扩散限制和环境筛选对子午岭森林群落构建的相对贡献

【目的】改善区域生态环境是促进农业生产、实现可持续发展的重要前提,而加强植被的恢复重建是改善生态环境的重要途径。本研究拟通过对黄土高原子午岭森林群落构建过程的研究,为该区的植被恢复重建提供理论依据。【方法】采用典范变异分解和Mantel检验两种互补的方法,通过分离环境因子/距离（度量环境筛选）和空间因子/距离（间接度量扩散限制）对群落物种组成/距离的相对贡献,确定环境筛选和扩散限制在该区植物群落构建中的相对重要性。【结果】不同群落类型间的物种组成差异显著,空间和环境因子共同解释了草本、灌木、乔木三层29%—65%的物种组成变异（P＜0.01）。而二者的贡献特点在不同层次有所差异,乔木层和灌木层主要以空间因子为主导;而在草本层中,空间和环境因子具有相似的贡献率。草本、灌木、乔木三层的物种非相似性距离与环境距离和地理距离都显著相关（P＜0.05）,草本层具有较大的环境距离相关系数,而灌木层和乔木层具有较大的地理距离相关系数。【结论】扩散限制和环境筛选相互作用,共同影响着黄土高原森林群落的构建过程。本研究的结果并没有否定环境筛选在黄土高原群落构建中的重要性,而是更加强调了扩散限制在该区的主导性。因此,在黄土高原森林群落的恢复重建中,应该同时考虑环境异质性和地理空间的差异性。     

宝天曼自然保护区树附生苔藓空间格局分析

采用单变量g(r)函数,选用同质性泊松、异质性泊松、同质性托马斯和异质性托马斯4个零模型,分析了宝天曼自然保护区内1 hm2样地中11种树附生苔藓物种的空间分布格局.结果显示,11个物种中,有6个物种在同质性泊松模型下表现出聚集分布,在同质性托马斯模型下的聚集程度有所减弱,但在异质性泊松模型下完全变为随机分布.与同质性泊松模型下的分布相比,在异质性泊松模型下,有4个物种在较大尺度上的聚集分布变为随机分布;而在同质性托马斯模型下,有2个物种在较小尺度上的聚集分布变为随机分布.研究表明:1)生境异质性和扩散限制均对树附生苔藓空间分布格局的形成有影响,且生境异质性起主要作用;2)生境异质性可在小尺度上影响树附生苔藓的空间分布,扩散限制也能在大尺度上发挥作用.     

