尺度与密度:测定不同尺度下的种群密度

群落中的种群密度由于空间尺度的变化而存在着一定差异,那么,某一种群的密度随着空间尺度的变化会发生怎样的变化?抑或某一物种相对于另一物种而言,随着空间尺度的变化其密度会怎样变化?这是与尺度有关的种群密度问题,当属生态学的基本问题.该文提出这样的问题,并把不同尺度下的种群密度称之为尺度密度(scale density).O-Ring函数的实质是计算不同尺度下的种群密度.因此,在研究实例中,应用O-Ring函数计算了典型草原处于不同恢复阶段的羊草(Leymuschinensis)种群、米氏冰草(Agropyron michnoi)种群,以及米氏冰草种群相对于羊草种群在不同尺度下的种群密度,结果发现:羊草和米氏冰草2个种群的尺度密度,在小尺度范围内严重退化群落均高于恢复演替群落,这一结果验证了“胁迫梯度假说”,同时表明该结果是放牧胁迫下正相互作用所致;通过比较羊草种群与米氏冰草相对于羊草的尺度密度发现,在严重退化的群落中,羊草与米氏冰草的种间关联为负联结,这种负联结是由正相互作用引起的,而在恢复8年和恢复21年群落中,二者之间是正联结,当为竞争所致.该实例说明分析种群密度随尺度变化的规律对于深入认识生态学问题可能会有很大帮助.     

Vertical distribution pattern of mixed root systems of desert plants Reaumuria soongarica and Salsola passerina under different environmental gradients

植物种间相互作用及其对环境胁迫的响应一直是物种共存和生物多样性维持研究的一个热点, 从地下根系入手来探讨混生群落植物种间关系及其对环境胁迫响应的研究少见报道。该文以荒漠草原区(灵武)、典型荒漠区(张掖)和极端荒漠区(酒泉) 3个不同生境条件下单生与混生红砂(Reaumuria soongarica)和珍珠猪毛菜(Salsola passerina)为实验材料, 采用分层取样法对其垂直根系参数进行测定和分析, 探讨了两种植物根系分布对混生及荒漠环境梯度的响应。结果表明: 同一生境条件下, 混生红砂和珍珠猪毛菜比根长和比表面积均高于单生, 说明红砂、珍珠猪毛菜混生后其根系相互作用关系表现为互惠, 促进了植株对土壤养分和水分的吸收。不同生境条件下, 同一生长方式的红砂根系分布深度均大于珍珠猪毛菜, 且根系消弱系数也普遍高于珍珠猪毛菜, 说明二者在不同生境条件下占据不同生态位, 红砂表现为深根性, 根系位于土壤深层, 珍珠猪毛菜表现为浅根性, 根系分布于土壤浅层。随着荒漠环境胁迫增强, 单生和混生红砂与珍珠猪毛菜的比根长和比表面积均呈现出极端荒漠区>典型荒漠区>草原荒漠区的规律, 且生境越干旱, 混生群落根系分离越明显; 单生与混生红砂根系消弱系数也逐渐增大, 在极端干旱区达到最大值, 珍珠猪毛菜变化不大, 表明红砂-珍珠猪毛菜混生群落根系生态位分离随荒漠环境胁迫增强而加大, 验证了环境胁迫梯度假说。可见“地上聚生, 地下分离”的混生方式可能是红砂-珍珠猪毛菜混生群落适应干旱胁迫环境的生长策略。     

是理信息系统与基于个体的空间直观景观模型

对空间直观的生态现象进行模拟的方法有多种 ,如反应扩散模型 (reaction- diffusion models) ,斑块模型 (patch models)等。这些方法已被应用到植物种群和群落 [13]以及动物种群 [16]的研究中。此外 ,还有一种方法是基于个体的模型方法 (individual-based models) (IBMs) ,它是一种基于有机体的模型(organism- based models) ,具有模拟个体间的差异和个体间相互作用的能力。模型的建立基于两条基本的生物学原理 ,由于遗传和环境的差异 ,有机体个体在生理和行为上的表现是不同的 ;有机体受与其相邻的周围其它有机体的影响最大。地理信息系…     

