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排序方式: 共有1921条查询结果,搜索用时 375 毫秒
1.
Richard G. Condon 《Human ecology: an interdisciplinary journal》1991,19(3):287-321
Birth seasonally at high latitudes is a complex phenomenon which is undoubtedly affected by a subtle interaction between environmental rhythmicity (most notably in photoperiod and temperature) and cultural adaption. There is intriguing evidence that human gonadotrophic activity (and hence fertility) may be affected by seasonal fluctuations in light intensity and duration. Nevertheless, cultural factors are important insofar as they mediate between environmental rhythmicity and human fertility/birth patterns. This article examines the distribution of births over several decades in an Inuit community located 300 miles north of the Arctic Circle. Several shifts in birth seasonality are noted, the most significant of which is a dramatic shift from pronounced seasonality in the 1970s to non-seasonality in the 1980s. Longitudinal ethnographic fieldwork has allowed an examination of social and economic changes accounting for the rather sudden disappearance of birth seasonality. These include increasing reliance upon wage employment and social assistance, decreased dependence upon subsistence hunting and trapping, changing attitudes on the part of young people entering their prime reproductive years, and the introduction of television, radio, and southern-style recreational activities. 相似文献
2.
In Central Europe as in most other temperate regions of the world, Buddleja davidii has become a very successful invader. A thorough observation, documentation and analysis of the spread of invasive species is the precondition for the understanding of invasion processes. Therefore, I documented the occurrence of the species along a west–east transect as well as an altitudinal transect, and I tried to reconstruct the spread of the species in the course of the last decades along railroad areas, which have proved to be the most favorized habitats for colonization of Buddleja. Additionally, a literature review is given on its general spread and distribution in Germany. Based on the investigation of 52 stations, the results show that the species, in Germany, has its optimum in the Rhein-Ruhr- and the Rhein-Main-area, that its abundance significantly decreases from west to east and with increasing altitude. A literature review combined with own investigations shows, that it was very successful in Germany on ruins of World War II but decreased and sometimes totally disappeared in cities of East Germany and of the altitudinal higher regions of Germany, i.e. also in many towns of South Germany. In West Germany, the recent spread started about three decades ago and is still in process. As cold winters seem to be the limiting factor for the spread of Buddleja, even an accelerated spread of this species and perhaps a loss of its ruderal character can be expected, considering the progress of climate change. 相似文献
3.
Digital images of ex situ germplasm stored in the Sardinian Germplasm Bank (BG-SAR) were used for the application of image analysis techniques at the Stazione Sperimentale di Granicoltura per la Sicilia. The analysed accessions refer to 148 taxonomic units belonging to 102 genera and 47 families, typical of the Sardinian flora, and of the Mediterranean basin in general.The images of diaspores were acquired by a flatbed scanner and elaborated with a macro specially developed for the morphometric and colorimetric measurements. This method allowed carrying out a database for the characterization of autochthonous germplasm in entry to the bank and the realization of statistic classifiers for the discrimination of genera and species within the following families: Apiaceae, Boraginaceae, Caryophyllaceae, Cistaceae, Fabaceae and Scrophulariaceae. Such classifiers, based on the linear discriminant analysis (LDA) technique and checked by cross-validation, showed a performance included between 74.3% and 96.4%.In addition, for the genus Astragalus, it was possible to elaborate a classifier able to identify very similar taxa of a species complex, obtaining a performance between 83.7% and 100%. Such analysis proved the validity of the methodology also from the taxonomic point of view.Suggestions for subsequent methodological progress, which could offer applications in other research issues, such as ecological analysis, soil seed bank and archaeological botany are proposed. 相似文献
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Repeated observations are made on species and numbers of individuals in some islets. The changes after 14 years are reported for 11 islets. They include several extinctions and invasions. Great changes in numbers of individuals were found, especially for many of the annuals, in some of them as great as between 0–10 and over 10 000 individuals. The greatest constancy was found in a few dominant and subdominant perennials.Dedicated to Prof.K. H. Rechinger on the occasion of his 80th birthday. 相似文献
8.
Hildemar Scholz 《Plant Systematics and Evolution》1987,155(1-4):277-282
The syntypes ofBromus madritensis var.delilei
Boiss. comprise two different elements: specimens ofB. haussknechtii
Boiss. and ofB. fasciculatus
C. Presl s.l. By its lectotypification and on the basis of new morphological characters, the validation ofB. fasciculatus subsp.delilei (Boiss.)H. Scholz 1971 was substantiated. This subspecies represents the eastern marginal segregate of the south-Mediterranean species.B. fasciculatus var.alexandrinus
Thell. is a minor variant of the typical subspecies.Dedicated to Prof.K. H. Rechinger on the occasion of his 80th birthday. 相似文献
9.
Based on pollen and floral morphology,Blechum grandiflorum is transferred toRuellia, and the nameR. mirandana is proposed for this species. A new species,Ruellia tuxtlensis, is described which is distinguishable fromR. mirandana by its longer spike and elliptic bracts. It is presently known only from the lowlands of Veracruz, Mexico. 相似文献
10.
我国浙江与日本和我国台湾森林植物区系的联系 总被引:6,自引:0,他引:6
作者在“试论浙江省森林植物区系”一文中对我国浙江与日本和我国台湾森林植物区系的联系已作了扼要的说明,本文就是在此基础上作更详尽的论述。浙江省东濒大海,隔海相望,东北方向有日本,其本部岛屿的南端为九州,和浙江北部的纬度相近,具有亚热带气候特征,出现了和浙江相类似的常绿阔叶林和竹林,九 相似文献