关键词： Beilschmiedia miersii   Chile   herbivory   protected areas   seedling establishment  

摘要： Beilschmiedia miersii is an endemic endangered tree of central Chile, protected only in La Campana National park. The regeneration of B. miersii is very low, presumably due to strong fruit and seedling predation by livestock. The aim of this study was to establish whether herbivores impact recruitment in populations of the species. In particular, we want to compare the herbivore effect in non-protected populations with protected populations inside a national park. We compared demographic features and the regeneration process in four populations, two located inside and two outside the park. We expect populations inside the park to exhibit a significantly greater recruitment, expressed in seedling establishment and survival, relative to those outside the park. Outside the park, livestock predation on fruits and herbivory on seedlings could hamper recruitment. However, fruit and seedling predation was similarly high both inside and outside the park, posing a significant constraint on the regeneration of B. miersii. The main associated causes were the presence of livestock and seedling desiccation. If the survival of B. miersii is to be achieved, managing livestock pressure, possibly through zoning, seems mandatory. (C) 2001 Elsevier Science Ltd. All rights reserved.

关键词： PESTICIDES & wildlife   AMPHIBIANS   CARBARYL   CHEMICALS   ENVIRONMENTAL aspects  

摘要： Global declines in amphibians likely have multiple causes, including widespread pesticide use. Our knowledge of pesticide effects on amphibians is largely limited to short-term (4-d) toxicity tests conducted under highly artificial conditions to determine lethal concentrations (LC50). We found that if we used slightly longer exposure times (10-16 d), low concentrations of the pesticide carbaryl (3-4% of LC50(4-d)) killed 10-60% of gray treefrog (Hyla versicolor) tadpoles. If predatory cues also were present, the pesticide became 2-4 times more lethal, killing 60-98% of tadpoles. Thus, under more realistic conditions of increased exposure times and predatory stress, current application rates for carbaryl can potentially devastate gray treefrog populations. Further, because predator-induced stress is ubiquitous in animals and carbaryl's mode of action is common to many pesticides, these negative impacts may be widespread in nature.

关键词： competition   carnivores   riparian woodland   behavioral ecology  

摘要： Some of the models proposed to explain Plio-Pleistocene hominid behavior and the formation of early East African archaeological sites are based on the assumption that the riparian habitats in which most of them occur were places of low interspecific competition. Competition is expressed here in terms of carnivore and hominid. interactions. In this paper, a study of carnivore interaction in open and closed habitats is presented. The results indicate that riparian woodland shows the lowest degree of competition in savanna ecosystems. This suggests that if Plio-Pleistocene carnivores were adapted like their modern counterparts, the paleoecological settings of early sites could have provided hominids with enough safety to process carcasses and behave as shown in "central-place", "near-kill location" and "refuge" foraging models. (C) 2001 Academic Press.

关键词： herb layer   nitrogen   nutrient input   nutrient retention   phosphorus   plant competition  

摘要： Loss of nutrients following pulses of nutrient input in northern hardwood forests and the general effects of atmospheric deposition on forest communities are of concern. Uptake of nutrients by ground layer vegetation, including herbs and tree wildlings, may be important in both of these processes. We brought plants from the field (Catskill Mts, New York) and grew them under controlled environment conditions at two nutrient input levels to determine responses of Oxalis acetosella and Acer saccharum to increased nutrient input and tree wildling density. Oxalis nutrient concentration increased for many nutrients compared to field plants. Both species doubled their P concentration when P input doubled. Biomass of Oxalis was unaffected by both nutrient input level and Acer wildling density. Acer showed a similar response to increased nutrient input and its density did not affect the response of Oxalis to increased nutrient input. Results indicate that both species may be important to nutrient retention in northern hardwood forests. (C) 2001 Elsevier Science B.V. All rights reserved.

关键词： lattice animals   exact enumeration   computer algorithms  

摘要： We have developed an improved algorithm that allows us to enumerate the number of site animals on the square lattice LIP to size 46. We also calculate the number of lattice trees up to size 44 and the radius of gyration of both lattice animals and trees up to size 42. Analysis of the resulting series yields an improved estimate, lambda =4.062570(8), for the growth constant of lattice animals, and, lambda (0)=3.795254(8), for the growth constant of trees, and confirms to a very high degree of certainty that both the animal and tree generating Functions have a logarithmic divergence. Analysis of the radius of gyration series yields the estimate, nu =0.64115(5), for the size exponent.

