Soil quality and human migration in Kenya and Uganda     

Clark L. Gray 《Global Environmental Change》2011,21(2):421-430

Soil degradation is widely considered to be a key factor undermining agricultural livelihoods in the developing world and contributing to rural out-migration. To date, however, few quantitative studies have examined the effects of soil characteristics on human migration or other social outcomes for potentially vulnerable households. This study takes advantage of a unique longitudinal survey dataset from Kenya and Uganda containing information on household-level soil properties to investigate the effects of soil quality on population mobility. Random effects multinomial logit models are used to test for effects of soil quality on both temporary and permanent migration while accounting for a variety of potential confounders. The analysis reveals that soil quality significantly reduces migration in Kenya, particularly for temporary labor migration, but marginally increases migration in Uganda. These findings are consistent with several previous studies in showing that adverse environmental conditions tend to increase migration but not universally, contrary to common assumptions about environmentally-induced migration.  相似文献   

Population dynamics and tolerance to desiccation in a crustacean ostracod adapted to life in small ephemeral water bodies   总被引：1，自引：0，他引：1  

Josep A. Aguilar-Alberola  Francesc Mesquita-Joanes 《Limnologica》2011,41(4):348-355

Given their small size, isolation and unpredictability, temporary rockpools present high environmental stress and impoverished communities of species that have adapted to such stressful conditions. Special adaptations of the invertebrates living in these habitats include tolerance to desiccation and fast ontogenetic development in order to maintain stable populations and face high risk of extinction. Dozens of small rockpools (mostly with Ø < 1 m) can be found in east Spain on limestone substrate, where the only known Iberian populations of Heterocypris bosniacaPetkovski et al. (2000), an ostracod species with geographic parthenogenesis, have been recently found. In this survey, two of these rockpools have been monitored during the main hydroperiod between the fall of 2005 and summer 2006 to test the ability of H. bosniaca parthenogenetic populations to face unpredictable hydroperiod dynamics. Pools were visited weekly, and limnological data and ostracod samples were obtained from either water or substrate in dry periods. Ostracod individuals were counted and assigned to growth instars to monitor population changes. In the laboratory, experimental cultures allowed the estimation of survival dependence on the substrate desiccation rate. Throughout the hydrological cycle studied, several hatching periods were observed, usually preceded by desiccation, followed by substrate hydration and water dilution by rain. The demographic changes observed indicate that H. bosniaca populations are able to persist in intermittently inundated environments and produce several generations per annual hydrological cycle. In addition, adult individuals were able to survive in the wet mud of dry pools for longer than five weeks. The experimental data suggest a lower average survival time when exposed to desiccation processes, and that the velocity of substrate water loss is a determining factor for the survival rate of ostracods resisting dry events in temporary ponds. As shown by ostracods’ life histories in temporary aquatic environments undergoing unpredictable desiccation events, a combined strategy of adult tolerance to short periods of water scarcity and rapid hatching from resting egg banks can be advantageous for the monopolization of small-sized ephemeral habitats.  相似文献   

拟建宁海电厂附近潮间带底栖生物群落生态   总被引：3，自引：0，他引：3  

杨俊毅  高爱根  陈全震  胡锡钢  杨关铭 《海洋学研究》2004,22(3):48-55

2002年12月对拟建宁海电厂附近海域3条潮间带断面的底栖生物生态进行了调查,共鉴定出潮间带大型底栖生物71种,平均生物量为1753.92g/m2,平均栖息密度为839个/m2。生物多样性指数和K-优势曲线都显示了位于拟建电厂选址区内的潮间带底栖生物群落已经受到了扰动。  相似文献   

Thermal utility of desert vegetation for the Egyptian tortoise and its conservation implications     

