海三棱藨草种群的密度与生物量动态

本文研究了上海市南汇县东海农场海堤外侧滩涂上海三棱藨草种群的密度动态、高度生长动态、生物量动态以及它们之间及其与环境之间的相互关系。研究结果表明:在环境条件相对稳定的地带A和B内,海三棱藨草种群的高度、高度生长和生物量在生长期内符合Logisfis增长。种群生物量动态与密度动态可分为3个阶段,其中阶段Ⅱ符合Yoda等提出的-3/2自疏定律。地带B为海三棱藨草种群生长的最适地带。地带C内生境条件极不稳定,种群的数量动态变化亦相当剧烈。在不同环境条件下,密度制约因素和非密度制约因素对种群数量动态的相对作用是不同的。在环境条件较稳定的生境中(地带A和B),密度制约因素是决定种群数量动态的主要因素;在环境条件变化剧烈的生境中(地带C),非密度制约因素是决定种群数量动态的主要因素。     

海三棱藨草种群的物候与分布格局研究

海三棱藨草群落是生长在海岸带滩涂原生裸地上的原生植被,在上海地区分布面积达20多万亩。本项工作研究了上海市南汇县东海农场海堤外侧滩涂上海三棱藨草种群的物候和分布格局。根据滩涂高程以及海三棱藨草种群生长状况,可以划分成三个地带,即地带A,海三棱藨草与芦苇群落交错区;地带B,海三棱藨草种群生长最适的中潮位地带;地带C,梅三棱藨草种群定居地带。由于三个地带内,生境条件不同,海三棱藨草种群的物候有明显差异。从地带A至C,海三棱藨草种群的分布格局依次为随机分布、均匀分布和随机分布或群聚分布。其空间分布格局在随时间变化的同时也在空间上改变其位置。     

海三棱蔍草种群的物候与分布格局研究

海三棱藨草群落是生长在海岸带滩涂原生裸地上的原生植被,在上海地区分布面积达20多万亩。本项工作研究了上海市南汇县东海农场海堤外侧滩涂上海三棱藨草种群的物候和分布格局。根据滩涂高程以及海三棱藨草种群生长状况,可以划分成三个地带,即地带A,海三棱藨草与芦苇群落交错区;地带B,海三棱藨草种群生长最适的中潮位地带;地带C,海三棱藨草种群定居地带。由于三个地带内,生境条件不同,海三棱藨草种群的物候有明显差异。从地带A至C,海三棱藨草种群的分布格局依次为随机分布、均匀分布和随机分布或群聚分布。其空间分布格局在随时间变化的同时也在空间上改变其位置。     

密度对三种莎草科植物克隆生长的影响

以三种莎草科克隆植物藨草(Scirpus triqueter), 海三棱藨草(Scirpus mariqueter)和糙叶苔草(Carex scabrifolia)为研究对象, 通过盆栽受控实验, 探讨三种初始种植密度处理(1 株/盆、4 株/盆和16 株/盆)对个体表现与种群增长的影响。结果表明, 三种植物种群经过一个月左右的适应后均开始加速增长, 生长季后期增长率逐渐降低, 而海三棱藨草种群甚至出现了一定程度的衰退。生长季中前期藨草在中低密度处理下密度增长率高于高密度和整簇种植处理, 而海三棱藨草、糙叶苔草种群的整体密度增长与初始种植密度成反比。最终收获时, 藨草和海三棱藨草不同处理下的密度、冠层高度、最高高度、地上生物量和地下生物量均没有显著差异, 糙叶苔草在低种植密度下的密度最低, 中等种植密度下冠层高度最高。藨草、海三棱藨草的单株平均生物量与密度呈显著负相关, 而藨草、糙叶苔草的总生物量与密度呈显著正相关, 三种莎草科植物的根冠比都没有随密度发生显著变化。三种莎草科植物在高密度下的种内竞争效应均强于中密度。     

