森林害虫发生的空间模式研究进展

森林昆虫种群表现出多样的时空模式,空间同步性是其中最常见的。回顾了森林昆虫空间同步性的特点、形成机制及研究方法方面的进展。森林害虫发生的同步性是广泛存在的,但不同昆虫种类的同步性大小不同。空间同步性常随距离的增大而下降,还与时间尺度有关。Moran效应和扩散是解释空间同步性的两种主要机制,通常Moran效应的影响要比扩散大。从虫害发生数据的获取、同步性的度量及成因3个方面介绍了空间同步性的研究方法方面的进展。利用树轮生态学原理重建森林虫害发生历史的方法可在事后获取可靠的数据,很值得国内研究者借鉴和应用。在空间自相关度量上,空间统计学方法和地统计学方法都是非常有力的手段,但由于不能处理多时间点数据而限制了其在同步性研究中的应用。在同步性成因研究中,利用变异分解将基于距离的Moran特征向量图(dbMEM)作为空间变量研究害虫发生的驱动力是比较新颖的研究方法。     

Extensive spatial genetic structure revealed by AFLP but not SSR molecular markers in the wind-pollinated tree, Fagus sylvatica

Studies of fine-scale spatial genetic structure (SGS) in wind-pollinated trees have shown that SGS is generally weak and extends over relatively short distances (less than 30-40 m) from individual trees. However, recent simulations have shown that detection of SGS is heavily dependent on both the choice of molecular markers and the strategy used to sample the studied population. Published studies may not always have used sufficient markers and/or individuals for the accurate estimation of SGS. To assess the extent of SGS within a population of the wind-pollinated tree Fagus sylvatica, we genotyped 200 trees at six microsatellite or simple sequence repeat (SSR) loci and 250 amplified fragment length polymorphisms (AFLP) and conducted spatial analyses of pairwise kinship coefficients. We re-sampled our data set over individuals and over loci to determine the effect of reducing the sample size and number of loci used for SGS estimation. We found that SGS estimated from AFLP markers extended nearly four times further than has been estimated before using other molecular markers in this species, indicating a persistent effect of restricted gene flow at small spatial scales. However, our SSR-based estimate was in agreement with other published studies. Spatial genetic structure in F. sylvatica and similar wind-pollinated trees may therefore be substantially larger than has been estimated previously. Although 100-150 AFLP loci and 150-200 individuals appear sufficient for adequately estimating SGS in our analysis, 150-200 individuals and six SSR loci may still be too few to provide a good estimation of SGS in this species.     

典型亚热带森林生态系统碳密度及储量空间变异特征

以浙江省森林生态系统为研究对象,基于GIS网格布点,采集了838个森林样地样本(土壤、枯落物等),结合浙江省森林资源监测中心相关数据,利用地统计学和Moran's I相结合的方法系统研究了浙江省森林生态系统碳密度及碳储量空间变异特征。结果表明:浙江省森林生态系统平均碳密度为145.22 t/hm~2,其中森林植被、土壤、枯落物和枯死木层碳密度分别为27.34、108.89、1.79、1.38 t/hm~2。克里格空间插值和局部Moran's I指数结果表明碳密度空间分布规律呈现从西南向东北方向逐渐递减的趋势,与浙江省地形、地势较为一致,受海拔、树龄、森林类型、台风气候等自然因素和人类活动共同影响。浙江省森林生态系统碳储量为877.19 Tg C,森林植被、土壤、枯落物和枯死木层碳储量分别为203.88、656.20、10.84、6.27 Tg C,分别占总碳储量的23%、75%、1.3%、0.7%。在浙江省森林生态系统碳储量空间分布格局中,土壤层是森林生态系统中最大的碳库,约是森林植被层的3.22倍,是整个浙江省森林生态系统碳储量最主要的贡献者。浙江省森林资源丰富,大多数森林仍处于中幼龄林阶段,碳密度水平较低,但是中幼龄林生长速度较快,加强对全省中幼龄林的健康管理,是未来整体提升浙江省森林生态系统固碳潜力的关键。     

Genetic diversity in pollen beetles (Meligethes aeneus) in Sweden: role of spatial,temporal and insecticide resistance factors

