关键词： competition   Cynomys ludovicianus   herbivory   mesquite   prairie dogs   Prosopis glandulosa   seed disappearance   seedling establishment   succession   tree-grass dynamics  

摘要： Explanations for documented increases in woody plant dominance in grasslands and savannas of North America include atmospheric CO2 enrichment and changes in climate, livestock grazing, and fire regimes. However, tree/shrub encroachment has also coincided with the eradication of a once widespread native herbivore, the black-tailed prairie dog (Cynomys ludovicianus). We used field experiments and repeat aerial photography to demonstrate that prairie dogs, and the herbivores and granivores associated with their colonies, probably maintained grassland and savanna by preventing woody species such as Prosopis glandulosa (honey mesquite) from establishing or attaining dominance. Prosopis seed and pod disappearance was 3-99 times greater within prairie dog colonies. Ants were the primary agent of seed removal, whereas prairie dogs and associated vertebrates were the primary agents of pod removal. Survival of Prosopis seedlings protected from vertebrate herbivory was similar on and off prairie dog colonies (approximate to 60%), whereas survival of unprotected seedlings was 3 times greater off- than on-colony. On-colony, prairie dogs and associated herbivores girdled and destroyed all Prosopis saplings within 2 d of planting;survival of 1-yr-old seedlings was reduced by 50% after 3 mo of exposure to on-colony herbivores. Despite high levels of woody plant seed disappearance and seedling herbivory, on-colony ''seedling'' reserves were substantial (950 plants/ha). Thus, prairie dogs and the fauna that occur on their colonies suppressed rather than eliminated Prosopis from the colony site. Removal of prairie dogs led to rapid development of Prosopis stands. Repeat aerial photography showed that Prosopis canopy cover on a colony eradicated in 1950 (27%) increased to a level (61%) comparable to that of off-colony Prosopis stands (65%) within 23 yr. These data illustrate how transitions from grassland to woodland vegetation can be mediated by a rodent herbivore. They further demons

关键词： 结核杆菌   毒力   动物模型   菌株   感染  

摘要： 采用标准毒力的Ｈ３７ＲＶ菌株和经Ｌ－Ｊ培基传代减毒的菌株，对Ｃ５７ＢＬ／６Ｎ小鼠进行尾静脉注射和腹腔注射感染，就树造动物各器官的结核菌实验模型进行了探讨。结果表明，树造胸腔器官（肺和心脏）的动物模型以尾静脉感染为好，树造肝、脾和腹股沟淋巴结结核的动物模型以腹腔注射感染为宜。如要成功地树造结核感染的动物模型，最好将所购回的标准菌株在实验动物体内恢复毒力后再使用。

关键词： Acer pseudoplatanus   amino acids   aphids   CO2   Fagus sylvatica   leafhoppers   populations  

摘要： Five species of sap-feeding homoptera were studied on Fagus sylvatica and Acer pseudoplatanus and exposed to elevated concentrations of carbon dioxide (600 mu L L(-1)). The concentration of total soluble amino acids in foliage of F. sylvatica was unaffected by growing saplings in elevated atmospheric CO2 concentrations. Although experiments on individual aphids indicated poorer performance of Phyllaphis fagi (fewer, smaller nymphs produced), resultant populations did not differ from those in ambient (350 mu L L(-1)) conditions. The area of beech foliage stippled by the leafhopper Fagocyba cruenta was similar at ambient and elevated CO2 concentrations. The concentration of total amino acids and that of serine of A. pseudoplatanus foliage were significantly lower at elevated CO2 concentrations. However, the relative growth rates of two aphid species Drepanosiphum platanoidis and Periphyllus testudinaceus and one leafhopper Ossiannilssonola callosa were not significantly different in elevated CO2. No evidence was found that, under the conditions of these experiments, populations of aphids and leafhoppers will change as concentrations of CO2 increase.

