Generation time and temporal scaling of bird population dynamics

Theoretical studies have shown that variation in density regulation strongly influences population dynamics, yet our understanding of factors influencing the strength of density dependence in natural populations still is limited. Consequently, few general hypotheses have been advanced to explain the large differences between species in the magnitude of population fluctuations. One reason for this is that the detection of density regulation in population time series is complicated by time lags induced by the life history of species that make it difficult to separate the relative contributions of intrinsic and extrinsic factors to the population dynamics. Here we use population time series for 23 bird species to estimate parameters of a stochastic density-dependent age-structured model. We show that both the strength of total density dependence in the life history and the magnitude of environmental stochasticity, including transient fluctuations in age structure, increase with generation time. These results indicate that the relationships between demographic and life-history traits in birds translate into distinct population dynamical patterns that are apparent only on a scale of generations.     

河北小五台山海拔梯度上青杨的种群结构和空间分布

通过研究小五台山自然保护区内天然青杨种群的平均胸径、密度、大小级结构以及空间分布格局在不同海拔梯度上的差异,以揭示环境变化对青杨种群特征的影响.结果显示:青杨种群的平均胸径沿海拔梯度表现为N型变化,并在海拔1 600 m达到最小;种群密度在海拔梯度上的变化趋势与平均胸径相反.从整体上看,除海拔1 700 m表现为下降型外,青杨种群大小级结构在其它海拔梯度上都表现为增长型.通过Morisita指数和扩散系数的研究发现,种群空间分布以随机分布和均匀分布为主,以及10 m×10 m是进行青杨格局分析的较合适尺度.同时对种群中大小级植株空间分布的分析结果表明青杨种群的分布格局与种群年龄结构密切相关.此外,环境指标的分析结果表明温度是造成青杨种群在海拔梯度上分布差异的主要环境因子.     

Concurrent density dependence and independence in populations of arctic ground squirrels

No population increases without limit. The processes that prevent this can operate in either a density-dependent way (acting with increasing severity to increase mortality rates or decrease reproductive rates as density increases), a density-independent way, or in both ways simultaneously. However, ecologists disagree for two main reasons about the relative roles and influences that density-dependent and density-independent processes have in determining population size. First, empirical studies showing both processes operating simultaneously are rare. Second, time-series analyses of long-term census data sometimes overestimate dependence. By using a density-perturbation experiment on arctic ground squirrels, we show concurrent density-dependent and density-independent declines in weaning rates, followed by density-dependent declines in overwinter survival during hibernation. These two processes result in strong, density-dependent convergence of experimentally increased populations to those of control populations that had been at low, stable levels.     

燕麦表型可塑性与繁殖分配的研究

在不同的种植密度（种子数／m^2.D1,75;D2,300;D3,525;D4,750;D5,975)下，燕麦（Avena sativa L.）表现出较高的表型可塑性，其单株分蘖数、穗数、小穗数、不孕小穗数、种子数、植物体大小、繁殖体大小、营养体大小、穗粒数、穗粒重和单分蘖重等性状值均随密度的增加而减少，表现出明显的密度依赖性。无效分蘖数及其占分蘖总数的比例、种子单粒重及株高在密度处理间无显著差异，这些性状是非密度依赖的，植物体几何形状的变化模式属异速生长型，繁殖分配比例为一恒定值，对性状间回归分析的结果表明，处子数量和种子大小间不存在负的表型相关，植物单株与单分蘖大小依赖的繁殖输出以及繁殖体与营养体大小间显著的正相关关系都是线笥的，由于单位面积上的繁殖输出随种群密度的增加而增加，因此植物个体繁殖输出的变化不足以补偿因密度变化而造成的差异。     

贵州省平坝县森林景观异质性研究

运用平坝县森林资源分布图,通过透明网格纸人工统计有关数据,分别计算景观要素优势度、景观斑块密度、景观要素斑块密度和森林景观粒级结构,由此对平坝县的森林景观异质性进行了静态分析.研究表明,平坝县森林景观受环境因子、植被自然演替和人类活动的共同控制,总体异质程度较高.控制因子中,人类活动影响最大.     

