Tentaculites: evidence for a brachiopod affinity?

Transmission electron microscope studies of fractured surfaces reveal that the shells of Tentaculites are constructed of calcite with a ridge and groove structure and cross-bladed fabric heretofore unique to some articulate brachiopods. A possible affinity with brachiopods or phoronids is suggested for Tentaculites.     

End-cretaceous brachiopod extinctions in the chalk of denmark

The results of a detailed study of the brachiopods of the most complete Cretaceous-Tertiary boundary in Denmark, Nye Klslashed circlev, show an extinction pattern for this marine invertebrate group compatible with that reported for pelagic foraminifera and coccoliths and with the impact scenario. The extinction is abrupt, coinciding with the Maastrichtian-Danian boundary. There is no warning in the form of decreasing density, decreasing diversity, or early extinction of specialized groups. The basal few meters of the Danian are almost devoid of brachiopods, and a Danian brachiopod fauna starts almost as abruptly as the Maastrichtian fauna disappeared. The new fauna is similar to the Maastrichtian as regards density and diversity, and at maximum six species are common to both stages. The northwest European Masstrichtian chalk is composed mainly of the remains of coccoliths and pelagic foraminifera. The mass extinction of these groups led to a total cessation of chalk production. The chalk is overlain by a thin clay bed deposited partly under anoxic conditions. This combination of anoxia and clay deposition coupled with a cessation of productivity led to the extinction of specialized groups such as the chalk brachiopods. The surviving species included forms that could survive in well-aerated shallow marine waters on substrates other than chalk.     

Pholidostrophiid brachiopods: origin of the nacreous luster

The "nacreous" luster characteristic of the pholidostrophiid group of fossil brachiopods results from a shell structure that produces superimposed sets of natural optical-diffraction gratings made of calcite. The wall structure is crossed lamellar, parallel to the shell surfdce; thus flakiness and development of reflecting surfaces are facilitated.     

Secondary evolutionary escalation between brachiopods and enemies of other prey

The fossil record of predation indicates that attacks on Paleozoic brachiopods were very rare, especially compared to those on post-Paleozoic mollusks, yet stratigraphically and geographically widespread. Drilling frequencies were very low in the early Paleozoic (<1%) and went up slightly in the mid-to-late Paleozoic. Present-day brachiopods revealed frequencies only slightly higher. The persistent rarity of drilling suggests that brachiopods were the secondary casualties of mistaken or opportunistic attacks by the enemies of other taxa. Such sporadic attacks became slightly more frequent as trophic systems escalated and predators diversified. Some evolutionarily persistent biotic interactions may be incidental rather than coevolutionary or escalatory in nature.     

辽东山区次生林主要树种种群结构和格局

用“径级大小替代年龄大小”和“空间差异替代时间变化”的方法,分别研究了辽东山区4种主要群落（柞木林、硬阔林、杨桦林和杂木林）主要树种种群的结构和分布格局,以及应用方差/均值比的t值检验法、聚块性和扩散型指数分析其格局状况,并用聚集强度指数负二项参数K值度量了它们的聚集程度.结果表明:①蒙古栎、水曲柳、核桃楸、枫桦和山杨龄级存在明显的低龄缺损,为间歇型种群,其中蒙古栎、水曲柳和核桃楸属于增长型种群,枫桦和山杨属衰退型种群,色木槭、紫椴和春榆种群年龄结构呈不规则的倒J型种群结构,龄级完整,属于稳定型增长种群;②这些主要树种种群中,除了杨桦林群落中枫桦和山杨格局呈随机分布外,其他种群的格局都趋于聚集分布;③各主要树种种群等级分布格局具有一定的规律性,即种群在幼苗和幼树阶段为聚集分布,而在中树和大树阶段为随机或均匀分布,且各主要树种种群从幼苗到大树格局聚集强度逐渐降低,种群呈扩散趋势;④辽东山区次生林主要树种种群结构和格局的形成主要是由于其生物学特性和所处环境作用的结果.      

Brachiopods: biomechanical interdependences governing their origin and phylogeny

The adaptive advantage of epibenthic articulate brachiopods over inarticulate forms resulted from a modification of the mechanics of shell opening from an indirect hydraulic system to a direct muscular one. As a consequence, the articulate brachiopods were able to reduce the complex muscular system of the ancestral inarticulates, freeing two-thirds of the space within the shell for enlargement of the feeding apparatus. The original hydraulic mechanism of the inarticulate brachiopods most likely evolved from the hydrostatic skeleton of metameric lower invertebrates, probably polychaete-like annelids, as shown by a biomechanical analysis. The transitional stages between such annelids and inarticulate brachiopods are presented and explained as adaptive improvements in body construction.     

