麻城枳椇种群结构及动态分析

为了阐明枳椇天然种群的年龄结构和发展趋势,保护现有资源,对麻城五脑山枳椇天然种群进行样地调查,分析了种群龄级动态,编制了种群静态生命表,进行了时间序列预测.结果表明:枳椇种群龄级结构动态指数V_(pi)=51.58%0,呈增长型;环境筛的抑制出现在第Ⅳ龄级,其后种群动态趋向稳定;存活曲线介于Deevey-Ⅱ型和Deevey-Ⅲ型之间,更接近Deevey-Ⅱ型;时间序列分析表明,由于林下更新层幼苗数量较大,种群具有较强增长和恢复能力.研究表明,枳椇种群的生长发育符合其自身生物学特性,种子库充足,种群处于稳定增长型.种群保护应避免景区建设对种群更新造成干扰.     

安徽琅琊山青檀种群数量动态

以种群生命表和生存分析理论为基础,采用胸径大小分级法和分段匀滑技术,编制琅琊山青檀（Pteroceltistatarinowii）种群静态生命表,绘制了死亡率曲线、消失率曲线、存活曲线和生存函数曲线并分析种群数量特征,结合种群动态量化方法和时间序列预测模型分析种群数量动态变化。结果表明：（1）琅琊山青檀种群属稳定增长型。种群径级结构大体呈倒“J”型分布,中、幼龄阶段个体数量较为丰富,老龄阶段个体数量相对较少,种群在发育过程中存在一定波动性,但种群数量变化动态指数Kp,i。和Kp,i（考虑外部干扰时）均大于0。（2）青檀种群死亡率曲线和消失率曲线变化趋势基本一致,均出现2个高峰,一个出现在第Ⅱ龄级,另一个出现在第XI（或Ⅻ）龄级;存活曲线经统计检验趋于Deevey-Ⅱ型。（3）青檀种群的生存率曲线单调下降,累计死亡率曲线单调上升,生存率下降趋势表现为前期高于后期,累计死亡率则相反;生存函数曲线显示,青檀种群具有前期薄弱、中期稳定和后期衰退的特点。（4）在未来2、4、6、8和10a内,青檀种群幼龄级个体数量相对丰富,种群呈稳定增长趋势。     

庞泉沟自然保护区华北落叶松种群生命表与谱分析

以种群生命表及生存分析理论为基础,将林木依胸径大小分级,以林木径级结构代表年龄结构,采用分段匀滑技术,编制庞泉沟自然保护区华北落叶松种群特定时间生命表,绘制死亡率曲线、消失率曲线、存活曲线、生存函数曲线,分析种群数量特征;同时结合谱分析方法,分析华北落叶松种群数量的动态变化.结果表明:(1)华北落叶松种群年龄结构表现为稳定型,但林下幼苗、幼树相对较少.(2)华北落叶松种群死亡率和消失率曲线变化趋势基本一致,均出现两个高峰,一个出现在第11、12龄级阶段,另一个出现在第15龄级阶段;存活曲线趋于Deevey-Ⅱ型.(3)4个生存函数曲线表明,华北落叶松种群具有前期稳定、中后期锐减和末期衰退的特点.(4)种群动态的谱分析显示,华北落叶松种群动态除受基波影响外,还存在着明显的小周期波动,在第7龄级这一小周期波动与华北落叶松的高生长有关;在15龄级这一小周期波动与华北落叶松进入生理衰退期有关.     

连云港市枫树湾景区枫香种群结构与分布格局

城市风景林是现代园林城市的重要硬件,城市风景林的结构稳定和健康延续关系到城市的自然和谐,进而影响到城市的可持续发展。调查城市风景林的森林结构与空间分布特征,分析种质资源存在的生态问题及潜在风险,提出相应的调整和补救措施,对于提升城市风景林的景观质量,改善人居环境具有重要意义。通过野外调查,采用空间代替时间和相邻格子法,对连云港枫树湾景区枫香种群结构和分布格局进行了研究。结果表明,(1)连云港枫树湾森林群落为典型的落叶阔叶林,群落中枫香占绝对优势(重要值合计561.477),呈单一优势群落。(2)枫香种群的年龄结构呈现一定程度的偏态分布,多数样地径级结构不完整,且不同生境之间种群结构存在差异。种群内幼树幼苗整体不足,部分龄级个体缺失,存活曲线出现断点,种群呈现衰退型变化。(3)从静态生命表看,种群的Ⅰ、Ⅲ和Ⅹ龄级的死亡率(qx)为负值,而第Ⅶ龄级的死亡率较大(85%),个体存活率(ax)在Ⅰ龄级后总体上随径级的增大而减少。生命期望(ex)出现了多次波动,幼苗与壮龄阶段的生命期望值低于幼、中龄树。(4)利用负二项参数(K)、扩散系数(C)、扩散型指数(Iδ)、Cassie指标(Ca)、丛生指数(I)、平均拥挤度指数(m*)和聚块性指标(m*/m)等参数对种群空间格局进行了分析,表明枫香种群的空间分布格局为集群分布,但不同样地种群的集群程度存在一定差异。总体上看,枫树湾枫香种群趋于衰退,部分样地种内竞争激烈,建议进行适度疏伐,增进林内光照;而生境偏僻、林下灌草过于繁茂的地段,建议进行适量清杂,并实施人工植苗或辅助更新,促进种群的结构调整和健康演替。     

