Interactions between spatially separated herbivores indirectly alter plant diversity

Above‐ and belowground herbivores promote plant diversity when selectively feeding on dominant plant species, but little is known about their combined effects. Using a model system, we show that neutral effects of an aboveground herbivore and positive effects of a belowground herbivore on plant diversity became profoundly negative when adding these herbivores in combination. The non‐additive effects were explained by differences in plant preference between the aboveground‐ and the belowground herbivores and their consequences for indirect interactions among plant species. Simultaneous exposure to aboveground‐ and belowground herbivores led to plant communities being dominated by a few highly abundant species. As above‐ and belowground invertebrate herbivores generally differ in their mobility and local distribution patterns, our results strongly suggest that aboveground–belowground interactions contribute to local spatial heterogeneity of diversity patterns within plant communities.     

The combined effects of energy and disturbance on species richness in protist microcosms

The supply of energy, and the frequency of disturbance can both affect species diversity, often, although not always, producing unimodal diversity patterns along an energy or disturbance gradient. However, it has been suggested that diversity is a combined function of both factors, and the dynamic equilibrium model proposed by Huston (1979) is one formalization of this suggestion. This idea has received little direct testing. Here we carry out such a test using protist microcosms, in a factorial manipulation of six levels of energy (quantity of organic resource) and five levels of disturbance (frequency of temperature shock). Species richness responded to both energy supply and disturbance frequency, although not always unimodally. Patterns of response changed over time, and there was some evidence of an interaction between energy and disturbance at two of six time intervals. However, the specific form of this interaction differs from that predicted by the dynamic equilibrium model, and overall, the results provide little support for the model.     

Effects of organism size and community composition on ecosystem functioning

We tested (1) if the size of dominant species influenced ecosystem functioning in food webs consisting of bacteria, algae, and protozoa; (2) whether those effects changed in importance through time; and (3) how those effects compared with differences in diversity among experimental food webs. We constructed food webs using two size fractions of organisms that differed in individual mass by approximately two orders of magnitude. We measured total biomass and respiration (total CO₂ production) as two aspects of ecosystem functioning. We also compared these size‐dependent patterns in functioning across two levels of species richness. Initially, organism size strongly influenced total community biomass. With time, however, biomass and respiration eventually converged in communities dominated by large or small species. We conclude that after sufficient time for community development any differences in ecosystem functioning resulted from differences in community composition, including species richness, but not the size of the dominant organisms.     

A new statistical approach for assessing similarity of species composition with incidence and abundance data

The classic Jaccard and Sørensen indices of compositional similarity (and other indices that depend upon the same variables) are notoriously sensitive to sample size, especially for assemblages with numerous rare species. Further, because these indices are based solely on presence–absence data, accurate estimators for them are unattainable. We provide a probabilistic derivation for the classic, incidence‐based forms of these indices and extend this approach to formulate new Jaccard‐type or Sørensen‐type indices based on species abundance data. We then propose estimators for these indices that include the effect of unseen shared species, based on either (replicated) incidence‐ or abundance‐based sample data. In sampling simulations, these new estimators prove to be considerably less biased than classic indices when a substantial proportion of species are missing from samples. Based on species‐rich empirical datasets, we show how incorporating the effect of unseen shared species not only increases accuracy but also can change the interpretation of results.     

Correlations between forest stand diversity and landscape pattern in Otepää Nature Park, Estonia

Rank correlations between tree species diversity in forest stands and parameters of landscape pattern were calculated using data from 4933 locations in Otepää Nature Park. Stand diversity was characterised by the number of tree species in the stand formula and by the index of dominance of tree species’ coverage. Landscape diversity was characterised by locally calculated pattern parameters from three categorical map layers (1:10 000 base map, 1:10 000 soil map, combination of these maps) and from six numerical variables (elevation, slope angle, four channels of a Landsat 7 ETM image).A weak trend appeared for more diverse forest stands to be located in more diverse landscapes according to the base map. Forest stand diversity is also higher on steeper slopes and in places surrounded by slopes of varying steepness. The correlation between landscape diversity and biodiversity depends on the radius of the kernel in which landscape characteristics are calculated. Evidence of an indicative neighbourhood could be seen in many spatial relationships. The spatial correlation between stand diversity and indices calculated from the base map was most visible at distances ranging from 400 to 500 m; surface elevation and its variation correlates with stand diversity at distances of 100–200 m. Some relationships between forest diversity and landscape diversity that had a different sign of correlation in proximate and distant kernels can be interpreted as a need to standardise local landscape indices with the index values in a wider neighbourhood as a reference.     

