共查询到20条相似文献，搜索用时 46 毫秒
1.
The latitudinally diachronous appearance of angiosperm pollen during the Cretaceous is well documented, but the subsequent diversification and accompanying significant changes in floristic dominance have not been assessed quantitatively for a wide range of paleolatitudes. Trend surfaces fitted to within-palynoflora diversity data from 1125 pollen and spore assemblages show that angiosperms first become floristically prominent in low paleolatitude areas( approximately 20 degrees N to 20 degrees S). Non-magnoliid dicotyledons show a similar but slightly delayed pattern of increase and are the principal component of angiosperm diversity from all areas sampled. Monocotyledons and magnoliid dicotyledons are significant primarily in low to middle paleolatitude palynofloras( approximately 50 degrees N to 20 degrees S) during the latest Cretaceous. As angiosperms become increasingly prevalent the importance of most non-angiosperm taxa either decreases or remains unchanged. The only apparent exception is a striking increase in gnetalean diversity concurrent with the initial angiosperm diversification at low paleolatitudes. 相似文献
2.
Wilf P Cúneo NR Johnson KR Hicks JF Wing SL Obradovich JD 《Science (New York, N.Y.)》2003,300(5616):122-125
Tropical South America has the highest plant diversity of any region today, but this richness is usually characterized as a geologically recent development (Neogene or Pleistocene). From caldera-lake beds exposed at Laguna del Hunco in Patagonia, Argentina, paleolatitude approximately 47 degrees S, we report 102 leaf species. Radioisotopic and paleomagnetic analyses indicate that the flora was deposited 52 million years ago, the time of the early Eocene climatic optimum, when tropical plant taxa and warm, equable climates reached middle latitudes of both hemispheres. Adjusted for sample size, observed richness exceeds that of any other Eocene leaf flora, supporting an ancient history of high plant diversity in warm areas of South America. 相似文献
3.
Alroy J Aberhan M Bottjer DJ Foote M Fürsich FT Harries PJ Hendy AJ Holland SM Ivany LC Kiessling W Kosnik MA Marshall CR McGowan AJ Miller AI Olszewski TD Patzkowsky ME Peters SE Villier L Wagner PJ Bonuso N Borkow PS Brenneis B Clapham ME Fall LM Ferguson CA Hanson VL Krug AZ Layou KM Leckey EH Nürnberg S Powers CM Sessa JA Simpson C Tomasovych A Visaggi CC 《Science (New York, N.Y.)》2008,321(5885):97-100
It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic. 相似文献
4.
Limits of microbial existence: temperature and pH 总被引：10，自引：0，他引：10
A microscopic survey made to detect the presence of bacteria in hot springs of varying temperature and pH characteristics revealed that in neutral and alkaline hot springs bacteria are found at temperatures up to the boiling point of water (92 degrees to 100 degrees C, depending on the altitude). In hot springs of increasing acidity the upper temperature limit at which bacteria are found decreases; at pH 2 to 3 the upper temperature limit is 75 degrees to 80 degrees C. Bacteria have thus been able to evolve with the ability to grow at either high temperature or high acidity, but not at both high temperature and high acidity. These results suggest that there are physicochemical limitations of the environment beyond which life is impossible. 相似文献
5.
【目的】以青步甲属(Chlaenius)昆虫为研究对象,对甘肃子午岭天然次生林区干扰程度不同的生境类型中青步甲属物种的组成和分布格局进行研究,揭示物种对环境的依赖性和指示作用。【方法】采用巴氏诱罐法诱捕昆虫,研究子午岭次生林区干扰程度不同的7种代表性植被类型,对青步甲属的物种多样性与物种数量和分布的影响。【结果】子午岭天然次生林区不同生境类型共采集青步甲标本776头,隶属于10个种,其中毛青步甲(Chlaenius pallipes Gebler)、黄缘青步甲(Ch.spoliatus Rossi)、后黄斑青步甲(Ch.posticalis Motschulsky)和黄边青步甲(Ch.circumdatus Brulle)是该地区的常见种,个体数量之和占该属个体总数的77.4%。生境类型影响青步甲属物种的丰富度和数量分布,其数值由高到低依次为人工油松林、天然油松林、针阔混交林、阔叶混交林、杂木林、灌丛和草地,其中丰富度（S）指数依次为8.63,8.39,8.29,6.33,5.27,4.39,4.21;物种多样性指数(H′)由高到低依次为针阔混交林（1.867）、人工油松林（1.829）、阔叶混交林（1.701）、天然油松林（1.637）、杂木林（1.591）、灌丛（1.533）和草地（1.099）;均匀度指数(ED)的变化趋势与物种多样性指数(H′)基本一致。人为或自然干扰程度影响青步甲属物种的种类组成和个体数量分布,严重干扰减少物种种类和数量;在轻度干扰的情况下,物种的种类和数量最多;在几乎没有人为干扰的生境中,个体数量有下降趋势。【结论】青步甲物种多样性及物种数量和分布受生境类型及生境受干扰程度的影响。 相似文献
6.
