岛屿群落组成的嵌套格局及其应用

近年来 ,岛屿群落组成的嵌套结构引起了众多研究者的关注。在一个岛屿生境系统中 ,小岛屿中出现的物种大多数也出现在物种相对丰富的大岛屿中。这是一种非随机的物种分布格局。嵌套结构被认为是分析群落组成机制的重要工具 ,并引发了自然保护区最优化设计原理的新一轮争议。然而 ,随着研究的深入 ,围绕嵌套结构的意义、方法学、成因和普适性等方面出现了许多不同的观点与假说。本文就上述方面作了系统的介绍和分析 ,认为嵌套结构从群落的组成方面为岛屿生物地理学提供了新的视角 ,在保护生物学上具有重要意义。在成因上 ,仅考虑单因子的作用是偏狭的 ,多数是多因子综合作用的结果。在方法上 ,应充分认识不同方法的适应条件 ,以降低误差。嵌套结构并不是普适的 ,它受到如矩阵的大小和填充度、生物类群和生境的差异性等因素的影响     

千岛湖雀形目鸟类群落嵌套结构分析

2006年4月至2007年11月, 采用截线法对千岛湖20个岛屿上的雀形目鸟类种类组成进行调查, 检验其群落是否符合嵌套式分布的格局。此外通过野外直接记录与辨认法对岛屿上的植物种类组成进行调查, 同时通过查阅文献资料和野外调查获得鸟类体长、分布宽度和生境专属性等生活史特征参数, 以及采用GIS分析测定岛屿面积和隔离度参数, 进而分析和探讨雀形目鸟类群落嵌套格局的影响因素。结果显示, 千岛湖岛屿雀形目鸟类群落呈现显著的嵌套结构, 岛屿面积、植物物种丰富度和生境专属性对其嵌套结构具显著性的影响。千岛湖岛屿雀形目鸟类存在着选择性灭绝过程; 植物物种丰富度和鸟类生境专属性则通过影响鸟类在不同生境下的分布对鸟类群落嵌套结构产生影响。上述结果表明千岛湖岛屿雀形目鸟类群落嵌套格局同时受到栖息地和物种两方面因素的影响, 为此我们认为应更多地关注那些面积较大和植物物种丰富度较高的岛屿, 以及生境专属性较高的种类等鸟类多样性及其栖息地的保护策略。     

舟山群岛蝶类群落嵌套分布格局及其影响因素

片断化生境中群落的物种组成常呈现嵌套分布格局。2013年7-8月, 我们在浙江舟山群岛采用截线法对28个岛屿上的蝴蝶群落进行了野外调查, 探讨了岛屿物种嵌套分布格局及其影响因素。通过测量采集标本获得蝶类的生活史特征(最小需求面积、翅展和体重), 查阅文献资料获得蝶类的栖息地特征(岛屿面积、距最近大陆距离和距最近大岛距离), 分析了影响蝶类群落嵌套结构的因素。研究结果显示: (1)舟山群岛蝶类群落符合嵌套分布格局; (2)岛屿面积和物种最小需求面积对嵌套格局的形成有显著影响; (3)舟山群岛蝶类群落嵌套格局的形成支持选择性灭绝假说; (4)随机检验零模型结果显示该嵌套分布格局并非采样偏差造成的。因此, 在制定舟山群岛区域蝶类保护措施时, 应优先考虑那些分布在面积较大岛屿的和最小需求面积较大的物种。     

广州城市绿地留鸟嵌套分布格局及其影响因素

城市景观特征对鸟类群落结构的影响是当前城市生态学值得关注的主题,对其的研究可为城市建设与鸟类保护的协同发展提供科学依据。为探讨鸟类群落组成在不同城市景观特征下的变化规律,于2017—2019年对广州市20个城市绿地斑块进行鸟类调查,分析鸟类嵌套格局及其影响因素。1）共记录鸟类18目50科139种,每个绿地斑块记录鸟类22～53种,其中留鸟最多,为75种,占53.96%。2）利用可处理物种多度信息矩阵的WNODF进行嵌套格局分析,发现绿地斑块中留鸟群落表现出显著的反嵌套结构。3）留鸟群落在绿地斑块中的分布是非随机的,被动取样假说不是该区域鸟类嵌套格局的原因,选择性灭绝、生境嵌套和人为干扰可能对该区域鸟类反嵌套格局的形成有一定作用。     