关键词： Animals   Body Constitution   Bronchi   Lung Volume Measurements   Mice   Rats   Rodentia   Species Specificity  

摘要： Size-dependent structural patterns in the conductive bronchial tree of four species of myomorph rodents of different body weight were determined by lung casts. The lungs of the harvest mouse, Micromys minutus, body weight 5-7 g, the house mouse, Mus musculus, body weight 35-45 g, the brown rat, Rattus norvegicus, body weight 200-400 g, and the African giant pouched rat, Cricetomys gambianus, body weight 1,200-1,800 g, were inflated to 20 cm H2O, frozen, freeze-dried, hardened, and filled with silicone rubber. The casts were pruned, and branching pattern, diameter, and volume of the conductive bronchial tree were determined using a binocular magnifier. All four species have four lobes on the right lung and an undivided left lung, and the central bronchial tree on either side shows an identical monopodial branching pattern. Although the ramification of the central conductive bronchi is not size-dependent, the diameter and volume are. The diameter of the left main bronchus equals 1.24% of body length in Micromys and 0.6% in Cricetomys, and the conductive bronchial tree makes up 13% of the total lung volume in Micromys and 6% in Cricetomys. Relatively wider airways and a decline in airway resistance with declining body mass in small mammals compared to large ones result in a high ventilatory dead space, which is compensated for by a higher breathing frequency. (C) 1996 Wiley-Liss, Inc.

关键词： 乙型肝炎   疾病模型   免疫组化  

摘要： 目的：观察树是否可成为感染人ＨＢＶ的动物模型。方法：应用免疫组化及原位杂交技术，对实验组及对照组树肝组织进行研究分析。结果：应用羊抗－ＨＢｓ多抗检测树肝组织中的ＨＢｓＡｇ时，出现假阳性反应，阳性物为非目的抗原，应用生物素标记的ＨＢＶＤＮＡ探针进行肝组织原位杂交时，出现非特异性的显色反应，结论：提示在动物模型实验中，应设立严格的对照实验和应用不同反应系统进行校对考核。

关键词： Amino Acid Sequence   Animals   Base Sequence   Blotting   Northern   DNA   Complementary   Female   Gene Expression   Gonadorelin   Immunohistochemistry   In Situ Hybridization   Male   Mesencephalon   Molecular Sequence Data   Oligonucleotide Probes   Protein Precursors   RNA   Messenger   Research Support   U.S. Gov't   P.H.S.   Tupaiidae  

摘要： Reproductive maturation and regulation is centrally orchestrated by gonadotropin-releasing hormone (GnRH). GnRH produced in the vertebrate hypothalamus acts on the pituitary to regulate gonadotropins. In nonplacental mammalian species, it has recently been shown that a second GnRH gene is expressed in mesencephalic cells. Here, we report the cDNA sequences and expression patterns for two distinct genes encoding the hypothalamic and mesencephalic GnRH forms in the brain of a placental mammal, the tree shrew (Tupaia glis belangeri). The novel mammalian GnRH form, designated here as [His(5)Trp(7)Tyr(8)]GnRH (often sailed chicken GnRH II), is expressed in neurons of the mesencephalon and is the first nonhypothalamic form to be isolated from a mammal. Its peptide sequence is identical to the form previously reported in fish, amphibians, reptiles, and birds, revealing that it has remained unchanged for 500 million years. In contrast, the sequences of the hypothalamic GnRH decapeptides vary by as much as 50% across vertebrate species. The remarkable sequence conservation of mesencephalic GnRH suggests that it has been highly constrained throughout evolution, perhaps indicating an important, consented nongonadotropic role. The discovery and localization of two mRNAs encoding distinct GnRH forms in an advanced mammal suggest that other mammals, including primates, may also have a second GnRH gene with expression localized in the midbrain. (C) 1996 Academic Press, Inc.