芽孢杆菌植酸酶分子生物学研究进展

来源于芽孢杆菌的中性植酸酶具有良好的热稳定性,适合作为消化道呈中性鲤科鱼类的饲料添加剂。该植酸酶晶体具有独特的螺旋桨样空间结构,钙离子在其稳定性和催化活性的结构功能关系中具有重要作用,并表现出特有的催化机理。该基因与已知植酸酶基因的结构有所不同,是一种新的植酸酶。目前主要采用多种原核表达系统对其进行表达。比较表明,芽孢杆菌表达系统和酵母表达系统是实现芽孢杆菌植酸酶规模化生产的有效途径。     

Variation in the Agronomic and Morphological Traits of Iranian Chickpea Accessions

Landraces of chickpea (Cicer arietinum L.) in Iran have not been adequately characterized for their agronomic and morphological traits. Such characterization would be helpful in the development of improved cultivars, so in this study 362 chickpea accessions, collected from the major chickpea growing areas of Iran, were evaluated to determine their phenotypic diversity. High coefficients of variation (CVs)were recorded in pods/branch, seeds/pod, yield/plant, seeds/plant, pods/plant and branches/plant. Using principal component (PC) analysis, the first four PCs with eigenvalues more than 1 contributed 84.10% of the variability among accessions, whereas PC5 to PC10 were less than unity. PC1 was positively related to days to first maturity, days to 50% flowering and days to 50% maturity. The characters with the greatest weight on PC2 were seeds/plant and yield/plant, whereas PC3 was mainly related to pods/plant, seeds/pod and 100-seed weight, and PC4 was positively related to pods/branch and negatively to branches/plant. The germplasm was grouped into four clusters using cluster analysis. Each cluster had some specific characteristics of its own and the cluster I was clearly separated from clusters Ⅱ, Ⅲ and Ⅳ. These accessions are an important resource for the establishment of a core collection of chickpeas in the world.     

唐古特白刺研究现状与建议

唐古特白刺(Nitraria tangutorum Bobr.)是白刺属中较进化的植物种,众多克隆株系形成"白刺包",具有重要的生态防护价值,其浆果状核果也具有较高的经济利用价值.由于种内异交和种间杂交,唐古特白刺种内变异十分丰富,其中表现最为明显的是果实性状变异.而果色、果味、果序重等性状差异,对于生产成本、加工工艺以及产品质量等都有较大影响,从而限制了白刺果的产业化开发.开展种质资源、优树选择、杂交和倍性育种等方面的研究,对唐古特白刺进行遗传改良,选育高产、味佳、核小、色泽美观且生态价值高的果用与生态兼用型白刺品种,并进一步使其无性系化、种植园化,则是推动沙区白刺资源开发、利用以及当地生态与经济发展的关键.     

运用微卫星DNA标记分析我国野生鹌鹑遗传多样性

运用微卫星DNA标记对我国境内分布的两种野生鹌鹁（野生日本鸣鹁、野生普通鹌鹑）和家鹑群体的遗传多样性进行分析。通过计算反映群体变异的多态信息含量（PIC）、固定指数、平均杂合度、基因分化系数等相关指标,结果表明：野生普通鹌鹑群体遗传多样性更为丰富,每个座位平均检测出4．67个等位基因,群体多态信息含量和平均杂合度亦为最高,分别为0．5732和0．6621;家鹁最低,分别为0．5467和0．5933;野生日本鸣鹑介于两者之间;在3个鹌鹑群体中,野生日本鸣鹑与家鹑群体遗传多样性差异程度较小。以标准遗传距离为基础的模糊聚类分析发现：家鹑与野生日本鸣鹑群体模糊等价矩阵系数为0．937,而与野生普通鹌鹑的系数为0．738,这也表明家鹑与野生日本鸣鹁有更近的亲缘关系,进一步从分子水平上证实家鹑起源于野生日本鸣鹁。