互花米草与海三棱藨草的生长特征和相对竞争能力

外来物种互花米草(Spartinaalterniflora)已对我国特有种海三棱藨草 (Scirpusmariqueter)发生了竞争取代。作者通过在长江口崇明东滩湿地取样和盆栽竞争实验,比较了二者的主要生长特征和种间相对竞争能力。结果表明:无论是先锋种群还是成熟种群,互花米草的高度、盖度、地上生物量、地下生物量和平均每花序种子数都显著大于海三棱藨草;海三棱藨草的密度和单位面积结实枝条数显著大于互花米草。两种植物成熟种群的单位面积种子产量和种子的萌发率没有显著差异。种内竞争和种间竞争显著降低了两种植物的平均每株产生的无性小株数、结实株数、地上生物量和地下球茎数(海三棱藨草产生球茎),互花米草的种间竞争能力 (相对邻里效应指数 )显著大于海三棱藨草。互花米草在生长上的优势可能导致其在种间竞争上的优势,从而使互花米草能够在海三棱藨草群落中成功入侵。     

长江口九段沙湿地海三棱藨草生物量分配特征及其影响因子

海三棱藨草(Scirpus mariqueter)为长江河口盐沼湿地先锋植物。以长江口九段沙湿地为主要研究区域,在江亚南沙、上沙、中下沙等不同区域设置固定站点,进行植被和环境因子的取样调研,分析研究了海三棱藨草的生物量分配特征及其主要影响因子,以期为海三棱藨草的培育与恢复、盐沼湿地生态系统的保护与利用提供科学依据。结果表明:(1)不同站点海三棱藨草的茎基高度、球茎生物量占比、根茎与球茎之比均不存在显著差异(P0.05),而植株密度、植株高度、根茎生物量占比、果实生物量占比、茎叶生物量占比、须根生物量占比、果实与根茎之比、果实与球茎之比在不同站点间存在显著差异(P0.05);(2)不同站点的沉积物电导率、盐度、容积密度(5—10、25—30 cm土层)、总碳含量(10—15、20—25、25—30 cm土层)、总氮含量(5—10 cm土层)存在显著差异(P0.05);(3)海三棱藨草的果实与根茎的生物量之比和沉积物5—10、25—30 cm总碳含量,0—5、5—10 cm总氮含量,0—5 cm容积密度,茎基高度6种因子的组合存在极显著相关(P0.01);而其他生物量分配指标与本文涉及到的环境因子、植物表形参数均不存在显著相关性(P0.05)。海三棱藨草生物量分配特征是其自身生长特征与环境因子综合作用的结果。在今后的研究中需拓展生境因子涵盖范围,深入分析多因子综合作用对海三棱藨草生物量分配特征的影响。     

互花米草与海三棱蔗草的生长特征和相对竞争能力

外来物种互花米草(Spartina alterniflora)已对我国特有种海三棱蔗草(Scirpus mariqueter)发生了竞争取代。作者通过在长江口崇明东滩湿地取样和盆栽竞争实验,比较了二者的主要生长特征和种间相对竞争能力。结果表明：无论是先锋种群还是成熟种群,互花米草的高度、盖度、地上生物量、地下生物量和平均每花序种子数都显著大于海三棱蔗草;海三棱蔗草的密度和单位面积结实枝条数显著大于互花米草。两种植物成熟种群的单位面积种子产量和种子的萌发率没有显著差异。种内竞争和种间竞争显著降低了两种植物的平均每株产生的无性小株数、结实株数、地上生物量和地下球茎数(海三棱蔗草产生球茎),互花米草的种间竞争能力(相对邻里效应指数)显著大于海三棱蔗草。互花米草在生长上的优势可能导致其在种间竞争上的优势,从而使互花米草能够在海三棱蔗草群落中成功入侵。     