关键词： plant colonization   Ficus   endozoochory   bird and bat frugivory   fig wasps   Krakatau   dispersal   avian raptors   island ecology  

摘要： Since the biologically extirpating eruption of Krakatau (Sunda Strait) in 1883, Rakata (Krakatau's remnant) and two closely adjacent islands, Sertung and Panjang, have been colonized by over 200 species of vascular plants. They now carry species-poor mixed tropical forest, including some twenty-three species of Ficus. Data on the sequence of colonization over the last century by twenty-four Ficus species, twenty-three species of volant frugivores, and by agaonid fig-wasps, presumably from the large islands of Java and Sumatra, each some 44km distant, are summarized. The potential of the volant frugivores as dispersers of fig seeds is assessed, the pollination problems involved in the colonization of islands by figs are reviewed and patterns of colonization by fig species and by their bird and bat dispersers are identified and discussed. In 1930 a new island, Anak Krakatau, emerged from Krakatau's submerged caldera. This active volcano suffered a self-sterilizing eruption in 1952/1953 and has been colonized, under considerable constraint from its own volcanic activity, probably largely from the (selected) species pool present on Rakata, Sertung and Panjang, 2-4 km away. Its vegetation is at an earlier successional stage (grassland and Casual ina woodland) than that of the three older islands, and in 1992 the Casuarina woodland was in an early stage of transition to mixed forest. The colonization of Anak Krakatau by Ficus species, agaonid wasps and volant frugivores over a critical decade (1982-92) is reviewed, including preliminary assessments of the effects of pollinator limitation on four pioneer fig species and indications of a possible effect of the presence of avian raptors, particularly the peregrine falcon, on fig colonization and forest diversification.

关键词： Pollinating insects   Trees   Phylogeny   Genera   Seeds   Pollen   Insect pollination   Biogeography  

关键词： biomass allocation   browsers   herbivory   production   spinescence  

摘要： Length, branch production, orientation, spinescence and biomass were measured for current shoots of Acacia tortilis shrubs in a range of habitats in Botswana. All shoot characteristics varied between individuals and between habitats with longer, less spinescent shoots produced in the habitat recently protected from wildlife. Biomass allocated to woody material increased with shoot length at the expense of leaf mass, whilst investment in straight prickles was as much as 6% of shoot dry mass. Shoot length had significant effects on total current shoot mass per shrub which was greatest in the recently protected area but the mean number of shoots per shrub also varied between habitats. Age and history of disturbance, including herbivory, appear to be important determinants of. morphology and growth pattern of individual shrubs. Fitness of A. tortilis individuals and the consequence of flexibility in growth responses for vegetation structure and community organization are discussed.

关键词： habitat use and preference   mixed wild and domestic ungulate community   niche overlap and interspecific competition   southern Africa savanna woodland  

摘要： 1. The spatial distribution of two wild ungulates, impala and kudu, and of domestic cattle, was monitored across seasons in a 9400 ha ranch of the 'highveld' of Zimbabwe. Habitat use, preference, selectivity and overlap were estimated. Predation was negligible and the study concentrated on interspecific competition. 2. Cattle were contained in paddocks, and were moved regularly, while wild ungulates moved freely. Wild ungulate habitat use, preference and selectivity between paddocks with and without cattle were compared, as was the variation in broad diet, group size and densities. 3. All herbivores were selective, with a marked preference for the nutrient-rich Acacia/Dichrostachys vegetation type. Terminalia communities were almost completely avoided. Selectivity increased as the dry season progressed. Habitat overlap was always high. 4. Interspecific competition occurred between cattle and impala, especially during the wet season and the hot dry season. Impala showed a switch in habitat preference and an increase in selectivity and started to concentrate on 'refuge habitat'. Some also switched in their diet composition. During the hot dry season, when resources were at their lowest, most impala stopped using paddocks with cattle. 5. Kudu seemed relatively unaffected by the presence of cattle: the variations observed in kudu spatial behaviour may have been caused by competition with impala.