首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
Analysis of sample survey data on the species composition of waterfowl kill for resident and nonresident hunters for provinces of Canada during 1974 and 1975 showed that a successful game bird hunter who hunted in more than one area (degree block) had both a higher average season kill and more successful days of hunting in which one or more birds were bagged, than one who hunted in the same area during the season. Adjustment for days hunted resulted in a higher daily hunting for those who hunted in more than one degree block. However, the higher kill of the successful hunter is attributable more to a larger number of days hunted than to a larger kill per successful day. Also, hunters hunting in more than one degree block had their successful hunting days more evenly spread across the season. The estimates of kill per successful hunter and days hunted for stratified sampling by areas of hunting were considerably more efficient than simple random sampling.  相似文献   

2.
Species–energy theory is a commonly invoked theory predicting a positive relationship between species richness and available energy. The More Individuals Hypothesis (MIH) attempts to explain this pattern, and assumes that areas with greater food resources support more individuals, and that communities with more individuals include more species. Using a large dataset for North American birds, I tested these predictions of the MIH, and also examined the effect of habitat complexity on community structure. I found qualitative support for the relationships predicted by the MIH, however, the MIH alone was inadequate for fully explaining richness patterns. Communities in more productive sites had more individuals, but they also had more even relative abundance distributions such that a given number of individuals yielded a greater number of species. Richness and evenness were also higher in structurally complex forests compared to structurally more simple grasslands when controlling for available energy.  相似文献   

3.
This paper reviews the opportunities available for food businesses to encourage consumers to eat healthier and more nutritious diets, to invest in more sustainable manufacturing and distribution systems and to develop procurement systems based on more sustainable forms of agriculture. The important factors in developing more sustainable supply chains are identified as the type of supply chain involved and the individual business attitude to extending responsibility for product quality into social and environmental performance within their own supply chains. Interpersonal trust and working to standards are both important to build more sustainable local and many conserved food supply chains, but inadequate to transform mainstream agriculture and raw material supplies to the manufactured and commodity food markets. Cooperation among food manufacturers, retailers, NGOs, governmental and farmers' organizations is vital in order to raise standards for some supply chains and to enable farmers to adopt more sustainable agricultural practices.  相似文献   

4.
It has been repeatedly suggested that primates trade social services for fitness benefits in their relationships with the opposite sex. We tested this proposal in a colony of captive chimpanzees, Pan troglodytes, by examining behavioural data on grooming, agonistic support and food sharing in relation to genetically established paternity. We found no support for the notion of trade. First, males did not sire more offspring with females that they actively groomed more frequently, that they supported more often or with which they shared food more frequently. Correspondingly, females did not give birth to more offspring sired by males from which they received more services. Second, males that showed more affiliative behaviour towards females in general did not sire more progeny. Furthermore, females did not bear more offspring sired by males to which they themselves directed more sociopositive behaviour. Results from this captive colony are compatible with those reported for chimpanzees under natural conditions. Copyright 1999 The Association for the Study of Animal Behaviour.  相似文献   

5.
R. E. Lees  R. Steele  R. A. Spasoff 《CMAJ》1976,114(4):333-337
A total of 1117 visits by patients to two hospital emergency departments and 15 family physicians'' offices for nontraumatic complaints over two 2-week periods were studied. Patients visiting the two settings fell into two distinct subgroups, and they appeared to select where to seek care by the acuteness and duration of the complaint. Several highly significant differences were noted between the two groups: those who visited an emergency department had complaints of shorter duration, underwent more investigations (which more often gave abnormal results), were more likely to undergo investigation for mental symptoms, had more consultations, received counselling and drug therapy less often (but intramuscular injections more often), were admitted to hospital more often, returned for further care for the same complaint less often, complied with disposal instructions less often, were more likely to receive fewer than 5 days'' care and were less likely to receive more than 31 days'' care; those without a family physician more often received additional care (were referred, admitted or asked to return).  相似文献   

6.
Abstract

Comparisons were made between members of Missouri Citizens for Life (MCL) and of the Abortion Rights Alliance (ARA) of Missouri. ARA members were more educated, urbanized, and had fewer children. MCL members were predominantly Catholic, and compared to ARA members, highly religious. ARA members were more inclined to favor equality of the sexes, especially in their approval of the ERA. ARA members were politically more liberal and more committed to free speech for social deviants. MCL members were much more committed to a conservative approach to matters of personal morality. MCL members regarded suicide and euthanasia as more objectionable than did their ARA counterparts, but they were also more militaristic.  相似文献   