《Journal of Arid Environments》2013

We examined the monthly shrub use and the thermal utility of the desert shrub, Artemisia monosperma, by the globally endangered Egyptian tortoise, Testudo kleinmanni, in Sinai, Egypt. A. monosperma is a common desert shrub that is often used by the Egyptian tortoise as a refuge. Egyptian tortoises had the highest mean carapace temperature and lowest carapace temperature range during summer months, which coincided with the aestivation period and the Egyptian tortoise's use of larger shrubs. Our results suggest that the thermal characteristics of larger shrubs are important to the microhabitat use of the Egyptian tortoise and likely long-term survival. Larger shrubs were effective as thermal refuges that ameliorated and stabilized micro-climatic variation. Smaller shrubs were not an adequate thermal refuge in the summer because the mean temperature, and its fluctuation range beneath them was too high to offer adequate refuge during aestivation. The tortoises used the smaller shrubs in the fall, winter, and spring seasons for basking, thermoregulation, and concealment and used shrubs with a cover diameter greater than one meter during the aestivation season. The future conservation of the Egyptian tortoise should focus on protecting and restoring existing habitat by maintaining large perennial shrubs for refuge and aestivation sites.  相似文献   

基于手机位置数据的四川九寨沟7.0级地震人流分析     

李东平  黄乐  陈海鹏  刘倩倩 《中国地震》2017,33(4):602-612

2017年8月8日四川九寨沟7.0级震后,浙江省地震局利用大数据采集了1031.99万条手机位置记录和4.46万个空间格网位置。本文结合24hr连续定位的手机数据,使用手机位置数据分别对九寨沟灾区人口从时间和地理维度上进行了量化分析,估计了多维人口分布的偏差,同时,探讨了剔除微观误差数据用户来估算灾区通讯基站退服分布的方法。该项工作为震后快速获取灾区人口实时动态分布提供了有效途径,同时也为地震灾害评估提供了较准确的依据。  相似文献   

基于遥感和GIS方法的科尔沁沙地边界划定   总被引：2，自引：0，他引：2  

闫妍  朱教君  闫巧玲  郑晓  宋立宁 《地理科学》2014,34(1):122-128

基于已有文献,依据科尔沁沙地的形成历史与早期分布,确定科尔沁沙地的核心区;以核心区为基础,采用生态学取样方法,选取与核心区边界相交的16个方向上的交叉点为样本,以Landsat-5 TM影像为主要数据源,采用光谱混合模型、穗帽变换等遥感和GIS方法,通过反复试验设定阈值,提取每个方向的分界特征,据此勾画出科尔沁沙地的分界线。此后,进行实地考察和Google Earth高清影像验证,最终确定科尔沁沙地生态区域的边界。结果表明,科尔沁沙地面积为52 300 ± 360 km²,验证后精度在94%以上。研究结果为科尔沁沙地生态恢复与环境整治提供确切基础范围。  相似文献   

Amphipod-supported food web: Themisto gaudichaudii, a key food resource for fishes in the southern Patagonian Shelf     

Luciano N. Padovani  María Delia Viñas  Felisa SánchezHermes Mianzan 《Journal of Sea Research》2012,67(1):85-90

The trophic role of the hyperiid amphipod Themisto gaudichaudii in the southern Patagonian shelf food web was assessed from the analysis of stomach contents of the local fish assemblage. A total of 461 trawl samples were collected during seven seasonal cruises. A total of 17 out of 38 fish species were found to ingest T. gaudichaudii. This amphipod was a main prey item in five of these species, showing high values of alimentary index: Seriolella porosa (99.9%), Macruronus magellanicus (68.8%), Micromesistius australis (59.1%), Patagonotothen ramsayi (48.6%), and Merluccius hubbsi (10.9%). The contribution of T. gaudichaudii, in weight, to their summer diet was 60%, on average. This contribution was minimal in winter and maximal in summer. Fisheries studies have indicated that these five species, mainly M. magellanicus, account for almost 85% of the fish biomass in the area. Although the remaining 15% did not feed heavily on T. gaudichaudii, they are known to prey on the main hyperiid predators. Our study shows that T. gaudichaudii contributes greatly, both directly and indirectly, to supporting the fish community. We thus proposed that T. gaudichaudii plays a key role as a “wasp-waist” species in the sub-Antarctic region, similar to that of krill in Antarctic waters, channeling the energy flow and enabling a short and efficient food chain.  相似文献   