Rana pipiens complex: mating call structure and taxonomy

Geographic variability in call structure indicates that four largely allopatric populations of leopard frogs are present in the central United States. These forms appear to maintain their distinctness in narrow zones of sympatry, and most adult males can be separated morphologically. It is suggested that the four forms represent distinct species and that the idea of gradual clinal variability in one wide-ranging species is wrong.     

基于线粒体控制区的海南岛3种弹涂鱼的遗传多样性

采集中国海南岛3种弹涂鱼群体并进行遗传多样性研究,通过使用线粒体控制区基因部分序列作为遗传标记,获得3种弹涂鱼共195个长度为836 bp的D-loop基因片段序列,分析其群体的遗传多样性、遗传分化、种群历史动态。结果表明:（1）弹涂鱼多样性最为丰富,大鳍弹涂鱼次之,大弹涂鱼较为缺乏。（2）遗传分化指数(F_st) 表明海南岛弹涂鱼群体中三亚的与临高、东方、乐东的存在中等程度分化,分子方差分析（AMOVA）结果表明总体不存在遗传分化;大弹涂鱼群体F_st表明文昌和东方的群体存在分化,AMOVA 分析结果表明总体存在中等程度分化;弹涂鱼与大鳍弹涂鱼亲缘关系较近,通过线粒体控制区基因标记可将它们较好地区分。（3）中性检验和不配对分布结果表明大弹涂鱼文昌群体经历过扩张。综合分析结果表明,大弹涂鱼应该作为优先保护的种类。     

云南沟谷雨林建群种绒毛番龙眼居群的遗传多样性

【目的】了解云南特有的沟谷雨林主要建群种绒毛番龙眼居群的遗传多样性及遗传结构特征,为雨林植被恢复的采种规划和恢复效果评估提供重要参考。【方法】采用SSR分子标记技术,检测分析云南省西双版纳州和普洱市思茅区的绒毛番龙眼3个天然居群和1个人工居群共82个样本的SSR多态性,采用POPGENE v.1.32、GenAlEx 6.501和STRUCTURE 2.3.3等进行遗传多样性及遗传结构分析。【结果】19对SSR引物共检测到88个等位基因,每对引物平均4.632个,19个位点的Shannon’s信息指数（I）变化范围为0.264~1.687,平均为0.879;多态信息指数（PIC）变化范围为0.128~0.729,平均为0.422,期望杂合度（He）的变化范围为0.138~0.765,平均为0.473;4个居群I和He的均值分别为0.785,0.437。19个位点的遗传分化系数（F_ST）均值为0.069,基因流（Nm）的均值为3.363。STRUCTURE分析将绒毛番龙眼4个居群82个样本分为4个类群,基于遗传距离的UPGMA聚类显示4个居群聚为2个分支,菜阳河天然林居群、普文人工林居群和普文天然林居群聚为一支,勐养镇天然林居群单独为另一支。【结论】绒毛番龙眼的遗传多样性处于中等水平;居群间的遗传分化较低,遗传变异主要来源于居群内;建议特别关注居群内个体的选择和保护,在沟谷雨林植被恢复中设定天然居群多样性水平的恢复目标,并通过科学的采种规划实现这一目标。     

雷公山灌木林群落结构及其优势种 种群特征关系研究

种群是群落结构和功能的基本单元,群落的优势种对群落结构和环境的形成起着主导作用,然而,优势种对群落结构形成的作用机制以及其种群特征与群落结构的关系鲜见报到。调查了总面积为656 m2雷公山灌木林地,共设置4 m伊4 m样方41 个,获得相关群落和种群参数,运用SPSS 17.0 分析了群落结构参数与种群结构参数之间的关系。结果表明：物种多样性指数与群落内优势种种群粗密度、种群扩散系数、平均树高的偏相关系数分别为-0.927***、-0.928***、-0.913***,均呈显著负相关,即物种多样性指数随着群落内优势种种群粗密度、种群扩散系数、平均树高的数值增大而减小,呈现负相关关系。群落内优势种个体较多不利于建立物种丰富的植物群落结构。进一步验证了优势种在群落中的重要地位和作用。     

