关键词： mcroinvertebrates   abundance   diversity   habitat heterogeneity   biomass  

摘要： We analyzed benthic samples (n = 128) collected from four cypress-tree population areas within a large, shallow Arkansas reservoir over a 2-year period to investigate macroinvertebrate community distribution patterns and their relation to physical and chemical parameters. The calculated biomass, abundance and diversity of the benthic macroinvertebrate community varied significantly both temporally and spatially. Variations of these variables are most likely explained by significant differences in the concentration of carbon and nitrogen in sediments across lake sites, and on a smaller scale, the presence or absence of cypress trees. Benthic macroinvertebrate abundance, biomass, and diversity significantly decreased with distance from tree.

关键词： Australia   Desert Uplands   fauna   fire   grazing   interaction   management   rangelands   vegetation  

摘要： We studied the response of vegetation and vertebrate assemblages to fire and grazing. and their interacting effects, in Eucalyptus woodland in north-eastern Australia. hi this vegetation type, many pastures remain free of cattle grazing due to the occurrence of a native shrub poisonous to livestock. Vegetation (floristic data and 22 habitat variables) and vertebrate fauna (birds. mammals, reptiles) were sampled in 29 standardized 50 x 50-m quadrats in the 2001 wet season. representing Four treatments: sites burnt recently (within 2 y) and grazed by cattle (4-8 ha per livestock unit): sites unburnt (last burnt > 2 y ago) and grazed: sites burnt recently and ungrazed: and unburn and ungrazed sites. Fire and grazing had a significant influence on vegetation: both grazing and fire reduced ground cover (fire in grazed sites 51-23%, tire in ungrazed sites 68-39%)) and increased the cover of forbs (8%, in burnt and grazed sites, 3%, if ungrazed) and tussock grasses (20%) in grazed and unburnt sites and 5%) when ungrazed). Grazing caused a shift in floristic composition from the perennial hummock grass Trioda pungens to tussock grasses (e.g. Aristida spp.. Enneapogon spp.), forbs (e.g. Phyllanthus spp.) and shrubs (e.g. Acacia spp.). Of the vertebrate groups, birds responded more to fire effects (9 species), reptiles to grazing effects (6 species) and mammals to the interaction (2 species). Species reacted to increases in bare ground (e.g. crested pigeon Ocyphaps lophotes, hooded robin Melanodryas cucullatus. Ctenophorus nuchalis) and to the dominant ground cover (e.g. Ctenotus pantherinus) or change in vegetation architecture (e.g. singing honeyeater Lichenostomus virescens, variegated fairy-wren Malurus lamberti). The clearest example of an interacting effect was the cycle of complementary dominance between the rodents Pseudomys delicatulus and P. desertor, the latter's post-fire recovery becoming more muted in sites where cattle grazed (modelled time for population recov

关键词： species diversity   structural diversity   trophic level   shrub encroachment   vegetation structure  

摘要： Shrub encroachment due to heavy grazing has led to dramatic changes in and savanna landscape structure worldwide. It is considered to be one of the most threatening forms of rangeland degradation altering plant diversity. However, possible impacts of shrub encroachment on species diversity at higher trophic levels remain poorly understood. Additionally, indirect effects, such as changes of trophic interactions, are often ignored when trying to understand changes in biodiversity patterns. In this study, conducted in the southern Kalahari, we explored how the diversity of small carnivores and their prey is affected by shrub encroachment. We analysed the relationships between abundance and diversity of small carnivores, the availability of their main prey groups (coleopterans, termites, grasshoppers, rodents) and the structural diversity of the landscape (shrub, grass and herb cover). Eight hundred track surveys were conducted to determine carnivore abundance on 20 rangeland habitats, which represented a gradient of grazing intensity. Prey availability was surveyed for each study site and related to vegetation cover. Results show a significant impact of shrub cover on abundance and diversity of carnivores and their prey. The diversity of both, carnivores and their prey, showed a hump-shaped response to increasing shrub cover whereas relative carnivore abundance decreased. Availability of prey groups was affected differently by shrub cover increase. Diversity of carnivores was best predicted by shrub cover (R-2>0.7, p<0.001) indicating the overriding role of habitat structure as compared to prey availability. We conclude that intermediate shrub cover values enrich structural diversity of savanna landscape and in consequence sustain diversity of small carnivores and their prey in and and semiarid ecosystems. (C) 2006 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.