2011 年夏季胶州湾三种大型水母的种群动态研究   总被引：4，自引：3，他引：1  

王世伟  张光涛  孙松  王彦涛  赵增霞 《海洋与湖沼》2012,43(3):471-479

2011年8月1日-9月30日,对胶州湾三种大型水母沙海蛰(Nemopilema nomurai)、白色霞水母(Cyanea nozakii)、海月水母(Aurelia aurita)的种群数量变动及空间分布情况开展了目测调查,同步获得了气象、水温、盐度、叶绿素a、浮游动物丰度、种类组成等数据,调查频率为每周2次。调查期间,海月水母表现出逐渐降低的趋势,沙海蛰与白色霞水母种群均于8月11日达到数量高峰,8月底及9月中旬之后依次衰落,至9月底,三种水母基本消失。三种水母的种群平均丰度变化范围分别为:沙海蛰0-230.8ind/km2;霞水母0-150.2ind/km2;海月水母0-123.4ind/km2。从分布区域来看,海月水母主要位于近岸区,沙海蜇主要分布于湾口和中部深水区,而白色霞水母则在高峰期和次高峰期分别集中于深水区和近岸区。结合往年资料,作者认为,海月水母种群能够在胶州湾内进行自我补充并完成其生活史,而胶州湾沙海蛰与霞水母的种群补充则可能主要依赖于湾外种群。另外,目测方法的准确性可能受到气象条件的影响。  相似文献   

近年来生态学研究热点透视——基于“中国生态大讲堂”100期主题演讲的总结     

于贵瑞  于秀波 《地理科学进展》2014,33(7):925-930

“中国生态大讲堂”(China Ecological Forum, CEF)是一个中国生态学领域的综合学术论坛;它以“传播新知识,交流新思想,展示新成果”为宗旨,举办系列学术讲座、春冬季专题研讨会、高级研讨班以及焦点论坛等学术交流活动。自2005年创办以来,“中国生态大讲堂”已经组织了100期主题演讲和12次大型学术研讨会、6次专题研讨会、2次高级研讨班,成为广大科研人员进行学术交流的重要平台。迄今,已有300人次的知名科学家、中青年学者在大讲堂作了学术讲演,其中150人次是来自国外研究机构的知名学者。从近年来演讲的主题来看,“气候变化与生态系统适应性”、“生态系统评估和管理”和“生态系统服务”等是生态学研究的热点问题。自2009年以来,根据“中国生态大讲堂”研讨会整理出版的《中国生态大讲堂系列丛书》已经出版了5本,涵盖了当前生态学研究的主要领域及其关键科学问题,反映了当代生态学研究的科学前沿。本文通过对“中国生态大讲堂”讲座和研讨会主题的梳理,探讨了近年来生态学研究前沿领域和热点问题,希望能为中国生态系统研究者提供参考。  相似文献   

中国水库生态学研究的回顾与展望   总被引：40，自引：7，他引：33  

韩博平 《湖泊科学》2010,22(2):151-160

水库是通过人工筑坝形成的水体,其早期功能主要是防洪、发电、灌溉和航运等,但随着全球水资源供需矛盾的加剧,水库供水成为缓解供水压力的最主要途径.水坝是人类影响地球表面水体最重要的工程建筑,筑坝修建水库利用水资源对全球水环境系统产生了巨大的影响.中国是水资源短缺的国家,水库供水在国民经济发展中发挥着重要作用,大量水库的建成也对我国水环境系统产生了多方面的影响.刘建康先生在1955年发表了我国水库生态学研究的第一篇论文,揭开了我国水库生态学研究的序幕.我国水库生态学大致分为三个阶段,1955-1975年的起步阶段、1976-2000年以水库渔业生产为目标的研究阶段和2001年至今以水库水质管理为目标的研究阶段.当前,水质、水质模拟、富营养化、环境容量和生态调度等已成水库生态学研究中的关键词.我国水库研究主要集中在珠江流域和长江流域,以大型供水水库为对象.在水利学科领域,有大量有关水库水文、水动力学和调度的研究论文,这些工作还未能被以生物和化学为研究基础的生态或环境科学的学者所重视.多数以水库为对象的生态学研究还没有很好地体现水库作为人工湖泊的特殊性.近10年来,中国水库生态学经历了从任务导向到学科导向的生态学研究过渡,有不断增加学科交流的趋势.有理由相信,作为水库大国,中国水库生态学和湖沼学今后将会有一很大的发展,并对我国淡水生态学和湖沼学作出重要的贡献.  相似文献