Genetic structure of the invasive Colorado potato beetle Leptinotarsa decemlineata populations in China

The Colorado potato beetle(CPB), Leptinotarsa decemlineata Say, is an infamous invasive species worldwide. It was first found in Xinjiang Uygur Autonomous Region of China in 1993 and spread to Northeast China in 2013. To better understand the genetic structure and the diffusion path of their populations in China, we used nine polymorphic microsatellite loci to elucidate the genetic diversity, genetic structure and gene flow among nine CPB populations across Xinjiang and Northeast China. The results show that:(1) Two genetically separated clusters were identified by phylogenetic tree, principal coordinate analysis(PCoA) and Bayesian cluster method. Cluster one contained populations from Xinjiang, China. Cluster two contained populations from Northeast China. A genetic differentiation existed between the two clusters.(2) Three populations in Northeast China hold an obvious genetic differentiation according to the phylogenetic tree and PCoA, indicating that multiple introductions may occur in Northeast China.(3) The Altay population in Xinjiang showed a closer genetic relationship with the populations in Northeast China which may be due to the fact that they collectively originated in neighboring Russia.(4) Among all populations, Mulei and Wusu had obvious gene migrations from Tacheng, indicating that the inland populations are most likely to originate from Tacheng, Xinjiang.     

敦煌绿洲不同生境胡杨种群结构与空间格局研究

在敦煌绿洲天然胡杨林内设置5个样地(共计6.25 hm<'2>),应用相邻格子法,进行每木调查,结合7种聚集度指标,研究了不同生境胡杨种群的年龄结构与空间分布格局.结果表明:研究区幼苗缺失,幼树极少,年龄结构大体呈倒金字塔型,为衰退种群;林分偏老,十分稀疏矮小.不同生境胡杨种群年龄结构差异显著,其中后坑胡杨种群的年龄结...     

Brachiopods versus Mussels: Competition, Predation, and Palatability

Unlike other shell-enclosed marine invertebrates, articulate brachiopods are repellent to predators. Fish, sea stars, snails, and crabs all prefer bivalve molluscs such as mussels to articulates. The mussels tested are mobile and out-compete immobile articulates when space is limited. In subtidal field experiments, mussels alone and predators alone each reduced the survivorship of articulates. However, adding mussels to articulates in the presence of ambient predation increased brachiopod survivorship by diverting predation from the brachiopods to the mussels. Competition from mussels (or mussel-like bivalves) is a plausible cause of the post-Paleozoic decline of articulates.     

冀北山地杨桦次生林优势种群结构及时间序列预测分析

运用径级结构、静态生命表和时间序列预测分析方法,研究了冀北山地杨桦次生林群落结构和主要优势种群的动态变化过程,揭示了主要优势种群各径级数量动态规律。结果表明:冀北山地杨桦次生林群落物种组成丰富,垂直结构较为明显。山杨、五角枫和蒙古栎种群,幼龄个体多,老龄个体少,基本上属于进展型种群,而白桦种群的小径级和高径级的个体都较少,主要以幼树和中树居多,属于衰退型种群。蒙古栎种群存活曲线接近于DeeveyⅢ型。时间序列分析表明,在未来的Ⅱ径级、Ⅳ径级和Ⅵ径级中,白桦种群呈现大径级株数增加的趋势,白桦种群维持困难;山杨种群和五角枫种群小径级株数呈现减少的趋势,中径级株数呈现增加的趋势,表明山杨和五角枫保持相对稳定性,而蒙古栎呈现衰退的态势。因此对4种优势种群,分别实施不同的经营措施,促进种群的自然更新和群落演替。     

南京仙林地区次生阔叶林群落的初步研究

在野外实地调查的基础上,利用群落学研究手段对南京仙林地区的次生林群落进行了研究分析。结果表明:群落内共有植物60种,隶属于32科49属,科属种组成较为分散,优势科或优势属不明显;科属区系分析表明,泛热带分布和北温带分布的科属所占比例较大,分别为45.83%、21.28%和33.33%、19.51%,这说明群落区系分布类型真正的热带性质不明显,且具有热带性质和温带性质交融与过渡的特点。乔灌层的物种频度分布分别为ABCD=E和ABCDE,灌木层物种分布较为均匀,而乔木层有进一步演替的可能。该群落结构层次较为简单,可分为乔木上层、乔木下层、灌木层、层间和草本层;其中,乔木层中的主要优势树种为短柄枹栎、构树、牡荆和马尾松,它们的重要值分别为16.10%、12.79%、9.31%和9.20%,而灌木层的优势树种为刚竹、短柄枹栎、野蔷薇、白檀和构树等。乔木层主要种群径级结构特征表明,短柄枹、构树等树种属于增长种群,而马尾松、化香等属于衰退种群。保护利用好该类型的森林群落对仙林地区的生态环境建设具有十分重要的意义。     