关键词： Species Tree   Gene Tree   Additional Data File   Gene Gain   Tree Reconciliation  

摘要： Background: Comparative genomic studies are revealing frequent gains and losses of whole genes via duplication and pseudogenization. One commonly used method for inferring the number and timing of gene gains and losses reconciles the gene tree for each gene family with the species tree of the taxa considered. Recent studies using this approach have found a large number of ancient duplications and recent losses among vertebrate genomes. Results: I show that tree reconciliation methods are biased when the inferred gene tree is not correct. This bias places duplicates towards the root of the tree and losses towards the tips of the tree. I demonstrate that this bias is present when tree reconciliation is conducted on both multiple mammal and Drosophila genomes, and that lower bootstrap cut-off values on gene trees lead to more extreme bias. I also suggest a method for dealing with reconciliation bias, although this method only corrects for the number of gene gains on some branches of the species tree. Conclusion: Based on the results presented, it is likely that most tree reconciliation analyses show biases, unless the gene trees used are exceptionally well-resolved and well-supported. These results cast doubt upon previous conclusions that vertebrate genome history has been marked by many ancient duplications and many recent gene losses.

关键词： 系统发育树   熵   基于序列互信息的距离   线粒体完全基因组   比对   距离矩阵   邻位相连方法  

摘要： 本文系统地提出了一种用于完全基因组上基于序列互信息的距离在构建脊椎动物进化史中的应用。传统的序列距离要求进行序列比对，而在整个基因进化史中，诸如重排列的事件破坏了全长比对。并且，目前还没有用于完全基因组进化研究的统计模型。因此，现有的工具和方法诸如多重序列比对和各种序列进化模式不能直接应用于完全基因组上。当前，一些用于完全基因组的不需序列比对的距离已被发展起来，并用于物种进化的分析。在本文中，我们提出了一种新的基于序列互信息的距离。该距离不需要序列比对，并且是基于完全基因组上DNA序列或蛋白质序列的组分向量的。本论文中，我们首先利用互信息定义了一距离，并从数学上给出了严格证明。接着，通过使用完全线粒体基因组，我们将该距离应用于分析64种脊椎动物在进化上的关系，得到了这些物种的系统发育树。该树显示这些线粒体基因组被区分成三个主要的群组。其中，一个群组对应于哺乳类，一个群组对应于鱼类，另外一个群组对应于古生物类(包括鸟类和爬行类)。基于我们新的距离建立的树的拓扑结构与当前广泛认同的脊椎动物的系统发育树是吻合的。

关键词： canopy   fibre content   grass structure   grazing   nitrogen   phosphorus  

摘要： The tree-grass interactions of African savannas are mainly determined by varying rainfall patterns and soil fertility. Large savanna trees are known to modify soil nutrient conditions, but whether this has an impact on the quality of herbaceous vegetation is unclear. However, if this were the case, then the removal of trees might also affect the structure and quality of the grass layer. We studied the impact of large nitrogen- and non-nitrogen fixing trees on the sub-canopy (SC)rass layer in low- and high-rainfall areas of differing soil fertility in eastern and southern Africa. We compared the structure and nutrient levels of SC grasses with those outside the canopy. Grass leaf nitrogen and phosphorus contents beneath tree canopies were elevated at all study sites and were up to 25% higher than those outside the canopy in the site of lowest rainfall and soil fertility. Grass leaf fibre and organic matter (ONI) contents were slightly enhanced beneath tree canopies. At the site of highest rainfall and soil fertility, grasses beneath the canopy had significantly lower ratios of stem:leaf biomass and dead:living leaf material. Grass species composition differed significantly, with the highly nutritious Panicum spp. being most abundant underneath tree crowns. In the two drier study sites, soil nitrogen and OM contents were enhanced by 30% beneath trees. N-fixation capacity of trees did not contribute to the improved quality of grass under the canopy. We conclude that trees improve grass quality, especially in dry savannas. In otherwise nutrient-poor savanna grasslands, the greater abundance of high-quality grass species with higher contents of N and P and favourable grass structure beneath trees could attract grazing ungulates. As these benefits may be lost with tree clearance, trees should be protected in low fertility savannas and their benefits for grazing wildlife recognised in conservation strategies. (c) 2007 Rubel Foundation, ETH Zurich. Published by Elsevier Gmb

