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931.
土地处理系统是在干旱 -半干旱过渡区实现污水无害化、资源化的有效技术。内蒙古霍林河矿区污水土地处理系统设计与运行结果表明 ,该区具备推广土地处理技术的良好条件 ,土地处理系统应以慢速渗滤和污水资源利用型为主 ,实现污水处理与生态环境建设的结合。污水资源的利用有助于增加镶嵌型复合生态系统的稳定性 ,加速人工林的成林郁闭 ,增加林木蓄积量 ,改善干旱、半干旱地区的生态环境 相似文献
932.
本文在比较全面、系统地总结改革开放15年来,南方稻田耕作制度调整与改革所取得的成效的基础上,指出了目前南方稻田耕作制度存在的问题,提出了在新形势下南方稻田耕作制度调整与改革的对策和思路,对指导目前南方稻田耕作制度的改革具有重要参考价值. 相似文献
933.
The evolution of a mating system, and specifically mating frequency, is dependent on the costs and benefits to both sexes of mating once or several times. In butterflies, males transfer a spermatophore that contains both sperm and accessory gland products. Accessory gland substances contain nutrients which, in some species, females use to increase their reproductive output and longevity. Nutrients contained in these packaged ejaculates represent investment by males in reproduction. Consequently, the nutritional composition of spermatophores may vary depending on the mating system. There are two lines of arguments concerning the evolution of the nutrient content of ejaculates. One hypothesis argues that male nuptial gifts evolved in the context of certainty of paternity and ease of finding mates; thus spermatophores of polyandrous males (with lower certainty of paternity and greater ease of finding mates) should contain less protein than those of monandrous males, since more spermatophores are produced on average. The other hypothesis argues that polyandry evolved in the context of maximization of male transfer of nutrients to females, and hence spermatophores of polyandrous males should contain more protein than those of monandrous males. In an attempt to distinguish between these two hypotheses, we determined how protein content of ejaculates varied with the degree of polyandry in nine species of pierid and two species of satyrid butterflies. We found that both relative ejaculate mass and protein content increased with the degree of polyandry. Hence our results are consistent with the view that polyandry has evolved in the context of male transfer of nutrients to females, and provides another example of a male adaptation to multiple mating in butterflies. 相似文献
934.
Mate sampling behaviour of black grouse females (Tetrao tetrix) 总被引:2,自引:0,他引:2
Pekka T. Rintamäki Rauno V Alatalo Jacob Höglund Arne Lundberg 《Behavioral ecology and sociobiology》1995,37(3):209-215
We studied female mate sampling behaviour in lekking black grouse (Tetrao tetrix). Females mainly visited males occupying territories in the centre of the lek with relatively large territories. They were also more likely to visit males that had high attendance. The same factors were also correlated with male mating success. A multiple regression model including these factors explained more of the variance in female visits per male (53%) than in mating success (33%). The pattern of female sampling conformed with a pool comparison (best-of-n) tactic. Such a tactic is expected if the costs of sampling are low. Females of high body mass visited more males than lighter females, however, which indicates that females may vary in their search tactics and suggests that there may be search costs. The existence of costs is further suggested by the fact that if the mate from a previous year was still present, females always mated with the same male in the following year. Though search costs were not measured directly, our findings suggest that some costs are negligible (e.g. energetic exhaustion or predation) whereas others (timing of mating) may be more important. 相似文献
935.
边镜贸易作为我国作为开放的重要组成部分,进展显著。本文在概述我国边境贸易发展所产生的环境问题的基础上,以我国最大的陆边口岸--满州里市为例,运用灰色预测,动态规划等方法探讨边境贸易与环境保护协调发展的途径。 相似文献
936.
937.
The Botanist Effect Revisited: Plant Species Richness, County Area, and Human Population Size in the United States 总被引:3,自引:0,他引:3
Abstract: The "botanist effect" is thought to be the reason for higher plant species richness in areas where botanists are disproportionately present as an artefactual consequence of a more thorough sampling. We examined whether this was the case for U.S. counties. We collated the number of species of vascular plants, human population size, and the area of U.S. counties. Controlling for spatial autocorrelation and county area, plant species richness increased with human population size and density in counties with and without universities and/or botanical gardens, with no significant differences in the relation between the two subsets. This is consistent with previous findings and further evidence of a broad-scale positive correlation between species richness and human population presence, which has important consequences for the experience of nature by inhabitants of densely populated regions. Combined with the many reports of a negative correlation between the two variables at a local scale, the positive relation between plant species richness in U.S. counties and human population presence stresses the need for the conservation of seminatural areas in urbanized ecosystems and for the containment of urban and suburban sprawl. 相似文献
938.
Identification of Shark Species Composition and Proportion in the Hong Kong Shark Fin Market Based on Molecular Genetics and Trade Records 总被引:7,自引:0,他引:7
939.
建立我国生态环境标准体系的初步构想 总被引:9,自引:0,他引:9
我国的生态环境标准极其薄弱,建立生态环境标准体系是我国生态环境保护的迫切需要。借鉴我国目前针对污染防治的环境标准体系,提出了我国生态环境标准体系的基本框架,以及生态环境标准制订的原则和重点。 相似文献
940.
通过盆栽试验和现场布点试验,研究了铜、砷在水稻-土壤体系中迁移的规律。结果表明,该体系对铜、砷污染具有相当大的缓解作用;土壤中水溶性可交换态铜、砷含量很低;铜、砷主要累积在水稻根部;土壤中铜、砷相互有拮抗作用,确定土壤铜、砷临界值应考虑多因素综合作用。 相似文献