生境破碎化对动物种群存活的影响

生境破碎是生物多样性下降的主要原因之一。通常以岛屿生物地理学、异质种群生物学和景观生态学的理论来解释不同空间尺度中生境破碎化的生态学效应。生境破碎化引起面积效应、隔离效应和边缘效应。这些效应通过影响动物种群的绝灭阈值、分布和多度、种间关系以及生态系统过程,最终影响动物种群的存活。野外研究表明,破碎化对动物的影响,因物种、生境类型和地理区域不同而有所变化,因此,预测物种在破碎生境中的存活比较困难。研究热点集中于：确定生境面积损失和生境斑块的空间格局对破碎景观中物种绝灭的相对影响,破碎景观中物种的适宜生境比例和绝灭阈值,异质种群动态以及生态系统的生态过程。随着3S技术的发展,生境破碎化模型趋于复杂,而发展有效的模型和验证模型将成为一项富有挑战性的任务。     

景观生态学:两栖动物生态学研究的新途径

全球两栖动物正以远超过自然灭绝的高速率灭绝,这与生境丧失和景观破碎化有着直接关系。生境丧失导致两栖动物的生存空间减少,使局部种群消失,而景观破碎化则导致两栖动物种群之间的隔离度增加,不利于动物的繁殖和扩散。但两者往往是同时出现,相互作用。复合种群、景观连接度、景观遗传学及景观模型模拟等理论和方法的发展,为在生境丧失与破碎化景观下两栖动物的种群结构、组成和动态变化研究提供了理论基础和技术方法。同时景观生态学中特别重视研究的尺度,生境破碎化是发生在景观尺度下的生境变化过程,因此对生境破碎化的影响应该从现有的主要集中在斑块尺度和斑块-景观尺度转变到景观尺度上来。     

具年龄结构的种群在破碎化生境中的空间分布模型

随着人类和其他生物赖以生存的环境破碎化程度的加剧,许多以前是连续分布的物种,目前不得不在破碎化生境(斑块)中求生存,所以,种群在破碎化生境(斑块)中分布问题的研究对生物保护和生境重建意义重大．本文运用Leslie矩阵和Markov链建立了一个具年龄结构的种群在破碎化生境中随时间动态变化的分布模型,讨论了种群在该生境中持续存在以及灭绝的条件．     

异质种群动态模型:破碎化景观动态模拟的新途径

景观破碎化导致物种以异质种群方式存活,使得基于异质种群动态模拟破碎化景观动态成为可能。异质种群动态模型的发展为景观动态模拟奠定了良好基础。根据空间处理方式的不同,异质种群模型可分为三大类,可不同程度地用于描述破碎化景观动态。(1)空间不确定异质种群模型,假定所有局域种群间均等互联,模型中不包含空间信息,仅能用于景观斑块动态描述;(2)空间确定异质种群模型,假设局域种群在二维空间上以规则格子形式排列,是一种准现实的空间处理方式,可用于景观动态的简单描述;(3)空间现实异质种群模型,包含了破碎化景观中局域种群的几何特征,可直接用于真实景观动态的模拟研究。空间现实的和基于个体的异质种群模型不但是未来异质种群模型发展的主流,也将成为未来破碎化景观动态研究的重要工具。为了更加准确完整地描述破碎化景观动态,不但应该综合运用已有的各种异质种群模型方法,更要引进新模型来刎画多物种、多变量、高维度、复杂连接的破碎化景观格局与过程。     

基于目标种保护的生态廊道构建——以崇明岛为例

景观破碎化和适宜生境面积减少是生物多样性降低与物种灭绝的重要因素之一。生态廊道的构建为陆行野生动物扩大活动范围提供了空间途径,从而增加了物种基因交流的机会, 提高了种群的生存能力。上海市崇明岛是一个地理上孤立的冲积沙岛,随着岛上森林斑块的减少与破碎化,依赖林地生境生存的陆行动物个体与种群数量大大减少。本文以崇明岛为例,选择上海市一级保护动物刺猬作为目标种,在分析其生活习性和基质斑块空间分布特征的基础上,利用最小耗费模型和GIS手段,实现了生境斑块之间的最佳连接,建立了以目标动物保护为目的的生态廊道规划方案。     

