Dividing the algal soup: is there niche separation between native bivalves (Echyridella menziesii) and non-native Daphnia pulex in New Zealand?     

《新西兰海洋与淡水研究杂志》2012,46(1):45-59

ABSTRACT

New Zealand's native freshwater mussels (kākahi, kāeo) are considered to be in decline, yet the mechanisms driving this are unclear. The widespread establishment of highly efficient filter-feeding, non-native Daphnia in New Zealand lakes may have led to competition for algae with kākahi. We conducted a controlled laboratory experiment to determine whether differences exist in algal resources utilised by kākahi and North American Daphnia pulex. Echyridella menziesii (adults and juveniles) and D. pulex were exposed to mixed algal samples for three hours to determine whether similar algal resources were removed by the grazers. Relative to controls, both adult and juvenile E. menziesii removed a broad range of algal taxa including diatoms, green algae and filamentous species, ranging in size from 33.6 to 348.0?μm. High densities of D. pulex were unable to cause depletion of these same algae species. Our results suggest niche overlap is limited between the two grazers; E. menziesii utilises larger particles than D. pulex.  相似文献   

化感作用对中肋骨条藻与东海原甲藻竞争演替的影响   总被引：2，自引：2，他引：0  

王江涛  李慧  曹婧  张议文 《海洋学报》2012,34(2):169-178

为了检验化感作用对赤潮藻类生长和竞争的影响,对中肋骨条藻滤液进行了培养实验,结果显示中肋骨条藻滤液对其自身的生长呈现出化感抑制现象,而且抑制作用在磷限制条件下尤为显著。自化感作用的程度与藻的生长阶段有关,指数期滤液对中肋骨条藻的抑制作用比衰亡期滤液略强。不同滤液添加比例实验进一步验证了中肋骨条藻自化感作用的存在。降解实验表明在某些机制的作用下,化感物质会随时间而发生降解。在所有的滤液培养实验中,中肋骨条藻对东海原甲藻的生长没有明显影响,这可能是由于东海原甲藻对滤液中的化学物质有较强的耐受能力。中肋骨条藻滤液的共培养实验结果显示,中肋骨条藻与东海原甲藻表现出演替现象,东海原甲藻最终获得竞争优势。实验结果表明化感作用可能会影响中肋骨条藻和东海原甲藻的竞争演替。  相似文献   

Comparison of simultaneous and combinatorial auction designs in fisheries quota market     

M.S. Iftekhar  J.G. Tisdell 《Marine Policy》2012,36(2):446-453

Individual transferable quota (ITQ) markets are being used successfully to distribute quotas in single region and single species fisheries. In many parts of the world, the development of well crafted markets for multispecies or multiregional fisheries is still evolving. As a result, there exists an opportunity to inform policy by providing research insights into the relative merits of alternative market designs for such fisheries.This study explored the relative merits of a simultaneous ascending auction design and an iterative combinatorial auction design for a hypothetical multiple region quota market. In a simultaneous auction, separate auctions are run in parallel for individual species or regions. During intermediate rounds, fishers can adjust their bids in auction depending on their position in the other auction. In a combinatorial auction, a fisher can purchase a combination of quotas (or a package quota) for different fish species or regions in the same auction. Being able to acquire bundles of species or regions allows fishers to take advantage of complementarities. To date, the potentials of such auctions have not been thoroughly tested in fisheries quota markets. This study found that while a simultaneous auction design was more efficient than combinatorial auction design overall, combinatorial market design took fewer rounds to make final allocations and performed better in high synergy environments.  相似文献   

以持续可居性为核心的经济适用房设计     

黄一如  贺永 《中国勘察设计》2009,(1):22-26

在对低收入家庭的居住现状与居住空间需求的调查研究基础上,结合2008年全国保障性住房设计方案竞赛的回顾与思考,提出社会保障型住宅设计的策略与原则。  相似文献   

Is the native deer Mazama gouazoubira threatened by competition for food with the exotic hare Lepus europaeus in the degraded Chaco in Córdoba, Argentina?     

M.B. Kufner  L. Sepúlveda  G. Gavier  L. Madoery  L. Giraudo   《Journal of Arid Environments》2008,72(12):2159-2167

Using microhistological analysis of faeces, we studied the diets of the wild Chacoan Brown brocket deer (Mazama gouazoubira) and the exotic European hare (Lepus europaeus) by comparing plant species frequency in faeces with plant species availability. Research was conducted in the dry southern portion of South American Chaco, in forests subjected to livestock ranching in the north of Córdoba province, Argentina. The diet of the Brown brocket deer was more closely related to forage availability (C=0.82195) than the diet of the European hare (C=0.38565). Dicots comprised 90% of the Brown brocket deer diet and were preferred throughout the year, while gramineous species were consumed in low amount. In the diet of the European hare, gramineous species were frequent (65 to 87%) and preferred in every season but in winter, when dicots were consumed in higher proportions (92%). Differences in feeding habits and in habitat use would allow both herbivores to coexist; however, probable competition for food with the European hare during the dry period, in addition to habitat loss, threatens survival of the Brown brocket deer.  相似文献   

