Global tests of biodiversity concordance and the importance of endemism

Understanding patterns of biodiversity distribution is essential to conservation strategies, but severe data constraints make surrogate measures necessary. For this reason, many studies have tested the performance of terrestrial vertebrates as surrogates for overall species diversity, but these tests have typically been limited to a single taxon or region. Here we show that global patterns of richness are highly correlated among amphibians, reptiles, birds and mammals, as are endemism patterns. Furthermore, we demonstrate that although the correlation between global richness and endemism is low, aggregate regions selected for high levels of endemism capture significantly more species than expected by chance. Although areas high in endemism have long been targeted for the protection of narrow-ranging species, our findings provide evidence that endemism is also a useful surrogate for the conservation of all terrestrial vertebrates.     

The contribution of species richness and composition to bacterial services

Bacterial communities provide important services. They break down pollutants, municipal waste and ingested food, and they are the primary means by which organic matter is recycled to plants and other autotrophs. However, the processes that determine the rate at which these services are supplied are only starting to be identified. Biodiversity influences the way in which ecosystems function, but the form of the relationship between bacterial biodiversity and functioning remains poorly understood. Here we describe a manipulative experiment that measured how biodiversity affects the functioning of communities containing up to 72 bacterial species constructed from a collection of naturally occurring culturable bacteria. The experimental design allowed us to manipulate large numbers of bacterial species selected at random from those that were culturable. We demonstrate that there is a decelerating relationship between community respiration and increasing bacterial diversity. We also show that both synergistic interactions among bacterial species and the composition of the bacterial community are important in determining the level of ecosystem functioning.     

Effects of macrophyte species richness on wetland ecosystem functioning and services

Wetlands provide many important ecosystem services to human society, which may depend on how plant diversity influences biomass production and nutrient retention. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species-in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.     

Ecosystem consequences of species richness and composition in pond food webs

Resolving current concerns about the role of biodiversity on ecosystems calls for understanding the separate roles of changes in species numbers and of composition. Recent work shows that primary productivity often, but not always, saturates with species richness within single trophic levels. However, any interpretation of such patterns must consider that variation in biodiversity is necessarily associated with changes in species composition (identity), and that changes in biodiversity often occur across multiple trophic levels. Here we present results from a mesocosm experiment in which we independently manipulated species richness and species composition across multiple trophic levels in pond food webs. In contrast to previous studies that focused on single trophic levels, we found that productivity is either idiosyncratic or increases with respect to species richness, and that richness influences trophic structure. However, the composition of species within richness levels can have equally or more marked effects on ecosystems than average effects of richness per se. Indirect evidence suggests that richness and associated changes in species composition affect ecosystem attributes through indirect effects and trophic interactions among species, features that are highly characteristic of natural, complex ecosystems.     

具有密度制约的两种群食物链模型解的整体性态

讨论了一个具有密度制约的两种群食物链模型解的整体性态。首先,讨论该模型解的整体存在性和一致有界性,然后应用线性化方法和Lyapunov函数方法讨论了该模型非负平衡点的局部渐近稳定性和全局渐近稳定性。     

可验证其他成员是非签名者的环签名

环签名方案是签名者在不泄露身份的情况下生成的一个签名。验证者可以验证签名确实是环成员生成的,但不能确定哪一个成员是真实的签名者。于是提出了可否定的环签名方案,利用这一方案,签名者可以向接受者证明其他成员并不是真实的签名人,但同时并不暴露自己的真实身份。     

Rapid and recent origin of species richness in the Cape flora of South Africa.

The Cape flora of South Africa grows in a continental area with many diverse and endemic species. We need to understand the evolutionary origins and ages of such 'hotspots' to conserve them effectively. In volcanic islands the timing of diversification can be precisely measured with potassium-argon dating. In contrast, the history of these continental species is based upon an incomplete fossil record and relatively imprecise isotopic palaeotemperature signatures. Here we use molecular phylogenetics and precise dating of two island species within the same clade as the continental taxa to show recent speciation in a species-rich genus characteristic of the Cape flora. The results indicate that diversification began approximately 7-8 Myr ago, coincident with extensive aridification caused by changes in ocean currents. The recent origin of endemic species diversity in the Cape flora shows that large continental bursts of speciation can occur rapidly over timescales comparable to those previously associated with oceanic island radiations.     