千岛湖两栖爬行类动物群落结构嵌套分析

生境片段化是导致生物多样性降低的主要原因之一.该文采用样线法对千岛湖23个岛屿的两栖爬行类进行了调查,并结合植物种类调查数据和GIS技术提取的栖息地景观参数,使用“BINMATNEST”软件和Spearman相关性分析等方法,对这些岛屿上的两栖爬行类群落的分布格局及其影响因素进行分析.结果表明,千岛湖两栖爬行类群落整体上呈现嵌套分布格局;嵌套格局与岛屿面积和生境类型相关显著.因此,在制定千岛湖地区两栖爬行动物保护措施时,应优先考虑面积较大和生境类型多的岛屿.     

海洋岛屿生物多样性保育研究进展

海洋岛屿生态系统因具有明显的海域地理隔离而区别于陆地生态系统,被誉为生物地理与进化生态学研究的"天然实验室".陆地或其它邻近岛屿的种源物种迁移到新的岛屿后,经历地理隔离、特征置换或适应辐射等一系列的岛屿进化过程,形成与种源物种具有显著遗传差异的岛屿特有种.岛屿在小面积范围内分化形成大量的特有种,是岛屿生物多样性最为重要的特点之一.但是,岛屿种群由于分布范围局限、生境脆弱且种群规模较小,岛屿种群较陆地种群具有更高的灭绝风险.本文通过对海洋岛屿物种的起源与演化、遗传结构以及岛屿物种的濒危与保护3个热点问题的讨论,阐述岛屿生物多样性的形成机制、濒危肇因以及岛屿生物多样性保育的重要性.     

物种保护的理论基础——从岛屿生物地理学理论到集合种群理论

全球面临着生境破碎化的危机,物种保护已成为人类面临的重大课题,并不是所有的人对岛屿生物地理学理论的产生及其关注的海洋岛屿都很熟悉,但是越来越多生物赖以生存的自然栖息地的丧失和破碎化都是有目共睹的,岛屿生物地理学和集合种群理论是目前物种保护的两个基本理论,物种迁入率和绝灭率的动态变化决策岛屿上的物种丰富度是岛屿生物地理学理论的核心内容,而集合种群理论关注的是局部种群之间个体迁移的动态以及物种的续存条件,在概述两个理论形成、发展及其核心内容的基础上,着重比较它们的异同点以及在生态学理论和实践中的应用,并论述物种保护理论范式从岛屿生物地理学向集合种群理论转变的基本背景和原因。     

上海闵行区园林鸟类群落嵌套结构

城市中的园林绿地呈现斑块状分布,其栖息地特征与岛屿栖息地相似。2008年11月至2009年10月,对上海市闵行区内的7块城市绿地进行调查,记录雀形目鸟类的分布情况,并运用Nestedness temperature calculator软件,检验其群落结构是否符合嵌套结构。运用Arc GIS软件分析该地区的卫星图片,收集7块样地的面积、绿地盖度、水源距离和人为干扰程度等数据,结合实地调查所得到的数据,分析这一嵌套结构的形成原因和影响因素。结果显示：上海市闵行区城市绿地中的雀形目鸟类分布是显著的嵌套结构,园林面积、绿地面积和水源情况都对其嵌套结构有显著影响。但是与真正岛屿上存在的群落分布嵌套结构不同,人为干扰程度对这一结构也有非常明显的影响。基于上述结果可以看出,影响上海市园林鸟类的群落嵌套结构的主要原因是栖息地的结构和人为干扰程度。因此,建议在规划和建设城市公园和绿地时,应该偏重于面积较大,植被盖度和丰富度高,结构合理的园林,并且尽量减少人为干扰。     