景观破碎化对植物种群的影响

景观破碎化是目前存在的一种普遍现象,是由于人为因素或其它非人为因素的干扰所导致的景观破碎分离并由简单趋向复杂的过程。它直接或间接影响着景观的结构、功能及其动态。本文首先简要介绍景观破碎化的成因和不同研究角度与水平上景观破碎化影响的表现;然后着重分析景观破碎化对植物种群的大小和灭绝速率、扩散和迁入、遗传和变异以及存活力等的影响;同时归纳现阶段研究景观破碎化对植物种群影响的主要方法和模型;最后提出目前景观破碎化对植物种群影响研究中存在的三个主要问题：缺乏原始的资料、成熟的模型和破碎化与其他因素,如污染、气候变化等,交互作用的识别。     

近40年东北地区陆栖脊椎动物种群数量及其生境变化评估

生物多样性是生态平衡维持和生态过程与功能实现的基础,东北地区是我国乃至全球生物多样性最为丰富的地区之一。为研究和探讨东北地区陆栖脊椎动物种群数量与生境变化之间的关系,利用物种调查数据和生境遥感观测数据,以地球生命力指数、生态系统面积和破碎度等指示性指标,综合评估了近40年东北地区陆栖脊椎动物种群数量及其生境变化。结果表明:1970—2010年,东北地区陆栖脊椎动物种群数量下降了近70.1%,森林脊椎动物种群数量减少了近80.9%,草原和荒漠生态系统脊椎动物种群数量增加了近180.9%。1980—2010年,湿地物种种群数量减少了近75.7%。1980—2015年期间,农业和城镇建设用地增幅分别达到25.2%和32.3%,不断挤占和蚕食着自然生态空间,致使自然生境面积不断减少,减幅约为8.0%。自然生境景观破碎化程度总体呈现加重趋势,尤其是森林生境,破碎化指数增加约42.7%。但是,2005年之后,自然生境景观破碎化程度加重趋势趋缓,与2005年之后脊椎动物种群数量减少幅度减缓趋势一致。森林砍伐、人口增长、城镇化、交通建设等造成的自然生态系统破碎度增加和栖息地质量下降对大型兽类影响比较显著。     

农业景观生物多样性与害虫生态控制

现代农业的一个重要特征就是人类对农田生态系统的干扰强度及频率不断增加,严重影响农业景观的结构及其生物多样性.农业景观结构的变化及其生物多样性的丧失,必然引起生态系统服务功能的弱化,不利于实施以保护自然天敌为主的害虫生态控制.农业的集约化经营导致自然生境破碎化,减少了农业景观的复杂性,使得作物和非作物变成一种相对离散化的生境类型和镶嵌的景观格局;破碎化的生境不仅会减少某些物种的丰度,还会影响物种之间的相互关系及生物群落的多样性和稳定性.非作物生境类型如林地、灌木篱墙、田块边缘区、休耕地和草地等,是一种比较稳定的异质化环境.非作物生境较少受到干扰,可以为寄生性和捕食性节肢动物提供适宜的越冬或避难场所以及替代猎物、花粉和花蜜等资源,因此,非作物生境有利于自然天敌的栖息和繁衍,也有利于它们迁入邻近的作物生境中对害虫起到调节和控制作用.景观的格局-过程-尺度影响农田生物群落物种丰富度、多度、多样性以及害虫与天敌之间的相互作用.从区域农业景观系统的角度出发,运用景观生态学的理论和方法来研究作物、害虫、天敌等组分在不同斑块之间的转移过程和变化规律,揭示害虫在较大尺度和具有异质性的空间范围内的灾变机理,可为利用农业景观生物多样性来保护农田自然天敌,实施害虫的区域性生态控制提供新的研究思路和手段.     

