Invasive plants versus their new and old neighbors: a mechanism for exotic invasion

Invading exotic plants are thought to succeed primarily because they have escaped their natural enemies, not because of novel interactions with their new neighbors. However, we find that Centaurea diffusa, a noxious weed in North America, has much stronger negative effects on grass species from North America than on closely related grass species from communities to which Centaurea is native. Centaurea's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results may help to explain why some exotic species so successfully invade natural plant communities.     

阿尔金山国家级自然保护区的对齿藓属(Didymodon Hedw.)植物调查

在野外调查和采集标本的基础上,对阿尔金山国家级自然保护区对齿藓属植物的分类、区系地理成分和垂直分布进行研究。结果表明:该保护区的对齿藓属植物共计19种,共发现新疆新记录种7种。从种的区系地理成分水平上将其可划分为世界广布成分、北温带成分(占比38%)、旧世界温带成分(占比11%)、东亚-北美间断分布成分(占比27%)、中国特有成分(占比22%),表现出明显的北温带和东亚-北美间断分布成分,并且中国特有成分占有重要地位;垂直分布可划分为高山荒漠带(10种)、山地荒漠带(11种)、高寒草原带(12种)、高山草甸带(4种)、高山稀疏植被带(1种)。文中对该保护区对齿藓属植物的形态特征及其在该保护区的分布进行了描述,并编制了该保护区对齿藓属植物的分种检索表。     

Dieldrin and DDT: effects on sparrow hawk eggshells and reproduction

Patterns of reproductive failure in declining populations of several European and North American raptorial species were duplicated experimentally with captive American sparrow hawks Falco sparvcrius that were given a diet containing two commonly used organochlorine insecticides. Major effects on reproduction were increased egg disappearance, increased egg destruction by parent birds, and reduced eggshell thickness.     

Two unusual unionid hermaphrodites

In a survey of the gonads of 97 species of North American freshwater mussels representing 59 genera, only four species were found to be hermaphroditic (monoecious). Among several other "occasional" hermaphrodites, two were unique in that the same follicles in the gonads produced eggs and sperm simultaneously. Evidently the control mechanism failed to function normally in these species [Actinonaias ellipsiformis and villosa (formely micromya) iris (Lea)]. This simultaneous production of eggs ans sperm is apparently quite unusual among mollusks.     

Ecology of colors of firefly bioluminescence

Dark-active North American fireflies emit green bioluminescence and dusk-active species emit yellow, in general. Yellow light and yellow visual spectral sensitivity may be adaptations to increase the signal-to-noise (that is, foliage-reflected ambient light) ratio for sexual signaling during twilight. The peaks of the electroretinogram visual spectral sensitivities of four species tested, two dark- and two dusk-active, correspond with the peak of their bioluminescent emissions.     

Significance of "tethyan" fossils in the american cordillera

Equatorial faunas of the ancient Tethyan seaway, which extended from western Europe to southeastern Asia, comprise some of the most diverse marine taxa in the fossil record. Comparable or identical "Tethyan" species that occur far from the Tethyan seaway in Paleozoic and Mesozoic rocks of the North and South American Cordillera have long been considered as a major biogeographic anomaly. Two leading theories to account for the occurrence of these anomalous "Tethyan" faunas in the Cordillera are that they were transported long distances to the east on tectonic blocks(suspect terranes that originated near the Tethys) or that they migrated westward via undiscovered marine corridors through continental areas of Pangea. An alternative model is that these "Tethyan" fauna were pantropic species that extended with attenuated diversities into the eastern proto-Pacific Ocean. This pantropic model can better account for the distribution patterns of many Paleozoic and early Mesozoic "Tethyan" species in the American Cordillera and provides a steady state hypothesis against which the other models can be tested. The distribution of pre-Cretaceous "Tethyan" faunas is similar to the known pantropic distribution of many Cretaceous and Cenozoic tropical biotas. During the Cenozoic, taxa were most diverse in the Tethys and Indo-West Pacific regions but extended with attenuated diversity to many parts of the equatorial Pacific Ocean, including the west coasts of North and South America. The eastern Pacific occurrence of many Indo-West Pacific species provides a modern analog for the occurrence of many anomalous "Tethyan" fossils in the American Cordillera.     

