum in the competitive Lotka-Volterra model. It is known that there exist exceptional cases in which, contrary to the limiting similarity expectation, all phenotypes coexist along a trait axis. Earlier studies established that the distance between surviving phenotypes is in the magnitude of the niche width 2σ provided that the carrying capacity curve differs from the exceptional one significantly enough. In this paper we studied the outcome of competition for small perturbations of the exceptional (Gaussian) carrying capacity. We found that the average distance between the surviving phenotypes goes to zero when the perturbation vanishes. The number of coexisting species in equilibrium is proportional to the negative logarithm of the perturbation. Nevertheless, the niche width provides a good order of magnitude for the distance between survivors if the perturbations are larger than 10%. Therefore, we conclude that limiting similarity is a good framework of biological thinking despite the lack of an absolute lower bound of similarity.     

两种绣线菊低温锻炼与脱锻炼处理对蛋白质表达的影响

通过2维双向电泳法,研究抗寒能力与光合能力不同的金山绣线菊与华北绣线菊,低温锻炼处理对蛋白质表达所产生的影响。结果表明,低温锻炼处理对2种绣线菊蛋白质表达的影响显著不同,在低温锻炼与脱锻炼处理中,金山绣线菊产生低温诱导特异蛋白,华北绣线菊没有低温诱导特异蛋白表达;蛋白质双向电泳图谱分析表明,华北绣线菊与金山绣线菊经过低温锻炼后发生蛋白质差异表达,经质谱鉴定其中的3种显著差异表达的蛋白质分别为2种未知新蛋白,2种未知蛋白的部分氨基酸序列分别为VSHLAGFSSNNPK、LKADKPTLLSEAK;DPNDHPNPFTVK、DGNGFFLYLLDPDSSK、NGDGMFLYLLDGLESK,另一种差异蛋白为抗坏血酸过氧化物酶;低温锻炼处理使绣线菊中与光合作用密切相关的蛋白质抗坏血酸过氧化物酶发生了显著的变化。     

Partitioning of functional diversity reveals the scale and extent of trait convergence and divergence

Questions: Trait differentiation among species occurs at different spatial scales within a region. How does the partitioning of functional diversity help to identify different community assembly mechanisms? Location: Northeastern Spain. Methods: Functional diversity can be partitioned into within‐community (α) and among‐communities (β) components, in analogy to Whittaker's classical α and β species diversity concept. In light of ecological null models, we test and discuss two algorithms as a framework to measure α and β functional diversity (the Rao quadratic entropy index and the variance of trait values). Species and trait (specific leaf area) data from pastures under different climatic conditions in NE Spain are used as a case study. Results: The proposed indices show different mathematical properties but similarly account for the spatial components of functional diversity. For all vegetation types along the climatic gradient, the observed α functional diversity was lower than expected at random, an observation consistent with the hypothesis of trait convergence resulting from habitat filtering. On the other hand, our data exhibited a remarkably higher functional diversity within communities compared to among communities (α?β). In contrast to the high species turnover, there was a limited functional diversity turnover among communities, and a large part of the trait divergence occurred among coexisting species. Conclusions: Partitioning functional diversity within and among communities revealed that both trait convergence and divergence occur in the formation of assemblages from the local species pool. A considerable trait convergence exists at the regional scale in spite of changes in species composition, suggesting the existence of ecological redundancy among communities.     

Plant species diversity and environmental heterogeneity: spatial scale and competing hypotheses