海三棱藨草及互花米草对模拟盐胁迫的响应及其耐盐阈值

盐度作为滨海湿地的关键环境因子之一,影响盐沼植物的存活、生长及分布。未来海平面上升引起的盐水入侵,将导致滨海湿地的盐沼植物面临高盐胁迫的挑战,进而影响滨海湿地生态系统的结构和功能。本研究选择长江口中低潮滩的主要先锋植物海三棱藨草(Scirpus mariqueter)和互花米草(Spartina alterniflora)为对象,通过人工控制实验,比较不同盐度处理下两种盐沼植物存活、营养生长及繁殖的响应,并确定两种盐沼植物存活的耐盐阈值,从而比较未来盐水入侵背景下,本地物种海三棱藨草及外来物种互花米草对盐胁迫的响应和适应性。结果表明:(1)海三棱藨草和互花米草的存活率随着盐度的增加均呈下降趋势,相同盐度处理下互花米草的存活率显著高于海三棱藨草的存活率(P0.05);(2)盐胁迫明显影响了海三棱藨草和互花米草的生长,随着盐度的增加,海三棱藨草株高、地上生物量及地下生物量均呈逐渐下降的趋势,而互花米草株高、地上生物量及地下生物量呈先增加后下降的趋势,均在盐度为10‰时最高;(3)海三棱藨草和互花米草的分蘖数及结穗率均随着盐度增加呈下降趋势,盐胁迫在一定程度上抑制了两种植物的繁殖能力;(4)互花米草存活的耐盐阈值为43‰,高于海三棱藨草存活的耐盐阈值(21‰);(5)外来物种互花米草比本地物种海三棱藨草具有更强的耐盐性,未来海平面上升引起的盐水入侵将对本地物种海三棱藨草产生更加严重的影响。     

盐度及种间相互作用对海三棱藨草、互花米草萌发及生长的影响

盐度和种间作用是影响湿地植物群落构建的关键因子。然而,已有研究主要集中于植物成体阶段,我们对生活史早期更新阶段的种间相互作用了解十分有限。崇明东滩国家级自然保护区是位于长江口的重要湿地,外来入侵植物互花米草对优势土著物种海三棱藨草的竞争排斥对当地生态系统造成了严重的负面影响。通过受控实验探讨了盐度及种间作用对海三棱藨草和互花米草种子萌发及生长的影响,以深入了解更新过程在盐沼湿地植物群落构建中的作用。结果表明,在培养皿中盐度对海三棱藨草的萌发有显著抑制作用,互花米草的萌发率受盐度影响不显著但萌发进程被延迟。混种处理对两者的萌发存在一定促进效应,且其作用强度受到盐度的调控。海三棱藨草与互花米草种子在萌发阶段的相互促进并非是通过化感作用实现的,可能是由于萌发过程对盐分的吸收减弱了盐胁迫的影响。盆栽条件下,两物种混种时的萌发及生长表现（高度、地上生物量）较单种时有所下降,但差异不显著。种间竞争受环境胁迫程度及生活史阶段的影响,竞争作用在胁迫较弱的淡水环境及生活史后期更强。盐沼湿地植物群落在形成早期受到盐度等环境因子的影响较大,不同植物对盐胁迫的响应是影响种群建成的主导因素,后期种间竞争的重要性不断增加,最终决定了植物群落的整体格局。     

不同生境下假臭草生长特征分析

通过测定庄稼地、弃耕地、桉树林、公路边4种生境下假臭草叶面积(LA)、比叶面积(SLA)、LDMC和株高等形态特征、植株各构件生物量及生物量分配比和假臭草种群盖度、密度等种群数量性状,研究不同生境类型下假臭草个体的形态特征、生物量及生物量分配和种群生长状况的差异。结果表明:光照和土壤养分对假臭草的形态特征、生物量及生物量分配和种群数量性状的影响显著;低光照、高土壤养分生境下假臭草的LA、SLA、株高较高,假臭草叶片的LDMC较小,植株的花序数较少,生物量主要向叶和茎器官进行分配,根和花果器官的生物量分配则受到限制;高光照、养分贫瘠生境下假臭草的LA、SLA、株高较低,假臭草叶片的LDMC较大,生物量主要向根和花果器官进行分配,种群的盖度、密度、生物量和高度等种群数量性状较低,种群生长状况较差;高光照、肥沃养分生境为假臭草的最适生境,假臭草构件的资源配置较为优化,株高、基径粗、冠宽和花序数等形态指标较大,种群盖度、密度、生物量等种群数量性状较大,种群生长较好。     