为了解浙江省马铃薯地方种质资源特征特性,鉴定并筛选出优异种质,2019—2020年对浙江省第三次全国农作物种质资源普查与收集行动中征集的95份马铃薯种质资源的13个质量性状和6个数量性状进行了调查和分析。结果表明,浙江省马铃薯地方种质资源的表型遗传多样性比较丰富。质量性状的Shannon-Wiener多样性指数为0.380～1.686,其中,病毒病的多样性指数最高,说明收集的种质资源存在不同程度的病毒性退化;食味的多样性指数最低,食味优的种质有88份,占资源数的92.63%。10个形态性状的多样性指数平均值为1.079,其中薯形、肉色和花冠色3个性状的遗传多样性最为丰富。6个数量性状的多样性指数均高,平均值为2.84,块茎产量、主茎数尤为突出。块茎干物质含量在18.1%～25.8%,其中干物质含量≥20%的种质有73份,占资源数的76.84%。95份种质资源按照块茎形态特征可归类为小马铃薯种质62份、中大马铃薯种质21份和彩色马铃薯12份。小马铃薯种质黄皮黄肉,干物质含量较高,蒸煮食味优。根据种质的表型特异性,筛选出优异种质9份,可用于生产开发和育种利用。 相似文献
7.
专用微生物肥对不同连作障碍土壤根际微生物区系的影响 总被引：5，自引：0，他引：5
为探究专用微生物肥对不同连作障碍程度土壤根际微生物区系的影响,采用不同连作障碍程度的土壤为栽培介质,施用2%的专用微生物肥后进行辣椒土培盆栽试验,取根际土壤进行稀释平板计数和PCR-DGGE分析。结果表明:随着土壤连作障碍程度的增加,根际土壤细菌和放线菌数量减少,真菌数量增加;施用专用微生物肥后,土壤微生物种群密度发生显著性变化,其中土壤连作障碍程度轻、中、重组细菌数目分别增加了78.6%、66.7%、54.5%,真菌数目分别减少了5.0%、12.5%、7.5%,放线菌数目分别增加了18.2%、9.1%、23.5%。通过分析PCR-DGGE指纹图谱发现,随着生理性土壤连作障碍程度的加剧,根际土壤微生物的丰富度和多样性指数降低,施用专用微生物肥后,微生物种群数目和种群结构发生改变,多样性指数升高。说明专用微生物肥对根际土壤微生物种群密度和种群结构有显著性影响,但是由于土壤连作障碍程度的不同产生效果不同。 相似文献
8.
During the last interglacial, sea level was as high as present, 4000 to 6000 years before peak Northern Hemisphere insolation receipt 126,000 years ago. The sea-level results are shown to be consistent with climate models, which simulate a 3 degrees to 4 degrees C July temperature increase from 140,000 to 130,000 years ago in high latitudes, with all Northern Hemisphere land areas being warmer than present by 130,000 years ago. The early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred. These results indicate that a fuller understanding of the Milankovitch-climate connection requires consideration of fields other than just insolation forcing at 65 degrees N. 相似文献
9.
Brock TD 《Science (New York, N.Y.)》1985,230(4722):132-138
Water environments with temperatures up to and above boiling are commonly found in association with geothermal activity. At temperatures above 60 degrees C, only bacteria are found. Bacteria with temperature optima over the range 65 degrees to 105 degrees C have been obtained in pure culture and are the object of many research projects. The upper temperature limit for life in liquid water has not yet been defined, but is likely to be somewhere between 110 degrees and 200 degrees C, since amino acids and nucleotides are destroyed at temperatures over 200 degrees C. Because bacteria capable of growth at high temperatures are found in many phylogenetic groups, it is likely that the ability to grow at high temperature had a polyphyletic origin. The macromolecules of these organisms are inherently more stable to heat than those of conventional organisms, but only small changes in sequence can lead to increases in thermostability. Because of their unique properties, thermophilic organisms and their enzymes have many potential biotechnological uses, and extensive research on industrial applications is under way. 相似文献
10.
