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This paper summarizes the main physical and economic features of manganese nodules, cobalt-rich manganese crusts and marine polymetallic sulfide deposits in the Pacific region. The most favourable areas for deposits of commerical interest are shown on a map of the Pacific. The gross metal sales values of hypothetical mines are compared to estimated size of world metal markets in the year 2000. It is suggested that a prudent policy for the major developed-country governments is to support research on those marine minerals that appear to have the potential to become a major source of minerals in the next century. 相似文献
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KATHARINA DEHNEN-SCHMUTZ† JULIA TOUZA‡ CHARLES PERRINGS§ MARK WILLIAMSON 《Conservation biology》2007,21(1):224-231
Abstract: Ornamental horticulture has been recognized as the main pathway for plant invasions worldwide. We examined the link between propagule pressure created by the presence of ornamental plants in the market and their ability to escape from cultivation and establish in the wild. A random sample of 534 non-native ornamental species on sale in nineteenth century Britain showed that 27% of these species were recorded growing outside cultivation and 30% of those were established. Species that had escaped from cultivation were more frequently on sale both in the nineteenth century and today than nonescaping species. We used logit regression models to identify biological and socioeconomic variables that affect species' abilities to escape cultivation and become established. Frequencies in the market in the nineteenth century and today were good explanatory variables that distinguished escaping from nonescaping species, whereas for the transition from casual to established status these two socioeconomic variables were either absent or only of weak significance. Biological characteristics that increased the probability that a species would escape from cultivation were species height, a European native range, and being an annual. Climbing plants and species intolerant of low temperatures were less likely to escape. In contrast, the establishment probability was greater if the species belonged to a genus native to Britain and increased as the number of continents in a plant's native range increased. Annual plants had a reduced probability of establishment. Market presence, prices, and the date of introduction are among the socioeconomic factors that have had important effects on the observed course of invasions. 相似文献
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