人为活动对舟山群岛大中型兽的影响：大中型兽受威胁原因分析

威胁舟山群岛大中型兽的主要因素是人为活动对自然栖息地造成的面积损失,破碎,质量下降和捕杀。自然栖息地面积已损失了56．3％,自然栖息地破碎成许多碎片,破碎程度在加深,而自然栖息地质量在1912～1950年间严重下降。大中型兽受威胁历史可分为三个阶段,1912年前,大中型兽受威胁较轻;1912～1950年间,大中型兽受到严重威胁,主要威胁因素是自然栖息地面积损失,破碎和森林覆盖率下降;1950年至现在,大中型兽受威胁同样很重,主要威胁因素是自然栖息地面积损失,破碎和捕杀。自然栖息地面积损失,破碎和质量下降对大中型兽绝灭有重要影响。自然栖息地面积损失、破碎和人为捕杀是大中型兽濒危、分布区缩小和数量下降的主要原因。社会,政治,经济等因素决定了自然栖息地面积损失,破碎和质量变化的速率以及捕杀的水平。     

破碎化次生林斑块面积及栖息地质量对繁殖鸟类群落结构的影响

于1998～2000年夏季。运用GPS定位系统确定了12块面积范围为6．5～112．8hm。的彼此隔离的森林斑块。比较了斑块面积和栖息地质量对繁殖鸟类群落结构的影响。结果表明：不同面积斑块中繁殖鸟类的群落结构有所差异。各斑块所容纳的繁殖鸟类的物种数从4种到26种不等。鸟类物种数随着斑块面积的增大而增多。不同鸟类对斑块面积的反应并不相同,耐边缘种偏爱面积较小的斑块。而非边缘种偏爱在大面积的斑块中繁殖。斑块栖息地质量也是影响鸟类群落结构的重要因素,质量好的斑块包容的鸟类物种较多。鸟类物种丰富度与斑块质量的相关性(R2=0．67)小于与斑块面积的相关性(R2=0．88)。各斑块中的鸟类群落结构在不同年份间比较相似。栖息地破碎化不但缩小了栖息地面积。同时也不同程度地降低了栖息地的质量。从而消极地影响着鸟类群落结构的稳定性和鸟类的物种多样性。     

物种数和面积、纬度之间关系的研究

本文在排除了“平衡假说”中的“岛屿效应”的情况下,估算了世界部分国家兽类,鸟类,爬行类和两栖类的物种－面积,物种－纬度及物种－面积－纬度关系式中的参数。研究发现,大陆连续栖息地性的ｚ值并不比岛屿或栖息地“岛屿”性的ｚ值小,ｚ值与面积样本大小和范围有关。栖息地异质性对ｚ值的大小也起着很重要的作用。本文建立了全球脊推动物物种－面积－纬度相关模型,即Ｌｏｇｓ＝ｂ＿ｏ＋ｂ＿１·ＬｏｇＡ＋ｂ＿２·Ｌ,总复合相关系数达０．９０２８（ｐ＜０．０１）,可用于预测或评估全球脊推动物种数分布或由于栖息地破坏后物种数消失的情况。     

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。     

物种的全球性丧失能得到制止吗？

物种的全球性丧失能得到制止吗？１物种绝灭危机问题是否该引起人们的重视？地球上的物种正以惊人的速度绝灭！１９８６年由美国国家科学院和史密森研究院共同发起的“生物多样性全国论坛”,论证了人类对自然生境破坏致使物种绝灭的危机正日益严重,甚至比得上约在６千５...     