Population cycles in small rodents

We conclude that population fluctuations in Microtus in southern Indiana are produced by a syndrome of changes in birth and death rates similar to that found in other species of voles and lemmings. The mechanisms which cause the changes in birth and death rates are demolished by fencing the population so that no dispersal can occur. Dispersal thus seems critical for population regulation in Microtus. Because most dispersal occurs during the increase phase of the population cycle and there is little dispersal during the decline phase, dispersal is not directly related to population density. Hence the quality of dispersing animals must be important, and we have found one case of increased dispersal tendency by one genotype. The failure of population regulation of Microtus in enclosed areas requires an explanation by any hypothesis attempting to explain population cycles in small rodents. It might be suggested that the fence changed the predation pressure on the enclosed populations. However, the fence was only 2 feet (0.6 meter) high and did not stop the entrance of foxes, weasels, shrews, or avian predators. A striking feature was that the habitat in the enclosures quickly recovered from complete devastation by the start of the spring growing season. Obviously the habitat and food quality were sufficient to support Microtus populations of abnormally high densities, and recovery of the habitat was sufficiently quick that the introduction of new animals to these enclosed areas resulted in another population explosion. Finally, hypotheses of population regulation by social stress must account for the finding that Microtus can exist at densities several times greater than normal without "stress" taking an obvious toll. We hypothesize that the prevention of dispersal changes the quality of the populations in the enclosures in comparison to those outside the fence. Voles forced to remain in an overcrowded fenced population do not suffer high mortality rates and continue to reproduce at abnormally high densities until starvation overtakes them. The initial behavioral interactions associated with crowding do not seem sufficient to cause voles to die in situ. What happens to animals during the population decline? Our studies have not answered this question. The animals did not appear to disperse, but it is possible that the method we used to measure dispersal (movement into a vacant habitat) missed a large segment of dispersing voles which did not remain in the vacant area but kept on moving. Perhaps the dispersal during the increase phase of the population cycle is a colonization type of dispersal, and the animals taking part in it are likely to stay in a new habitat, while during the population decline dispersal is a pathological response to high density, and the animals are not attracted to settling even in a vacant habitat. The alternative to this suggestion is that animals are dying in situ during the decline because of physiological or genetically determined behavioral stress. Thus the fencing of a population prevents the change in rates of survival and reproduction, from high rates in the increase phase to low rates in the decline phase, and the fenced populations resemble "mouse plagues." A possible explanation is that the differential dispersal of animals during the phase of increase causes the quality of the voles remaining at peak densities in wild populations to be different from the quality of voles at much higher densities in enclosures. Increased sensitivity to density in Microtus could cause the decline of wild populations at densities lower than those reached by fenced populations in which selection through dispersal has been prevented. Fencing might also alter the social interactions among Microtus in other ways that are not understood. The analysis of colonizing species by MacArthur and Wilson (27) can be applied to our studies of dispersal in populations of Microtus. Groups of organisms with good dispersal and colonizing ability are called r strategists because they have high reproductive potential and are able to exploit a new environment rapidly. Dispersing voles seem to be r strategists. Young females in breeding condition were over-represented in dispersing female Microtus (17). The Tf(C)/Tf(E) females, which were more common among dispersers during the phase of population increase (Fig. 6), also have a slight reproductive advantage over the other Tf genotypes (19). Thus in Microtus populations the animals with the highest reproductive potential, the r strategists, are dispersing. The segment of the population which remains behind after the selection-via-dispersal are those individuals which are less influenced by increasing population densities. These are the individuals which maximize use of the habitat, the K strategists in MacArthur and Wilson's terminology, or voles selected for spacing behavior. Thus we can describe population cycles in Microtus in the same theoretical framework as colonizing species on islands. Our work on Microtus is consistent with the hypothesis of genetic and behavioral effects proposed by Chitty (6) (Fig. 7) in that it shows both behavioral differences in males during the phases of population fluctuation and periods of strong genetic selection. The greatest gaps in our knowledge are in the area of genetic-behavioral interactions which are most difficult to measure. We have no information on the heritability of aggressive behavior in voles. The pathways by which behavioral events are translated into physiological changes which affect reproduction and growth have been carefully analyzed by Christian and his associates (28) for rodents in laboratory situations, but the application of these findings to the complex field events described above remains to be done. Several experiments are suggested by our work. First, other populations of other rodent species should increase to abnormal densities if enclosed in a large fenced area (29). We need to find situations in which this prediction is not fulfilled. Island populations may be an important source of material for such an experiment (30). Second, if one-way exit doors were provided from a fenced area, normal population regulation through dispersal should occur. This experiment would provide another method by which dispersers could be identified. Third, if dispersal were prevented after a population reached peak densities, a normal decline phase should occur. This prediction is based on the assumption that dispersal during the increase phase is sufficient to ensure the decline phase 1 or 2 years later. All these experiments are concerned with the dispersal factor, and our work on Microtus can be summarized by the admonition: study dispersal.     

Disentangling the drivers of β diversity along latitudinal and elevational gradients

Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (β diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in β diversity caused simply by changes in the sizes of species pools. For example, forest inventories sampled along latitudinal and elevational gradients show the well-documented pattern that β diversity is higher in the tropics and at low elevations. However, after correcting for variation in pooled species richness (γ diversity), these differences in β diversity disappear. Therefore, there is no need to invoke differences in the mechanisms of community assembly in temperate versus tropical systems to explain these global-scale patterns of β diversity.     