关键词： 树Qu   实验动物   动物模型   研究   应用   病毒病肿瘤   心血管疾病  

摘要： 树鼠句是一种低等的灵长类动物 ,其解剖结构、神经系统、性周期及新陈代谢等方面都近似于人类 ,具有易捕捉、价廉易养、使用方便等有利条件。目前国内外对树鼠句的研究相当广泛和深入 ,几乎涉及了医学和生物学的各个领域 ,已成功地建立了肿瘤、病毒感染及心血管等多方面的人类疾病动物模型。介绍了近年来国内外一些有代表性的研究成果 ,力图说明树鼠句作为一种新型实验动物 。

摘要： The composition, species richness and abundance of zooplankton communities were studied in two highly contaminated areas: (1) mainly by heavy metals and other toxic and non-toxic matter, and (2) mainly by fine particles of nepheline and other minerals and organic matter, in the large, subarctic Imandra Lake (northwestern Russia), based on data collected between 1978 and 1990. Reduction in the relative abundance of the typical inhabitants of northern oligotrophic lakes and their substitution by tolerant-to-pollution, widely distributed, circumpolar species were the general trends for the communities. In both lake areas, water quality changes occurred in response to reductions in contamination of metals, mineral particles and organic matter in the mid 1980s. Water chemistry improvements, including decreased concentrations of pollutants, have resulted in partial recovery of zooplankton communities, increase in species richness, density of individuals, and shifts in composition of the dominance group. However, both lake areas are still contaminated and re-establishment of communities typical of a non-polluted lake did not occur between the mid 1980s and mid 1990s. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.

关键词： sicklepod   Senna tora   Cassia obtusifolia   Mitrapsylla albalineata   Conotrachelus sp.   biological control  

摘要： A survey of the phytophagous arthropod fauna associated with sicklepod, Senna obtusifolia, was undertaken between 1991 and 1993 to find biological control agents for this increasingly serious weed in Australia and its closely related congener, Senna tora. The survey concentrated in Mexico on the Gulf coast, the Pacific coast, and the Yucatan peninsula. Additional searching was undertaken in the state of Morelos, Mexico and Honduras. Some 108 phytophagous insect species were found. Literature searches and preliminary observation indicated that 10 species were sufficiently stenophagous to warrant further consideration as potential biocontrol agents. Two species, Mitrapsylla albalineata (Homoptera: Psyllidae) and Conotrachelus sp. 'Morelos' (Coleoptera: Curculionidae), have been brought to Australia for further study. (C) 2001 Academic Press.

关键词： STZ   树鼩   注药   链脲佐菌素   胰岛   动物模型   DM   数量   维持   诱导  

摘要： 目的：探讨链脲佐菌素（STZ）树糖尿病（DM）动物模型的建立及其空腹血糖（FBG）标准和最佳药物剂量。方法：45只树随机分为正常对照组、STZ80、100、120、150mg/kg组5个组，测定其注药前、后FBG，并于注药后第4、10周处死，取胰腺做光镜、电镜检查。结果：FBG≥111mmol/L的树胰腺胰岛数量明显减少，胰岛直径也明显缩小，胰岛β细胞数量减少，肿胀，可见数量不等的β细胞脱颗粒，甚至无紫红色颗粒，淀粉染色阳性，符合DM成模动物胰腺病理改变。正常对照组、STZ 80mg/kg组无一成模；100mg/kg组患病率10%（1/10），仅维持1周即自然阴转；120、150mg/kg组患病率均为88.9%（8/9），前者维持时间短，注药后第4周自然阴转率50%（4/8），第10周为100%（8/8）；后者维持时间长，注药后第4周自然阴转率37.5%（3/8），第10周为62.5%（5/8）。150mg/kg组成模后第6周有1只树死亡，其余各组树 无一死亡。结论：STZ能诱导树FDBE-DM模型，树 DM模型标准为FBG≥11.1mmol/L，最佳STZ剂量为150mg/kg。