千岛湖岛屿小型兽类群落分布格局及其影响因素

2007年秋季和2008年春季,采用夹夜法对千岛湖14个岛屿进行小型兽类群落组成调查,研究其群落空间分布格局及其影响因素。两季度共布置夹16 800只,捕获小型兽类1 037只,隶属2目2科7属11种。其中啮齿目（Rodenria）鼠科（Muridae）9种,食虫目（Insectivora）鼩鼱科（Soricdae）2种。结果显示：千岛湖小型兽类群落呈非随机分布格局;嵌套分析表明,千岛湖岛屿小型兽类群落呈现极显著嵌套格局,植物丰富度和生境专属性两项参数对其嵌套格局的形成具有显著影响,从而使适应力强的物种能够在多样的环境中生存,而适应力弱的物种则局限在特定的环境中。由于取样强度差异会过高地估计嵌套程度,故在研究中应尽量去除取样强度的干扰。     

南京市土壤集合组成及其嵌套性分析

随着工业化和城市化的加速发展,土壤资源与土壤环境压力日益增加。近20a来,南京市城镇化发展迅速,而且城镇的发展正导致原来相对自然的大片土壤面积减少,深入研究南京市土壤组成以及嵌套性特征,有助于了解土壤类型的分布特征,正确估计城镇化的后果,在保护土壤资源以及土壤多样性方面具有一定的理论意义和现实意义。以南京市各乡镇等级单位的土壤集合为研究对象,对南京市的土壤组成及嵌套性进行了分析。结果显示,在南京市各乡镇等级单位中共有47个土种,其中优势土种6种,常见土种13种、稀有土种25种、濒危土种3种。土壤集合在组成上呈现出不完全嵌套格局,分布于土种数较少的乡镇等级单位中的土种多数也分布在土种数较多的乡镇等级单位中。土壤类型数（S）与面积（A）是幂函数关系,其最佳回归拟合方程为：S=0．7284A^0.5922。嵌套格局与南京市的土种面积、地形以及地理位置关系密切,面积大的乡镇等级单位有更多的土种主要原因是它们有更广阔的生境范围,具有更高的生境多样性（如水域、沼泽、地形地貌、丘陵等）,随着面积的缩小,某些特定的生境类型随着逐渐丧失,与此相关的一些土种也随之消失,于是就产生了嵌套结构。     

The influence of colonization in nested species subsets

Biotic communities inhabiting collections of insular habitat patches often exhibit compositional patterns described as nested subsets. In nested biotas, the assemblages of species in relatively depauperate sites comprise successive subsets of species in relatively richer sites. In theory, nestedness may result from selective extinction, selective colonization, or other mechanisms, such as nested habitats. Allopatric speciation is expected to reduce nestedness. Previous studies, based largely on comparisons between land-bridge and oceanic archipelagos, have emphasized the role of selective extinction. However, colonization could also be important in generating strong patterns of nestedness. We apply a recently published index of nestedness to more than 50 island biogeographic data sets, and examine the roles of colonization, extinction, endemism, and, to a limited extent, habitat variability on the degree on nestedness. Most data sets exhibit a significant degree of nestedness, although there is no general tendency for land-bridge biotas to appear more nested than oceanic ones. Endemic species are shown to generally reduce nestedness. Comparisons between groups of non-endemic species differing in overwater or inter-patch dispersal ability indicate that superior dispersers generally exhibit a greater degree of nestedness than poorer dispersers, a result opposite that expected if colonization were a less predictable process than extinction. These results suggest that frequent colonization is likely to enhance nestedness, thereby increasing the compositional overlap among insular biotas. The prevalence of selective extinction in natural communities remains in question. The importance of colonization in generating and maintaining nested subsets suggests that (1) minimum critical areas will be difficult to determine from patterns of species distributions on islands; (2) multiple conservation sites are likely to be required to preserve communities in subdivided landscapes; and (3) management of dispersal processes may be as important to preserving species and communities as is minimizing extinctions.     