The importance of demographic niches to tree diversity

Most ecological hypotheses about species coexistence hinge on species differences, but quantifying trait differences across species in diverse communities is often unfeasible. We examined the variation of demographic traits using a global tropical forest data set covering 4500 species in 10 large-scale tree inventories. With a hierarchical Bayesian approach, we quantified the distribution of mortality and growth rates of all tree species at each site. This allowed us to test the prediction that demographic differences facilitate species richness, as suggested by the theory that a tradeoff between high growth and high survival allows species to coexist. Contrary to the prediction, the most diverse forests had the least demographic variation. Although demographic differences may foster coexistence, they do not explain any of the 16-fold variation in tree species richness observed across the tropics.     

Comment on "Neutral ecological theory reveals isolation and rapid speciation in a biodiversity hot spot"

Latimer et al. (Reports, 9 September 2005, p. 1722) used an approximate likelihood function to estimate parameters of Hubbell's neutral model of biodiversity. Reanalysis with the exact likelihood not only yields different estimates but also shows that two similar likelihood maxima for very different parameter combinations can occur. This reveals a limitation of using species abundance data to gain insight into speciation and dispersal.     

Glacial refugia: hotspots but not melting pots of genetic diversity

Glacial refuge areas are expected to harbor a large fraction of the intraspecific biodiversity of the temperate biota. To test this hypothesis, we studied chloroplast DNA variation in 22 widespread European trees and shrubs sampled in the same forests. Most species had genetically divergent populations in Mediterranean regions, especially those with low seed dispersal abilities. However, the genetically most diverse populations were not located in the south but at intermediate latitudes, a likely consequence of the admixture of divergent lineages colonizing the continent from separate refugia.     

吉林蛟河近熟林树种多样性格局尺度依赖性分析

生境过滤和扩散限制是影响群落多样性格局组建的主要生态学过程,研究了物种多样性格局组建过程中不 同生态学过程起作用的空间尺度。利用单物种-面积模型检验了其中40 种木本植物对邻域物种丰富度的影响,并 且利用同质性泊松、异质性泊松、同质性托马斯和异质性托马斯过程分析了单物种-面积关系偏离中性状况的显著 性。研究结果表明,毛榛、鼠李、早花忍冬、茶条槭和花曲柳在0 ~50 m 空间尺度上为生物多样性促进种;糠椴和千 金榆分别在0 ~25 m 和0 ~35 m 尺度上为生物多样性抑制种;其他绝大多数树种表现为中性种。扩散限制对群落 多样性格局组建影响较大,而生境过滤作用影响相对较小。异质性托马斯过程同时剔除了生境过滤和扩散限制影 响,分析结果显示0 ~20 m 尺度上促进种在群落中占据支配地位;在20 m 尺度上中性种比例随着空间尺度增加 而增大,在群落多样性构建过程中占据主导地位;群落中抑制种比例较低,并且随着空间尺度变化幅度不大。因 此,生态位分化和中性作用共同决定了群落多样性结构的构建过程,二者的相对重要性与空间尺度密切相关。      

Avian persistence in fragmented rainforest

What factors determine the persistence of species in fragmented habitats? To address this question, we studied the relative impacts of forest deterioration and fragmentation on bird species in 12 rainforest fragments in Kenya, combining 6 years of individual capture-recapture data with measurements of current captures and museum specimens. Species mobility, as estimated from species-specific dispersal rates, and tolerance to habitat deterioration, as estimated from change in fluctuating asymmetry with increasing habitat disturbance, explained 88% of the variation in patch occupancy among eight forest bird species. Occupancy increased with mobility and with tolerance to deterioration, where both variables contributed equally to this relationship. We conclude that individual-level study, such as of dispersal behavior and phenotypic development, can predict patterns of persistence at the species level. More generally, for conservation tactics to stand a high chance of success, they should include action both within sites, to minimize habitat deterioration, and across landscapes, to maximize dispersal.     