高阶相互作用对宿主-寄生群落动态的影响

物种间相互作用是影响生物群落稳定性和多样性的重要因素。基于Lotka-Volterra竞争模型,通过构建多宿主种群的种内和种间高阶相互作用模型,研究宿主种群的间接竞争效应对寄生群落动态的影响机制。为有效地揭示高阶作用对种群动态的影响,通过对比宿主-寄生群落的现象模型以及机制模型,利用机制模型产生的合理数据集对现象模型中高阶项的参数进行拟合,进而探讨了高阶相互作用在群落动态中的作用。结果显示,完整的高阶相互作用模型在描述多宿主-寄生系统的群落动态中表现最优,而直接相互作用模型对群落动态的描述相对较差,即同时考虑种间和种内的高阶相互作用模型更加符合机制模型所描述的群落动态。此外,种内高阶作用和种间高阶作用产生不对称效应,宿主间的种间高阶作用对群落产生的影响较种内高阶作用更为显著。该研究结果在一定意义上丰富了宿主-寄生生物群落的稳定性研究,为理解物种间相互作用的多样性研究提供了依据。     

Branching and metabolic exponents in seven woody plants

West、Brown和Enquist提出的植物分形网络模型(简称WBE模型)认为: 植物的分支指数(1/a, 1/b)决定植物的代谢指数, 当分支指数1/a、1/b分别为理论值2.0、3.0时, 代谢速率与个体大小的3/4次幂成正比, 但是恒定的3/4代谢指数并不能全面地反映植物的代谢情况。基于分支指数的协同变化, Price、Enquist和Savage对WBE模型进行扩展, 提出植物分支参数协同变化模型(简称PES模型)。该文借助于PES模型分析了7种木本植物的分支指数和代谢指数。结果表明: 物种间叶面积与叶生物量呈异速生长关系, 基于叶面积得到的分支指数1/a和代谢指数θ在物种间无显著差异, 基于叶生物量得到的分支指数1/a、1/b和代谢指数θ在物种间均存在显著差异, 但基于叶面积和叶生物量分别拟合出的整体分支指数1/a、1/b和代谢指数θ与理论值均无显著差异, 且用叶面积作为代谢速率的替代指标比用叶生物量分析得出的代谢指数与理论值更接近。今后研究应当关注植物叶面积与叶生物量的异速生长关系对植物代谢速率及相关功能特性的影响。     

植物邻体间的正相互作用

植物间的正负相互作用是构建植被群落的重要因素,也是群落生态学研究的中心内容之一。近20a来,植物间正相互作用的研究得到快速发展。综述了正相互作用的定义,不同植物群落中的直接、间接正相互作用及其发生机制,正相互作用研究的实验和模型方法,正负相互作用随胁迫梯度的变化及正相互作用对群落构建的影响。探讨了正相互作用研究前景:(1)进一步理解正负相互作用的平衡及其对群落构建的影响;(2)加深对全球变暖背景下的正相互作用的认识;(3)需把正相互作用研究同进化联系起来;(4)充分发挥正相互作用在生态系统中的推动力作用,把正相互作用应用到生态恢复中,为恢复退化生态系统服务。     

沿干旱梯度小叶锦鸡儿灌丛化对草本植物叶片矿质元素浓度及地上生物量累积的影响

草原灌丛化通过改变物种之间的相互作用深刻影响着群落的结构和功能。然而，当前有关灌木如何影响不同功能群草本植物对矿质元素吸收和累积的研究仍明显不足。在内蒙古草原沿干旱梯度选取了4个研究地点，对比分析了小叶锦鸡儿(Caragana microphylla)灌丛斑块内和斑块外群落中禾草和非禾草功能群植物叶中矿质元素浓度以及地上生物量生产的差异，旨在阐明干旱和灌木对群落草本植物叶元素累积的影响，揭示灌草间相互作用的元素利用特征及其随干旱梯度的变化。结果显示：1)随干旱加剧，灌丛斑块内的非禾草功能群植物地上生物量保持恒定，但叶中的K、Ca、Mg、Fe、Mn和Cu元素浓度显著增加(P<0.05)。该结果表明群落中的非禾草功能群植物通过提高叶中的矿质元素水平来抵御和适应干旱胁迫。2)随干旱加剧，灌丛对非禾草功能群植物地上生物量，叶中Ca、Fe、Cu和Zn,禾草功能群植物叶中的P的累积影响从负(RII<0)或中性(RII=0)转变为正效应(RII>0)。该结果与胁迫梯度假说相符，表明灌木对草本植物的促进效应随干旱胁迫加剧而增加。3)灌丛的“沃岛”效应是驱动灌木对草本植物元素累积正效应...     