Iwasa Y Arima T Fleming RM Siegrist T Zhou O Haddon RC Rothberg LJ Lyons KB Carter HL Hebard AF Tycko R Dabbagh G Krajewski JJ Thomas GA Yagi T 《Science (New York, N.Y.)》1994,264(5165):1570-1572
The fullerene C(60) can be converted into two different structures by high pressure and temperature. They are metastable and revert to pristine C(60) on reheating to 300 degrees C at ambient pressure. For synthesis temperatures between 300 degrees and 400 degrees C and pressures of 5 gigapascals, a nominal face-centered-cubic structure is produced with a lattice parameter a(o) = 13.6 angstroms. When treated at 500 degrees to 800 degrees C at the same pressure, C(60) transforms into a rhombohedral structure with hexagonal lattice parameters of a(o) = 9.22 angstroms and c(o) = 24.6 angstroms. The intermolecular distance is small enough that a chemical bond can form, in accord with the reduced solubility of the pressure-induced phases. Infrared, Raman, and nuclear magnetic resonance studies show a drastic reduction of icosahedral symmetry, as might occur if the C(60) molecules are linked. 相似文献
11.
封育对人工针叶林林下植物多样性恢复的影响 总被引：1，自引：0，他引：1
该文以河北省木兰林管局较强封育、较弱封育和非封育等3种封育强度的人工油松林和人工华北落叶松林林下植被为研究对象,对其物种丰富度、群落结构特征、物种多样性指数、群落相似度等4个方面进行了比较。结果表明:不同封育强度下人工针叶林林下草本植被差距较大,较强封育区油松林和落叶松林比非封育区的物种数分别多33种和21种,高度大2.49倍和3.28倍,盖度值大52.21%和54.87%;而木本植物的密度、盖度差距等不明显。各封育强度下植被反映物种多样性的Simpson指数值差异并不显著,部分Shannon-Wiener指数差异显著。随着封育强度的变弱,相同树种各标准地间的林下物种组成差异增大。油松林和落叶松林林下植物在较强封育下物种种类和群落结构相似程度不大,但在非封育的极强干扰胁迫下,两个不同的建群种林下植物种类和群落结构表现出较为接近的特征。外界的严重干扰影响人工针叶林林下植被,人为干扰一旦停止,针叶林林下植被的恢复较快。限制人、畜对林下植被的干扰,加强封育,可有效恢复和增加林下植被的物种多样性。这说明人工林群落加强封育、减小干扰直接影响着群落的生物多样性的高低及其生态效益。 相似文献
12.
采用RAPD技术对野生与养殖花羔红点鲑群体各17个个体进行了DNA多态性检测.用13个随机引物在野生群体和养殖群体中分别扩增出119和86条DNA片段,其中多态性片段数分别为64和51条,多态性片段的比例分别为52.46%和41.80%,平均杂合度分别为0.2177和0.1802,遗传相似率分别为0.7844和0.7985,群体间遗传相似率为0.6468,由此得出野生群体的遗传多样性高于养殖群体.通过Nei指数统计的花羔红点鲑群体内遗传多样度平均为0.1989,群体间遗传多样度为0.1359,群体间遗传分化为34.53%.Shannon遗传多样性指数表明,两群体中的遗传变异有64.05%来自群体内,只有35.95%来自群体间,此分化值与Nei指数估测得到的遗传分化相近. 相似文献
13.
【目的】研究甘肃省引进大豆种质资源的遗传多样性,为大豆育种提供优异亲本。【方法】利用SPSS 17.0软件和R语言软件进行描述性统计、相关分析、主成分分析和聚类分析,对国内外引进的417份大豆种质资源进行适应性和遗传多样性分析。【结果】417份大豆种质资源中有363份在甘肃中部地区能够正常成熟,折合产量最高为3 901.65 kg/hm2,百粒重最高为 42.71 g。16个表型性状遗传多样性指数介于0.084 2~1.916 0,变异系数在18.17%~35.70%,除子叶色外,其余性状间均存在一定程度的相关性。将363份种质划分为8个类别,甘肃省大豆种质与我国华北和黄淮地区大豆种质相似系数比较接近。【结论】引进大豆种质资源遗传多样性丰富,筛选出26份特异种质资源。 相似文献
14.