马鞍列岛岩礁生境鱼类群落结构时空格局

基于2009年马鞍列岛潮下带岩礁生境的多网目三层组合刺网逐月调查数据,对鱼类群落月相和季度间的变化、区域尺度上的空间差异和群落的稳态进行了探讨,应用优势种相对丰度和生物量、定居性鱼类和洄游种的季节动态、非度量多维标度(nMDS)和生物量丰度曲线(ABC)分析方法对群落时空格局进行了分析。结果显示:季节性洄游种集中出现在夏秋季,但对岩礁生境的利用表现出不同区域的强度差异;小黄鱼Larimichthys polyactis和黄姑鱼Nibea albiflora周年利用岩礁生境,但强度有别,尤其在冬季;定居性鱼类褐菖鲉Sebastiscus marmoratus、斑头鱼Agrammus agrammus和大泷六线鱼Hexagrammos otakii在春末夏初的种群密度最高,同样表现出某些或大部分月份的区域差异;而河口种中国花鲈Lateolabrax maculatus则更多地选择秋冬季出现在岩礁生境。多元分析结果揭示了当地岩礁生境鱼类群落格局上显著的季节和区域差异,这是定居性鱼类对岩礁生境利用的阶段性变化和区域差异、结合洄游种季节迁移和选择性分布等因素作用下共同形成的格局。ABC分析进一步发现,丰富的鱼类生态类型形成了夏季岩礁生境更为稳定的群落状态,而冬季相反;同时各季度A区的群落干扰明显强过B区。研究表明,产卵季节海域西北部的岩礁生境很可能起着主要的产卵场功能,而东南部区域各季度皆侧重于幼鱼育肥场的功能表达。丰富的种类区系加之优势种的季节性交替出现,共同塑造了岩礁生境极具动态的鱼类群落格局,对维持岛礁海域鱼类多样性以及局部区域生态系统的稳定性起着非常重要的作用。     

Global dispersal of free-living microbial eukaryote species

The abundance of individuals in microbial species is so large that dispersal is rarely (if ever) restricted by geographical barriers. This "ubiquitous" dispersal requires an alternative view of the scale and dynamics of biodiversity at the microbial level, wherein global species number is relatively low and local species richness is always sufficient to drive ecosystem functions.     

Assembly and co-occurrence patterns of rare and abundant bacterial sub-communities in rice rhizosphere soil under short-term nitrogen deep placement

Nitrogen (N) deep placement has been found to reduce N leaching and increase N use efficiency in paddy fields. However, relatively little is known how bacterial consortia, especially abundant and rare taxa, respond to N deep placement, which is critical for understanding the biodiversity and function of agricultural ecosystem. In this study, Illumina sequencing and ecological models were conducted to examine the diversity patterns and underlying assembly mechanisms of abundant and rare taxa in rice rhizosphere soil under different N fertilization regimes at four rice growth stages in paddy fields. The results showed that abundant and rare bacteria had distinct distribution patterns in rhizosphere samples. Abundant bacteria showed ubiquitous distribution; while rare taxa exhibited uneven distribution across all samples. Stochastic processes dominated community assembly of both abundant and rare bacteria, with dispersal limitation playing a more vital role in abundant bacteria, and undominated processes playing a more important role in rare bacteria. The N deep placement was associated with a greater influence of dispersal limitation than the broadcast N fertilizer (BN) and no N fertilizer (NN) treatments in abundant and rare taxa of rhizosphere soil; while greater contributions from homogenizing dispersal were observed for BN and NN in rare taxa. Network analysis indicated that abundant taxa with closer relationships were usually more likely to occupy the central position of the network than rare taxa. Nevertheless, most of the keystone species were rare taxa and might have played essential roles in maintaining the network stability. Overall, these findings highlighted that the ecological mechanisms and co-occurrence patterns of abundant and rare bacteria in rhizosphere soil under N deep placement.     