Non-additive and non-stationary properties in the spatial distribution of a large marine fish population

Density-independent and density-dependent variables both affect the spatial distributions of species. However, their effects are often separately addressed using different analytical techniques. We apply a spatially explicit regression framework that incorporates localized, interactive and threshold effects of both density-independent (water temperature) and density-dependent (population abundance) variables, to study the spatial distribution of a well-monitored flatfish population in the eastern Bering Sea. Results indicate that when population biomass was beyond a threshold a further increase in biomass-promoted habitat expansion in a non-additive fashion with water temperature. In contrast, during years of low population size, habitat occupancy was affected positively only by water temperature. These results reveal the spatial signature of intraspecific abundance distribution relationships as well as the non-additive and non-stationary responses of species spatial dynamics. Furthermore, these results underscore the importance of implementing analytical techniques that can simultaneously account for density-dependent and density-independent sources of variability when studying geographical distribution patterns.     

The cost of habitat selection in prairie voles: an empirical assessment using isodar analysis

The ideal free distribution assumes that habitat selection is without cost and predicts that fitness should be equal in different habitats. If habitat selection has a cost, then individuals should only move to another habitat when potential fitness in the new habitat exceeds that in the source habitat by an amount greater than the cost of habitat selection. We used isodar techniques to assess the cost of habitat selection. In an experimental landscape, we monitored density, movement, and reproductive success of adult female prairie voles, Microtus ochrogaster, in adjacent paired habitats with low and high cover. We tested the following hypotheses: (1) adult female prairie voles exhibited density-dependent habitat selection; (2) the cost of habitat selection was density-independent. Habitat quality based on population density and fitness of adult females was higher in high cover habitats. Net movement was from low cover to high cover habitats. The results indicated that adult female prairie voles exhibited density-dependent habitat selection. Furthermore, there was a significant cost of habitat selection, and the cost was density-independent.     

Temperature change and complex dynamics

Density-dependent factors, such as population growth rate and migration, influence dynamic behaviour in ecological models. Temperature, an abiotic and density-independent factor, is also an important determinant of insect population growth. We investigated the endogenous dynamics of a density-dependent response-surface model that included temperature, based on time series for two aphid species. We investigated the effects of temperature and random noise on the model dynamics. In most cases, an increase in temperature resulted in a higher predicted equilibrium density; it could induce complex dynamics. Noise at the level of the natural variation in temperature resulted in extinctions in some models. Our results from these models indicate that aphid populations might become more abundant, and less stable in some circumstances, if there is climate warming. Received: 25 November 1996 / Accepted: 30 June 1997     

Population variability among three small mammal species in the semiarid Neotropics: the role of density-dependent and density-independent factors

We addressed the role of density-dependent (direct and delayed) and density-independent (precipitation) factors in shaping the dynamics of fluctuating populations of three small mammal species. Using a stepwise regression procedure, we tested the effects of nonlagged population density (log₁₀ N_t-1), lagged population density (log₁₀ N_t-2), and annual precipitation on the per capita rate of population change of Phyllotis darwini, Akodon olivaceus , and Thylamys elegans in two habitat types of a semiarid region of Chile. The most irruptive species ( P. darwini ) showed direct and delayed density-dependent effects in equatorial subpopulation, and only direct density-dependence in polar subpopulation. The per capita rates of population change of A. olivaceus showed direct density-dependent and precipitation effects in both habitats types, while T. elegans showed direct density-dependence and precipitation effects in the equatorial subpopulation but only a marginal effect of direct density-dependence in the polar subpopulation. The presence of delayed density-dependent strongly suggests the importance of biological interactions in shaping the dramatic irruptions exhibited by P. darwini.     