Nested bird and micro-habitat assemblages in a peatland archipelago

Biotic assemblages of insular habitats are nested when poor assemblages are subsets of richer ones. Nestedness of species assemblages is frequent and may result from selective extinction or frequent colonization in insular habitats. It may also be created by a nested distribution of habitats among islands or by sampling bias. We sampled 67 isolated peatlands (7–843 ha) in southern Quebec, Canada, to measure nestedness of bird species assemblages among peatlands and assess the habitat nestedness hypothesis. Species and microhabitat assemblages were both strongly nested among peatlands. Whether sites were ranked by species richness, microhabitat richness or peatland area had no effect on nestedness. However, microhabitat nestedness was significantly reduced when sites were sorted by area rather than by microhabitat richness. As expected, if bird-microhabitat associations are responsible for the nested pattern of distribution, we found a positive correlation between the contributions of bird species and microhabitats to individual site nestedness. Nevertheless, microhabitat assemblages were significantly less nested than bird species assemblages, possibly because of frequent recolonization by birds or uneven sampling among sites. Received: 12 June 1998 / Accepted: 20 September 1998     

Effects of site and species characteristics on nested patterns of species composition in sedge meadows

Biotas of both geographical islands and habitat islands are often nested subsets of the biotas of successively more species-rich islands within the same system. The life history characteristics of a species may determine how that species contributes to the general pattern of species nestedness. Here, I investigate the floras of 56 sedge meadow wetlands in northern Illinois (USA) in order to characterize the degree of nestedness in these communities, determine which individual plant species contribute to the nested pattern, and investigate species characteristics that might be related to nonrandom patterns of distribution in individual plant species. The entire assemblage of species at all sedge meadows was significantly nested. Species richness and area were significantly correlated, and the nested pattern was closely related to site area, suggesting that species drop out of the assemblage in a predictable order as site area decreases. Some individual species exhibited nonrandom distributions across the sites, occurring more often in large, species-rich sites. Large sites were more likely than smaller sites to contain conservative species, i.e., those typical of pristine natural habitat, whereas nonconservative species were distributed more randomly among sites. Nested patterns of distribution of conservative species with respect to site area may result from their high probability of extinction on small sites or from a tendency for required habitats to co-occur on the same large sites. This revised version was published online in June 2006 with corrections to the Cover Date.     

Terrestrial bird community patterns on the coralline islands of the Dahlak Archipelago, Red Sea, Eritrea

Aim This study aims to explain the patterns of species richness and nestedness of a terrestrial bird community in a poorly studied region. Location Twenty‐six islands in the Dahlak Archipelago, Southern Red Sea, Eritrea. Methods The islands and five mainland areas were censused in summer 1999 and winter 2001. To study the importance of island size, isolation from the mainland and inter‐island distance, I used constrained null models for the nestedness temperature calculator and a cluster analysis. Results Species richness depended on island area and isolation from the mainland. Nestedness was detected, even when passive sampling was accounted for. The nested rank of islands was correlated with area and species richness, but not with isolation. Idiosyncrasies appeared among species‐poor and species‐rich islands, and among common and rare species. Cluster analysis showed differences among species‐rich islands, close similarity among species‐poor and idiosyncratic islands, and that the compositional similarity among islands decreased with increasing inter‐island distance. Thus, faunas of species‐poor, smaller islands were more likely to be subsets of faunas of species‐rich, larger islands if the distance between the islands was short. Main conclusions Species richness and nestedness were related to island area, and nestedness also to inter‐island distances but not to isolation from the mainland. Thus, nestedness and species richness are not affected in the same way by area and distance. Moreover, idiosyncrasies may have been the outcome of species distributions among islands being influenced also by non‐nested distributions of habitats, inter–specific interactions, and differences in species distributions across the mainland. Idiosyncrasies in nested patterns may be as important as the nested pattern itself for conservation – and conservation strategies based on nestedness and strong area effects (e.g. protection of only larger islands) may fail to preserve idiosyncratic species/habitats.     

