Ground‐nesting by the chimpanzees of the Nimba Mountains,Guinea: environmentally or socially determined?

The chimpanzees (Pan troglodytes verus) of the Nimba Mountains, Guinea, West Africa, commonly make both elaborate ("night") and simple ("day") nests on the ground. In this study we investigated which factors might influence ground-nesting in this population, and tested two ecological hypotheses: 1) climatic conditions, such as high wind speeds at high altitudes, may deter chimpanzees from nesting in trees; and 2) a lack of appropriate arboreal nesting opportunities may drive the chimpanzees to nest on the ground. In addition to testing these two hypotheses, we explored whether ground-nesting is a sex-linked behavior. Data were collected monthly between August 2003 and May 2004 along transects and ad libitum. To identify the sex of ground-nesting individuals, we used DNA extracted from hair samples. The results showed that the occurrence and distribution of ground nests were not affected by climatic conditions or a lack of appropriate nest trees. Support was found for the notion that ground-nesting is a sex-linked behavior, as males were responsible for building all of the elaborate ground nests and most of the simple ground nests sampled. Elaborate ground nests occurred mostly in nest groups associated with tree nests, whereas simple ground nests usually occurred without tree nests in their vicinity. These results suggest that ground-nesting may be socially, rather than ecologically, determined.     

天山南麓山前平原植物群落物种多样性及空间分异研究

荒漠灌丛是天山南麓山前平原主要植被类型.本研究定量分析了山前平原植物群落物种多样性及生境尺度异质性的影响.结果表明:(1)天山南麓山前平原的植物群落多样性指数Simpson、均匀度指数McIntosh及丰富度指数Margalef都较低,在地貌带的过渡上,植物分布呈现均匀化.(2)海拔和地下水埋深是影响天山南麓山前平原植物群落物种多样性的重要环境指标.海拔梯度与物种多样性指数Simpson、Margalef及McIntosh均呈显著的线性正相关关系,物种多样性均随海拔高度的增加而增加;地下水埋深与物种多样性指数呈极显著的线性负相关关系,物种多样性随地下水埋深的增加而减小.(3)土壤含盐量与物种多样性指标无显著关系,但土壤含盐量与地下水埋深相关性显著,这是天山南麓山前平原土壤盐分空间异质性的一个重要特点.土壤盐分含量变化影响着植物群落物种组成,随土壤盐分含量增加,群落中盐生植物种类逐渐占据优势.(4)海拔的变化是决定天山南麓山前平原灌丛群落生境差异的主导因子.海拔差异表征了山前平原地貌、水文地质条件及土壤的变化,而随海拔变化的水热、水盐等干扰体系的差异则进一步导致了异质性的生境,进而影响不同植被类型中群落组成结构和多样性的差异.     

Dispersal differences predict population genetic structure in Mormon crickets

Research investigating the geographical context of speciation has primarily focused on abiotic factors such as the role of Pleistocene glacial cycles, or geotectonic events. Few study systems allow a direct comparison of how biological differences, such as dispersal behaviour, affect population genetic structure of organisms that were subdivided during the Pleistocene. Mormon crickets exist in solitary and gregarious 'phases', which broadly correspond with an east-west mtDNA division across the Rocky Mountains. Gregarious individuals form bands that can move up to 2 km daily. This study assessed whether population genetic structure results mainly from deep Pleistocene vicariance or if we can also detect more recent genetic patterns due to phase and dispersal differences superimposed on the older, deeper divisions. We found that separation in refugia was a more important influence on genetic divergence than phase, with the Rockies acting as a barrier that separated Mormon cricket populations into eastern and western refugia during Pleistocene glacial cycles. However, patterns of isolation by distance differ between eastern and western clades for both mitochondrial and nuclear DNA, with greater divergence within the eastern, solitary clade. An mtDNA haplotype mismatch distribution is compatible with historical population expansion in the western clade but not in the eastern clade. A persistent (and possibly sex-biased) difference in dispersal ability has most likely influenced the greater population genetic structure seen in the eastern clade, emphasizing the importance of the interaction of Quaternary climate fluctuations and geography with biotic factors in producing the patterns of genetic subdivision observed today.     

Tree-line changes along the Andes: implications of spatial patterns and dynamics

The Andes provide an extensive latitudinal and topographical framework for studying the factors that control the spatial patterns of forests (timberlines) and their species components expressed through the presence of tree growth forms (tree lines). Despite consistent overall similarities in landscape patterns, many processes must be unique, given the dramatic differences in species richness and biophysical constraints along the Andes. In all cases evaluated to date, morphological plasticity is a common trait of plant species that dominate at tree lines. In fact, many changes observed can be related to species-specific traits. Physiological limitations on tree growth form only explain species limits, while disturbances and cyclical climate fluctuations interact to affect many landscape patterns. Over long periods of time, tree lines provide unique habitats and perhaps opportunities for speciation. Understanding the spatial organization of tree-line dynamics is one viable research approach for evaluating the likely past fluxes and possible future changes.     