生境破碎化对食果动物及种子传播的影响

食果动物与依赖其传播种子的植物间在进化过程中形成互惠关系,生境破碎化往往干扰种子传播过程,继而破坏这种关系.生境破碎化通常降低食果动物的多样性,但亦有相反的情况出现.食果动物对生境破碎化的适应能力不同,泛性森林动物和广食性动物具有较强的适应性.生境破碎化对依赖动物传播的植物影响有差异,多数植物受到负面影响,但也有一些植物不受影响,甚至受益.动物在破碎生境中对种子传播的有效性是种子搬运量、传播距离、种子萌发及种群建立等环节的综合效果.破碎化生境中种子的搬运量与动物的觅食行为和食物选择有关;种子传播距离受食物资源可获得性的改变和生境斑块异质性的影响;种子萌发和更新种群建立成功与否决定于是否存在有效的种子传播者.生境破碎化如何影响种子传播以及动植物相互关系,尤其是异质斑块的空间分布如何影响食果动物的传播有效性、破碎化生境下动植物互惠共生关系如何建立,生境破碎化导致的植物入侵对本地植物种子传播的影响是未来需要深入研究的问题.     

生境破碎化对生物多样性的影响研究综述

生境破碎化与生物多样性的关系是理论生态学的研究热点。本文在综述国内外相关研究内容的基础上,阐述了生境破碎化的概念内涵与度量,介绍了生境破碎化研究的主要理论基础、研究内容与研究进展;总结了目前生境破碎化研究存在度量破碎景观格局的方法尚未统一、研究方法有待精确以及生境破碎化与生物多样性的阈值效应尚未发现等问题。今后,半干旱地区生境破碎化对生物多样性影响的研究需要加强,空间分析理论和方法将会在生境破碎化对生物多样性影响的研究中得到更多应用。     

Effects of landscape and patch-level attributes on regional population persistence

Species responses are influenced by processes operating at multiple scales, yet many conservation studies and management actions are focused on a single scale. Although landscape-level habitat conditions (i.e., habitat amount, fragmentation and landscape quality) are likely to drive the regional persistence of spatially structured populations, patch-level factors (i.e., patch size, isolation, and quality) may also be important. To determine the spatial scales at which habitat factors influence the regional persistence of endangered Ord's kangaroo rats (Dipodomys ordii) in Alberta, Canada, we simulated population dynamics under a range of habitat conditions. Using a spatially-explicit population model, we removed groups of habitat patches based on their characteristics and measured the resulting time to extinction. We used proportional hazards models to rank the influence of landscape and interacting patch-level variables. Landscape quality was the most influential variable followed by patch quality, with both outweighing landscape- and patch-level measures of habitat quantity and fragmentation/proximity. Although habitat conservation and restoration priorities for this population should be in maximizing the overall quality of the landscape, population persistence depends on how this goal is achieved. Patch quality exerted a significant influence on regional persistence, with the removal of low quality road margin patches (sinks) reducing the risk of regional extinction. Strategies for maximizing overall landscape quality that omit patch-level considerations may produce suboptimal or detrimental results for regional population persistence, particularly where complex local population dynamics (e.g., source-sink dynamics) exist. This study contributes to a growing body literature that suggests that the prediction of species responses and future conservation actions may best be assessed with a multi-scale approach that considers habitat quality and that the success of conservation actions may depend on assessing the influences of habitat factors at multiple scales.     

Habitat fragmentation and extinction thresholds on fractal landscapes

Habitat fragmentation is a potentially critical factor in determining population persistence. In this paper, we explore the effect of fragmentation when the fragmentation follows a fractal pattern. The habitat is divided into patches, each of which is suitable or unsuitable. Suitable patches are either occupied or unoccupied, and change state depending on rates of colonization and local extinction. We compare the behaviour of two models: a spatially implicit patch-occupancy (PO) model and a spatially explicit cellular automaton (CA) model. The PO model has two fixed points: extinction, and a stable equilibrium with a fixed proportion of occupied patches. Global extinction results when habitat destruction reduces the proportion of suitable patches below a critical threshold. The PO model successfully recreates the extinction patterns found in other models. We translated the PO model into a stochastic cellular automaton. Fractal arrangements of suitable and unsuitable patches were used to simulate habitat fragmentation. We found that: (i) a population on a fractal landscape can tolerate more habitat destruction than predicted by the patch-occupancy model, and (ii) the extinction threshold decreases as the fractal dimension of the landscape decreases. These effects cannot be seen in spatially implicit models. Landscape struc-ture plays a vital role in mediating the effects of habitat fragmentation on persistence.     

Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population

1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations. 2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration. 3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes. 4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners. 5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes.     