栖息地片断化对动物种群间基因流的影响及其测定方法

栖息地片断化指在人为活动和自然干扰下,大面积连续分布的自然栖息地被其它非适宜栖息地分隔成许多面积较小的斑块(岛屿)的过程。栖息地片断化是导致生物多样性丧失和物种绝灭的主要因素,也是威胁自然界生物生存的重要因素之一。栖息地片断化将影响基因在种群间和种群内的运动(基因流),开展栖息地片断化研究对保持物种间遗传多样性具有重要意义。本文介绍了片断化程度和基因流的测定方法。回顾了国内外的研究现状,并探讨了片断化对种群间基因流的影响和对濒危物种保护的意义。     

物种多样性变化格局与时空尺度

物种多样性时空格局作为生物多样性研究的重要内容, 是针对物种的数量变化和物种的生物学多样性程度,在不同尺度范围内探讨物种多样性的时空格局及其变化规律。本文首先讨论物种多样性的空间格局,特别是不同尺度上的“物种－面积”模式,分析了纬度梯度、栖息地因素对物种多样性格局形成的作用。在时间尺度上,本文分析了物种多样性在不同时间尺度的变化格局：从生物长期进化的地史时间看,物种多样性稳定增长受到周期性大绝灭事件中断。最新研究表明,物种多样性时间格局决定于最近一次大绝灭后的初始状态。在较短的时间范围内,如生态群落演替、季节周期等,物种多样性变化呈现特殊的模式。此外,也发现寄主上寄生物种的多样性有随着时间而增加的趋势。     

动物的易绝灭特征与保护优先性

各种人为干扰和自然因素促使大量物种走向濒危和绝灭。物种濒危和绝灭不是随机的。具有某些特征的物种容易濒危和绝灭 ,即易绝灭特征。易绝灭特征包括个体大 ,繁殖力低 ,扩散能力弱 ,营养级高 ,家域大 ,种群小 ,种群波动大 ,分布范围窄 ,种群密度低 ,栖息地特化程度高和特殊栖息地类型等。研究物种的易绝灭特征可以为生物多样性提供预防性 (proac tive)的优先保护措施。尽管物种的易绝灭特征已经用于实际的物种保护中 ,然而由于物种的各种特征对物种濒危和绝灭的影响十分复杂 ,各个易绝灭特征还有待于进一步深入的、准确的研究。探讨适合不同类群和不同地区物种的易绝灭特征是十分必要的。由于特殊地史发育、中医药传统和边境频繁的非法野生动物贸易 ,我国动物的濒危模式可能与国外有所不同。     

人为活动对舟山群岛大中型兽的影响：大中型兽受威胁状态分析

本文根据历史记载对比和皮张收购资料分析研究了舟山群岛大中型兽的受威胁状态。结果显示,舟山群岛曾有大中型兽16种,5种已绝灭,3种处于濒危状态,3种分布区缩小（一种种群数量正在下降）,3种种群保持稳定,2种种群动态不明;食肉动物的绝灭率大于食草动物;大型动物绝灭率较高;岛屿物种绝灭率高于邻近大陆。文章还比较了确定种群趋势的几种方法。     

评世界保护联盟新的物种受威胁分类系统草案

为了进一步了解物种受威胁的情况和发展,以加强物种保护工作,世界保护联盟制定了一个新的物种受威胁分类系统草案,把物种受威胁的程度分为９个级别,即绝灭种、野生状态下的绝灭种、极危种、濒危种、渐危种、敏感种、安全的／危险性小的种、不充分了解的种和未估价的种。本文对这个分类系统草案作了简略的评介。     

A neutral model of edge effects

In this paper a spatially implicit neutral model for explaining the edge effects between habitats is proposed. To analyze this model we use two different approaches: a discrete approach that is based on the Master equation for a one step jump process and a continuous approach based on the approximation of the discrete jump process with the Kolmogorov-Fokker-Planck forward and backward equations. The discrete and continuous approaches are applied to analyze the species abundance distributions and the time to species extinction. Moreover, with the aid of the continuous approach a realistic classification of the behavior of species in local communities is developed. The species abundance dynamics at the edge between two distinct habitats is compared with those located in the homogeneous interior habitats using species abundance distributions and the first time to species extinction. We show that the structure of the links between local community and the metacommunity plays an important role on species persistence. Specifically, species at the edge between two distinct metacommunities have higher extinction rate than those in the interior habitats connected only to one metacommunity. Moreover, the same species might be persistent in the homogeneous interior habitat, but its probability of extinction from the edge local community could be very high.     

