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41.
浙江省香榧病虫害及害虫天敌种类调查   总被引:7,自引:0,他引:7  
文章系浙江省近年来香榧病虫害和害虫天敌的调研总结。重点对省内主要香榧生产县(市)进行调查。共收录害虫57种,分别隶属8目28科,病害5种,以及害虫天敌16种,分别隶属7目11科。收集浸渍幼虫标本50余号,针插标本2200余号,其中包括了大多数的主要害虫。并且对绝大部分的标本在收集的第一现场进行了摄影记录。  相似文献   
42.
存续了近50年的户籍制度及相关法律对中国社会产生了深刻的影响,尤其是对农民的基本权利:选举权和被选举权、居住和迁徙的自由、财产权、受教育的权利等产生了巨大影响,导致了严重的不公平。应逐步剥离户籍制度所附带的利益,完善相关法律和政策,对户籍制度进行彻底的改革。  相似文献   
43.
In order to design effective conservation measures for the orangutan, accurate information on their distribution and densities are needed. Nest counts along line transects allow for fairly accurate assessment of orangutan density. However, large sample sizes are needed to obtain accurate estimations of the decay rate of nests, preventing a rapid estimate. Moreover, due to the structure of tropical forests, nest numbers above and near the trail are underestimated. In this study, a rapid assessment method for the estimation of orangutan density is developed, allowing for the estimation of density with a single survey. Procedures are provided for estimating a correction factor which adjusts for underestimating nest numbers near the transect trail. Furthermore, we provide a shortcut to rapidly assess nest decay rate without the need for consecutive surveys. Finally, recommendations are made for determining orangutan density using two different techniques. These techniques incorporate correction factors and a shortcut to accurately assess orangutan density with only one or two visits to an area.  相似文献   
44.
  • 1. A 2‐year experimental seining programme and underwater visual censuses were undertaken to quantify the direct effects of active demersal fishing on the population structure and relative abundance of two sympatric seahorse species of conservation concern: the European long‐snouted seahorse, Hippocampus guttulatus Cuvier 1829 and the short‐snouted seahorse, Hippocampus hippocampus L. The influence of habitat preference on population‐level responses to changes in habitat structure following a reduction in fishing effort was also investigated.
  • 2. It was predicted that the benthic habitat would be more structurally complex after fishing ceased and that seahorse densities would increase in response to reduced fishing mortality. Furthermore, it was predicted that the magnitude of the increase in density would be greater for H. guttulatus than for H. hippocampus, because the former species prefers complex vegetated habitats while the latter species uses sparsely vegetated habitats.
  • 3. As predicted, the amount of habitat cover increased significantly when seining ceased, primarily through increases in the abundance of drifting macroalgae and unattached invertebrates. Despite similarities in life histories, the two seahorse species responded differently in terms of magnitude and direction to reduced fishing effort: the abundance of H. guttulatus increased significantly while H. hippocampus decreased in abundance.
  • 4. Results suggest that active demersal fishing may influence the magnitude and direction of the responses of benthic marine fishes to exploitation through its impacts on habitat structure. An increase in habitat cover appeared to favour higher densities of H. guttulatus when seining effort was reduced. By contrast, repeated seining, which maintained less complex habitats, appeared to favour greater abundances of H. hippocampus.
  • 5. Given differences in habitat preference among benthic marine fishes subject to incidental capture in fisheries, simultaneous attempts to manage populations of sympatric species may require complementary strategies that support the persistence of diverse habitat types.
Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
45.
不同接种调查方法对抗水稻纹枯病遗传研究的影响   总被引:22,自引:0,他引:22  
以抗感反应显著不同的水稻代表品种,研究了不同接种调查方法在抗纹枯病遗传研究中的适用性。结果表明,带菌短牙签嵌入接种,植株间始病迅速且整齐一致,感病品种发病适度,不同品种间抗感差异最为明显。病情调查的适宜时间在抽穗后30d左右(视品种灌浆期长短而异)或发病初期,而在明显拔节到抽穗阶段,品种内由于茎杆伸长时间的差异,病斑发展的差异增大,致使品种间抗感差异不易被识别。并且还讨论了不同病情调查项目的适用性。  相似文献   
46.