Trade-off between height and branch numbers in Stellera chamaejasme on slopes of different aspects in a degraded alpine grassland

权衡关系是生活史对策理论的基础, 株高和枝条数的权衡关系对理解植物在不同生境下的表型可塑性有重要意义。该研究选择祁连山北坡高寒退化草地, 利用ArcGIS建立研究区域的数字高程模型(DEM), 并提取样地坡向数据, 采用广义相加模型(GAM)与偏相关分析相结合的方法, 分析了不同坡向影响下狼毒(Stellera chamaejasme)种群株高和枝条数的关系。结果表明: 随着坡向由北坡转向东坡、南坡、西坡, 草地群落地上生物量和盖度呈“减小—增大—减小”的变化趋势, 群落高度则先增大后减小; 坡向是影响狼毒株高和枝条数空间分异的主要地形因子; 随着坡向由北、东转向西、南, 狼毒种群株高呈下降趋势, 而枝条数呈上升趋势, 二者表现出此消彼长的权衡关系, 狼毒植株比叶面积先增大后减小。不同坡向狼毒株高和枝条数的权衡关系, 反映了异质生境中资源多重竞争下狼毒生物量分配机制和提高种群适应性的种群更新策略。     

Relationship between functional diversity and productivity in meadow and marsh plant communities

功能多样性-生产力关系研究结果支持质量比假说和多样性假说, 但对于这两种假说的适用条件尚有争议。通过对吉林省西部草甸和沼泽植物群落的地上生物量、2个物种多样性指标(物种丰富度和Shannon-Weaver指数)、7种植物性状的两类功能多样性指标(群落权重均值和Rao二次熵), 以及土壤环境因子进行调查测量, 研究了群落功能多样性与生产力的关系。结果表明: 1)功能多样性与生产力的关系比物种多样性与生产力的关系更为密切; 2)功能群落权重均值解释生产力变异的能力好于Rao二次熵, 即优势物种对群落生产力的影响作用更大; 3)水淹条件影响着功能多样性与生产力的关系, 以群落权重均值为基础的质量比假说适于解释草甸群落功能多样性与生产力的关系, 而以Rao二次熵为基础的多样性假说适于解释有强烈环境筛(水淹)的沼泽群落功能多样性与生产力的关系。     

Response of resource allocation of Saussurea leontodontoides during its fruiting stage to the elevation

植物资源分配是目前植物生态学研究的热点问题, 主要集中在性分配和繁殖分配两个方面。该研究以分布在青藏高原的狮牙草状风毛菊(Saussurea leontodontoides)作为研究材料, 研究了6个海拔高度上果期植株的繁殖特征及资源分配的差异, 并用异速模型分析了繁殖性状及资源分配与个体大小的关系。结果显示: 1)狮牙草状风毛菊的个体大小、繁殖器官生物量、营养器官生物量、种子数和营养分配均与海拔存在极显著负相关关系, 百粒质量和繁殖分配与海拔存在极显著正相关关系。2)在不同海拔高度下, 百粒质量、种子数、繁殖器官生物量及营养分配与植株个体大小呈正相关关系; 繁殖分配与植株个体大小呈负相关关系; 而营养器官生物量与植株个体大小呈极显著正相关关系。这表明海拔和个体大小对狮牙草状风毛菊的繁殖对策有不同程度的影响, 狮牙草状风毛菊通过增加繁殖部分的生物量和百粒质量来适应高海拔的胁迫环境。     

Do interactions between plant and soil biota change with elevation? A study on Fagus sylvatica