美国黑核桃与核桃、核桃楸木材材性的比较研究

对引种美国黑核桃 (Juglansnigra)与国产核桃 (Juglansregia)、核桃楸 (Juglansmandshurica)木材解剖构造和主要木材材性的测定表明 ,美国黑核桃的心材解剖特征与核桃、核桃楸相比没有区别 ,而边材的木纤维壁厚、木纤维腔径比和壁腔比、木纤维比量、木射线比量差异均显著或极显著 ,其它特征没有差异 ;美国黑核桃主要木材物理力学性质与国产核桃、核桃楸以及北方常见的速生树种杨树、泡桐相比 ,木材材质好 ,但木材干缩性略差 ;美国黑核桃木材化学性质能满足胶合板生产要求。综合分析表明 ,美国黑核桃是可以在我国适生地区进行推广发展的优良工业用材树种。     

Prospects for an invasion: competition between Aedes albopictus and native Aedes triseriatus

Competition between larval populations of the native North American treehole mosquito Aedes triseriatus and Aedes albopictus, recently introduced from Asia to North America, was assessed by comparing per capita growth rate estimates for experimental cohorts of larvae developing under a variety of initial density combinations in fluid obtained from tires or from treeholes. Estimates of carrying capacities and competition coefficients indicate that competition between the two species will result in stable coexistence in treehole communities but local extinction of A. triseriatus in tire habitats.     

田间自然条件下葡萄黑痘病抗性鉴定

葡萄黑痘病是危害葡萄生产的重要真菌病害之一,进行葡萄黑痘病抗性鉴定筛选抗病种质具有重要的意义。采用田间自然鉴定的方法,分析48份葡萄材料(北美种群内种间杂种、中国野葡萄、欧美杂种及欧亚种)对黑痘病的抗性差异。结果表明:不同葡萄材料对黑痘病抗性有着很大的差异。北美种群2个砧木品种、中国野葡萄华东葡萄湖南-1和山葡萄通化3号、欧美杂种均较欧亚种抗病,5BB、SO4、湖南-1、通化3号、京亚、8611、夏黑、翠峰和巨峰等表现为高度抗病;欧亚种对黑痘病的抗性表现为抗病和感病2种类型,其中紫地球、红提、玫瑰香等表现感病。研究结果为葡萄生产栽培和抗黑痘病育种提供理论依据。     

21世纪北美体育特许经营产业的发展及启示

北美体育特许经营产业是世界上最为发达的体育特许经营产业,进入21世纪以来,在全球经济一体 化和北美地区经济持续不景气的背景下,北美体育特许经营产业出现了新的发展形势,主要通过文献资料 法对北美体育特许经营产业发展现状进行分析,总结北美体育特许经营行业的发展经验,为我国相关体育 产业的发展提供借鉴。     

Mammalian evolution and the great american interchange

A reciprocal and apparently symmetrical interchange of land mammals between North and South America began about 3 million years ago, after the appearance of the Panamanian land bridge. The number of families of land mammals in South America rose from 32 before the interchange to 39 after it began, and then back to 35 at present. An equivalent number of families experienced a comparable rise and decline in North America during the same interval. These changes in diversity are predicted by the MacArthur-Wilson species equilibrium theory. The greater number of North American genera (24) initially entering South America than the reverse (12) is predicted by the proportions of reservoir genera on the two continents. However, a later imbalance caused by secondary immigrants (those which evolved from initial immigrants) is not expected from equilibrium theory.     

Epidermal patterns of the lemma in some fossil and living grasses and their phylogenetic significance

Morphological study of fossil grass anthoecia of Berriochloa and Nassella collected from Miocene-Pliocene strata in Kansas has revealed well-preserved epidermal structure. This seems to be the first micromorphological information known from fossil grass floral bracts. The epidermal pattern on the lemma in the fossils and their living counterparts are evidence in support of the view that the North American species of Stipa of the section Hesperostipa Elias and species of Piptochaetium have a common ancestry in Berriochloa, and that species of both taxa have been distinct from species of the Nassella, Oryzopsis, and other Stipa since at least the Miocene or Pliocene.     

Evidence for a major meteorite impact on the Earth 34 million years ago: implication for eocene extinctions

A deep-sea core from the Caribbean contains a layer of sediment highly enriched in meteoritic iridium. This layer underlies a layer of North American microtektites dated at 34.4 million years ago and coincides with the extinction of five major species of Radiolaria. It is suggested that a massive, chemically undifferentiated meteorite collided with the earth, producing the tektites and leading to extinctions 34 million years ago.     

