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The majority of wild Sumatran tigers are believed to live in 12 Tiger Conservation Landscapes covering approximately 88 000 km2. However, the actual distribution of tigers across Sumatra has never been accurately mapped. Over the past 20 years, conservation efforts focused on the Sumatran tigers have increased, but the population continues to decline as a result of several key threats. To identify the status of the Sumatran tiger distribution across the island, an island-wide questionnaire survey comprised of 35 respondents from various backgrounds was conducted between May and June 2010. The survey found that Sumatran tigers are positively present in 27 habitat patches larger than 250 km2 and possibly present in another 2. In addition, a review on major published studies on the Sumatran tiger was conducted to identify the current conservation status of the Sumatran tiger. Collectively, these studies have identified several key factors that have contributed to the decline of Sumatran tiger populations, including: forest habitat fragmentation and loss, direct killing of tigers and their prey, and the retaliatory killing of tigers due to conflict with villagers. The present paper provides management authorities and the international community with a recent assessment and a base map of the actual distribution of Sumatran tigers as well as a general overview on the current status and possible future conservation challenges of Sumatran tiger management. 相似文献
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采用溶液培养的方法,在燕麦苗期,研究了磷素充足供应和缺磷胁迫两种条件下根系形态指标的变化。结果表明,经过30d的缺磷胁迫,燕麦根系生物量显著低于充足供磷处理,但根系总长并未表现为缺磷处理显著低于充足供磷处理,而且根冠比、比根长却表现为缺磷处理显著高于磷素充足供应处理。缺磷条件下比根长的增加与根轴直径的减小是一致的,因此根轴横向生长减弱可能是导致缺磷燕麦根系比根长增加的原因。由于比根长的增加意味着消耗同样的同化产物,却可以形成具有较大吸收范围的根系,因此燕麦根轴直径减小、比根长的增加是燕麦对缺磷胁迫的适应。 相似文献
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应用系统诊断方法,对科尔沁沙地系统的特征、存在问题及成因进行了分析,认为沙地系统衰退最根本的原因是政策、管理体制的不合理及科技人才的短缺;引起土地沙漠化的直接原因为急剧增长的人口、严重短缺的农村牧区燃料资源以及农业科技意识的淡薄.在此基础上还提出了沙地系统可持续发展的战略对策. 相似文献
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稻田气力式变量施肥机关键部件的设计与试验 总被引:18,自引:16,他引:2
目前在水稻的机械追肥作业中以离心圆盘式撒肥机为主,该方式在作业幅宽方向上的撒施均匀性不稳定,且难以实现作业幅宽方向上的变量施肥。为了满足水稻变量追肥作业的需要,达到化肥减施增收的目的,设计了一种外槽轮式排肥、以空气流为肥料输送和撒播动力的稻田气力式变量施肥机。文章对该机器的关键部件进行了仿真和测试试验,研究了排肥轮转速与排肥量之间的相关关系,并对排肥管道长度对排肥出口风速与排肥滞后时间的影响、排肥管出口相对高差对排肥滞后时间的影响进行了试验。试验结果表明:排肥轮转速与排肥量之间存在极显著的线性相关关系,相关系数R2=0.998,调节排肥轮转速可以较精确的调节施肥量的大小,在变量作业时,结合施肥量的需求及施肥机具的前进速度,对排肥轮的转速进行实时调节,从而达到变量施肥的目的。当机具前进速度为1 m/s,排肥轮转速在10~40 r/min之间变化时,单凭转速调节可实现每公顷施肥量在40~200 kg范围内的变量调节,此外,各排肥口的排肥量误差小于±5%,基本上达到了施肥均匀性的要求。文章还研究了排肥管道长度及安装高差对排肥滞后时间的影响,结果表明:排肥管道长度对排肥出口风速有显著影响,排肥管长度和出口安装的高差对排肥滞后性亦有显著的影响,因此,为了尽可能减小因排肥滞后对排肥均匀性的影响,应避免排肥管过长,并尽量使排肥管出口不高于入口。该研究为进一步的样机制造和优化提供了依据。 相似文献