Theoretical models predict weakening of negative biotic interactions and strengthening of positive interactions with increasing abiotic stress. However, most empirical tests have been restricted to plant-plant interactions. No empirical study has examined theoretical predictions of interactions between plants and below-ground micro-organisms, although soil biota strongly regulates plant community composition and dynamics. We examined variability in soil biota effects on tree regeneration across an abiotic gradient. Our candidate tree species was European beech (Fagus sylvatica L.), whose regeneration is extremely responsive to soil biota activity. In a greenhouse experiment, we measured tree survival in sterilized and non-sterilized soils collected across an elevation gradient in the French Alps. Negative effects of soil biota on tree survival decreased with elevation, similar to shifts observed in plant-plant interactions. Hence, soil biota effects must be included in theoretical models of plant biotic interactions to accurately represent and predict the effects of abiotic gradient on plant communities.     

The Effect of Positive Interactions on Temporal Turnover of Community Composition along an Environmental Gradient

It has been demonstrated that the interplay between negative and positive interactions simultaneously shapes community structure and composition. However, few studies have attempted to examine the effect of facilitation on compositional changes in communities through time. Additionally, due to the difficulties in collecting the long-term data, it would be useful to indicate the rate of temporal turnover using a readily obtainable metric. Using an individual-based model incorporating plant strategies, we examined the role of facilitation on the temporal turnover of communities located at different positions along an environmental gradient for three model scenarios: CM without facilitation; CFM-U, a unimodal relationship between facilitation and environmental severity; and CFM-L, a positively linear relationship between facilitation and environmental severity. Our results demonstrated that facilitation could increase, decrease or have no remarkable effect on temporal turnover. The specific outcome depended on the location of the focal community across the environmental gradient and the model employed. Compared with CM, the inclusion of positive interactions (i.e. CFM-U and CFM-L), at intermediate environmental stress levels (such as S = 0.7 and 0.8) resulted in lower Bray-Curtis similarity values; at other severity levels, facilitation slowed down (such as S = 0.3 and 0.4 at low to medium stress levels, and S = 0.9 at high stress levels) or had only a subtle effect (such as at S = 0.1) on temporal turnover. We also found that the coefficient of variation (CV) in species abundances and the rate of temporal variability showed a significant quadratic relationship. Our theoretical analysis contributes to the understanding of factors driving temporal turnover in biotic communities, and presents a potential metric (i.e. CV in species abundances) assessing the consequences of ongoing environmental change on community structure.     

Positive interactions among plants

Experimental evidence for positive interactions, or facilitation, among plants has increased markedly during the last 10 years. Experiments documenting facilitation have been conducted in many diverse ecological systems, which suggests that positive interactions may be fundamental processes in plant communities. Here, I review the evidence for facilitation, the mechanisms by which facilitation operates, and the effects facilitation has on community structure. Facilitative mechanisms may act simultaneously with resource competition or allelopathy, and the overall effect of one species on another may be the product of multiple, complex interactions. Positive interactions may also determine community spatial patterns, permit coexistence, enhance diversity and productivity, and drive community dynamics. Once viewed as anecdotal and idiosyncratic, facilitation is now contributing to a more complete understanding of community structure and dynamics.     

Positive Interactions： Crucial Organizers in a Plant Community

For more than a century, ecologists have concentrated on competition as a crucial process for community organization. However, more recent experimental investigations have uncovered the striking Influence of positive Interactions on the organization of plant communities. Complex combinations of competition and positive interactions operating simultaneously among plant species seem to be widespread In nature. In the present paper, we reviewed the mechanism and ecological importance of positive Interactions In plant communities, emphasizing the certainties and uncertainties that have made It an attractive area of research. Positive Interactions, or facilitation, occur when one species enhances the survival, growth, or richness of another. The Importance of facilitation in plant organization increases with ablotlc stress and the relative Importance of competition decreases. Only by combining plant interactions and the many fields of biology can we fully understand how and when the positive Interactions occur.     

Do biotic interactions shape both sides of the humped‐back model of species richness in plant communities?

A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity-diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity.     