Habitat specialization predicts genetic response to fragmentation in tropical birds

Habitat fragmentation is one of the most severe threats to biodiversity as it may lead to changes in population genetic structure, with ultimate modifications of species evolutionary potential and local extinctions. Nonetheless, fragmentation does not equally affect all species and identifying which ecological traits are related to species sensitivity to habitat fragmentation could help prioritization of conservation efforts. Despite the theoretical link between species ecology and extinction proneness, comparative studies explicitly testing the hypothesis that particular ecological traits underlies species‐specific population structure are rare. Here, we used a comparative approach on eight bird species, co‐occurring across the same fragmented landscape. For each species, we quantified relative levels of forest specialization and genetic differentiation among populations. To test the link between forest specialization and susceptibility to forest fragmentation, we assessed species responses to fragmentation by comparing levels of genetic differentiation between continuous and fragmented forest landscapes. Our results revealed a significant and substantial population structure at a very small spatial scale for mobile organisms such as birds. More importantly, we found that specialist species are more affected by forest fragmentation than generalist ones. Finally, our results suggest that even a simple habitat specialization index can be a satisfying predictor of genetic and demographic consequences of habitat fragmentation, providing a reliable practical and quantitative tool for conservation biology.     

Bottlenecks for plant recruitment in woodland remnants: An ornithochorous shrub in a Mediterranean ‘relictual’ landscape

Habitat fragmentation may lead to declines in plant populations and ultimately to extinction through a disruption of demographic processes, which may result in bottlenecks or even a collapse in regeneration. Nevertheless, very few studies have assessed the net effects of habitat fragmentation on plant recruitment integrating its multiple demographic processes. Using data from a four-year field study, we analyze how habitat fragmentation affects particular demographic processes and the overall magnitude of plant recruitment. We use as a case study the bird-dispersed shrub Myrtus communis in Mediterranean woodland patches within an extremely fragmented landscape (～1% woodland cover). By means of observations and experiments, we quantified fecundity, fruit removal by frugivores, seed rain, post-dispersal seed predation by rodents and seedling emergence and survival. Within each patch, we quantified post-dispersal processes in different target microhabitats. We considered the life cycle to be a combination of consecutive life stages connected by transitional processes with specific probabilities. We calculated the overall probability of recruitment for each patch as the product of all of these probabilities. The demographic processes negatively affected by fragmentation were bird-generated seed rain and seedling emergence and survival, which were attributable, respectively, to lower fruit abundance and poorer habitat quality in the smaller patches. The negative effect of fragmentation on M. communis recruitment became stronger when all the demographic processes were integrated. Of all processes, seedling emergence and, above all, seedling survival were clearly bottlenecks for recruitment that were associated with habitat fragmentation. Results from our observations and experiments were consistent with natural patterns of regeneration given that we found higher seedling densities in larger patches and old population structures (with no saplings/juveniles) in some small patches. Our study shows that habitat fragmentation has serious negative effects on recruitment in M. communis due to demographic bottlenecks in seedling establishment. The available evidence (this and a companion study) suggests that the impoverishment of habitat quality associated with habitat fragmentation (edge effects, disturbances associated with management and microhabitat availability) can explain these results. Given that restoration at a landscape scale is likely to be extremely difficult, initial management actions should aim to improve habitat quality in the smallest woodland remnants.     

Species’ response patterns to habitat fragmentation: do trees support the extinction threshold hypothesis?

In fragmented landscapes the relationship between the probability of occurrence of single species and the amount of suitable habitat is usually not proportional, with a threshold habitat level below which the population becomes extinct. Ecological theory predicts that, although the reduction in species’ occurrence probabilities (and eventually the extinction threshold) is a direct consequence of habitat loss, habitat fragmentation might reduce species’ occurrence probabilities and affect the location of this threshold by reducing its predicted occurrence to lower levels of habitat amount. However, little is known about the validity of this extinction threshold hypothesis. Here, we performed analyses on the relationships between the probability of occurrence of eight tree species and the availability of forest habitat for two different empirical scenarios of low and moderate to high fragmentation. We partitioned the effects of habitat amount versus fragmentation by using two metrics: (1) the percentage of forest cover, and (2) the proportion of this percentage occurring in the largest forest patch. We find that, although decreasing forest cover had negative effects on the occurrence of tree species irrespective of fragmentation levels, forest fragmentation significantly modified the response pattern in six tree species, although only one species confirmed the extinction threshold hypothesis, which we interpret as a consequence of high degree of forest specialism and low dispersal ability. For most species, fragmentation either had positive effects or did not affect significantly the species’ probability of occurrence. This indicates that the effects of habitat fragmentation on tree species are weak relative to the effects of habitat amount, which is the main determinant of the reduction in species’ occurrence probabilities, and eventually species extinction, in fragmented landscapes.     