濒危植物脱皮榆种群结构与分布格局研究

对山西南部中条山和霍山脱皮榆的种群结构与分布格局进行了研究,其中根据大小结构图和存活曲线分析脱皮榆种群动态,应用扩散系数、聚集指数、平均拥挤度、聚块性指数、聚集强度、Cassie指数(1/K)、Poisson分布和负二项分布的χ2拟合检验等方法研究分布格局.结果表明,脱皮榆种群幼苗个体比例较大,总体上近于增长型种群.脱皮榆分布格局呈聚集型,这主要与物种本身的生物学和生态学特性密切相关,同时受群落内生境异质性的影响.图2表2参14     

中国特有珍稀濒危树种银缕梅种群结构和空间格局

选择浙江和安徽两地的银缕梅(Parrotia subaequalis)种群为研究对象,以空间序列代替时间变化的方法研究银缕梅种群结构,采用方差/均值比的t检验法进行分布格局的判定,并结合丛生指数(Ⅰ)、负二项参数(K)、Cassie指数(CA)和聚块性指数(IPA)分析聚集度.结果表明,银缕梅种群分布格局表现为由低龄级的集群分布向高龄级的随机分布过渡的趋势,但总体上呈集群分布,这主要与银缕梅种群的萌蘖繁殖方式、种内自疏及生境异质性有关.对种群龄级结构、种群存活曲线和静态生命表的分析,均反映出银缕梅种群结构波动性较大,稳定性差,更新能力不足,为衰退型种群.     

近自然生态恢复条件下杉木老龄林群落优势树种种群结构与空间格局

为探明杉木人工林生态系统在长时间近自然生态恢复条件下的优势种种群特征,应用相邻格子法对福建南平西芹教学林场75年生杉木老龄林群落优势树种种群结构与空间格局进行分析.结果表明:木荷、丝栗栲、刨花楠种群结构呈现反“J”型,属于增长型种群,杉木、细齿柃木种群呈现正“J”型,属于衰退型种群.在种群水平上,杉木呈现均匀分布,木荷、细齿柃木群落呈现聚集分布,刨花楠、丝栗栲呈现随机分布,且聚集程度,细齿柃木>木荷>刨花楠>丝栗栲>杉木.木荷种群大树阶段呈现随机分布,幼苗、幼树、中树均表现聚集分布;刨花楠、丝栗栲种群不同发育阶段均呈现聚集分布;细齿柃木幼苗阶段呈现聚集分布,幼树阶段呈现随机分布,中树阶段呈现均匀分布;且杉木和细齿柃木不同发育阶段的扩散系数随龄级的递增而变大.杉木老龄林正处于向地带性常绿阔叶林演替过程中的一个过渡阶段.综上表明:近自然生态恢复有效丰富了杉木老龄林群落的植被种类,在退化了的杉木人工林生态系统恢复和重建工作中,杉木的混交树种选择应优先考虑竞争力强的乡土树种,如木荷、刨花楠、丝栗栲等.     

濒危兰科植物流苏石斛的种群数量动态

运用静态生命表、生殖力表和Leslie矩阵模型,研究了云南西双版纳地区流苏石斛两个种群——A种群(21°58′N,101°13′E,保护区之外)和B种群(21°54′N,101°17′E,保护区内)的种群数量动态.结果表明:种群存活曲线表现为Deevey-型.A、B种群均表现出幼龄个体死亡率高,中龄级个体数量少,说明中龄阶段曾受到较大的人为干扰.种群的净增长率(Ro)、内禀增长率(rm)和周限增长率(λ)都较低,表现为衰退种群,Leslie矩阵模型分析表明在未来25年种群各龄级的个体数及种群总数均表现出持续下降趋势.种群下降可能是由于当地人为的采挖和严重的生境破碎化所导致.图2表4参16     