Survival variability and population density in fish populations

To understand the processes that regulate the abundance and persistence of wild populations is a fundamental goal of ecology and a prerequisite for the management of living resources. Variable abundance data, however, make the demonstration of regulation processes challenging. A previously overlooked aspect in understanding how populations are regulated is the possibility that the pattern of variability--its strength as a function of population size--may be more than 'noise', thus revealing much about the characteristics of population regulation. Here we show that patterns in survival variability do provide evidence of regulation through density. Using a large, global compilation of marine, anadromous and freshwater fisheries data, we examine the relationship between the variability of survival and population abundance. The interannual variability in progeny survival increases at low adult abundance in an inversely density-dependent fashion. This pattern is consistent with models in which density dependence enters after the larval stage. The findings are compatible with very simple forms of density dependence: even a linear increase of juvenile mortality with adult density adequately explains the results. The model predictions explain why populations with strong regulation may experience large increases in variability at low densities. Furthermore, the inverse relationship between survival variability and the strength of density dependence has important consequences for fisheries management and recovery, and population persistence or extinction.     

土地整理对区域景观格局的影响——以湖北省安陆市辛榨乡基本农田整理项目为例

土地整理是区域景观变化的主要驱动力之一，其生态影响可以通过景观格局的变化表现出来．结合国家投资基本农田整理项目的空间数据与属性数据。选取景观单元特征指数、景观多样性指数、景观破碎化指数等三大类指数与9小类指标，在AutoCAD与MapGIS平台上提取与处理空间数据和属性数据。并计算出各指标量整理前后的变化．结果表明：土地整理后斑块密度指数减少，景观多样性指数降低，破碎度指数减小，水田的优势度增高且更具有连通性，景观异质程度下降，景观类型有向单一化和非均衡化方向发展的趋势。景观中各类型斑块在空间上的分布也出现非均衡化．     

Distinct types of diffuse large B-cell lymphoma identified by gene expression profiling

Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin's lymphoma, is clinically heterogeneous: 40% of patients respond well to current therapy and have prolonged survival, whereas the remainder succumb to the disease. We proposed that this variability in natural history reflects unrecognized molecular heterogeneity in the tumours. Using DNA microarrays, we have conducted a systematic characterization of gene expression in B-cell malignancies. Here we show that there is diversity in gene expression among the tumours of DLBCL patients, apparently reflecting the variation in tumour proliferation rate, host response and differentiation state of the tumour. We identified two molecularly distinct forms of DLBCL which had gene expression patterns indicative of different stages of B-cell differentiation. One type expressed genes characteristic of germinal centre B cells ('germinal centre B-like DLBCL'); the second type expressed genes normally induced during in vitro activation of peripheral blood B cells ('activated B-like DLBCL'). Patients with germinal centre B-like DLBCL had a significantly better overall survival than those with activated B-like DLBCL. The molecular classification of tumours on the basis of gene expression can thus identify previously undetected and clinically significant subtypes of cancer.     

科尔沁沙地冰草居群形态多样性研究

应用常规统计学方法，对科尔沁沙地冰草5个居群共计100个单株的5个形态学形状(穗长、穗宽、穗轴第一节间长、小穗小花数)进行了分析，各居群均在穗轴第一间节长这一性状表现出最大变异(CV=32．00％)，在穗长上表现出最小变异(CV=18．07％)．采用Shanno-Weaver信息指数，科尔沁沙地冰草居群多样性指数为1．5545，显示了较高的遗传多样性。     

Adaptive plasticity in mate preference linked to differences in reproductive effort

There is abundant evidence for the existence of marked mate preferences in natural populations, but the occurrence of within-population variation in mate preferences has received little attention and is often regarded as nonadaptive deviation from the optimal norm. Here we show experimentally that the preference of female collared flycatchers Ficedula albicollis for male forehead patch size, a sexually selected trait, varies with the time of breeding, an environmental factor with strong effects on reproductive success. Contrary to expectations based on time-constrained choice models, only late-breeding females prefer males with a large patch size. The variation in mate preference matches a seasonal change in female reproductive success: long-term data reveal a positive relationship between female reproductive success and male patch size exclusively in late breeders. In addition, female reproductive effort, as assessed by clutch size, appears to be adjusted relative to both timing of breeding and male phenotype. We conclude that not only can mate preferences display adaptive plasticity within populations, but this plasticity can also be linked to differences in reproductive investment.     

The effect of migration on local adaptation in a coevolving host-parasite system

Antagonistic coevolution between hosts and parasites in spatially structured populations can result in local adaptation of parasites; that is, the greater infectivity of local parasites than foreign parasites on local hosts. Such parasite specialization on local hosts has implications for human health and agriculture. By contrast with classic single-species population-genetic models, theory indicates that parasite migration between subpopulations might increase parasite local adaptation, as long as migration does not completely homogenize populations. To test this hypothesis we developed a system-specific mathematical model and then coevolved replicate populations of the bacterium Pseudomonas fluorescens and a parasitic bacteriophage with parasite only, with host only or with no migration. Here we show that patterns of local adaptation have considerable temporal and spatial variation and that, in the absence of migration, parasites tend to be locally maladapted. However, in accord with our model, parasite migration results in parasite local adaptation, but host migration alone has no significant effect.     