Population fluctuations and regulation in great snipe: a time-series analysis

1. During the last centuries, the breeding range of the great snipe Gallinago media has declined dramatically in the western part of its distribution. To examine present population dynamics in the Scandinavian mountains, we collected and analysed a 19-year time series of counts of great snipe males at leks in central Norway, 1987-2005. 2. The population showed large annual fluctuations in the number of males displaying at lek sites (range 45-90 males at the peak of the mating season), but no overall trend. 3. We detected presence of direct density-dependent mechanisms regulating this population. Inclusion of the density-dependent term in a Ricker-type model significantly improved the fit with observed data (evaluated with Parametric Bootstrap Likelihood Ratio tests and Akaike's Information Criterion for small sample size). 4. An analysis of (a number of a priori likely) environmental covariates suggests that the population dynamics were affected by conditions influencing reproduction and survival of offspring during the summer, but not by conditions influencing survival at the wintering grounds in Africa. This is in contrast to many altricial birds breeding in the northern hemisphere, and supports the idea that population dynamics of migratory nidifugous birds are more influenced by conditions during reproduction. 5. Inclusion of these external factors into our model improved the detectability of density dependence. This illustrates that allowing for external effects may increase statistical power of density dependence tests and thus be of particular importance in relatively short time series. 6. In our best model of the population dynamics, two likely density-independent offspring survival covariates explained 47.3% of the variance in great snipe numbers (predation pressure estimated by willow grouse reproductive success and food availability estimated by the amount of precipitation in June), whereas density dependence explained 35.5%. Demographic stochasticity and unidentified environmental stochasticity may account for the remaining 17.2%.     

Multiple sources of evidence for density dependence in the endangered Hawaiian stilt (Himantopus mexicanus knudseni)

Hawaiian stilts (Himantopus mexicanus knudseni) are an endangered subspecies of the Black-necked stilt endemic to the Hawaiian Islands. Despite long-term study, the main drivers of Hawaiian stilt population dynamics are poorly understood. We tested for density dependence using two sources of evidence: a 30-year time series of annual estimated range-wide abundance, and two 15+ year time series of reproductive success. Using separate methods with independent data, sources allowed us to make up for the potentially positive bias of one approach with the more conservative nature of the second. We compared nonlinear density-dependent and density-independent population model fits to our time-series data, using both frequentist and Bayesian state-space approaches. Across both approaches, density-dependent models best fit observed population dynamics, with lower AICc and cross-validation statistics compared to density-independent models. Among density-dependent models, a conditional model in which density-independent dynamics occur below a population size threshold (~850–1,000 birds), and then density-dependent dynamics occur above that threshold, performed best across Bayesian and frequentist model comparisons, with the Ricker model ranked next or equivalently. Our analysis of reproduction data revealed a strong negative effect of local adult density on nest success (proportion of nests hatching at least one chick) at Kealia National Wildlife Refuge on Maui, where few alternative breeding habitats are available, but no such effect at another site where many nearby alternative wetlands are available. These congruent results across independent datasets and analytical approaches support the hypothesis that Hawaiian stilts exhibit density dependence across their range.     

桤柏混交林种群生物量动态与密度调节

研究了四川省盐亭县桤柏混交林中桤木和柏木种群的生物量动态、密度动态及 种群密度对生物量动态的调节．结果表明,桤木种群生物量在１８ ａ内符合逻辑斯蒂增长, 柏木种群生物量在２０ ａ内呈幂函数增长．而种群密度在 １８ ａ内均呈负幂函数降低在桤 柏混交林中．密度制约是决定种群生物量动态的主要因素,棺木和柏本平均单株生物量较 符合Ｙｏｄａ提出的－３／２自疏定律为快,其自疏系数分别为一２．３３和一３．９７．个体平均生 物量的增长比由密度下降引起的生物量降低快,因此,两种群生物量在密度调节过程中仍 然保持增长状态．其中柏木是生物量增长旺盛的种群．     