Ontogeny in animal colonies: a persistent trend in the bryozoan fossil record

The principal modes of zooid and colony growth in encrusting cheilostome bryozoans have undergone a major evolutionary transition during the last 100 million years. Comparisons of species within successive North American fossil faunas reveal a persistent trend in which one mode of growth is gradually supplanted by another. Ecological evidence from living faunas and the polyphyletic nature of this trend suggest that the transition has adaptive significance.     

Species pool and dynamics of marine paleocommunities

Foraminiferal communities in the Cenozoic shelf deposits of the North American Atlantic Coastal Plain exhibit little unity during almost 55 million years of successive transgressions and regressions. Transgression communities are composed of a dynamic mixture of immigrants and newly evolved species. During regressions, species within these communities either became extinct or emigrated. Some emigrants returned during subsequent transgressions, but many did not. The neritic species of the Atlantic and Gulf continental margins constitute a species pool. Immigrants and emigrants transferred into and out of the species pool, while extinctions and originations repeatedly altered its species composition. While the results indicate a lack of local community unity, at the same time they demonstrate the necessity of a species pool to sustain species diversity.     

猪繁殖与呼吸综合征病毒YA株ORF5基因的克隆与序列分析

以猪繁殖与呼吸综合征病毒（PRRSV）YA株为材料，采用RT－PCR扩增其ORF5基因全长cDNA并进行序列测定和比较分析。结果YA株ORF5基因cDNA编码区长603bp，可编码200个氨基酸残基。与欧洲型代表株LV株、美洲型代表株VR－2332株在氨基酸水平上的同尖性分别为58％和90％，与国内首株分离株(CH－1a)的同源性高达95％，推测YA株属于美洲型。根据YA株ORF5基因编码的氨基酸序列，与具有代表性的12株美洲型毒株和2株欧洲型毒株绘制进化系统树，结果也显示YA株与美洲型分离毒株的遗传关系较近，而与欧洲毒株的遗传关系较远。进一步采用序列分析软件对推导的氨基酸进行比较分析，发现YA株ORF5编码的E蛋白存在5个潜在的N－糖基化位点，6个抗原位点，其糖基化位点的数目及抗原位点的分布与其它美洲毒株均存在一定程度的差异，但3个最主要的抗原表位相对保守。     

Iguanid lizard from the upper cretaceous of Brazil

Pristiguana brasiliensis, new genus and species, from the Upper Cretaceous Baurú Formation of Brazil, is the oldest fossil referable to the living lizard family Iguanidae. It resembles living primitive South American iguanids in some features, but also shows similarity to members of the related family Teiidae. Iguanid fossils do not appear in North America until the early Eocene, probably by waif dispersal from South America during the late Paleocene or early Eocene. A southern continental (Gondwanan) origin of iguanids is more plausible than the northern one often suggested.     

A multispecies overkill simulation of the end-Pleistocene megafaunal mass extinction

A computer simulation of North American end-Pleistocene human and large herbivore population dynamics correctly predicts the extinction or survival of 32 out of 41 prey species. Slow human population growth rates, random hunting, and low maximum hunting effort are assumed; additional parameters are based on published values. Predictions are close to observed values for overall extinction rates, human population densities, game consumption rates, and the temporal overlap of humans and extinct species. Results are robust to variation in unconstrained parameters. This fully mechanistic model accounts for megafaunal extinction without invoking climate change and secondary ecological effects.     

The kangmar dome: a metamorphic core complex in southern xizang (tibet)

The Kangmar metamorphic-igneous complex is one of the most accessible examples of an enigmatic group of gneiss domes (the North Himalayan belt) that lies midway between the Greater Himalaya and the Indus-Tsangpo suture in southern Tibet. Structural analysis suggests that the domal structure formed as a consequence of extensional deformation, much like the Tertiary metamorphic core complexes in the North American Cordillera. Unlike its North American counterparts, the Kangmar dome developed in an entirely convergent tectonic setting. The documentation of metamorphic core complexes in the Himalayan orogen supports the emerging concept that extensional processes may play an important role in the evolution of compressional mountain belts.     

Pleistocene avifaunas and the overkill hypothesis

At the end of the North American Pleistocene, birds and mammals suffered comparable degrees of generic extinction. Both the magnitude and pattern of avian extinction are incompatible with the hypothesis that humans played a major role in causing the demise of numerous North American mammalian genera at this time.