Introduced species and their missing parasites

Damage caused by introduced species results from the high population densities and large body sizes that they attain in their new location. Escape from the effects of natural enemies is a frequent explanation given for the success of introduced species. Because some parasites can reduce host density and decrease body size, an invader that leaves parasites behind and encounters few new parasites can experience a demographic release and become a pest. To test whether introduced species are less parasitized, we have compared the parasites of exotic species in their native and introduced ranges, using 26 host species of molluscs, crustaceans, fishes, birds, mammals, amphibians and reptiles. Here we report that the number of parasite species found in native populations is twice that found in exotic populations. In addition, introduced populations are less heavily parasitized (in terms of percentage infected) than are native populations. Reduced parasitization of introduced species has several causes, including reduced probability of the introduction of parasites with exotic species (or early extinction after host establishment), absence of other required hosts in the new location, and the host-specific limitations of native parasites adapting to new hosts.     

心室复极空间不一致性表示方法的探讨

本文采用二镒样条小波变换提取心电信号的特征点,从羊心脏表面64通道的心电信号中,提取各通道的QT间隔和兴奋恢复间隔（ARI）,分别求出二者以极差法、标准差法和变异系数定义的离散度,通过统计检验P值,比值三种方法定义的QT和ARI离散度在心肌缺血后的变化,发现三种定义的QT离散度,在心肌缺血前后都不具有显著性差异,并以变异系数离散度的P值最大,而心肌缺血使得ARI离散度明显增加,三种定义的ART离散度在心肌缺血前后都具有显著性差异,以变异系数离散度的P为最小,可见三种方法定义的离散度均有效,而变异系数离散度较极差法、标准差法离散度更具有统计意义上的优越性。     

竹＋草植被恢复模式斑块特点及其干扰分析

苦竹＋牛鞭草退耕种植5年后，苦竹与牛鞭草呈斑块分布状态．调查分析表明：牛鞭草中的苦竹斑块受人为影响较大，表现出斑块数量、斑块密度和边界密度均大于苦竹林中的牛鞭草斑块，斑块分维数则小于苦竹林中的牛鞭草斑块；而苦竹林中牛鞭草的生长受苦竹林所围成的斑块分维数、边界密度的增大和面积的减小影响逐渐消失；苦竹林中有牛鞭草分布的最小斑块面积在2．4～6．2m2之间，具体需视斑块分维数和边界密度大小而定．本调查分析在一定程度上可为现实的竹斑块、草斑块的经营管理布局提供参考．     

Group formation stabilizes predator-prey dynamics

Theoretical ecology is largely founded on the principle of mass action, in which uncoordinated populations of predators and prey move in a random and well-mixed fashion across a featureless landscape. The conceptual core of this body of theory is the functional response, predicting the rate of prey consumption by individual predators as a function of predator and/or prey densities. This assumption is seriously violated in many ecosystems in which predators and/or prey form social groups. Here we develop a new set of group-dependent functional responses to consider the ecological implications of sociality and apply the model to the Serengeti ecosystem. All of the prey species typically captured by Serengeti lions (Panthera leo) are gregarious, exhibiting nonlinear relationships between prey-group density and population density. The observed patterns of group formation profoundly reduce food intake rates below the levels expected under random mixing, having as strong an impact on intake rates as the seasonal migratory behaviour of the herbivores. A dynamical system model parameterized for the Serengeti ecosystem (using wildebeest (Connochaetes taurinus) as a well-studied example) shows that grouping strongly stabilizes interactions between lions and wildebeest. Our results suggest that social groups rather than individuals are the basic building blocks around which predator-prey interactions should be modelled and that group formation may provide the underlying stability of many ecosystems.     

安徽舒城县土地利用类型斑块分形特征

运用分形理论,对舒城县土地利用类型图斑的周长、斑块边缘密度和斑块形状指数的标度-频度关系进行了定量分析,结果表明:平原区、岗丘区、山区土地利用类型图斑的数目分别为514、222、94,图斑数目逐渐减少,同时景观异质性和景观破碎度逐渐降低.平原区占据优势地位的斑块是耕地,其面积占到平原区斑块总面积80%以上.岗丘区耕地和林地斑块面积百分比分别为31%和61%,占据着优势地位.山区则是林地斑块,其面积百分比为87%.斑块边缘密度普遍较高,土地利用类型斑块边缘趋向复杂化;斑块形状指数大部分小于1.5,斑块形状总体处于比较简单的状态;土地利用类型图斑的周长、斑块边缘密度和斑块形状指数的标度-频度双对数关系显著,相关系数均超过0.9,呈高度负相关,其分形关系客观存在.     