Mechanisms underlying the impacts of exotic annual grasses in a coastal California meadow

Biological invasions can impact the abundance and diversity of native species, but the specific mechanisms remain poorly discerned. In California grasslands, invasion by European annual grasses has severely reduced the quality of habitat for native forb species. To understand how introduced grasses suppress native and exotic forbs, we examined the response of a Southern California grassland community to factorial removals of live grass and the litter produced in previous seasons. To examine the role that belowground competition for water plays in mediating the impact of grasses, we crossed grass and litter removal treatments with water addition. Our results show that forbs were almost equally suppressed by both competition from live grass and direct interference by litter. Water addition did not ameliorate the effect of grass competition, suggesting that water was not the resource for which plants compete. This evidence is consistent with the susceptibility of forbs to light limitation, especially considering that litter does not consume water or nutrients. Interestingly, despite different histories of co-occurrence with annual grass dominants, native and exotic forbs were comparably suppressed by exotic grasses. Our results indicate that suppression by both live and dead stems underlie the influence of exotic grasses on forb competitors.     

Les palynomorphes du Bajocien supérieur : un premier PALYNO-DATA pour les Monts de Rhar Roubane (Algérie nord occidentale)

Apart from the few works carried out in the North Tethyan basins, the palynological study of Mesozoic outcrops is still rare. Thus, the present study devoted to the Zahra Marls Formation (upper Bajocian) of the Rhar Roubane Mountains (northwestern Algeria), allowed us for the first time to inventory 44 different taxa. The palynological assemblages studied are strongly dominated by trilete spores (17 genera and 26 species), the most abundant of which are Concavissimisporites variverrucatus, Cyathidites australis and Cyathidites minor. Pollen grains are relatively frequent (10 genera and 16 species), while acritarchs and algae are represented by only two taxa (Micrhystridium sp. and Botryococcus sp.). In addition, the sporopollinic spectra dominated by the terrestrial elements are represented mainly by the spores of Pteridophyta and Bryophyta and gymnosperm pollen.     

祁连山青海云杉林群落结构的空间异质性

以动态监测样地(340 m×300 m)的网格(5 m×5 m)为基本单元,选择5个群落结构属性变量,采用分形几何学和地统计学方法对祁连山大野口流域青海云杉林群落结构的空间异质性进行研究.结果表明: 青海云杉林5个结构属性的变异程度大小依次为:密度＞平均冠幅＞显著度＞盖度＞平均树高,变异系数为43.7%～79.6%.Moran I系数表明,各个结构属性均有不同程度的空间自相关性,自相关大小顺序为:密度＞平均树高＞盖度＞平均冠幅＞显著度,变化范围为-0.047～0.382.指数理论变异函数模型能很好地拟合不同结构属性的空间变异,变程为24.6～68.1 m,各属性变量的结构比除盖度表现为中等空间相关,其他指标均为强烈空间相关,各属性指标分维数接近2,空间依赖性较小.植被密度和盖度空间分布呈带状结构和斑块结构叠加的特点,其他指标呈较强的斑块状空间结构,密度和盖度对平均冠幅、显著度和平均树高有一定的空间依赖性.青海云杉林群落结构空间异质性适宜的采样间隔和采样面积分别为10 m和0.5 hm².     

秦岭紫堇属植物及其地理分布修订

在室内查阅标本和查阅文献资料的基础上,结合野外实际调查,对秦岭地区紫堇属植物及其地理分布进行全面修订。结果表明:秦岭地区共有紫堇属植物28种,其中5种为秦岭特有种。地理分布格局研究表明:8种为秦岭广布种,7种为秦岭西部分布种,7种为秦岭中部分布种,1种为秦岭东部分布种,3种为秦岭中部和西部分布种,2种为中部和东部分布种。根据修订,给出了秦岭紫堇属植物分种检索表。     

秦岭南坡锐齿栎次生林空间结构特征分析

该研究采用坐标定位方法对秦岭南坡不同坡向锐齿栎次生林样地内胸径DBH≥5cm的乔木进行调查,记录树种名称、坐标、胸径、高度、冠幅、生长状况等因子,运用角尺度、大小比数和混交度3个指数分析不同坡向锐齿栎次生林的空间结构,探寻不同坡向锐齿栎林空间结构的形成和差异。结果显示:(1)调查样地内物种多样性丰富,锐齿栎重要值最大,长势良好,占据主要生态空间。(2)两种坡向中,角尺度取值为0.5的个体数均过半,表明随机分布是锐齿栎次生林的主要分布方式。(3)优势木、亚优势木、中庸木、劣态木和绝对劣态木所占比重均为20%左右,表明林木大小差异不明显,在空间结构单元中,林木较稳定,阳坡优势木个体数高于阴坡。(4)两种坡向中,混交度取值大于0.5林木个体分别为84%和73%,表明多数林木个体处于中度、强度和极强度混交状态。研究表明,秦岭南坡锐齿栎次生林聚集度不高、混交良好、分化程度较高,锐齿栎种群优势度明显,林分整体暂时处于相对稳定状态。