Extinction debt in a common grassland species: immediate and delayed responses of plant and population fitness

Changes in landscape structure and environmental conditions due to habitat fragmentation can have significant effects on plant populations. Decreasing genetic diversity and changing population structure can reduce plant fitness and influence the long-term persistence of populations. Dry calcareous grasslands in Estonia have witnessed a large decline in area within the last 80 years, but due to extinction debt, the species richness in these grasslands has not yet responded to this decline. In these calcareous grasslands, we studied genetic diversity, phenotypic performance and population characteristics of a common habitat-specialist grass, Briza media. A decrease in genetic diversity was associated with a decrease in plant reproductive output. In addition, we found that some fitness components of B. media showed a delayed response to landscape changes. Specifically, plant height and germination success were related to historical rather than to current landscape parameters, indicating a time-lagged response of plant performance to habitat fragmentation. Dependence on historical landscape structure may thus result in a future decline in population fitness even if habitat loss and fragmentation no longer continue. The documented effect of current environmental conditions, however, shows that fitness-related traits are already slowly adapting to the changing conditions. Our results indicate that even common habitat-specialist species can be susceptible to landscape changes and be threatened by decreased population performance in the future.     

Landscape structure and land use history influence changes in island plant composition after 100 years

Aim We investigated how current and historical land use and landscape structure affect species richness and the processes of extinction, immigration and species turnover. Location The northern part of the Stockholm archipelago, Baltic Sea, Sweden. We resurveyed 27 islands ranging from 0.3 to 33 ha in area. Methods We compared current plant survey data, cadastral maps and aerial photographs with records obtained from a survey in 1908, using databases and a digital elevation model to examine changes in plant community dynamics in space and time. We examined the effects of local and landscape structure and land use changes on plant species dynamics by using stepwise regression in relation to eight local and three landscape variables. The eight local variables were area, relative age, shape, soil heterogeneity, bedrock ratio, number of houses, forest cover change, and grazing 100 years ago. The three landscape variables were distance to mainland, distance to closest island with a farm 100 years ago, and structural connectivity. Hanski’s connectivity measure was modified to incorporate both connectivity and fragmentation. Results The investigated islands have undergone drastic changes, with increasing forest cover, habitation, and abandonment of grassland management. Although the total species richness increased by 31% and mean island area by 23%, we found no significant increase in species richness per unit area. Local variables explain past species richness (100 years ago), whereas both local and landscape variables explain current species richness, extinctions, immigrations and species turnover. Grazing that occurred 100 years ago still influences species richness, even though grazing management was abandoned several decades ago. The evidence clearly shows an increase in nitrophilous plant species, particularly among immigrant species. Main conclusions This study highlights the importance of including land use history when interpreting current patterns of species richness. Furthermore, local environment and landscape patterns affect important ecological processes such as immigration, extinction and species turnover, and hence should be included when assessing the impact of habitat fragmentation and land use change. We suggest that our modified structural connectivity measure can be applied to other types of landscapes to investigate the effects of fragmentation and habitat loss.     

Habitat fragmentation effects on fitness of plant populations – a review

Habitat fragmentation threatens the survival of many species and local populations. Habitat fragmentation has two major consequences: populations become more isolated and are reduced in size. Small compared with large populations have increased extinction risks because of different types stochasticity (e.g. genetic drift) and inbreeding, which can negatively affect the fitness of individuals or populations. Habitat fragmentation may also change the abiotic conditions of the surrounding landscape, which influences biotic interactions. This review gives an introduction to the theory of the effects of habitat fragmentation on mean fitness of plant populations. It intends to help bridge the gap between conservation biologists and conservation practitioners. The paper shortly introduces basic concepts of population biology, demography and genetics and cites relevant and new literature. Special attention is given to more common plant species, which have attracted far less conservation attention than rare species.