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.     

Are artificial wetlands good alternatives to natural wetlands for waterbirds? – A case study on Chongming Island, China

Loss of natural wetlands is a global phenomenon that has been a serious threat to the wildlife. A common practice is to construct artificial wetlands to compensate for the loss of natural wetlands. To test whether artificial wetlands as habitats for waterbirds are good alternatives to natural wetlands, we compared species richness, abundance, and seasonal dynamics of waterbird communities of natural (here tidelands) and artificial wetlands (here aquacultural ponds) on Chongming Island, China. Our results indicate that habitat preference of waterbirds showed seasonal difference: most of the shorebirds were found on tidelands in spring, whereas most of the natatorial birds were recorded in aquacultural ponds in winter. Waterbirds preferred the tidelands rather than aquacultural ponds in both spring and autumn, whereas they showed no preference for either the tidelands or the ponds in summer and winter. It is concluded that natural wetlands are better habitats for waterbirds than artificial wetlands on Chongming Island, while the artificial ones are also suitable habitats for waterbirds in winter. The waterbirds might use artificial wetlands only when natural wetlands are unavailable or of poor quality. An over-emphasis that artificial wetlands are suitable habitats for waterbirds might encourage land managers to convert natural wetlands into the artificial ones, resulting in considerable loss of bird diversity. Therefore, for the purpose of bird conservation, it would be a better practice to conserve natural wetlands rather than to construct artificial ones after destruction of natural wetlands.     

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.     

Lost and found: Short-term dynamics of the flora on 100 small islands in the White Sea

The aim was to uncover factors that influence short-term (decade) flora dynamics and species richness of northern marine islets characterized by poor flora and weak anthropogenic pressure. The study used presence–absence data of vascular plant species on 100 small uprising islets of the Kandalaksha Gulf of White Sea (Northern Karelia, Russia). We investigated the influence of islands' attributes on species richness and rates of flora dynamics. Two island types were analyzed separately: younger, stone-like and older, islet-like (which generally are larger and have higher diversity of habitats). Sampled islands were studied via classical biogeographical per island approach and metapopulation per species approach. Stone-like islands had noticeably poorer flora with higher rates of immigration and extinction when compared to those of islet-like islands. The species number for islet-like islands correlated positively with number of habitats, abundance of different habitat types and island area. Species richness of stone-like islands correlated positively only with number of habitat types. Plant species associated with birds, crowberry thickets and coastal rocks were the most stable, and the species of disturbed habitats were significantly less stable. Floristic changes that have occurred have been caused by the massive establishment of new species rather than the extinction of pre-existing taxa. Thus, most of these islands are still in the colonization (assortative) stage. While we found no relationship between island area and species number for stone-like islands, this relationship was seen on islet-like islands.     

Habitat fragmentation reduces plant progeny quality: a global synthesis

Most of the world's land surface is currently under human use and natural habitats remain as fragmented samples of the original landscapes. Measuring the quality of plant progeny sired in these pervasive environments represents a fundamental endeavour for predicting the evolutionary potential of plant populations remaining in fragmented habitats and thus their ability to adapt to changing environments. By means of hierarchical and phylogenetically independent meta‐analyses we reviewed habitat fragmentation effects on the genetic and biological characteristics of progenies across 179 plant species. Progeny sired in fragmented habitats showed overall genetic erosion in contrast with progeny sired in continuous habitats, with the exception of plants pollinated by vertebrates. Similarly, plant progeny in fragmented habitats showed reduced germination, survival and growth. Habitat fragmentation had stronger negative effects on the progeny vigour of outcrossing‐ than mixed‐mating plant species, except for vertebrate‐pollinated species. Finally, we observed that increased inbreeding coefficients due to fragmentation correlated negatively with progeny vigour. Our findings reveal a gloomy future for angiosperms remaining in fragmented habitats as fewer sired progeny of lower quality may decrease recruitment of plant populations, thereby increasing their probability of extinction.     