岷江上游刺旋花种群格局研究

在随机取样、解剖的基础上，对岷江上游灌丛优势种刺旋花（Convolvulustragacuthoiedes）建立种群静态生命表进行统计分析，以探索其在该地区特殊的生态学意义。结果表明：刺旋花种群的年龄结构为稳定发展型，存活曲线接近于decvyⅢ型；生活史中分别在1a和4～5a有两个死亡高峰；种群数量变化可用年龄结构模型Xx＝3．37·x－3．21（其中x表示年龄，Xx表示种群数量）来预测．X2检验法和区组样方方差法的格局分析结果都表明：刺旋花种群的分布格局随生境破碎程度和水分状况有很大差异，在不同样地分别趋向于随机分布和集群分布.     

塔里木河下游典型绿洲边缘物种多样性特征和种群分布格局

2008年夏季采用样带样方法对塔里木河下游典型绿洲边缘7个断面进行植被调查,采用α多样性指数(丰富度指数、Shannon-Wiener多样性指数、Simpson优势度指数和Pielou均匀度指数)和β多样性指数(Whittacker指数和Cody指数)分析环境梯度下种群多样性变化规律,利用种群分布格局指标(扩散系数、负二项参数、平均拥挤度、丛生指标和聚块性指标)定量分析绿洲边缘10个植物种群格局特征.结果表明:塔里木河下游典型绿洲边缘物种多样性特征受到土壤水分、盐分等因素限制,物种丰富度整体处于较低水平;α多样性指数表现为绿洲＞过渡带＞流动沙丘;从绿洲、过渡带到流动沙丘β多样性指数呈下降趋势;种群分布格局分析结果表明绿洲边缘10个植物种群均呈聚集分布,集群分布状态反映了干旱区植物种群对生存环境的适应特征.     

A resource-based approach to modelling the dynamics of interacting populations

The procedure for modelling the growth of single-species populations [Sakanoue, S., 2007. Extended logistic model for growth of single-species populations. Ecol. Model. 205, 159–168] is improved to be applicable to the study of the dynamics of interacting populations. The improved procedure is based on three assumptions: resource availability changes with population size as a variable, resource supply to populations and population demand for resources are defined as functions of resource availability and population size, and the variables of resource availability and population size shift in the supply function attracted to the demand function. These assumptions are organized into three equations. The equations can generate the dynamics models of plant, herbivore, and detritivore populations, and their own resources. The models can be used to describe prey–predator dynamics. They naturally contain nonlinear terms for the predator’s numerical and functional responses. Depending on the terms, the fluctuations in resource availability and population size stabilize. The three equations can also generate the dynamics models of different populations consuming the same resources. The analysis of zero isoclines of the models shows that a superior population can be simply defined as one with a higher intrinsic rate of natural increase, that a stable coexistence may be realized with the intraspecific interference or the interspecific facilitation of superiors, and that the interspecific interference or the intraspecific facilitation of inferiors may make the coexistence unstable and the inferiors winners depending on their initial population size.     

Characterizing the spatial structure of songbird cultures

Recent advances have shown that human-driven habitat transformations can affect the cultural attributes of animal populations in addition to their genetic integrity and dynamics. Here I propose using the song of oscine birds for identifying the cultural spatial structure of bird populations and highlighting critical thresholds associated with habitat fragmentation. I studied song variation over a wide geographical scale in a small and endangered passerine, the Dupont's Lark Chersophilus duponti, focusing on (1) cultural population structure, to determine a statistical representation of spatial variation in song and identify cultural units, and (2) the minimum patch size needed for an individual to develop a stable repertoire. I found that overall song diversity depends on variation among populations (beta-cultural diversity). Abrupt thresholds occurred in the relationships between individual song dissimilarity and geographic distance, and between individual song diversity and patch area. Spatial autocorrelation analysis showed that populations located as little as 5 km apart may have independently evolved their song traditions. Song diversity stabilized in patches as small as 100 ha supporting as few as 8-20 males. Song repertoires of smaller patches were significantly poorer. Almost one-quarter of the study populations inhabited patches <100 ha, and their cultural traditions appear to have eroded. The analysis of spatial patterns in birdsong may be a useful tool for detecting subpopulations prone to extinction.     