用微卫星标记分析泰山螭霖鱼的遗传多样性

本文首次对泰山螭霖鱼进行分子遗传学研究，以了解其遗传多样性，养殖群体和野生群体有无遗传差异等。共选用了31个微卫星标记，经筛选，其中14个能在螭霖鱼得到稳定的PCR扩增。PCR扩增产物用12％的非变性聚丙烯酰胺凝胶150V电泳6．8h后，银染显色，观察并统计分析。结果表明：泰山螭霖鱼野生群体和养殖群体在所有的位点均有相同的等位基因，PAGE结果都呈直线。这说明泰山螭霖鱼野生群体和养殖群体的遗传结构无差异，这也证明泰山螭霖鱼为一高度纯合的群体，是非常难得的育种和试验材料，保护这一珍惜物种资源具有重要意义。     

Sea otters: their role in structuring nearshore communities

A comparison of western Aleutian Islands with and without sea otter populations shows that this species is important in determining littoral and sublittoral community structure. Sea otters control herbivorous invertebrate populations. Removal of sea otters causes increased herbivory and ultimately results in the destruction of macrophyte associations. The observations suggest that sea otter reestablishment indirectly affects island fauna associated with macrophyte primary productivity.     

福建三明格氏栲群落的结构特征

本文在０．３公顷样地调查材料的基础上，分析了福建三明小湖地区格氏栲群落的植物区系成份、群落外貌、水平结构和垂直结构特征．该群落共有维管束植物１１０种，隶属于４２科６８属，其中单种属占６７．６％，包括藤本在内的高位芽植物占总数的８７．３％．乔木种群的空间格局以聚集分布为主，在垂直空间上常可分为三个亚层．物种多样性指数介于南亚热带季风常绿阔叶林和中亚热带常绿阔叶林之间．     

重庆涪陵磨盘沟桫椤种群结构与分布格局研究

以重庆涪陵磨盘沟桫椤群落为研究对象,对调查样地内的桫椤种群结构和分布格局进行了研究。结果表明：现阶段种群结构为增长型类型;桫椤种群至聚集分布,但聚集程度不是很高,聚集面积不是很大,这在一定程度上反映出小种群的特点。在此基础上分析了格局形成的原因,并提出保护建议。     

五大连池火山森林群落多样性与稳定性

  目的   五大连池完好的内陆单成因火山地貌,原生而完整的植被演替过程,是研究植被演替与生物多样性系统发育等的理想场所。研究五大连池火山森林群落物种多样性与稳定性特征,以及群落物种多样性与稳定性关系,为五大连池火山森林植被的演替、恢复与可持续发展提供科学依据。   方法   以4座老期火山森林群落为对象,对群落结构数量特征、群落内乔木、灌木和草本层物种多样性指数、群落年龄结构及紫椴Tilia amurensis和蒙古栎Quercus mongolica种群的年龄结构进行了研究。   结果   ①各山体森林群落的乔木层和灌木层物种数北坡较南坡丰富。总体来看,重要值≥1的树种仅南坡有1种,群落树种组成简单。②各山体整体上北坡群落物种的Margalef指数和Shannon-Wiener指数从大到小依次为乔木层、草本层、灌木层,Simpson指数和Pielou指数从大到小依次为乔木层、灌木层、草本层;南坡群落物种的各种多样性指数从大到小依次为草本层、乔木层、灌木层。③森林群落的年龄结构南北坡向都是稳定型,紫椴和蒙古栎种群的年龄结构也都是稳定型,为稳定群落。④北坡乔木层和灌木层的物种多样性指数高于南坡,而草本层的多样性指数低于南坡,同时南北坡向间群落物种多样性各指数呈极显著(P＜0.01)或显著(P＜0.05)差异,且变异系数都较大。   结论   五大连池老期火山森林群落结构较简单,北坡群落物种多样性较高,且群落稳定状态更好。图6表4参31