科尔沁沙地沙漠化过程中的物种多样性

对内蒙古科尔沁地区沙漠化过程中物种多样性的变化特征进行了分析 ,依据植物种在各类型沙漠化土地的出现频率和不同沙漠化阶段各生活型植物种的组成 ,探讨了沙漠化过程中植物种绝灭和定居特点 .物种多样性指数分析表明 ,沙漠化过程是一个物种多样性衰减的过程 ,沙漠化首先导致特有种的绝灭 ,其次为稀有种和普通种 .从植物的生活型来看 ,多年生草本和灌木类植物受沙漠化影响最大 ,而 1年生草本和半灌木类植物可存活于沙漠化过程各个阶段 .在沙漠化过程中植物种的绝灭速率大于定居速率 .     

Inconsistent detection of extinction debts using different methods

The extinction debt, delayed species extinctions following landscape degradation, is a widely discussed concept. But a consensus about the prevalence of extinctions debts is hindered by a multiplicity of methods and a lack of comparisons among habitats. We applied three contrasting species–area relationship methods to test for plant community extinction debts in three habitats which had different degradation histories over the last century: calcareous grassland, heathland and woodland. These methods differ in their data requirements, with the first two using information on past and current habitat area alongside current species richness, whilst the last method also requires data on past species richness. The most data‐intensive, and hence arguably most reliable method, identified extinction debts across all habitats for specialist species, whilst the other methods did not. All methods detected an extinction debt in calcareous grassland, which had undergone the most severe degradation. We conclude that some methods failed to detect an extinction debt, particularly in habitats that have undergone moderate degradation. Data on past species numbers are required for the most reliable method; as such data are rare, extinction debts may be under‐reported.     

Assessing the impact of reforestation on the diversity of Mediterranean terrestrial Gastropoda

In the Mediterranean basin, pine tree reforestation has been the most common management tool in restoring degraded and burnt areas, as well as for economic purposes. However, the quality of the biodiversity of these habitats has undergone little assessment. Terrestrial gastropods are suitable indicators of forest quality and long-term stability because of their strict dependence on microhabitat conditions and their slow dispersal rate. We sampled the gastropod population in a protected Mediterranean area in order to compare the species richness in seven main habitats. Holm oak wood and mixed-pine forests were the habitats with the lowest species density, and areas with a high level of heterogeneity exhibited the richest communities. In recent decades however, land abandonment and pine reforestation are leading to landscape homogeneity, which is perhaps the cause of the extinction of six open-habitat gastropod species in the Park. These results provide park authorities with insights into how to adapt management plans to enhance habitat quality for land snail and slug assemblages. More specifically, our results stress the need to create habitat heterogeneity to increase land mollusc diversity in large and continuous areas of mixed-pine forests.     

稻田蜘蛛群落的重建及与其种库的相关性

稻田生态系统是一个不稳定的生态系统,包括稻田和非稻田生境2个部分。随着水稻的移栽与收割,稻田蜘蛛群落周期性地呈现出群落重新形成、群落发展和群落瓦解3个阶段。这一群落的发展不同于自然群落的演替。因此,将稻田生境内蜘蛛群落的重新形成过程定义为群落的重建,而非稻田生境内的蜘蛛群落称之为稻田生境内蜘蛛群落的种库。群落重建是一个季节性的、可重复的动态变化过程,以群落的周期性彻底瓦解和周期性重新形成为最主要特征。种库为群落的重建提供移居者并接受群落瓦解时所迁出的蜘蛛.二者之间呈现出互补的相互关系。保护群落的种库将有助于自然天敌群落的重建。自然天敌群落的重建是自然天敌保护和持续利用的生态学基础的一个重要组成部分,对天敌的保护利用和天敌效能的提高有十分重要的意义。