里海地区能源安全及西方对该地区的地缘政治战略   总被引：1，自引：0，他引：1  

高淑琴  唐洪钊 《世界地理研究》2009,18(4):66-73,29

里海地处欧亚大陆的接合处,地理位置极其重要。近年来,随着一批新的里海大型油汽田的探明,里海的石油地位也迅速上升,再次成为世界关注的焦点。苏联解体后,里海地区一方面因其丰富的油气资源储备备受国际社会关注;另一方面,里海面临着激烈的国际竞争局面和不稳定的区域发展前景。本文论述了里海地区油气资源的储备和生产、出口现状以及国际竞争的局面,尤其是西方参与里海地区油气资源竞争的格局,这不仅引起该地区非国家主体的地缘政治的改变,从而也深刻影响着西方国家主体对该地区的战略和政策。  相似文献   

4种典型荒漠植物相互关系     

袁建立  郑凯  王亮 《中国沙漠》2014,34(3):740-746

我们调查了安西荒漠保护区内相邻的4种典型植物珍珠猪毛菜（Salsola passerina ）、合头草（Sympegma regelii ）、红砂（Reaumuria soongorica ）、泡泡刺（Nitraria sphaerocarpa ）个体大小与相对距离,通过对10种组合的个体大小与距离的回归分析,研究其彼此间的相互关系。结果显示：4种植物大小与距离之间是正相互关系,即竞争关系;种内竞争的重要性高于种间竞争的重要性,且竞争物种之间存在不对称性。此结果表明,物种间的这种竞争关系在一定程度上影响了荒漠地区植物群落的构建。  相似文献   

中国沿海集装箱港口体系的形成演化机理   总被引：30，自引：5，他引：25  

曹有挥  曹卫东  金世胜  李海建  王黎明 《地理学报》2003,58(3):424-432

立足当今中国的现实,从现代经济学观点与港口地理学原理相结合的新视角,对沿海集装箱港口体系的形成演化机理进行理论探索,揭示出竞争与合作机制的交互作用是推动沿海集装箱港口体系形成演化的内在动力,并归纳演绎了由低级均衡→非均衡相对集中→非均衡高度集中→高级均衡的沿海集装箱港口体系的一般演化模式。实证分析表明,中国沿海集装箱港口体系正处于由非均衡相对集中向非均衡高度集中阶段演化的过渡时期,其动力机制主要有：转型经济的促进作用、政府行为的调控作用和中心枢纽港的极化作用。  相似文献   

富营养水体中沉水植物与浮游藻类相互竞争的研究   总被引：21，自引：6，他引：15  

杨清心 《湖泊科学》1996,8(Z1):17-24

本文就沉水植物与浮游藻类在富营养水体中的相互竞争现象及机制作了初步研究。室内外实验结果表明,二者之间存在着复杂的相互竞争关系。在光资源竞争上,浮游藻类占有相对优势;对水中营养盐的竞争是单向的,沉水植物因可以从底泥中得到营养盐而处于优势地位;当光照和营养盐充足时沉水植物对浮游藻类有明显的生化抑制效应,这种抑制可能通过促进藻类沉降而起作用。二者的互竞争受水深、水温及水中营养盐含量的强烈影响,高水温、高营养盐含量及深水均不利于沉水植物,而助长了浮游藻类的竞争优势。沉水植物群落一旦形成较大的密度,就能对浮游藻类产生强烈的抑制,保持自己的优势地位。因此,沉水植被恢复应从水温和水位均较底的冬季开始,严格控制营养盐输入量是非常重要的。  相似文献   

氮、磷供给比例对实验微藻群落结构的影响   总被引：1，自引：1，他引：0  

李伟  何淑嫱 《湖泊科学》2014,26(5):767-772

生态理论预测,生境筛选和物种竞争可能会联合影响生物群落结构.然而,通过实验手段检测两者对群落结构的影响作用,特别是两者的作用效果是否会随时间推移而发生改变的研究还十分有限.本研究构建了实验微藻群落系统,通过改变微藻生长发育所必须的2种限制性因子氮素和磷素的供给比例,对微藻的结构特征及各微藻组分的种群动态变化进行持续跟踪,并通过对各微藻进行单一培养的方式来获取相关的性状指数,用以反映各微藻的耐低氮或耐低磷能力,进而检验生境筛选和物种竞争对微藻群落的影响作用,以及两者作用效果随时间推移而发生的改变.结果表明,生境筛选和物种竞争对微藻群落结构的影响会随着时间的推移而发生变化:实验初期生境筛选和物种竞争的影响作用均较弱;实验中期生境筛选发挥着较为重要的作用,具体表现在水体中氮素和磷素的供给比例直接影响了具有不同耐低氮或耐低磷能力的微藻种群数量分布;而实验末期物种竞争发挥着较为关键的作用,其中纤细角星鼓藻成为绝对优势种,而部分微藻因为竞争排斥作用而从系统中消失.未来的研究应全面考虑不同的时序变化和空间结构下生境筛选和物种竞争对群落结构的综合影响作用.  相似文献