Stochastic population dynamics in populations of western terrestrial garter snakes with divergent life histories

Comparative evaluations of population dynamics in species with temporal and spatial variation in life-history traits are rare because they require long-term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978-1996 for six populations of western terrestrial garter snakes (Thamnophis elegans) from two evolutionarily divergent ecotypes. Three replicate populations from a slow-living ecotype, found in mountain meadows of northeastern California, were characterized by individuals that develop slowly, mature late, reproduce infrequently with small reproductive effort, and live longer than individuals of three populations of a fast-living ecotype found at lakeshore locales. We constructed matrix population models for each of the populations based on 8-13 years of data per population and analyzed both deterministic dynamics based on mean annual vital rates and stochastic dynamics incorporating annual variation in vital rates. (1) Contributions of highly variable vital rates to fitness (lambda(s)) were buffered against the negative effects of stochastic variation, and this relationship was consistent with differences between the meadow (M-slow) and lakeshore (L-fast) ecotypes. (2) Annual variation in the proportion of gravid females had the greatest negative effect among all vital rates on lambda(s). The magnitude of variation in the proportion of gravid females and its effect on lambda(s) was greater in M-slow than L-fast populations. (3) Variation in the proportion of gravid females, in turn, depended on annual variation in prey availability, and its effect on lambda(s) was 4 23 times greater in M-slow than L-fast populations. In addition to differences in stochastic dynamics between ecotypes, we also found higher mean mortality rates across all age classes in the L-fast populations. Our results suggest that both deterministic and stochastic selective forces have affected the evolution of divergent life-history traits in the two ecotypes, which, in turn, affect population dynamics. M-slow populations have evolved life-history traits that buffer fitness against direct effects of variation in reproduction and that spread lifetime reproduction across a greater number of reproductive bouts. These results highlight the importance of long-term demographic and environmental monitoring and of incorporating temporal dynamics into empirical studies of life-history evolution.     

Transient population dynamics in periodic matrix models: methodology and effects of cyclic permutations

Many biological populations are subject to periodically changing environments such as years with or without fire, or rotation of crop types. The dynamics and management options for such populations are frequently investigated using periodic matrix models. However the analysis is usually limited to long-term results (asymptotic population growth rate and its sensitivity to perturbations of vital rates). In non-periodic matrix models it has been shown that long-term results may be misleading as populations are rarely in their stable structure. We therefore develop methods to analyze transient dynamics of periodic matrix models. In particular, we show how to calculate the effects of perturbations on population size within and at the end of environmental cycles. Using a model of a weed population subject to a crop rotation, we show that different cyclic permutations produce different patterns of sensitivity of population size and different population sizes. By examining how the starting environment interacts with the initial conditions, we explain how different patterns arise. Such understanding is critical to developing effective management and monitoring strategies for populations subject to periodically recurring environments.     

Importance of Habitat Quality and Landscape Connectivity for the Persistence of Endangered Natterjack Toads

Abstract: The natterjack toad (Bufo calamita) is endangered in several parts of its distribution, including Belgium, where it occurs mainly in artificial habitats. We parameterized a general model for natterjack population viability analysis (PVA) and tested its sensitivity to changes in the values of basic parameters. Then we assessed the relative efficiency of various conservation measures in 2 situations: a small isolated population and a system of 4 populations connected by rare dispersal movements. We based the population viability analysis on a stage‐structured model of natterjack population dynamics. We parameterized the model in the RAMAS GIS platform with vital rates obtained from our own field experience and from published studies. Simulated natterjack populations were highly sensitive to habitat quality (particularly pond drying), to dispersal from surrounding local populations, and to a lesser extent to values of fecundity and survival of terrestrial stages. Population trajectories were nearly insensitive to initial abundances, carrying capacities, and the frequency of extreme climatic conditions. The simulations showed that in habitats with highly ephemeral ponds, where premetamorphosis mortality was high, natterjack populations nearly always had a very high extinction risk. We also illustrated how low dispersal rates (<1 dispersing individual/generation) efficiently rescued declining local populations. Such source‐sink dynamics demonstrate that the identification and management of source populations should be a high priority.     

Demography of central and marginal populations of monkeyflowers (Mimulus cardinalis and M. lewisii)

Every species occupies a limited geographic area, but how spatiotemporal environmental variation affects individual and population fitness to create range limits is not well understood. Because range boundaries arise where, on average, populations are more likely to go extinct than to persist, range limits are an inherently population-level problem for which a demographic framework is useful. In this study, I compare demographic parameters and population dynamics between central and marginal populations of monkeyflowers, Mimulus cardinalis and M. lewisii, along an elevation gradient spanning both species' ranges. Central and marginal populations of both species differed in survival and fecundity. For M. lewisii, these components of fitness were higher in central than in marginal populations, but for M. cardinalis the converse was true. To assess spatiotemporal variation in population dynamics, I used transition matrix models to estimate asymptotic population growth rates (lambda) and found that population growth rates of M. lewisii were highest at the range center and reduced at the range margin. Population growth rates of M. cardinalis were highest at the range margin and greatly reduced at the range center. Life table response analysis decomposed spatiotemporal variation in lambda into contributions from each transition between life stages, finding that transitions from large nonreproductive and reproductive plants to the seed class and stasis in the reproductive class made the largest contributions to spatial differences in lambda. These transitions had only low to moderate sensitivities, indicating that differences in projected population growth rates resulted mainly from observed differences in transition matrix parameters and their underlying vital rates.     