Tree size censusing is essential for evaluations of trees and forests, but traditional field surveys are both time- and labor-intensive. Here, we discuss the use of panoramic 360-degree street views available on the Internet for censusing of roadside trees in urban regions. Use of scale-independent, fixed-sized street objects as recalibrating meters in tandem with imagery software enabled street-view images to be used effectively in the remote measurement of diameter at breast height (DBH), tree height, underbranch height, and canopy projection size. Comparison of four independent meters determined that stem limewhite-related meters (used for tree disease and bark-freeze injury control; usually 1.3 in height throughout China) had greater precision than road curb height, lane width, and traffic line width meters. The limewhite meter’s precision was slightly lower than those of the meters in combination (i.e., when at least three of the abovementioned meters were used for the same tree measurement), but no statistically significant differences were detected between the limewhite and combined meters (p > 0.05). In contrast, the road curb height, traffic line width, and lane width meters all had significantly lower precision. The highest levels of precision were 92%, 87%, and 80% for DBH, height (tree height and underbranch height), and tree canopy size measurements, respectively. Empirical recalibration of the image-based measurements did not improve data precision with reference to field surveys (p > 0.05). Moreover, similar results were obtained regardless of individual users, and repeatability for DBH measurements (r2 > 0.92), and maximum differences among individual users were 0.6–1.9 cm for DBH (averaged at 22 cm) and 8–50 cm for underbranch height (mean value at 8 m). Labor costs and time needed for this approach were one-thirtieth to one-tenth those required for field surveys. Thus, the use of street-view images represents a more resourceful approach to assess forest ecological services.  相似文献   
47.
人口数据空间化已经成为当今社会学、人口学、地理学等学科研究的热点问题。实现人口数据空间化并探究人口数据中所隐含的空间信息,不仅可以从侧面反映出一个地区的社会发展程度,同时也为实现该地区人口、经济、环境的协调发展提供建议。综合国内外关于实现人口数据空间化的研究现状发现,实现人口数据空间化的方法主要集中在以下2个方面:1利用影响人口分布的地理、环境等因子构建影响因子与人口数值之间的数学回归模型,拟合不同时间点、不同地域内人口分布变化情况;2应用不同的人口数据空间分析模型,探讨和研究人口在不同地域、不同时间段内的分布变化情况。  相似文献   
48.
人口老龄化是社会经济发展必然经历的阶段。目前,新疆老年人口基数较小,但增长迅速。文章对新疆老龄化发展现状和特征进行分析,分析了新疆老龄化产生的原因,最后提出了新疆应对老龄化问题的对策建议。  相似文献   
49.
Prior to 1995, the Montserrat oriole (Icterus oberi) was confined to ca. 30 km2 of hill forest on the Lesser Antillean island of Montserrat, but was not listed as globally threatened. Since then, the eruption of the Soufriere Hills volcano has destroyed more than half of the species’ range. Recent intensive monitoring has indicated that the species has also declined dramatically within the remaining intact forest, and is now critically threatened. Different monitoring and analytical methods indicate a decline of 8-52% p.a., and a remaining global population of ca. 100-400 pairs. This case study justifies the use of the restricted range criterion in designating threatened species. Despite intensive monitoring and the use of several analytical methods, it has proved surprisingly difficult to estimate the magnitude of the oriole’s decrease, or to control for potential artefacts in the census method. We discuss the reasons for this. The cause(s) of population decline in the intact forest are unclear, though two hypotheses appear plausible: a decrease in arthropod food, a result of volcanic ash fall, and an increase in nest predation as a result of increases in populations of opportunistic omnivores.  相似文献   
50.
对当前安徽省城镇贫困及问题的现状及产生根源作了深入剖析,并提出了相应的政策建议。作者认为贫困层问题的产生主要是由于制度创新不足和政策调整滞后所致,要从根本上解决这一问题,必须进行城镇劳动力就业制度、社会保障制度改革和创新,同时相应调整现有的一些政策。  相似文献   
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