7.
We observed the grooming interactions of 13 female rhesus monkeys (Macaca mulatta)before and for 12 weeks after the births of their infants. Mothers groomed for similar amounts of time before and after the birth of their infants, but after the birth, the grooming they directed to their infants may have been at the expense of that directed to other partners. Lactating females did not receive more grooming from other females but were approached more often, suggesting that they were more attractive. Mothers that groomed their infants most groomed others least, as if grooming time was limited for each mother or as if she was trying to compensate for avoiding interactions with other partners. Mothers of male infants groomed others more than mothers with female infants did, which might be due to mothers with daughters receiving more aggression and therefore avoiding interaction. Experienced and high-ranking mothers groomed their newborn infants considerably more than primiparous mothers did in the 24 hr following birth. Grooming was preferentially directed at close kin before the births of the infants. Mothers tended to groom higher-ranked partners more than they were groomed by them, and they tended to receive more grooming from lower-ranked partners than they gave, as suggested in models of rank attractiveness.  相似文献   

8.
A modified estimator of heritability is proposed under heteroscedastic one way unbalanced random model. The distribution, moments and probability of permissible values (PPV) for conventional and modified estimators are derived. The behaviour of two estimators has been investigated, numerically, to devise a suitable estimator of heritability under variance heterogeneity. The numerical results reveal that under balanced case the heteroscedasticity affects the bias, MSE and PPV of conventional estimator, marginally. In case of unbalanced situations, the conventional estimator underestimates the parameter when more variable group has more observations and overestimates when more variable group has less observations, MSE of the conventional estimator decreases when more variable group has more observations and increases when more variable group has less observations and PPV is marginally decreased. The MSE and PPV are comparable for two estimators while the bias of modified estimator is less than the conventional estimator particularly for small and medium values of the parameter. These results suggest the use of modified estimator with equal or more observations for more variable group in presence of variance heterogeneity.  相似文献   

9.
Modern sequence alignment algorithms are used routinely to identify homologous proteins, proteins that share a common ancestor. Homologous proteins always share similar structures and often have similar functions. Over the past 20 years, sequence comparison has become both more sensitive, largely because of profile-based methods, and more reliable, because of more accurate statistical estimates. As sequence and structure databases become larger, and comparison methods become more powerful, reliable statistical estimates will become even more important for distinguishing similarities that are due to homology from those that are due to analogy (convergence). The newest sequence alignment methods are more sensitive than older methods, but more accurate statistical estimates are needed for their full power to be realized.  相似文献   

10.
Color ornaments are often viewed as products of countervailing sexual and natural selection, because more colorful, more attractive individuals may also be more conspicuous to predators. However, while evidence for such countervailing selection exists for vertebrate color ornaments (e.g., Trinidadian guppies), similar studies have yet to be reported in invertebrates. Indeed, evidence for female mate choice based on extant variation in male coloration is limited in invertebrates, and researchers have not explicitly asked whether more attractive males are also more conspicuous to predators. Here we provide evidence that more chromatic male cabbage white butterflies (Pieris rapae) are more attractive to females but should also be more conspicuous to predators. Female P. rapae preferentially mate with more chromatic males when choosing from populations of males with naturally occurring or commensurate, experimentally induced color variation. Mathematical models of female color vision confirm that females should be able to discriminate color differences between prospective mates. Further, chromatic and luminance contrast scores from female visual system models better predicted male mating success than did measures of male color derived more directly from color spectra. Last, models of avian color vision suggest that preferred males should be more conspicuous to known avian predators.  相似文献   

11.
生物多样性是地球生物圈和人类发展的基础,是国际社会所共同关注的焦点问题。3S技术是集遥感、全球定位与地理信息系统于一体的高新技术手段,为生物多样性研究提供强有力的技术支持。近年来该领域的研究越来越受到人们的重视,并取得了大量的研究成果。  相似文献   

12.
This study examines wife-husband preference for children and subsequent fertility for a period of 5 years in the treatment and comparison areas of Matlab, Bangladesh. The two data sets used were: the In-depth Survey (1984) and the Demographic Surveillance System (1984-89). In the case of wives' preferences for children, subsequent childbearing was 13.8% higher than desired in the treatment area and 44.7% higher than desired in the comparison area. After controlling for all variables in the model, the likelihood of giving birth was 1.78 times higher for wives who wanted no more children, but whose husbands did want more, compared with couples where neither husband nor wife wanted more children. For couples where the wife wanted more, but the husband did not want more children, the likelihood of giving birth was 0.63 times that of couples where both the husband and wife wanted more children. This finding suggests that to enhance the decline in fertility in these two areas of Matlab, it will be necessary to motivate both wives and husbands to cease childbearing.  相似文献   

13.
It is increasingly common for water quality guidelines and risk assessments to consider the proportion of species at risk from a particular toxicant, based on the species sensitivity distribution (SSD) for that toxicant. There is a premise that the sensitivity data from species included in the SSD are sufficient to predict the effect on species for which there are no data. We discuss and review assumptions that follow this premise and find that for most toxicant SSDs include too few species, and that component species are biased toward particular taxonomic groups, common species and species from North America and western Europe. Consequently, protecting a given percentage, for example, 95%, of species in an SSD will likely protect more or less than 95% of species in nature, by an unknown amount. For the assumptions of SSDs to be better met, there is a need for tolerance data on more species, from more taxonomic and other groups, including rare species and those from widespread localities. In order to achieve this, we argue for the inclusion of rapid tests, which we define as toxicity tests designed to require less effort to conduct, relative to traditional tests, so sensitivity can be quickly and approximately determine in many species. Their use will allow for more species, more representative of natural communities, to be tested and therefore allow the construction of less biased SSDs and thus more accurate guidelines and assessments of risk.  相似文献   

