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131.
P. P. Popov 《Russian Journal of Ecology》2003,34(1):27-33
The structures and differentiation patterns of the Norway spruce (Picea abies) and Siberian spruce (P. obovata) populations have been studied in a wide area, including the transition zone of their continuous geographic range. The areas occupied by transitional populations have been detected. Series of distinct populations of the Norway and Siberian spruces are located to the west and east of them, respectively. 相似文献
132.
133.
中国的人口,资源,环境问题及若干战略选择 总被引:3,自引:0,他引:3
王毅 《中国人口.资源与环境》1993,3(1):50-54
中国具有十分特殊的基本国情,如何根据中国的国情以及特定的历史与现实条件,选择适宜的组织机制,实施正确的长期发展战略,加速中国的现代化进程,这是一个十分紧迫而又令人关注的重大课题。本文主要从人口、资源、环境等方面分析中国现代化所面临的困境,以及应采取的战略选择。 相似文献
134.
Abstract: Wide variation in reproductive success is common among amphibians that breed in seasonal ponds, but persistence of adults can buffer against these fluctuations, particularly for long-lived species. We hypothesized that the frequent episodes of catastrophic failure of the marbled salamander ( Ambystoma opacum ) enhance the importance of high terrestrial survival. At Rainbow Bay in South Carolina reproductive success was poor (<1 metamorph/breeding female) in nearly half of the 22 years that the species bred. Complete failure occurred in 6 of 22 years. To study catastrophic failure, we adapted an age-structured, individual-based model with density-dependent growth and survival of larvae. The model was based on extensive data from local field studies and experiments. With consistently good survival in the pond stages, the simulated population required survival probabilities in the upland stages (juveniles and adults) near 0.5/year to persist and near 0.8/year to achieve the increases observed. Catastrophic failure, occurring randomly with probability 0.5/year, created additional fluctuations in the population, raised the thresholds of survival required for persistence, and caused extinction under conditions that were otherwise favorable. The marbled salamander at Rainbow Bay is not at great risk of extinction because of catastrophic failure, but the risk increases dramatically if life span is decreased or frequency of failure is increased. Any reduction in terrestrial survival will have deleterious consequences by reducing the breeding populations at equilibrium, even if it does not jeopardize persistence. Our model provides assessments of risk that can be applied to poorly studied species with similar life histories, such as the endangered flatwoods salamander ( A. cingulatum ). 相似文献
135.
Kirk Hamilton 《Environment, Development and Sustainability》2003,5(3-4):419-436
Genuine saving measures the real change in0 total wealth, factoring in the depreciation of produced assets, depletion of natural resources, pollution damages, and expenditures on education. This paper presents a theoretical framework for measuring changes in wealth in total and per capita terms, establishes the link between savings measures and prospects for social welfare, and provides summary empirical estimates of the savings measures. China excepted, the majority of countries below median income are distinguished by apparent declines in total wealth per capita. 相似文献
136.
马宾 《中国人口.资源与环境》1992,(1)
研究人口——经济系统,首先从人口系统着手,并分别对各子系统进行分析和综合。对人口系统的研究着重于控制数量、强调人口素质,尤其是要求人口文化素质对科学技术转化生产力能够起到保证作用,其最终目的是促进社会经济的发展。 相似文献
137.
黄伟雄 《中国人口.资源与环境》2002,(5)
本文从资源、环境和人地关系的角度探讨我国的可持续发展问题 ,分析了影响我国可持续发展因素 ,指出中华民族的人口素质是我国可持续发展的关键 ,阐明科教兴国是我国可持续发展的必由之路 相似文献
138.
Estimation of the maximal population frequency of “alien” biotypes taking into account a priori data
L. A. Zhivotovsky A. A. Pomortsev E. V. Lyalina B. A. Kalabushkin V. A. Pukhal’skii 《Russian Journal of Ecology》2005,36(2):89-92
A method is described for calculating the probability that the percentage of alien biotypes is higher than a specified threshold (e.g., 5%) in a population in which a certain number of alien biotypes has been found preliminarily. The method is based on the Bayesian approach; it assumes that the researcher has preliminary (a priori) information on the frequency of these biotypes. This a priori information makes it possible to estimate the aforementioned probability more accurately than is possible with the use of the standard binomial estimation. The method is illustrated by the results of the estimation of cultivar purity in batches of stock and foundation seeds of spring barley with the use of protein markers.Translated from Ekologiya, No. 2, 2005, pp. 106–109.Original Russian Text Copyright © 2005 by Zhivotovsky, Pomortsev, Lyalina, Kalabushkin, Pukhalskii. 相似文献
139.
S. N. Sannikov I. V. Petrova N. S. Sannikova T. V. Filippova 《Russian Journal of Ecology》2005,36(6):377-382
Gradients of Nei's genetic distances between 15 samples of Pinus sylvestris L. trees were analyzed along three submeridional transects, from Scandinavia to the Mediterranean and Transcaucasia. As a result, distinct chorogenetic differentiation was revealed between the populations of this species growing in climatically specific regions of northern and southern Europe. Considerable Nei's distances (DN = 0.045–0.056) and their gradients, combined with differences in stable phenotypic characters (the composition of monoterpenes and morphological parameters of cones) determined at the Pyrenean and Caucasian mountain borders, suggest that the P. sylvestris species structure includes two South Eurasian subspecies, the Pyrenean P. sylvestris L., ssp. iberica Svoboda and the Transcaucasian P. sylvestris L., ssp. hamata (Stev.) Fomin. 相似文献
140.
我国人口问题与社会持续发展 总被引:3,自引:0,他引:3
钟兆站 《中国人口.资源与环境》1996,6(4):28-32
本文分析了我国人口的主要特点和人口问题,指出人口问题已成为我国社会、经济发展的重要制约因素,进而论述了人口与资源、环境、经济协调发展的基本原理和宏观对策 相似文献