Questions: What is the observed relationship between plant species diversity and spatial environmental heterogeneity? Does the relationship scale predictably with sample plot size? What are the relative contributions to diversity patterns of variables linked to productivity or available energy compared to those corresponding to spatial heterogeneity? Methods: Observational and experimental studies that quantified relationships between plant species richness and within‐sample spatial environmental heterogeneity were reviewed. Effect size in experimental studies was quantified as the standardized mean difference between control (homogeneous) and heterogeneous treatments. For observational studies, effect sizes in individual studies were examined graphically across a gradient of plot size (focal scale). Relative contributions of variables representing spatial heterogeneity were compared to those representing available energy using a response ratio. Results: Forty‐one observational and 11 experimental studies quantified plant species diversity and spatial environmental heterogeneity. Observational studies reported positive species diversity‐spatial heterogeneity correlations at all points across a plot size gradient from ～1.0 × 10^?1 to ～1.0 × 10¹¹ m², although many studies reported spatial heterogeneity variables with no significant relationships to species diversity. The cross‐study effect size in experimental studies was not significantly different from zero. Available energy variables explained consistently more of the variance in species richness than spatial heterogeneity variables, especially at the smallest and largest plot sizes. Main conclusions: Species diversity was not related to spatial heterogeneity in a way predictable by plot size. Positive heterogeneity‐diversity relationships were common, confirming the importance of niche differentiation in species diversity patterns, but future studies examining a range of spatial scales in the same system are required to determine the role of dispersal and available energy in these patterns.     

Species-specific distribution of two sympatric Maculinea butterflies across different meadow edges

An important consequence of habitat fragmentation is the increase of edge habitats. Environmental factors in the edges are different from those in the interiors, which causes changes in the distribution of plant and animal species. We aimed to study how edges affect the distribution of two butterfly species within meadow fragments. We therefore investigated the effect of distance from edge and edge type (road edge versus tree edge) on two sympatric large blue species (Maculinea teleius and M. nausithous). Our results showed that edge type had contrasting effects on the two species. M. teleius favoured both interiors and road edges, while M. nausithous preferred the tree edges. In the case of the latter species a strong positive edge effect was also found. This kind of within-habitat niche segregation is probably related to the different microenvironmental conditions at the edges. Foodplant density did not seem to limit the distribution of these species. Our results suggest that interiors of meadows are important for M. teleius, while tree edges maintain the habitats of the regionally rarer butterfly, M. nausithous.     

The paradox of the clumps mathematically explained

The lumpy distribution of species along a continuous one-dimensional niche axis recently found by Scheffer and van Nes (Scheffer and van Ness 2006) is explained mathematically. We show that it emerges simply from the eigenvalue and eigenvectors of the community matrix. Both the transient patterns—lumps and gaps between them—as well as the asymptotic equilibrium are explained. If the species are evenly distributed along the niche axis, the emergence of these patterns can be demonstrated analytically. The more general case, of randomly distributed species, shows only slight deviations and is illustrated by numerical simulation. This is a robust result whenever the finiteness of the niche is taken into account: it can be extended to different analytic dependence of the interaction coefficients with the distance on the niche axis (i.e., different kernel interactions), different boundary conditions, etc. We also found that there is a critical value both for the width of the species distribution σ and the number of species n below which the clusterization disappears.

上海市树附生苔藓植物生态位

生态位理论在植被生态研究中有着重要的应用价值,引入生态位理论对树附生苔藓植物进行了研究。在上海市市区和郊区主要公园、部分街道及校园,包括崇明岛等地区,共设立18个样点,调查发现43种树附生苔藓植物,其中藓类植物39种,苔类植物4种。根据盖度值计算了43种树附生苔藓植物的生态位宽度。结果表明,树附生苔藓植物种数(N)与生态位宽度(B)符合公式N=0.3423e-0.0369B,r=0.9347,大部分的树附生植物生态位宽度很窄,67.44%种类的生态位宽度小于0.1。本文计算了43种树附生苔藓植物的生态位重叠值,应用主分量分析法和最小生成树法对它们进行分类。将43种树附生苔藓植物分成3个生态类群,它们与生境关系显著。因此,在苔藓植物保护中应特别注意对树附生苔藓植物及其生境的保护。     