两种群捕食者-食饵模型解的整体性态

讨论了两种群捕食者-食饵模型解的整体性态。首先,讨论该模型解的整体存在性和一致有界性;其次,运用线性化方法得出该两种群模型的正平衡点和平凡平衡点均是无条件不稳定的,只有半平凡平衡点是局部渐近稳定的;最后,运用Lyapunov函数法得出该食物链模型的半平凡平衡点是全局渐近稳定的。     

一个离散单种群扩散模型的全局渐近稳定性

建立了一个物种在ｎ个缀块上相互扩散的数学模型并利用单调算子和凹算子的理论讨论了其全局渐近稳定性,得到了正平衡点全局渐近稳定和物种绝灭的条件．     

Supermassive black holes do not correlate with galaxy disks or pseudobulges

The masses of supermassive black holes are known to correlate with the properties of the bulge components of their host galaxies. In contrast, they seem not to correlate with galaxy disks. Disk-grown 'pseudobulges' are intermediate in properties between bulges and disks; it has been unclear whether they do or do not correlate with black holes in the same way that bulges do. At stake in this issue are conclusions about which parts of galaxies coevolve with black holes, possibly by being regulated by energy feedback from black holes. Here we report pseudobulge classifications for galaxies with dynamically detected black holes and combine them with recent measurements of velocity dispersions in the biggest bulgeless galaxies. These data confirm that black holes do not correlate with disks and show that they correlate little or not at all with pseudobulges. We suggest that there are two different modes of black-hole feeding. Black holes in bulges grow rapidly to high masses when mergers drive gas infall that feeds quasar-like events. In contrast, small black holes in bulgeless galaxies and in galaxies with pseudobulges grow as low-level Seyfert galaxies. Growth of the former is driven by global processes, so the biggest black holes coevolve with bulges, but growth of the latter is driven locally and stochastically, and they do not coevolve with disks and pseudobulges.     

四种群Lotka-Volterra混合系统的全局渐进稳定性

文章考虑周期系数的四种群Lotka-Volterra模型,种群间既有捕食关系又有竞争关系,得到该系统正周期解的存在性及全局渐进稳定性的条件.     

炎黄同期论献疑

通过对炎黄二帝社会经济生活史料的考证,认定炎帝是神农氏,生活在距今约六七千年前的母系氏族公社时代;黄帝轩辕氏生活在距今约四、五千年前的父系氏族公社时代,二帝相距一千多年。炎、黄两个部落三战阪泉之野,并结成联盟,战败蚩尤,应是炎帝的后代子孙姜姓部落,而不是炎帝本人。     

一类三物种互助模型正平衡解的全局稳定性

研究了一类具有齐次Neumann边界备件的三物种互助模型平衡解的全局稳定性,得出该反应扩散系统拥有唯一的正常数稳定解的结论。     

Zfy gene expression patterns are not compatible with a primary role in mouse sex determination

The Y chromosome determines maleness in mammals. A Y chromosome-linked gene diverts the indifferent embryonic gonad from the default ovarian pathway in favour of testis differentiation, initiating male development. Study of this basic developmental switch requires the isolation of the testis-determining gene, termed TDF in humans and Tdy in mice. ZFY, a candidate gene for TDF, potentially encodes a zinc-finger protein, and has two Y-linked homologues, Zfy-1 and Zfy-2, in mice. Although ZFY, Zfy-1 and Zfy-2 seem to map to the sex-determining regions of the human and mouse Y chromosomes, there is no direct evidence that these genes are involved in testis determination. We report here that Zfy-1 but not Zfy-2 is expressed in differentiating embryonic mouse testes. Neither gene, however, is expressed in We/We mutant embryonic testes which lack germ cells. These observations exclude both Zfy-1 and Zfy-2 as candidates for the mouse testis-determining gene.     

Tunicates and not cephalochordates are the closest living relatives of vertebrates

Tunicates or urochordates (appendicularians, salps and sea squirts), cephalochordates (lancelets) and vertebrates (including lamprey and hagfish) constitute the three extant groups of chordate animals. Traditionally, cephalochordates are considered as the closest living relatives of vertebrates, with tunicates representing the earliest chordate lineage. This view is mainly justified by overall morphological similarities and an apparently increased complexity in cephalochordates and vertebrates relative to tunicates. Despite their critical importance for understanding the origins of vertebrates, phylogenetic studies of chordate relationships have provided equivocal results. Taking advantage of the genome sequencing of the appendicularian Oikopleura dioica, we assembled a phylogenomic data set of 146 nuclear genes (33,800 unambiguously aligned amino acids) from 14 deuterostomes and 24 other slowly evolving species as an outgroup. Here we show that phylogenetic analyses of this data set provide compelling evidence that tunicates, and not cephalochordates, represent the closest living relatives of vertebrates. Chordate monophyly remains uncertain because cephalochordates, albeit with a non-significant statistical support, surprisingly grouped with echinoderms, a hypothesis that needs to be tested with additional data. This new phylogenetic scheme prompts a reappraisal of both morphological and palaeontological data and has important implications for the interpretation of developmental and genomic studies in which tunicates and cephalochordates are used as model animals.