Cascading effects of bird functional extinction reduce pollination and plant density

Reductions in bird numbers could hamper ecosystem services such as pollination, but experimental proof is lacking. We show that functional extinction of bird pollinators has reduced pollination, seed production, and plant density in the shrub Rhabdothamnus solandri (Gesneriaceae) on the North Island ("mainland") of New Zealand but not on three nearby island bird sanctuaries where birds remain abundant. Pollen limitation of fruit set is strong [pollen limitation index (PLI) = 0.69] and significant on the mainland but small (PLI = 0.15) and nonsignificant on islands. Seed production per flower on the mainland is reduced 84%. Mainland sites have similar adult densities, but 55% fewer juvenile plants per adult, than island sites. Seed addition experiments near adult R. solandri plants on the mainland found strong seed limitation 5 years after sowing for R. solandri but not for two other co-occurring woody species. This demonstrates a terrestrial trophic cascade.     

中沙和南沙群岛密点胡椒鲷的种群分析

对中国南海中沙群岛和南沙群岛采集的2个珊瑚礁栖性鱼类密点胡椒鲷(Plectorhynchus gaterinus)群体共19尾的mtDNA控制区核苷酸序列进行了扩增分析,获得了长度为510bp的同源序列,2个群体中共检测到变异位点31个,占全部序列的6.08%,2个群体共检测到15种单倍型。AMOVA分析表明,群体间的遗传变异仅占总遗传变异的1.97%,而98.03%的遗传变异源于群体内。2个密点胡椒鲷群体间的分化指数(Fst)仅为0.012,群体分化程度很低。以线粒体DNA控制区序列构建的NJ树揭示,2个群体的个体基本是随机交叉聚类,各群体内的个体均未单独成群,不能形成明显的类群分支。以上结果表明,密点胡椒鲷群体间遗传相似性较大,且存在较强的基因交流,尽管中沙和南沙群岛地理隔离明显,距离较大,但两个群岛的密点胡椒鲷地理分化不明显,仍可认为是一个大的种群。     

Growth-rings of trees: their correlation with climate

Many differences in the ring-width growth within a tree may be attributed to changing supplies of food and hormones. In moist sites or during periods of favorable climate, there may be sufficient food for the production of wide rings throughout the tree. But in dry sites or during years of low moisture and high temperatures, food competition within the tree is likely to be greater and the cambium at the base of the stem is likely to receive a limited food supply and may produce narrow rings. The cambium at the stem base depends upon the entire crown for food, hence ring growth reflects the tree's ambient climate. But, the cambium in the top of the tree or in the upper branches depends upon a more restricted portion of the crown for its food and hormone supplies. The rings produced by the cambium vary greatly from branch to branch and are less reliable indicators of the climate surrounding the entire tree than rings at the tree base. Therefore, ring series at the base of trees in semiarid sites provide the most reliable, as well as the longest, record of macroclimatic variation. Tree-ring widths in certain coniferous species growing in semiarid sites appear to represent the integrated effect of climate on food-making and food accumulation in the crown throughout the 14 to 15 months previous to and including the period of growth. Trees in warm, low-elevation sites may utilize winter moisture most efficiently; trees in cool, high-elevation or more northern sites may utilize early summer and early autumn moisture most efficiently. But even with these differences, a significant amount of variance is found to be common among tree-ring series from a wide range of sites, species, and geographical areas in western North America (14, 19, 34), emphasizing a common dependence of ring widths on the gross regional patterns of precipitation and temperature. The remaining variance, which is not correlated among sites, may be attributed to local en-vironmental and climatic differences, to variability among and within trees, and to compounding effects of occasional fires, insect or other infestations, and recurring years of high seed production. It is evident that a large portion of the variability in ring-width patterns from semiarid sites in western North America does reflect differences in climate from year to year. If ring chro- nologies are derived from a number of trees in semiarid sites and if adequate corrections for age and trend are made, these chronologies may be used to reconstruct a first approximation of annual, or somewhat longer period, climatic fluctuations in the past (19).     

