Floristic variation within kerangas (heath) forest: re-evaluation of data from Sarawak and Brunei

The variation in species composition of trees 7.6 cm gbh in thirty-eight plots (mostly c. 0.2 ha in extent) from physiognomically-defined kerangas forest were re-analyzed by principal components analysis ordination (species centering and standardization by sample norm). Analyses were performed separately on basal area abundances, on the densities of trees in three size classes (7.6, 30.5 and 61.0 cm gbh) and on the density of small and large trees (7.6-<30.5 and 30.5-<61.0 cm gbh). A total of 636 taxa were reduced to 381 for analysis, removing those of very low density and plot frequency.Three groups of plots were identified: forest at low elevation, and generally coastal, on deep humus podzols; forest at intermediate elevation on mostly red-yellow podzols with affinities to dipterocarp forest; and forest at high elevation on mostly peaty podzols. The first group was divisible into five subgroups along a drainage gradient, while the more poorly drained plots showing affinities to peatswamp forest. Forty to eighty of the taxa, depending on the criteria for selection, were sufficient to define a stable, reduced spatial structure of the data matrix. Two subgroups, both coastal on deep podzols, represent the extreme form of kerangas forest per se. A comparison of Agathis borneensis- and Shorea albida-dominated plots revealed few other associated and differentiating taxa.Patterns were clearest from analyses of basal area data and of densities of all and small trees. Ordinations and grouping of plots for small, but not large, tree densities were similar to those for basal area. Different species were differentiated on the basis of the abundance measure, leading to group (tabular) definition of associations in a dual manner. A new system of summarization is presented which combines basal area, density and frequency in a graded hierarchical approach.The association between vegetation and soil type was difficult to unravel because of the limited environmental space sampled. Soil type was confounded with elevation, rainfall and geographical location. A major factor is clay content probably affecting nutrient status and water holding properties. Modal analysis of small tree densities showed clearest patterns in this respect. There were no patterns at the family or genus level, nor in leaf size spectra within kerangas.Problems in the treatment, analysis and summarization of tropical forest data sets are discussed. These problems centre on the scale and intensity of field sampling and the advantages of measuring small trees leading to a dual basal area and density approach. All published studies, including this one, within kerangas forest have used inadequate sampling for the purposes of revealing species changes with respect to soil type and composition.     

Ecological boundaries in the context of hierarchy theory

Ecological boundaries have been described as being multiscalar or hierarchical entities. However, the concept of the ecological boundary has not been explicitly examined in the context of hierarchy theory. We explore how ecological boundaries might be envisioned as constituents of scalar hierarchical systems. Boundaries may be represented by the surfaces of constituents or as constituents themselves. Where surfaces would correspond to abrupt transition zones, boundary systems might be quite varied depending on hierarchical context. We conclude that hierarchy theory is compatible with a functional vision of ecological boundaries where functions can be largely represented as the processing or filtering of ecological signals. Furthermore, we postulate that emergent ecological boundaries that arise on a new hierarchical level may contribute to the overconnectedness of mature ecosystems. Nevertheless, a thermodynamic approach to the emergence and development of boundary systems does indicate that in many situations, ecological boundaries would persist in time by contributing to the energy production of higher hierarchical levels.     

Structure of herbaceous plant assemblages in a forested riparian landscape

We assessed patterns of herbaceous and woody species richness, plant-environment interactions, and correspondence between the herb and tree layer in a riparian landscape (the Ozark National Scenic Riverways, Missouri, USA). A total of 269 herb and 70 tree species were identified on 94 sample plots. Gradient analysis revealed that environmental variables and vegetation were influenced by a strong elevation gradient. However, high variability in environmental variables (pH, elevation, slope, sand, clay, organic matter) indicated a high level of substrate heterogeneity across the riparian landscape. We were unable to predict the composition of the herb understory from the canopy trees with any detailed accuracy and no clear characterization of herb species assemblages was found using cluster analysis or ecological land type (ELT) classifications. Canonical correspondence analysis (CCA) results for both tree and herb plots showed that elevation (height above river) and pH were the dominant environmental gradients influencing vegetation patterns on the first CCA axis while soil particle size exhibited the strongest correlation with the second CCA axis. Secondary gradients of importance included slope, soil container capacity, and organic matter. No significant linear or quadratic correlation was found between elevation and herb or woody species richness. Environmental variables alone or in combination, were weak predictors of herb and woody species richness, despite the patterns observed in the gradient analysis and the correlations observed in the CCA results. Ecotonal analysis showed that the herb layer exhibited a high species replacement rate at the lower elevations most susceptible to flooding (0–3 m). Above the flooding zone, there was more or less continuous species replacement, suggesting the presence of a gradual ecotone/ecocline. The tree layer exhibited much stronger discontinuities than the herb layer in the lower elevations along the height gradient (0–10 m). Recognizing the limitations of classification techniques for riparian herb assemblages and the importance of scale and heterogeneity in vegetation layers is especially important in light of mandates to preserve, protect, and manage for plant diversity.     

Ecological risk assessment of genetically modified crops based on cellular automata modeling

The assessment of ecological risk in genetically modified (GM) biological systems is critically important for decision-making and public acceptance. Cellular automata (CA) provide a potential modeling and simulation framework for representing relationships and interspecies interactions both temporally and spatially. In this paper, a simple subsystem contains only four species: crop, target pest, non-target pest and enemy insect, and a three layer arrangement of L × L stochastic cellular automata with a periodic boundary were established. The simulation of this simplified system showed abundant and sufficient complexity in population assembly and densities, suggesting a prospective application in ecological risk assessment of GM crops.     