1 Pollen beetles Meligethes aeneus are pests of oilseed Brassica crops that are subject to intensive chemical control. Resistance to pyrethroids has been reported. Although this insect is of great economic importance, little is known about its genetic properties and population structure. 2 Amplified fragment length polymorphism (AFLP) analysis with the restriction endonuclease combination EcoRI and PstI was performed on 133 samples of groups of three pollen beetles collected during 2001–04 from five different provinces of Sweden. Both susceptible and resistant insects were studied. Using one primer combination, more than 450 polymorphic DNA fragments were obtained and, in total, four primer combinations were used for analysis. A subsample of 59 single beetles was analysed using one primer combination. 3 AFLP profiles were analysed by similarity measures using the Nei and Li coefficient and Neighbour‐joining dendrograms were generated. The dendrogram built using 133 samples showed three distinct groups, each containing beetles representing one generation. Statistical analysis using analysis of molecular variance of single beetle samples showed no evidence of significant genetic difference between resistant and susceptible beetles. Instead, a clear difference between samples, depending on time of collection and generation, was observed. 4 The expected regional population structure, although statistically significant, explained little of the variation. The levels of genetic variation within populations were very high. There appears to be a high rate of gene flow between pollen beetle populations. The implications of this in the context of insecticide resistance are discussed.     

Statistical methods for temporal and space–time analysis of community composition data

This review focuses on the analysis of temporal beta diversity, which is the variation in community composition along time in a study area. Temporal beta diversity is measured by the variance of the multivariate community composition time series and that variance can be partitioned using appropriate statistical methods. Some of these methods are classical, such as simple or canonical ordination, whereas others are recent, including the methods of temporal eigenfunction analysis developed for multiscale exploration (i.e. addressing several scales of variation) of univariate or multivariate response data, reviewed, to our knowledge for the first time in this review. These methods are illustrated with ecological data from 13 years of benthic surveys in Chesapeake Bay, USA. The following methods are applied to the Chesapeake data: distance-based Moran''s eigenvector maps, asymmetric eigenvector maps, scalogram, variation partitioning, multivariate correlogram, multivariate regression tree, and two-way MANOVA to study temporal and space–time variability. Local (temporal) contributions to beta diversity (LCBD indices) are computed and analysed graphically and by regression against environmental variables, and the role of species in determining the LCBD values is analysed by correlation analysis. A tutorial detailing the analyses in the R language is provided in an appendix.     

Mitochondrial DNA variation in space and time in the northeastern Pacific gastropod, Littorina keenae

The present population structure of a species reflects the influence of population history as well as contemporary processes. To examine the relative importance of these factors in shaping the current population structure of Littorina keenae, we sequenced 762 base pairs of the mitochondrial ND6 and cytochrome b genes in 584 snails from 13 sites along the northeastern Pacific coast. Haplotype network analysis revealed a 'star-like' genealogy indicative of a recent population expansion. Nested clade and mismatch analyses also supported the hypothesis of sudden population expansion following a population bottleneck during the Last Glacial Maximum. Analysis of molecular variance and pairwise Phi(ST) showed no significant spatial population differentiation from Mexico to Oregon - not even across the recognized biogeographic boundary at Point Conception. This is probably due to high contemporary gene flow during the free-swimming larval stage of this snail. Surprisingly, we found a highly significant temporal population differentiation between a San Pedro sample from 1996 and one from 2005, which gave an estimate of effective population size (N(e)) of only 135. Nearly statistically significant changes in the frequency of a particular haplotype in three other populations over 2-3 years further support Hedgecock's 'sweepstakes' hypothesis. When by chance nearly all of the progeny from an aggregation of highly fecund sisters that possess a rare haplotype successfully recruit to become the next generation, the rare haplotype can become temporarily common across the entire species' range. This modification of the sweepstakes hypothesis can explain why the temporal variation that we observed was much greater than the spatial variation.     

Fine-scale genetic structure of life history stages in the food-deceptive orchid Orchis purpurea

In natural plant populations, fine-scale spatial genetic structure can result from limited gene flow, selection pressures or historical events, but the role of each factor is in general hard to discern. One way to investigate the origination of spatial genetic structure within a plant population consists of comparing spatial genetic structure among different life history stages. In this study, spatial genetic structure of the food-deceptive orchid Orchis purpurea was determined across life history stages in two populations that were regenerating after many years of population decline. Based on demographic analyses (2001-2004), we distinguished between recruits and adult plants. For both sites, there was no difference in the proportion of polymorphic loci and expected heterozygosity between life history stages. However, spatial autocorrelation analyses showed that spatial genetic structure increased in magnitude with life history stage. Weak or no spatial genetic structure was observed for recruits, whereas adult plants showed a pattern that is consistent with that found in other species with a predominantly outcrossing mating system. The observed differences between seedlings and adults are probably a consequence of changes in management of the two study sites and associated demographic changes in both populations. Our results illustrate that recurrent population crashes and recovery may strongly affect genetic diversity and fine-scale spatial genetic structure of plant populations.