Freshwater icefishes (Salangidae) in the Yangtze River basin of China: Spatial distribution patterns and environmental determinants

Synopsis We surveyed 86 lakes affiliated to the Yangtze River to assess the status of natural freshwater icefishes, and to study their spatial distribution patterns and environmental relationships. Results showed that the spatial patterns of icefish diversity and the occupancy of each species related closely to the historical process of habitat fragmentation. Statistical analyses indicated that the spatial structure of the icefish assemblage significantly related to the area- and isolation-related environmental variables. These results illustrated the significant impacts of hydrological engineering (dykes and floodgates) on the historical dynamics of the icefish populations, and shed light on the essentiality and feasibility of conserving and wise using freshwater icefishes by managing suitable habitats and re-connecting the river-lake network in the Yangtze River basin.     

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。     

Rampant drift in artificially fragmented populations of the endangered tidewater goby (Eucyclogobius newberryi)

Habitat fragmentation and its genetic consequences are a critically important issue in evaluating the evolutionary penalties of human habitat modification. Here, we examine the genetic structure and diversity in naturally subdivided and artificially fragmented populations of the endangered tidewater goby (Eucyclogobius newberryi), a small fish restricted to discrete coastal lagoons and estuaries in California, USA. We use five naturally fragmented coastal populations from a 300‐ km spatial scale as a standard to assess migration and drift relative to eight artificially fragmented bay populations from a 30‐ km spatial scale. Using nine microsatellite loci in 621 individuals, and a 522‐base fragment of mitochondrial DNA control region from 103 individuals, we found striking differences in the relative influences of migration and drift on genetic variation at these two scales. Overall, the artificially fragmented populations exhibited a consistent pattern of higher genetic differentiation and significantly lower genetic diversity relative to the naturally fragmented populations. Thus, even in a species characterized by habitat isolation and subdivision, further artificial fragmentation appears to result in substantial population genetic consequences and may not be sustainable.     

Modelling the effect of habitat fragmentation on range expansion in a butterfly

There is an increasing need for conservation programmes to make quantitative predictions of biodiversity responses to changed environments. Such predictions will be particularly important to promote species recovery in fragmented landscapes, and to understand and facilitate distribution responses to climate change. Here, we model expansion rates of a test species (a rare butterfly, Hesperia comma) in five landscapes over 18 years (generations), using a metapopulation model (the incidence function model). Expansion rates increased with the area, quality and proximity of habitat patches available for colonization, with predicted expansion rates closely matching observed rates in test landscapes. Habitat fragmentation constrained expansion, but in a predictable way, suggesting that it will prove feasible both to understand variation in expansion rates and to develop conservation programmes to increase rates of range expansion in such species.     

Consequences of forest fragmentation for the dynamics of bird populations: conceptual issues and the evidence

This paper reviews the consequences of forest fragmentation for the dynamics of bird populations. Owing to high mobility and large home ranges, birds usually perceive fragmented forests in a finegrained manner, i.e. embrace several forest fragments in functional home ranges. On a regional scale, however, coarse-grained clusters of fine-grained fragments (hierarchical fragmentation may sub-divide bird populations into isolated demes, which enter a domain of metapopulation dynamics. Distinctions are made between pure distance-area or population-level effects and more indirect community-level effects due to changes in landscape composition. Distance-area effects, such as insularization and decreasing fragment size, directly prevent dispersal and reduce population size. Landscape effects, such as reduced fragment-matrix and interior-edge ratios, increase the pressure from surrounding predators, competitors, parasites and disease. In short, forest fragmentation can be viewed as a two-step process. Initially, fine-grained fragmentation triggers distance-area and landscape effects on a local scale, which in turn, results in a range retraction of a population to non-fragmented or less fragmented parts of a region. At a certain point, non-fragmented areas become so widely spaced out that regional distance-area effects come into operation, giving rise to metapopulation dynamics. Although few bird metapopulations have yet been documented, metapopulation dynamics probably is a common characteristic of bird populations confined to 'hierarchical' fragmented forests.     

Fragmentation and genetic differentiation among subpopulations of the endangered Hawaiian mint Haplostachys haplostachya (Lamiaceae)

Haplostachys haplostachya was at one time a prevalent species in the mid-elevation (1650–1800 m) xerophytic shrubland between Mauna Loa and Mauna Kea on Hawaii. Grazing pressure by feral ungulates, destruction of habitat from military activity, and conversion of forest to pastures have fragmented its range to small subpopulations restricted to several cinder cones and portions of the remaining shrubland. Some subpopulations are still extensive, while others are reduced to 20 or fewer individuals. Genetic analyses using random amplified polymorphic DNA (RAPD) markers demonstrate that plants in subpopulations with a large number of individuals maintain levels of genetic variation similar to the entire population, whereas plants in a small subpopulation at Pu'u Leilani (14 individuals remaining) have reduced levels of variation. Of the 122 loci identified, 54 (44%) were polymorphic. Two large populations showed variation at 45 and 49 loci, but the Pu'u Leilani plants showed variation at only 37 loci. The mean expected heterozygosity ( H ) in this subpopulation was also lower (0.137 vs. 0.163 and 0.154) and genetic differentiation ( G _ST) was higher (0.167 vs. 0.018 and 0.052) than in other subpopulations. An examination of variation indicates that although plants of the three subpopulations are genetically similar, there is evidence of genetic restructuring among the subpopulations. The impact of these results towards conservation efforts of this and other endangered species is discussed.     

Population divergence of genetic (co)variance matrices in a subdivided plant species,Brassica cretica

Abstract The present study of Brassica cretica had two objectives. First, we compared estimates of population structure (Q_st) for seven phenotypic characters with the corresponding measures for allozyme markers (F_st) to evaluate the supposition that genetic drift is a major determinant of the evolutionary history of this species. Secondly, we compared the genetic (co)variance ( G ) matrices of five populations to examine whether a long history of population isolation is associated with large, consistent differences in the genetic (co)variance structure. Differences between estimates of F_st and Q_st were too small to be declared significant, indicating that stochastic processes have played a major role in the structuring of quantitative variation in this species. Comparison of populations using the common principal component (CPC) method rejected the hypothesis that the G matrices differed by a simple constant of proportionality: most of the variation involved principal component structure rather than the eigenvalues. However, there was strong evidence for proportionality in comparisons using the method of percentage reduction in mean‐square error (MSE), at least when characters with unusually high (co)variance estimates were included in the analyses. Although the CPC and MSE methods provide different, but complementary, views of G matrix variation, we urge caution in the use of proportionality as an indicator of whether genetic drift is responsible for divergence in the G matrix.     

复合种群动态研究进展

复合种群动态研究是当今保护生物学和生态学中最热门的课题之一。在此较为详细地介绍了复合种群动态的有关概念和术语、经验研究和理论探索的最新进展以及相关的预测模型 ,对我国开展相关研究有参考价值。     

云南昆明地区滇蛙和昭觉林蛙的形态特征及习性分化比较

根据对滇蛙（Rana pleuraden）和昭觉林蛙（R．chaochiaoensis）标本外部形态比较和野外观察结果,滇蛙和昭觉林蛙的雌雄性比大约在1：1之间,而它们的形态特征、栖境与习性、繁殖时间等均存在分化。昭觉林蛙更适应陆地生活。昆明地区的滇蛙和昭觉林蛙的繁殖策略不同,滇蛙的繁殖在3—7月,昭觉林蛙的在9—11月。昭觉林蛙选择在冬季繁殖,可以避开与其它蛙类的繁殖竞争,但其更深层次的生物学意义值得进一步探讨。