Habitat fragmentation resulting in overgrazing by herbivores

Habitat fragmentation sometimes results in outbreaks of herbivorous insect and causes an enormous loss of primary production. It is hypothesized that the driving force behind such herbivore outbreaks is disruption of natural enemy attack that releases herbivores from top-down control. To test this hypothesis I studied how trophic community structure changes along a gradient of habitat fragmentation level using spatially implicit and explicit models of a tri-trophic (plant, herbivore and natural enemy) food chain. While in spatially implicit model number of trophic levels gradually decreases with increasing fragmentation, in spatially explicit model a relatively low level of habitat fragmentation leads to overgrazing by herbivore to result in extinction of the plant population followed by a total system collapse. This provides a theoretical support to the hypothesis that habitat fragmentation can lead to overgrazing by herbivores and suggests a central role of spatial structure in the influence of habitat fragmentation on trophic communities. Further, the spatially explicit model shows (i) that the total system collapse by the overgrazing can occur only if herbivore colonization rate is high; (ii) that with increasing natural enemy colonization rate, the fragmentation level that leads to the system collapse becomes higher, and the frequency of the collapse is lowered.     

多功能农药降解基因工程菌株m-CDS-1环境释放安全评价

【目的】为了评价多功能农药降解基因工程菌株m-CDS-1的环境释放中间试验水平的安全性。【方法】通过农药检测、平板计数、Most probable number-PCR(MPN-PCR)和Denaturing Gradient Gel Electrophoresis(DGGE)等方法在江苏大丰进行了工程菌株m-CDS-1田间降解农药效果、定殖动态和对土壤微生物群落结构影响的研究。【结果】投加1.01×107CFU/g干土的工程菌株m-CDS-1在30d时均能完全降解10.71mg/kg的甲基对硫磷和1.29mg/kg的呋喃丹。平板计数表明工程菌株m-CDS-1在土壤中快速下降;MPN-PCR检测结果显示,在4d,15d和30d时,0～10cm混合土壤中该工程菌株的数目分别为2.15±0.98×106CFU/g干土,3.70±4.66×104CFU/g干土和检测不出。工程菌株m-CDS-1的投加不会对土壤可培养三大微生物菌群数量产生显著影响;基于细菌16S rDNA V3区的DGGE分析结果表明,施加农药对细菌菌落结构有显著影响,4d,11d,30d时农药施用区与空白对照区的图谱相似性分别为17.16%,49.81%和75.01%,但到60d时的相似性为98.62%。工程菌株m-CDS-1释放在前期对细菌群落结构有一定影响,4d,11d和30d工程菌株释放区相对于空白的相似性分别为49.57%,38.30%和83.30%。在60d时,空白、施药和施菌小区的图谱相似性都在90%以上。【结论】工程菌株m-CDS-1不仅可同时高效降解甲基对硫磷和呋喃丹,仍保持了实验室内的原有特性,而且不会成为优势菌群长期在土壤环境中存在,也不会对土壤微生物群落结构造成长期影响。     

Cellular origin of prealbumin in the rat

The synthetic rate of prealbumin and albumin in primary monolayer cultures of rat hepatocytes was measured by immunochemical methods. The isolated hepatocytes synthesized these proteins in the same ratio as that previously found for the whole body synthesis in vivo. It is concluded that the hepatocytes synthesize the main part of prealbumin in the rat.     

Identification of cellular components required for SV40 DNA replication in vitro

To investigate the cellular proteins involved in simian virus 40 (SV40) replication, extracts derived from human 293 cells have been fractionated into multiple components. When such fractions are combined with the virus-encoded T antigen (TAg) and SV40 origin containing plasmid DNA, efficient and complete replication is achieved, while each fraction alone is inactive. At present, a minimum of eight such cellular components have been identified. Previous experiments have demonstrated one of these to be the cell-cycle-regulated proliferating-cell nuclear antigen (PCNA). As PCNA has been identified as a processivity factor for DNA polymerase δ, we suggest that both polymerases α and β are involved in this system. Three further fractions have been identified. One is a partially purified fraction which, under certain conditons, is required with TAg for the formation of a pre-synthesis complex of proteins at the replication origin. The second of these factors, RF-A, is a complex of three polypeptides which may function as a eucaryotic SSB. The third, RF-C, is a factor which is required, with PCNA, for coordinated leading- and lagging-strand synthesis at the replication fork. Complete synthesis and segregation of the daughter molecules also requires the presence of topoisomerases I and II. These results suggest a model for DNA synthesis which involves multiple stages prior to and during replicative DNA synthesis.     

基于元胞自动机的生物性病原物类疾病传播模型

生物性病原物类疾病是单一植物群落中常见的一种传染病,它主要依靠风、雨和昆虫等外力传播病菌,传播过程中具有一定的潜伏性,元胞自动机是一种在时间和空间上离散,以每个个体状态的同步更新为前提来讨论系统整体性质的模型,本文利用其特点,将整个森林中的树木分为健康、潜伏期、发病期三类,以树木的营养状况和被感染时间长度为辅助变量,在考虑到树木得病后被治愈的情况后,建立了基于元胞自动机的树林生物性病原物类疾病传播模型．模拟结果表明,在不同的初始条件下,得病树所占的比例由疾病传播和被治愈的相对强度确定．疾病每次传播时,从爆发到被控制的过程具有相似的特点：随着恢复强度从小到大,初始阶段,被感染的树木迅速增加,接着进入传播速度相对缓慢的稳定过程,最终如果恢复机制足够强,则树林中的不健康树木会全部消失．