枣麦间作枣园主要蚧虫复合种群结构及生态位

为了有效地控制枣树蚧害,2002年在太谷地区对枣麦间作枣园的康氏粉蚧(Pseudococcus comstock Kuwane)、日本蜡蚧(Ceroplastes japonicus Green)和梨园蚧(Quadraspidiotus perniciosus Comstock)的复合种群结构及其生态位进行了系统研究.结果表明,在枣树发育早期,3种蚧虫分布范围主要在下、中部的东、南方位,康氏粉蚧的时空二维生态位的宽度较大,是该时期的优势种.到中期3种蚧虫复合种群的分布聚集在树冠上部的西、北方位,时 空二维生态位的宽度以日本蜡蚧较大,种间相似程度和竞争不明显.后期3种蚧虫的复合种群结构在各部位的各个方位的分布无明显差异,但梨园蚧的虫口密度较大,日本蜡蚧在生态位上占据较大的空间.与枣树发育的中期相比,3种蚧虫复合种群结构的相似性与种间竞争系数的平均值要小.蚧害预防应早期控制康氏粉蚧,中期调治3种蚧虫的危害,后期应采取措施压低越冬虫源.     

Importance of the stem cell microenvironment for ophthalmological cell-based therapy

Cell therapy is a promising treatment for diseases that are caused by cell degeneration or death. The cells for clinical transplantation are usually obtained by culturing healthy allogeneic or exogenous tissue invitro. However, for diseases of the eye, obtaining the adequate number of cells for clinical transplantation is difficult due to the small size of tissue donors and the frequent needs of long-term amplification of cells in vitro, which results in low cell viability after transplantation. In addition, the transplanted cells often develop fibrosis or degrade and have very low survival. Embryonic stem cells(ESCs) and induced pluripotent stem cells(i PS) are also promising candidates for cell therapy. Unfortunately, the differentiation of ESCs can bring immune rejection, tumorigenicity and undesired differentiated cells, limiting its clinical application. Although i PS cells can avoid the risk of immune rejection caused by ES cell differentiation post-transplantation, the low conversion rate, the risk of tumor formation and the potentially unpredictable biological changes that could occur through genetic manipulation hinder its clinical application. Thus, the desired clinical effect of cell therapy is impaired by these factors. Recent research findings recognize that the reason for low survival of the implanted cells not only depends on the seeded cells, but also on the cell microenvironment, which determines the cell survival, proliferation and even reverse differentiation. When used for cell therapy, the transplanted cells need a specific three-dimensional structure to anchor and specific extra cellular matrix components in addition to relevant cytokine signaling to transfer the required information to support their growth. These structures present in the matrix in which the stem cells reside are known as the stem cell microenvironment. The microenvironment interaction with the stem cells provides the necessary homeostasis for cell maintenance and growth. A large number of studies suggest that to explore how to reconstruct the stem cell microenvironment and strengthen its combination with the transplanted cells are key steps to successful cell therapy. In this review, we will describe the interactions of the stem cell microenvironment with the stem cells, discuss the importance of the stem cell microenvironment for cell-based therapy in ocular diseases, and introduce the progress of stem cell-basedtherapy for ocular diseases.     

Constructive Species’ Coexistence Mechanisms of Pine Oak Mixed Forest in Qinling Mountains Based on the Niche Differentiation

Based on the 15 plots of Pinus tabuliformis and Quercus aliena var. accuteserrata mixed forest in Qinling Mountains, we analyzed this community’s characteristics from the aspects of species composition, niche width and diameter class, also, we used the Canonical Correspondence Analysis to explore the effects of environment on plants’ distributions and conductive species’ morphological characteristics, the main results were as follows: (1) Fifteen plots record 139 vascular plants, belonging to 53 families 102 genera, the families which possessing higher richness were Rosaceae, Asteraceae, Liliaceae and Poaceae; (2) The niche widths of Ptabuliformis (Bi=2674) and Q var. accuteserrata (Bi=2679) were all higher than other accompanying plants, and there was little niche overlap value (< 01) between them; (3) Organic matter, total nitrogen, elevation and slope mainly effected plant’s distributions; (4) Four morphological characteristics of constructive species in CCA diagram presented a opposite distribution patterns, while elevation, slope position and available nitrogen were the main induced factors; (5) Community stability of this pine oak mixed forest was relatively higher based on Godron index, and two conductive species’ diameter class were all growing type. In conclusion, high habitat heterogeneity of terrain and soil nutrient brought niche differentiation and promoted species coexistence of pine oak mixed forest in Qinling Mountains.