Increased germination of diverse crop-wild hybrid sunflower seeds.

Gene flow from crop fields to wild populations produces hybrids that often differ from their wild counterparts in growth form, phenology, and life history characteristics. Germination and dormancy dynamics have a strong influence on population persistence, competitive dynamics, and ultimately, plant fitness. They may also play a role in modifying crop gene introgression, which has been of primary interest since the release of transgenic crops. We investigated how seed germination and dormancy were affected by sunflower crop wild hybridization in both laboratory and field experiments. Hybridization increased seed germination and decreased dormancy. Of the nine wild populations we assayed, most of their hybrids had higher germination than the wilds of the same population. However, absolute germination levels varied by population and testing environment. Hybrids produced by three different crop lines differed in germination, and their germination rankings shifted across populations. Increased germination in hybrids could accelerate crop gene introgression, provided that hybrids germinate in an appropriate period. Differences in relative germination of wild and hybrid seed indicated that the effect of germination on introgression will likely vary by population due, in part, to initial levels of dormancy in the population. Therefore, the implications of gene flow from crops with novel characteristics or from transgenic crops will also vary by population.     

Genetic determination and plasticity in the sun orientation of natural populations ofTalitrus saltator

As has been previously shown, talitrid crustaceans have an inherited compass which causes them to head in a direction appropriate to their original shoreline (even after several generations in the laboratory), while learnt components can improve the correctness of orientation in natural conditions. In order to extend this analysis to a greater range of populations and to show differences in the determination of direction finding behaviour, seven natural populations ofTalitrus saltator (Montagu) from differently oriented shores of the Ligurian (Marina di Vecchiano, Pisa), Tyrrhenian (Castiglione della Pescaia and Tombolo di Feniglia, Grossetto) and Adriatic (Casal Borsetti, Ravenna; Torre Fantine, Marina di Lesina and Lido di Siponta, Foggia). Italian coasts were compared for their rigidity-plasticity in sun orientation. The study was conducted from 1982 to 1985. Differences were given in relation to the dynamics of the shorelines, the stability of which changes over the years due to natural and artificial causes. Furthermore, in order to reveal something about the genetic determination of the compass, mass-crosses between geographically distant populations (Ligurian-Tyrrhenian on one side and Adriatic on the other) were performed, and the F1 and F2 inexpert offspring tested for sun orientation. The results show a partial or total disruption of the compass in cross offspring which is discussed in the light of oligogenic and polygenic transmission mechanisms.     

Modeling the Effect of Population Dynamics on the Impact of Rabbit Hemorrhagic Disease

Abstract:  The European wild rabbit ( Oryctolagus cuniculus ) is a staple prey species in Mediterranean ecosystems. The arrival and subsequent spread of rabbit hemorrhagic disease throughout southwestern Europe, however, has caused a decline in rabbit numbers, leading to considerable efforts to enhance wild rabbit populations, especially through habitat management. Because rabbit population dynamics depend on habitat suitability and changes in habitat structure and composition subsequent to habitat management, I evaluated the effects of population dynamics on the long-term impact of rabbit hemorrhagic disease on rabbit populations. I used an age-structured model with varying degrees of population productivity and turnover and different habitat carrying capacities, and I assumed the existence of a unique, highly pathogenic virus. My results suggest that disease impact may be highly dependent on habitat carrying capacity and rabbit population dynamics, and the model provided some insight into the current abundance of wild rabbits in different locations in southwestern Europe. The highest disease impact was estimated for populations located in habitats with low to medium carrying capacity. In contrast, disease impact was lower in high-density populations in habitats with high carrying capacity, corresponding to a lower mean age of rabbit infection and a resulting lower mortality from rabbit hemorrhagic disease. The outcomes of the model suggest that management strategies to help rabbit populations recover should be based on improving habitats to their maximum carrying capacity and increasing rabbit population productivity. In contrast, the use of strategies based on temporary increases in rabbit density, including vaccination campaigns, translocations, and temporal habitat improvements at medium carrying capacities, may increase disease impact, resulting in short-term decreases in rabbit population density.