Global patterns of predator diversity in the open oceans 总被引：1，自引：0，他引：1
The open oceans comprise most of the biosphere, yet patterns and trends of species diversity there are enigmatic. Here, we derive worldwide patterns of tuna and billfish diversity over the past 50 years, revealing distinct subtropical "hotspots" that appeared to hold generally for other predators and zooplankton. Diversity was positively correlated with thermal fronts and dissolved oxygen and a nonlinear function of temperature (approximately 25 degrees C optimum). Diversity declined between 10 and 50% in all oceans, a trend that coincided with increased fishing pressure, superimposed on strong El Ni?o-Southern Oscillation-driven variability across the Pacific. We conclude that predator diversity shows a predictable yet eroding pattern signaling ecosystem-wide changes linked to climate and fishing. 相似文献
15.
Tyler GL Ford PG Campbell DB Elachi C Pettengill GH Simpson RA 《Science (New York, N.Y.)》1991,252(5003):265-270
Magellan probes Venus' surface by 12.6-cm-wavelength vertical and oblique radar scattering and measures microwave thermal emission. Emissivity and root-meansquare slope maps between 330 degrees and 30 degrees E and 90 degrees N and 80 degrees S are dissimilar, although some local features are exceptions. Inferred surface emissivities typically are approximately 0.85, but vary from approximately 0.35 at Maxwell to approximately 0.95 northeast of Gula Mons and other locations. Lowest emissivities appear in topographically high areas; this relation suggests that a phase change or differences in chemical weathering occur at about 6055-kilometer radius. Initial results indicate that there are significant variations in the surface scattering function. 相似文献
16.
为了研究青藏高原高寒植被的空间分布格局及其对全球变暖的响应,以青藏高原高寒草地为研究对象,选取8个不同海拔梯度的典型试验区,每个试验区采取对照和增温2种处理。结果表明：（1）海拔梯度<4000 m的高寒草地禾本科为主要优势科,海拔梯度>4000 m的高寒草地莎草科为主要优势科;（2）中等海拔地区的高寒草地物种多样性相对较高,低海拔地区的高寒草地物种多样性高于高海拔地区;（3）主动增温和被动增温对青藏高原高寒草地物种多样性产生不同影响,但整体上均降低了物种多样性,且群落中优势科（禾本科和莎草科）对增温的响应更为敏感。因此,增温和海拔梯度对青藏高原高寒草地物种多样性产生重要影响,两者都降低了物种多样性。 相似文献
17.
18.
The highest oceanic temperatures are found at hydrothermal vents, where the polychaete Paralvinella sulfincola lives on vent sulfides within steep and dynamic thermal gradients. To determine P. sulfincola thermotolerance and preference, we developed a high-pressure aquarium that mimics in situ thermal gradients and permits P. sulfincola to move within the gradient. These polychaetes were thermotaxic, preferring temperatures of 40 degrees to 50 degrees C. Some individuals remained at 50 degrees C for 7 hours (the duration of the experiment), whereas others endured exposure to 55 degrees C for over 15 minutes, demonstrating that alvinellids prefer high temperatures and are among the most thermotolerant of marine organisms. 相似文献
19.
以马尾松种子园不同时期(建园初期、丰产期及衰老期)产出的子代为材料,采用SSR标记分析其遗传多样性,并结合子代测定数据分析交配系统对子代遗传品质的影响。研究结果表明,建园初期与丰产期的子代家系的Shannon多样性指数(I)较高,同为0.53,衰老期的子代家系则为0.47。观测杂合度(Ho)和期望杂合度(He)均以建园初期子代群体为最高,丰产期子代次之,衰老期最低。马尾松种子园建园初期与丰产期的子代均具有较高的遗传多样性。丰产期参与繁殖的父本数量最多,近交水平较低,从而保证了种子的品质。而种子园衰老期子代的遗传多样性明显下降,说明种子园的老化不仅影响种子产量,而且影响种子遗传品质。在亲本分析中,种子园建园初期、丰产期及衰老期的子代均未检测到自交情况。由此可进一步证实马尾松是典型的异交树种。 相似文献
20.
花棒群落物种多样性及其种群空间分布格局的研究 总被引：8，自引：4，他引：4
根据乌兰布和沙漠固定沙丘和半固定沙丘20个样方的调查数据,
对不同生境中花棒群落物种多样性及其种群空间分布格局进行了研究。
测定了各层次植物物种的重要值,采用多种方法计算各层次物种的丰富
度指数、均匀度指数和多样性指数,采用相邻格子样方法取样,应用方
差均值比的t检验和5种典型聚集度指标方法,研究了不同生境中花棒种
群的空间分布格局。结果表明,在不同生境类型中,花棒空间分布格局
均为集群分布,但集群程度有差异。同时,还对不同发育阶段花棒种群
的分布格局进行了分析,从幼苗到成树,其集群强度由大到小。 相似文献