Widespread origins of domestic horse lineages

Domestication entails control of wild species and is generally regarded as a complex process confined to a restricted area and culture. Previous DNA sequence analyses of several domestic species have suggested only a limited number of origination events. We analyzed mitochondrial DNA (mtDNA) control region sequences of 191 domestic horses and found a high diversity of matrilines. Sequence analysis of equids from archaeological sites and late Pleistocene deposits showed that this diversity was not due to an accelerated mutation rate or an ancient domestication event. Consequently, high mtDNA sequence diversity of horses implies an unprecedented and widespread integration of matrilines and an extensive utilization and taming of wild horses. However, genetic variation at nuclear markers is partitioned among horse breeds and may reflect sex-biased dispersal and breeding.     

松材线虫入侵初期三峡库区马尾松林及土壤性质的变化

近些年来,松材线虫入侵对三峡库区马尾松林造成严重危害,并严重威胁着三峡库区松林资源和三峡水利枢纽工程的生态安全。以不同的马尾松林生态系统(健康、感病1年、感病3年、感病5年、感病7年)为研究对象,采用样方法和每木调查法,分析松材线虫入侵早期马尾松林群落植物群落结构和土壤理化性质的动态变化。共调查了37种乔木物种,隶属于30科33属,其中马尾松是群落内的优势树种(IV=49.63%),樟树、槲栎、栓皮栎和檵木等树种的重要值也较高,为亚优势种;与健康林地相比,感病林地内马尾松的数量显著下降,平均胸径和平均树高呈现明显增加趋势;松材线虫入侵对群落内植物不同空间结构(乔木、灌木、草本)的物种多样性影响较大,且物种多样性指数随感病年限变化规律符合“中间高度膨胀理论”;此外,不同感病年限马尾松林群落内土壤的化学性质变化不显著,但是与水分相关的物理性质变化显著。本研究明确阐明了松材线虫入侵早期,三峡库区典型马尾松林群落内植物群落结构、物种多样性指数和土壤理化性质的动态变化,旨在为改变三峡库区单一的马尾松林结构、增加群落的健康程度,从而为三峡水利枢纽工程的生态安全提供基础依据。      

Tree dispersion, abundance, and diversity in a tropical dry forest

Patterns of tree abundance and dispersion in a tropical deciduous (dry) forest are summarized. The generalization that tropical trees have spaced adults did not hold. All species were either clumped or randomly dispersed, with rare species more clumped than common species. Breeding system was unrelated to species abundance or dispersion, but clumping was related to mode of seed dispersal. Juvenile densities decreased approximately exponentially away from adults. Rare species gave evidence of poor reproductive performance compared with their performance when common in nearby forests. Patterns of relative species abundance in the dry forest are compared with patterns in other forests, and are explained by a simple stochastic model based on random-walk immigration and extinction set in motion by periodic community disturbance.     

Community diversity: relative roles of local and regional processes

The species richness (diversity) of local plant and animal assemblages-biological communities-balances regional processes of species formation and geographic dispersal, which add species to communities, against processes of predation, competitive exclusion, adaptation, and stochastic variation, which may promote local extinction. During the past three decades, ecologists have sought to explain differences in local diversity by the influence of the physical environment on local interactions among species, interactions that are generally believed to limit the number of coexisting species. But diversity of the biological community often fails to converge under similar physical conditions, and local diversity bears a demonstrable dependence upon regional diversity. These observations suggest that regional and historical processes, as well as unique events and circumstances, profoundly influence local community structure. Ecologists must broaden their concepts of community processes and incorporate data from systematics, biogeography, and paleontology into analyses of ecological patterns and tests of community theory.