An evaluation of randomization models for nested species subsets analysis

Randomization models, often termed “null” models, have been widely used since the 1970s in studies of species community and biogeographic patterns. More recently they have been used to test for nested species subset patterns (or nestedness) among assemblages of species occupying spatially subdivided habitats, such as island archipelagoes and terrestrial habitat patches. Nestedness occurs when the species occupying small or species-poor sites have a strong tendency to form proper subsets of richer species assemblages. In this paper, we examine the ability of several published simulation models to detect, in an unbiased way, nested subset patterns from a simple matrix of site-by-species presence-absence data. Each approach attempts to build in biological realism by following the assumption that the ecological processes that generated the patterns observed in nature would, if they could be repeated many times over using the same species and landscape configuration, produce islands with the same number of species and species present on the same number of islands as observed. In mathematical terms, the mean marginal totals (column and row sums) of many simulated matrices would match those of the observed matrix. Results of model simulations suggest that the true probability of a species occupying any given site cannot be estimated unambiguously. Nearly all of the models tested were shown to bias simulation matrices toward low levels of nestedness, increasing the probability of a Type I statistical error. Further, desired marginal totals could be obtained only through ad-hoc manipulation of the calculated probabilities. Paradoxically, when such results are achieved, the model is shown to have little statistical power to detect nestedness. This is because nestedness is determined largely by the marginal totals of the matrix themselves, as suggested earlier by Wright and Reeves. We conclude that at the present time, the best null model for nested subset patterns may be one based on equal probabilities of occurrence for all species. Examples of such models are readily available in the literature. Received: 3 February 1997 / Accepted: 21 September 1997     

Nestedness of Southern Ocean island biotas: ecological perspectives on a biogeographical conundrum

Aim To use patterns of nestedness in the indigenous and non‐indigenous biotas of the Southern Ocean islands to determine the influence of dispersal ability on biogeographical patterns, and the importance of accounting for variation in dispersal ability in their subsequent interpretation, especially in the context of the Insulantarctic and multi‐regional hypotheses proposed to explain the biogeography of these islands. Location Southern Ocean islands. Methods Nestedness was determined using a new metric, d1 (a modification of discrepancy), for the indigenous and introduced seabirds, land birds, insects and vascular plants of 26 Southern Ocean islands. To assess the possible confounding effects of spatial autocorrelation on the results, islands were assigned to 11 major island groups and each group was treated as a single island in a following analysis. In addition, nestedness of the six Southern Ocean islands comprising the South Pacific Province (New Zealand islands) was analysed. All analyses were conducted for species and genera, for each of the taxa on its own, and for the complete data sets. Results Statistically significant nestedness was found in all of the taxa examined, with nestedness declining in the order seabirds > land birds > vascular plants > insects for the indigenous species. Vagility had a marked influence on nestedness and the biogeographical patterns shown by the indigenous species. This influence was borne out by additional analyses of marine taxa and small‐sized terrestrial species, both of which were more nested than the most nested group examined here, the seabirds. Assemblages of non‐indigenous species also showed nestedness, and nestedness was generally more pronounced than in the indigenous species. Surprisingly, vagility had a significant effect on nestedness in these assemblages too. Main conclusions Nestedness analyses provide a quantitative means of comparing biogeographical patterns for groups differing in vagility. These comparisons revealed that vagility has a considerable influence on biogeographical patterns and should be taken into account in analyses. Here, investigations of more vagile taxa support hypotheses for a single origin of the Southern Ocean island biota (the Insulantarctica scenario), whilst those of less mobile taxa support the more commonly held, multi‐regional hypothesis. All biogeographical analyses across the Southern Ocean (and elsewhere) will be influenced by the effects of dispersal ability, with composite analyses dominated by sedentary groups likely to favour multi‐regional scenarios, and those dominated by mobile groups favouring single origins. Mechanisms underlying nestedness in the region range from nested physiological tolerances in more mobile groups to colonization ability and patterns of speciation in less vagile taxa. Considerable nestedness in the non‐indigenous assemblages is largely a consequence of the fact that many of these species are European weedy species.     

