Interspecific relationships in the forest community dominated by Pinus kwangtungensis, an endangered species endemic to China

Interspecific relationships in a natural forest dominated by Pinus kwangtungensis, a rare and endangered pine species endemic to China, were studied based on inventory data from 7,200 m² plots in Nanling National Nature Reserve. With the aim to quantitatively analyze the relationships of P. kwangtungensis to other species in the forest community and to their habitat, the continuous transect sampling method was employed by placing a horizontal transect (10 m × 120 m) at a 100 m altitudinal interval from 1,100 m to 1,600 m a.s.l., which represents the altitudinal range of P. kwangtungensis in Nanling National Nature Reserve. Each transect was further divided into 12 contiguous quadrats (10 m × 10 m) for plant censuses. Both canonical correspondence analysis (CCA) and cluster analysis were used to detect the interspecific relationships. The results showed the following: 1) occurrence frequency of P. kwangtungensis in Nanling was ranked Class A in terms of Raunkiaer’s law of frequency. P. kwangtungensis dominated in the canopy more than in the subcanopy and understory; 2) both Spearman rank correlation (SRC) coefficients and Pearson correlation coefficients indicated that the number of positive covariation couplets was significantly higher than the negative covariation couplets in the forest community, although SRC appeared to be more sensitive than Pearson correlation analysis. Except for the negative covariation with Litsea elongata, P. kwangtungensis exhibited no significant correlation with other dominant species; 3) altitude, slope, slope aspect, slope shape, thickness of humus layer, and thickness of litter all had significant correlations with the three axes in CCA plot, and the environmental factors in the first two axes defined the ecological conditions of the community. The grouping of the 105 canopy tree species was made according to the characteristics of the species along the first axis. Altitude was the most effective factor influencing the distribution of P. kwangtungensis; 4) variability in spatial distribution among the 105 canopy tree species could be attributed to variations to site environmental factors. The results from CCA and cluster analysis indicated that environmental factors influenced the distribution and ecological characteristics of the plant species in the forest community dominated by P. kwangtungensis. __________ Translated from Acta Ecologica Sinica, 2006, 26(4): 1,063–1,072 [译自: 生态学报]     

半干旱地区湿地-干草原生态系统植物群落多样性分析

利用极点排序法对宁夏盐池县四儿滩湿地交错带的边界进行确定,并在此基础上研究其植物的生物多样性.结果表明：1）沿湿生带-交错带-旱生带的生境梯度,交错带划分结果为北样线交错带样方为N8 ～ N13,南样线为S15～ S24,东样线为E13 ～ E22,西样线为W23～W30.2）4条样线多样性指数与丰富度指数均表现为交错带＞旱生带＞湿生带,均匀度指数均表现为旱生带＞交错带＞湿生带,优势集中性指数均表现为湿生带＞交错带＞旱生带.3）受人为干扰和地形差异的影响,不同方向植物群落差异较大,北样线和东样线丰富度指数、多样性指数、均匀性指数较高,优势集中性指数较低.     

Desert vegetation distribution and species-environment relationships in an oasis-desert ecotone of northwestern China

Environmental heterogeneity significantly affects the structure of ecological communities. Exploring vegetation distribution and its relationship with environmental factors is essential to understanding the abiotic mechanism(s) driving vegetation succession, especially in the ecologically fragile areas. In this study, based on the quantitative analysis of plant community and environmental factors in 68 plots at 10 different transects in the Minqin oasis-desert ecotone(ODE) of northwestern China, we investigated desert vegetation distribution and species-environment relationships using multivariate analysis. Two-way indicator species analysis(TWINSPAN), detrended correspondence analysis(DCA), and canonical correspondence analysis(CCA) methods were used. A total of 28 species, belonging to 27 genera in 8 families, were identified. Chenopodiaceae, Zygophyllaceae, Gramineae, and Leguminosae were the largest families. Annual and perennial herbs accounted for 28.60% of the total number of plants, while shrubs(42.90%) were the most dominant. Nitraria tangutorum was the constructive species of the desert plant community. We divided the 68 plots surveyed in this study into 7 community types, according to the results of TWINSPAN. The distribution of these 7 communities in the DCA ordination graph showed that species with a similar ecotype were clustered together. Results of CCA indicated that groundwater was the dominant factor influencing vegetation distribution, while distance between plot and oasis(Dis) and soil electrical conductivity(EC) were the local second-order factors. Our study suggests that optimizing the utilization of groundwater in oases is key to controlling the degradation of desert vegetation. The favorable topographic conditions of sand dunes should be fully utilized for vegetal dune stabilization, and the influence of soil salinity on the selection of afforestation tree species should be considered.     

火地塘林区原生森林植被极点排序及分类

本文采用极点排序技术，对火地塘林区主要乔木种群及森林群落进行了排序分析，结果表明影响本林区乔木种群及群落分布格局的两个显著的主导的生态梯度是海拔高度和坡度梯度。以乔木树种构成及其相对优势度作为分类依据，将火地塘林区原生森林植被划分为2个森林类群；5个类型组；10个类型。     

Patterns of diel activity and species richness in young and small fishes of European streams: a review of 20 years of point abundance sampling by electrofishing

Originally developed to assess the relative abundance of ≥1+ fishes in large rivers, point abundance sampling by electrofishing (PASE) was adapted for 0+ fishes in the mid‐1980s. Being both economical and widely applicable, PASE for 0+ fish has become a commonly used sampling approach in Europe, but its use for estimating 0+ fish density and species richness has attracted particular concern because of size and species selectivity. As such, this review is both timely and necessary. It summarizes the development of PASE and evaluates its various applications: studies of 0+ fish community composition, relative abundance and density, species richness (S), population size structure, larval and juvenile growth dynamics, microhabitat use, diel dynamics of species–species and species–microhabitat interactions, and the analysis of data emanating from PASE databases. The use and potential misuse of replicate sampling in estimates of S are examined, with PASE data from various European rivers re‐analysed to assess geographical patterns in 0+ fish S. Comparisons of PASE and other approaches for estimating 0+ fish density and species richness have all demonstrated PASE to be cost‐effective and relatively reliable, but sampling accuracy and precision do decrease as fishes enter the juvenile period of development.     