人工繁殖白蛾黑基啮小蜂最适交配期和暴露期的选择

以蛹蜂比为1∶100和柞蚕(Antheraea pernyi Guerin-Meneville)蛹为替代寄主繁殖白蛾黑基啮小蜂(Tetrastichus nigricoxae Yang),测定室内人工繁蜂的最适交配期和接蜂暴露期。结果表明:当小蜂羽化出蜂后交配48～72 h时,寄生率(93.3%～94.2%)、羽化率(87.5%～90.8%)和平均子代出蜂量(1 010.4～1 213.3头)等寄生指标,均高于或显著高于24 h时的值(p<0.05),极显著高于0 h和96～144 h时(p<0.01)的值;当寄主蛹暴露给寄生蜂2～3 d时,寄生率(87.5%～95.8%)、羽化率(86.7%～95.8%)和平均子代出蜂量(1 274.5～1 365.6头)等繁蜂指标也高于或显著高于其他暴露期处理(p<0.05)。综合考虑蜂龄对寄生效果的影响,选择白蛾黑基啮小蜂人工繁殖的最适交配期和暴露期分别为羽化出蜂后2 d和2～3 d。     

The potential role of pathogens in biological control

It is now well established that pathogens such as viruses, fungi bacteria and protozoans can have profound effects on the dynamics of their invertebrate host populations. Theoretical models of invertebrate host-pathogen interactions which assume uniform structure of the pathogen population may reasonably explain the oscillatory behaviour observed in some systems, but do not adequately describe the existence of more constant populations found in other host-pathogen interactions. An examination of the literature relating to these relatively stable systems suggests that the common thread is the eventual transmission of some of the more protected, longer-lived stages of the pathogen occurring in reservoirs, such as the soil, host cadavers on trees, or the live host itself. In this letter, I propose a new theoretical model which incorporates this population structure and accounts for the range of dynamics observed in natural systems. In particular, I show that host populations may be regulated to low and relatively constant densities if sufficient numbers of pathogens are trans-located from pathogen reservoirs to habitats where transmission can occur. An understanding of pathogen reservoirs may be of value in the design of biological control programmes and may greatly increase the effectiveness of pathogens as biological control agents.     

基于TM遥感影像的福州景观生态格局分析

基于遥感、地理信息系统和景观生态学研究方法，以福州市为研究区域。对2003年的TM遥感影像图进行目视判读，得到的福州市土地利用现状图．应用FRAGSTATS软件计算福州市各景观格局指标，结果表明：研究区内景观类型以林地为主，建设用地次之，最小的为未利用地．从景观尺度上看，多样性指数较高，各种景观类型分布比较均匀；从景观类型尺度上看，斑块形状复杂程度中等，但形状大小差异较大，分离度指数比较高，表明福州市2003年间各景观类型在研究区内分布较为分散．     

我国森林生态类型国家级自然保护区景观格局变化趋势

我国森林生态类型国家级自然保护区在各类国家级自然保护区中占据主导地位,研究该类型国家级自然保护区景观格局变化趋势对于了解我国国家级自然保护区整体景观格局及森林资源的动态变化过程,合理设置国家级自然保护区具有重要意义.通过资料查阅与数据收集,运用Arcgis 9.3软件和Fragstats 3.3景观软件计算出不同年份新建森林生态国家级自然保护区的周长及多项景观指数,并研究这些景观指数的变化趋势;采用方差分析和相关分析方法分析不同年份和不同地区森林生态类型国家级自然保护区的面积、周长的特征差异及其与保护区物种数量等的关系.结果显示:斑块密度由3.366×10-3个/km2下降到1.337×10-3个/km2,边界密度由0.151km/hm2下降到0.028km/hm2,平均斑块分维数总体上均呈先增后减的趋势,表明我国森林生态国家级自然保护区整体景观形状呈现规则化、简单化趋势,景观格局逐渐稳定化、均匀化,景观异质程度和多样性水平呈下降趋势.方差分析表明不同年份建立的森林生态类型国家级自然保护区的面积及周长都不存在显著差异;相关分析表明不同地区保护区面积及周长均与物种数无显著相关性.该研究结果可为我国国家级自然保护区建设和合理设置提供一定的参考意见.