关键词： defensive traits   herbivory   leafminers   trichomes  

摘要： Variations in defensive and some other leaf traits were studied in a population of an oak species, Quercus dentata Thunberg, in northern Japan, with reference to attacks by ectophagous herbivores and leafminers. The oak population showed substantial individual variations in concentrations of total phenolics and condensed tannins, nitrogen content, trichome density, leaf area and budburst timing. With the exception of leaf mass per area, which showed a positive relation with leaf toughness and a negative relation with water content, no significant relation was observed between the plant traits studied, suggesting an absence of trade-off or linkage between them. The oaks also showed substantial individual variations in leaf area loss by ectophagous herbivores, densities of major leafminers (Phyllonorycter and Stigmella species) and survival of Phyllonorycter sap-feeding larvae. The density of trichomes showed a significant, negative relation with leaf area loss by ectophagous herbivores, but significant, positive relations with densities of some leafminers. The other leaf traits seldom showed significant relations with herbivore densities or survival. In this oak population, these traits may not have enough variations to be reflected in the abundance and performance of herbivores.

关键词： diversity skewness   tree balance   community structure   primates   phylogeny  

摘要： Life on Earth is characterized by strong diversity skewness: related lineages typically show pronounced variation in diversification success, and clades contain hyperdiverse and depauperate subclades. Previous studies have documented diversity skewness only for entire ( global) clades. We demonstrate methods for measurement and significance testing of diversity skewness of local assemblages and regional biotas;we illustrate this with an analysis of geographic structure in diversity skewness of primate assemblages. For primates, continental faunas differ in diversity skewness from expectations based on the global phylogeny: South American faunas have significantly low skewness and African faunas have significantly high skewness. However, no local assemblage has diversity skewness different from that expected based on sampling the continental fauna. We also document a latitudinal gradient in diversity skewness for the African assemblages and test for ( but do not find) associations of skewness with longitude, local species richness, and net primary productivity. Our data suggest that continental-scale biogeographic events rather than local-scale processes have shaped diversity skewness in modern primate faunas.

关键词： cattle   grazing ecosystems   grassland   impala   inorganic nitrogen   nutrient cycling   non-equilibrium rangelands   phosphorous   wildlife management  

摘要： Large herbivores can both positively and negatively affect primary productivity and rates of nutrient cycling in different ecosystems. Positive effects of grazers in grasslands have been attributed to migratory behavior of the dominant ungulate species and soil fertility. We studied the effects of grazers on aboveground net primary productivity (ANPP) and N cycling on central Kenyan rangeland characterized by intense, chronic grazing by a mixed community of cattle and resident native ungulates. Exclosure studies conducted at high and low levels of soil fertility showed that both soil fertility and annual rainfall patterns mediate the effects of grazers on ANPP and N cycling. In a low-rainfall year with short (1 month) growing seasons, grazers reduced aboveground productivity regardless of soil nutrient availability. However, in a high-rainfall year with a 5-month growing season, grazers increased ANPP on nutrient-rich glades and suppressed ANPP on nutrient-poor bushland sites. Concomitant studies of grazer effects on N cycling revealed complex interactions with the seasonal pattern of N-mineralization and inorganic N availability. Grazers increased the size of the inorganic N pool available to plants at the onset of the growing season, particularly in nutrient-rich glades. However, grazers also decreased N mineralization rates at all sites early in the growing season. Measures of N availability via ion-exchange resin bags suggested that the combined effects of grazers on inorganic N pool fluctuations and N-mineralization rates resulted in a net increase in N availability at glade sites and a net decrease in N availability at bushland sites. The net effect of grazers on soil N availability mirrored grazer effects on ANPP in the high-rainfall year. Overall, our results suggest that grazer effects on N dynamics are closely linked to effects on productivity and resilience to drought. Furthermore, even under optimal conditions of high soil fertility and above-average rai

关键词： Acacia   Balanites   eland   giraffe   spines   thorns   wildlife ranching  

摘要： Some plants respond to browsing with compensatory regrowth of plant tissues and with increased thorn growth. Associations between browsers and their preferred forage were examined through wandering quarter vegetation sampling and observational studies in an effort to understand how some plants respond to browsing by large African herbivores. Acacia seyal (n = 2680) A. drepanolobium (n = 1850), and Balanites glabra (n = 960) were three species of frequently browsed indigenous plants examined on Game Ranching Ltd. in Kenya. There were several statistically significant associations revealed. Individual A. seyal exposed to intensive browser utilization were observed to lose shoot tips, produce long thorns, and have relatively few flowers and fruits. Browser utilization was associated with increased lateral branching in A. drepanolobium and with an increased occurrence of short, thickened spines in B. glabra. Thorns, spines and flowers were measurable indicators of relative browser utilization, and may be useful features to monitor in the management of large African mammals and their prickly forage.