Distributions of forest birds and butterflies in the Andaman islands, Bay of Bengal: nested patterns and processes

The distributional patterns of forest birds and butterflies in the Andaman islands, an oceanic chain located off SE Asia, were tested for nestedness. Both taxa were highly nested. Nestedness could be due to colonization or extinction processes, area or distance effects or nestedness of habitats. Nestedness in forest bird distributions were strongly influenced by area and habitat related factors. Habitats were significantly nested in all three island groups, however most strongly for the North Andamans. However forest bird distributions in the North Andamans, as indicated by row order in the packed matrix, was not correlated with habitat diversity, suggesting that habitat related factors alone cannot account for these patterns. Other causal influences could be passive sampling, where common and abundant species and habitats are more likely to have a widespread distribution than rare species and habitats. The nested subset pattern seen in two unrelated taxa suggests that the Andamans are extinction dominated and that the protection of forests on large islands is critical for the conservation of its biodiversity.     

Nestedness of butterfly assemblages in the Zhoushan Archipelago,China: area effects,life-history traits and conservation implications

The nested subset pattern (nestedness) of faunal assemblages has been a research focus in the fields of island biogeography and conservation biology in recent decades. However, relatively few studies have described nestedness in butterfly assemblages in oceanic archipelago systems. Moreover, previous studies often quantified nestedness using inappropriate nestedness metrics and random fill algorithms with high Type I errors. The aims of this study are to examine the existence of nestedness and underlying causal mechanisms of butterfly assemblages in the Zhoushan Archipelago, China. We used the line-transect method to determine butterfly occupancy and abundance on 42 study islands from July to August 2014. We obtained butterfly life-history traits (wingspan, body weight and minimum area requirement) by field work and island geographical features (area and isolation) from the literature. We used the recently developed metric WNODF to estimate nestedness. Partial Spearman rank correlation was used to evaluate the associations of nestedness and island geographical features as well as butterfly life-history traits related to species extinction risk and colonization ability. The butterfly assemblages were significantly nested. Island area and minimum area requirement of butterflies were significantly correlated with nestedness after controlling for other independent variables. In contrast, the nestedness of butterflies did not appear to result from passive sampling or selective colonization. However, multi-year studies are needed to confirm that target effects are not muddling these results. Our results indicate that selective extinction may be the main driver of nestedness of butterfly assemblages in our study system. From a conservation viewpoint, we should protect both large islands and species with large area requirement to maximize the number of species preserved.     

Effects of Fragmentation and Sea-Level Changes upon Frog Communities of Land-Bridge Islands off the Southeastern Coast of Brazil

We investigate the composition of anuran communities of land-bridge islands off the southeastern coast of Brazil. These islands provide natural long-term experiments on the effects of fragmentation in the Brazilian Atlantic Forest (BAF). We hypothesize that Pleistocene sea-level changes, in combination with other abiotic variables such as area and habitat diversity, has affected anuran species richness and community composition on these islands. Data from the literature and collections databases were used to produce species lists for eight land-bridge islands and for the mainland adjacent to the islands. We assess the effects of area, number of breeding habitats and distance to the mainland upon anuran species richness on land-bridge islands. Additionally we use nestedness analysis to quantify the extent to which the species on smaller and less habitat-diverse islands correspond to subsets of those on larger and more diverse ones. We found that area has both direct and indirect effects on anuran species richness on land-bridge islands, irrespective of distance to the mainland. However, on islands with comparable sizes, differences in species richness can be attributed to the number and quality of breeding habitats. Anuran communities on these islands display a nested pattern, possibly caused by selective extinction related to habitat loss. Common lowland pond-breeders were conspicuous by their absence. In the BAF, the conservation of fragments with a high diversity of breeding habitats could compensate for the generally negative effect of small area upon species richness. We suggest that sea-level changes have an important role in shaping composition of anuran species on coastal communities.