荒漠草原异质生境下猪毛蒿种群动态

以荒漠草原猪毛蒿种群为对象,设置风沙土、灰钙土和基岩风化沉积土3个生境下增水30%、减水30%和对照3个处理,编制猪毛蒿种群的动态生命表,绘制种群存活和死亡曲线,分析异质生境下猪毛蒿种群动态规律,研究猪毛蒿年内年际间种群动态特征.结果表明: 猪毛蒿种群存活曲线趋于Deevey-Ⅰ型,即生长前期存活率较高,趋于稳定状态,死亡率基本维持在较低的水平,生育期末种群死亡率则上升较快.各生境下猪毛蒿个体的存活数均呈前期波动后期下降的趋势,风沙土和灰钙土生境下死亡率的波动变幅较大,增减水处理对猪毛蒿种群死亡率的影响无显著差异.土壤类型对猪毛蒿株高、冠幅、密度、盖度和生物量均有显著影响,降水处理对猪毛蒿株高、冠幅和盖度影响显著,对密度和生物量无显著影响,而土壤类型和降水处理的交互作用仅对株高和冠幅有显著影响.基岩风化沉积土生境下猪毛蒿生物量的可塑性指数显著高于风沙土和灰钙土,灰钙土和基岩风化沉积土生境下盖度可塑性显著高于风沙土.增水处理的密度可塑性指数显著高于对照和减水处理.株高和冠幅的可塑性指数较高,说明在不同的生境压力下,猪毛蒿可以通过优先调节这两个参数来应对生境的变化.     

Relative roles of density-dependent and density-independent factors in population dynamics of British deer

It has become increasingly clear that both density-dependent and density-independent factors may influence the dynamics of mammalian populations; it remains more difficult, however, to determine which factors may play the more significant role in influencing population number in any particular case. In this paper we review published and unpublished data in an analysis of the various factors affecting population size and trend in three European species of deer: Red Deer ( Cervus elaphus ), Fallow Deer ( Dama damd ) and Roe Deer ( Capreolus capreolus). We select these species deliberately because they span a range of body size and reproductive strategy - it seems that different demographic parameters might thus play different roles in the dynamics of the three-which may also be differentially sensitive to the effects of density-dependent and density-independent factors. For each species we examine the available evidence to determine the relative roles and effects of density-dependent feedback mechanisms and density-independent factors such as climate on recruitment and mortality.
Despite differences in bionomic strategy between Red Deer (as essentially a K -strategist) and the more r-selected Roe, few differences emerge between the three species in the relative roles of density-dependent and density-independent factors - or of the stage at the life cycle at which each factor may act. Overall, however, it is clear that variation in density-independent factors, such as climate, appears primarily to affect levels of mortality within a population, while effects of density are particularly marked in relation to changes in recruitment.     

Inter- and intra-specific patterns of density dependence and population size variability in Salmoniformes

Population dynamics are typically affected by a combination of density-independent and density-dependent factors, the latter of which have been conceptually and theoretically linked with how variable population sizes are over time—which in turn has been tied to how prone populations are to extinction. To address evidence for the occurrence of density dependence and its relationship with population size variability (pv), we quantified each of these for 126 populations of 8 species of Salmoniformes. Using random-effects models, we partitioned variation in the strength of density dependence and the magnitude of pv between and within species and estimated the correlation of density dependence and population size variability at both the between- and within-species levels. We found that variation in the strength of density dependence was predominately within species (I ² = 0.47). In contrast, variation in population size variability was distributed both between and within species (I ² = 0.40). Contrary to theoretical and conceptual expectations, the strength of density dependence and the magnitude of population size variability were positively correlated at the between species level (r = 0.90), although this estimate had 95 % credibility intervals (Bayesian analogues to confidence intervals) that overlapped zero. The within-species correlation between density dependence and population size variability was not distinguishable from zero. Given that density dependence for Salmoniformes was highly variable within species, we next determined the joint effects of intrinsic (density-dependent) and extrinsic (density-independent) factors on the population dynamics of a threatened salmonid, the Lahontan cutthroat trout (Oncorhynchus clarkii henshawi). We found that density-dependent and -independent factors additively contributed to population dynamics. This finding suggests that the observed within-species variability in density dependence might be attributable to local differences in the strength of density-independent factors.