The nested assembly of plant facilitation networks prevents species extinctions

Facilitation is a positive interaction assembling ecological communities and preserving global biodiversity. Although communities acquire emerging properties when many species interact, most of our knowledge about facilitation is based on studies between pairs of species. To understand how plant facilitation preserves biodiversity in complex ecological communities, we propose to move from the study of pairwise interactions to the network approach. We show that facilitation networks behave as mutualistic networks do, characterized by a nonrandom, nested structure of plant-plant interactions in which a few generalist nurses facilitate a large number of species while the rest of the nurses facilitate only a subset of them. Consequently, generalist nurses shape a dense and highly connected network. Interestingly, such generalist nurses are the most abundant species in the community, making facilitation-shaped communities strongly resistant to extinction, as revealed by coextinction simulations. The nested structure of facilitative networks explains why facilitation, by preventing extinction, preserves biodiversity.     

Plant–plant interactions,environmental gradients and plant diversity: A global synthesis of community-level studies

Previous syntheses on the effects of environmental conditions on the outcome of plant–plant interactions summarize results from pairwise studies. However, the upscaling to the community-level of such studies is problematic because of the existence of multiple species assemblages and species-specific responses to both the environmental conditions and the presence of neighbors. We conducted the first global synthesis of community-level studies from harsh environments, which included data from 71 alpine and 137 dryland communities to: (i) test how important are facilitative interactions as a driver of community structure, (ii) evaluate whether we can predict the frequency of positive plant–plant interactions across differing environmental conditions and habitats, and (iii) assess whether thresholds in the response of plant–plant interactions to environmental gradients exists between “moderate” and “extreme” environments. We also used those community-level studies performed across gradients of at least three points to evaluate how the average environmental conditions, the length of the gradient studied, and the number of points sampled across such gradient affect the form and strength of the facilitation-environmental conditions relationship. Over 25% of the species present were more spatially associated to nurse plants than expected by chance in both alpine and dryland areas, illustrating the high importance of positive plant–plant interactions for the maintenance of plant diversity in these environments. Facilitative interactions were more frequent, and more related to environmental conditions, in alpine than in dryland areas, perhaps because drylands are generally characterized by a larger variety of environmental stress factors and plant functional traits. The frequency of facilitative interactions in alpine communities peaked at 1000 mm of annual rainfall, and globally decreased with elevation. The frequency of positive interactions in dryland communities decreased globally with water scarcity or temperature annual range. Positive facilitation-drought stress relationships are more likely in shorter regional gradients, but these relationships are obscured in regions with a greater species turnover or with complex environmental gradients. By showing the different climatic drivers and behaviors of plant–plant interactions in dryland and alpine areas, our results will improve predictions regarding the effect of facilitation on the assembly of plant communities and their response to changes in environmental conditions.     

Extending the stress‐gradient hypothesis – is competition among animals less common in harsh environments?

The role of positive interactions has become widely accepted as a mechanism shaping community dynamics. Most empirical evidence comes from plant communities and sessile marine organisms. However, evidence for the relative role of positive interactions in organizing terrestrial animal communities is more limited, and a general framework that includes positive interactions among animals is lacking. The ‘stress gradient hypothesis’ (SGH) developed by plant ecologists predicts that the balance between positive and negative interactions will vary along gradients of biotic and abiotic stress, with positive interactions being more important in stressful environments. Paralleling the SGH, stress gradients for terrestrial herbivores could be equated to inverse primary productivity gradients, so we would expect positive interactions to prevail in more stressful, low productivity environments. However, this contradicts the typical view of terrestrial animal ecology that low primary productivity systems will foster intense competition for resources among consumers. Here we use alpine herbivores as a case study to test one of the predictions of the SGH in animal communities, namely the prevalence of positive interactions in low productivity environments. We identify potential mechanisms of facilitation and review the limited number of examples of interspecific interactions among alpine herbivores to assess the role of positive and negative interactions in structuring their communities. A meta‐analysis showed no clear trend in the strength and direction of interactions among alpine herbivores. Although studies were biased towards reporting significant negative inter actions, we found no evidence of competition dominating in harsh environments. Thus, our results only partially support the SGH, but directly challenge the dominant view among animal ecologists. Clearly, a sound theoretical framework is needed to include competition, positive and neutral interactions as potential mechanisms determining the structure of animal communities under differing environmental conditions, and the stress‐gradient hypothesis can provide a solid starting point.