新疆昭苏县沙尔套山天然草地植物群落数量分类与排序(简报)

运用WinTWINS和CANOCO中的DCA排序对沙尔套山主体山地的植被进行了数量分类和排序,将沙尔套山植被划分为16个群丛,进一步用DCA排序方法进行了排序,DCA排序结果与WinTWINS分类结果具有很好的一致性。     

植物群落排序方法概述

总结了几十年来植物群落排序研究的成果,探讨了各种排序方法在植物群落分析应用中的优点和不足之处,并对排序的有效性进行了讨论。     

Land cover,riparian zones and instream habitat influence stream fish assemblages in the eastern Amazon

The Amazon rainforest has experienced rapid land‐use changes over the last few decades, including extensive deforestation that can affect riparian habitats and streams. The aim of this study was to assess responses of stream fish assemblages to deforestation and land cover change in the eastern Amazon. We expected that percentage of forest in the catchment is correlated with local habitat complexity, which in turn determines fish assemblage composition and structure. We sampled 71 streams in areas with different land uses and tested for relationships between stream fish assemblages and local habitat and landscape variables while controlling for the effect of intersite distance. Fish assemblage composition and structure were correlated with forest coverage, but local habitat variables explained more of the variation in both assemblage composition and structure than landscape variables. Intersite distance contributed to variance explained by local habitat and landscape variables, and the percentage of variance explained by the unique contribution of local habitat was approximately equivalent to the shared variance explained by all three factors in the model. In these streams of the eastern Amazon, fish assemblages were most strongly influenced by features of instream and riparian habitats, yet indirect effects of deforestation on fish assemblage composition and structure were observed even though intact riparian zones were present at most sites. Long‐term monitoring of the hydrographic basin, instream habitat and aquatic fauna is needed to test for potential legacy effects and time lags, as well as assess species responses to continuing deforestation and land‐use changes in the Amazon.     

Spatial and temporal variation in fish community structure and diversity in the largest tropical flood‐pulse system of South‐East Asia

The Tonle Sap River and Lake (TSRL) is South‐East Asia's largest tropical flood pulse with a flow‐reversal system that supports one of the world's largest freshwater fisheries. However, among the world's tropical floodplains, the resources of the TSRL have received little ecological research. Here, we described the spatiotemporal TSRL fish diversity and community variation using daily records from 2012 to 2015 on fish abundance from six sites covering the TSRL system. We found that high fish diversity occurred in sites located in the middle of Tonle Sap Lake, and the lowest diversity was observed in the southern section. The spatial abundance distribution patterns displayed a river–lake gradient, with three fish assemblages that were clustered based on their composition similarities and were characterised by 96 indicator species. In the southern section, fish assemblages were characterised by longitudinal migratory fishes; in contrast, in the middle system, fish assemblages were represented by species with combined ecological attributes (i.e. longitudinal and lateral migratory species and floodplain residents). Towards the northern section, fish assemblages were composed of lateral migratory and floodplain resident species. Species richness and abundance peaked at approximately 2–2.5 and 4 months, respectively, after the peak flow in early October, during which Tonle Sap River resumes its normal flow direction (outflow). This suggests that seasonal flood pulses (i.e. rising and falling water levels) play a pivotal role in structuring spatiotemporal variation in the TSRL fish assemblages. Our study has implications for fisheries monitoring and conservation initiatives.     

Genotype by environment effects and selection for drought tolerance in tropical maize. I. Two mode pattern analysis of yield

Ten trials evaluated the performance of several late tropical maize populations (La Posta Sequía, Pool 26 Sequía and Tuxpeño Sequía) selected for tolerance to drought during flowering and grain filling and also for yield potential. Families (S₁ or full-sib) had been selected recurrently for six to eight years on an index of traits. Pattern (clustering and ordination) analysis was used to analyse the relative performance of entries that included cycles of selection for drought tolerance in the populations and non-drought tolerant checks. Mean environment (E) yields ranged from 1.0 to 10.4 t ha^-1. Analysis of variance showed that 97.9% of the total sums of squares was accounted for by E, and that, of the remaining sums of squares the G × E (genotype by environment interaction) was almost 3 times that of the contribution of G alone. Cluster analysis separated the checks, the earlier maturing drought tolerant entries and the later maturing drought tolerant entries. This was verified by principal component (PC) analysis of the G × E matrix. Grouping of the environments (i.e. based on entry performance), resulted in the separation of different types of droughts, and of medium and high yielding well-watered environments. The patterns of discrimination observed indicated that the yield gains under drought would have been unlikely to occur if selection had been done only in well-watered environments. Within each population, selection improved broad adaptation (higher mean yield) to both drought and well-watered environments and cycles of selection ‘jumped’ from non-drought-tolerant to drought-tolerant groups as their specific adaptation to drought environments increased.