14.
植物内生菌研究进展   总被引:1,自引:0,他引:1  
内生菌由于生长于植物体内且不引起植物病害所以不易被发现,它是一类具有高实用价值的植物内生微生物。经过人们的不断研究,越来越多的植物内生菌被发现,其活性代谢产物的优势也得到了更多研究者的认可。综述了国内外有关植物内生菌研究的主要成果和进展,并从植物内生菌的发现、研究历史、多样性、生理生化特性以及植物内生菌与宿主植物间的作用关系等多个层次进行了概述,以期为植物内生菌相关研究提供参考。  相似文献   

15.
16.
韩家亮  胡刚 《兽类学报》2012,32(4):362-367
因昼行性灵长类动物一天中相当一部分时间在其夜宿地度过,其夜宿行为在一定程度上影响着它们的活动方式与行为特点(Anderson,1998).对夜宿行为的观察可收集白天无法收集到的灵长类社会活动和社会关系的信息,如夜宿地分布(sleeping site)、睡眠时间(time)、睡眠抱团组成(huddling)等(Takahashhi,1997;Ogawa etal.,2007;黎大勇,2010),灵长类夜宿行为的研究对于分析了解其白昼活动方式与行为适应特点具有重要的启迪作用(Anderson,1998).  相似文献   

17.
The lycaenid butterfly, Maculinea rebeli, and its specialist parasitoid, Ichneumon eumerus, live in small, closed populations. Given the threatened status of the butterfly, it is reasonable to assume that its specialist parasitoid is even more vulnerable to local extinction than the butterfly host. Based on a mechanistic model recently developed for the tightly-woven community surrounding M. rebeli at a site in the Spanish Pyrenees, we investigate how the removal of habitat, and more particularly, specific habitat promoting the persistence of the butterfly, affects the population persistence of the parasitoid. Because of the relatively small impact of the parasitoid on the butterfly population in the Spanish Pyrenees, guidelines for conserving the parasitoid are only slightly more restrictive than those for its host. It is argued that at sites of more marginal quality for the butterfly than the reference site, achieving the dual aims of conserving both species will be more problematic. © Rapid Science Ltd. 1998  相似文献   

18.
包虫清对水稻前期害虫的控制效果及安全性   总被引:1,自引:0,他引:1  
研究包虫清(有效成分:氟虫腈、杀虫单)种衣剂不同包衣方式处理水稻种子对水稻生长前期主要害虫的控制效果。结果表明,不同处理对稻蓟马、稻飞虱防治效果达90%以上,持效期达30d以上。其中包衣旱育处理对三化螟、二化螟控制效果达85%以上。包虫清种衣剂对水稻种子、植株和稻田的主要蜘蛛较安全。  相似文献   

19.
FRENCH, SIMONE A, ROBERT W JEFFERY, AARON R FOLSOM, DAVID F WILLIAMSON AND TIM BYERS. History of intentional and unintentional weight loss in a population-based sample of women aged 55 to 69 years. Obes Res. 1995;3:163–170. Although both overweight and body weight fluctuation are related to chronic disease risk, little is known about the history of and reasons for body weight change in the general population. This paper reports the incidence of intentional and unintentional weight loss episodes during adulthood in a population-based sample of 26, 261 women aged 55 to 69 years. Intentional weight loss episodes of each of four amounts (5–9, 10–19, 20–49, 50+ lbs.) and unintentional weight loss episodes of 20 or more lbs. were recalled for each of three age periods (18–39, 40–54, 55+ years). At least one intentional weight loss episode of 5 or more lbs. was reported by 69% of women, 46% reported at least one intentional weight loss episode of 10 or more lbs, and 25% reported at least one intentional weight loss episode 20 or more lbs. At least one unintentional weight loss episode of 20 or more lbs. was reported by 29% of the women. Reasons for weight losses of 20 or more lbs. were also recalled. Women who had intentionally lost 20 or more lbs. were more likely to report weight losses due to low-calorie diets, exercise and weight loss groups, while women who had unintentionally lost 20 or more lbs. were more likely to report weight losses due to depression or stress. These findings question the common assumption that weight losses in adult women are primarily intentional and emphasize the need to distinguish the reasons for weight loss in studies examining the relationship between body weight changes and health outcomes.  相似文献   

20.
医院综合网络系统的设计与实现   总被引:1,自引:0,他引:1  
本文介绍了本市一家省级医院计算机综合网络系统的设计与实现。随着医院计算机应用水平的不断提高,对于计算机网络的要求也越来越高。本文在对医院的诸多信息子系统的应用功能进行分析的基础上,提出了切实可行的设计原则和解决的方案,并提出了网络的具体设计和网络实现方法,应用于医院的综合网络系统的建设。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号