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251.
Throughout the world, and particularly in densely populated countries like Britain, human activities exert a dominant influence on the abundance of both plants and animals. The commonness and rarity of plants in Britain has been plausibly linked to human land use. In Western Europe the identity of increasing and decreasing plants appears to depend on human population density, which is itself a crude measure of human impact on the landscape. The publication of new data on the changing distributions of scarce British plants allowed us to investigate the relationship between loss of scarce plants and human population density in Britain. Our results confirm that a direct effect of human population density on local plant extinctions can be detected at the regional scale in Britain. Although intensive agriculture is conventionally regarded as the greatest threat to British wildlife, our analysis suggests that urbanization may be at least as significant a danger.  相似文献   
252.
The evolution of graduated licensing systems in the past 25 years has resulted in dramatic growth in research on this topic. The most recent summary reports have covered the period up to 2007. In the present article more recent and ongoing research is categorized, summarized, and discussed.  相似文献   
253.
As part of a large epidemiologic study of lung cancer, 55,000 subjects, we have conducted a nation-wide survey of particulate exposures in the US trucking industry. The goal is to differentiate the risks from various types of particulate exposures, such as traffic emissions and general air pollution. We hypothesize that exposures defined by job and work site characteristics can be linked with subjects using their personal job histories. This report covers exposures at 36 randomly chosen large truck freight terminals in the US. Measurements were made of PM2.5, elemental carbon (EC), and organic carbon (OC) upwind of the terminal (background) and in work areas, and by personal samples. Significant differences in exposure intensity, microg m(-3), were found for work locations and jobs relative to background levels (GM[GSD]) at terminal sites: PM2.5 9.8[2.34], EC 0.5[3.24], and OC 5.0[1.76]. Using EC as a marker for diesel particles, work locations varied significantly: office 0.3[3.7], dock area 0.7[2.89] and shop area 1.5[3.52]), as did job titles (non-smokers): clerk 0.1[9.98], dock worker 0.8[2.13], and mechanic 2.0[3.82]. Cigarette smoking contributed substantially to personal exposures, approximately doubling PM2.5 and OC, but having less of an effect on EC. Large differences were seen across the terminal sites due to differences in local regional air pollution levels from traffic and other sources. We conclude that it will be possible to estimate current exposures of the cohort using an exposure assignment matrix based on job title, work location, and terminal site. This distribution overlaps substantially with the general public's exposure to these sources.  相似文献   
254.
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