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排序方式: 共有492条查询结果,搜索用时 31 毫秒
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Anna Brüniche-Olsen Menna E. Jones Jeremy J. Austin Christopher P. Burridge Barbara R. Holland 《Biology letters》2014,10(11)
The Tasmanian devil (Sarcophilus harrisii) was widespread in Australia during the Late Pleistocene but is now endemic to the island of Tasmania. Low genetic diversity combined with the spread of devil facial tumour disease have raised concerns for the species’ long-term survival. Here, we investigate the origin of low genetic diversity by inferring the species'' demographic history using temporal sampling with summary statistics, full-likelihood and approximate Bayesian computation methods. Our results show extensive population declines across Tasmania correlating with environmental changes around the last glacial maximum and following unstable climate related to increased ‘El Niño–Southern Oscillation’ activity. 相似文献
73.
A numerical model (`DiffDeni') has been developed to describe the disappearance of nitrate from the water column of 10–200 cm deep waters. The disappearance is caused by bacterial denitrification in the sediments. The model employs the molecular diffusion constant, an acceleration factor describing eddy diffusion, and three bacterial growth constants, viz. the inoculum size, the maximum growth rate and the half saturation constant for the hyperbolic process. The values of these system-constants were varied over a wide range. The curves obtained were compared with the curves for well-defined situations, viz. in which diffusion takes place without any or with a complete, immediate reaction. These cases have analytical solutions, and were simulated closely by the model `DiffDeni', though this model is based on different assumptions. It is shown that, when the bacterial growth rate is above a critical value, a negative exponential curve describes the nitrate disappearance well. On the other hand, a more complicated negative exponential equation can be used to describe the first phase of this denitrification in which bacterial activity is low and nitrate behaves as a conservative compound. The change-over period from phase 1 (no reaction) to phase 2 (complete, immediate reaction) which may vary between <1 and 50 days cannot be described analytically (mathematically correctly). The influence of temperature on denitrification is assessed and it is shown that both bacterial activity and diffusion may influence the denitrification rate. 相似文献
74.
基于条件价值法评估三亚海域生态系统多样性及物种多样性的维持服务价值 总被引:2,自引:0,他引:2
基于条件价值法(CVM)开展了三亚海域海洋保护区生态系统多样性和重要海洋物种多样性的维持服务价值评估。于2014年12月通过面对面调研的形式对三亚当地城镇居民进行问卷调查,建立了支付意愿(WTP)多元线性回归方程,再将此回归模型推广到海南全省城镇居民,从而评估了三亚海域海洋保护区生态系统多样性和重要海洋物种多样性的维持服务价值;同时也对CVM研究中的相关问题如问卷设计、偏差分析和CVM的可靠性与有效性等进行了验证和探讨。研究结果表明:(1)2014年三亚海域海洋保护区生态系统多样性及重要海洋物种多样性的维持服务总价值分别为3.734亿元和4.442亿元。(2)受教育程度和家庭人均年收入等社会经济信息变量对支付意愿具有显著的影响水平,符合经济学理论。(3) CVM作为陈述偏好性价值评估方法,评估结果受偏差的影响较大。为了尽可能减小偏差,需要从问卷的设计、调查员筛选培训、调查方式和被调查者等诸多方面严格把关。(4) CVM问卷支付数额的设计较好地界定了支付意愿的范围和分布形态,支付意愿具有较高的统计效率,CVM的可靠性得到较好的验证,显示了CVM评估法在估算生态系统服务非使用价值的有效性。鉴于居民的学历和收入在短时间内很难得到提升,建议相关海洋管理部门加强对三亚海域海洋保护区和海洋生物多样性的宣传教育,增强居民对三亚海洋保护区和海洋珍稀濒危生物的认知及保护意识。 相似文献
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Andrea M. Price Vera Pospelova Michael R. S. Coffin James S. Latimer Gail L. Chmura 《Ecology and evolution》2016,6(16):5648-5662
Few biogeographic studies of dinoflagellate cysts include the near‐shore estuarine environment. We determine the effect of estuary type, biogeography, and water quality on the spatial distribution of organic‐walled dinoflagellate cysts from the Northeast USA (Maine to Delaware) and Canada (Prince Edward Island). A total of 69 surface sediment samples were collected from 27 estuaries, from sites with surface salinities >20. Dinoflagellate cysts were examined microscopically and compared to environmental parameters using multivariate ordination techniques. The spatial distribution of cyst taxa reflects biogeographic provinces established by other marine organisms, with Cape Cod separating the northern Acadian Province from the southern Virginian Province. Species such as Lingulodinium machaerophorum and Polysphaeridinium zoharyi were found almost exclusively in the Virginian Province, while others such as Dubridinium spp. and Islandinium? cezare were more abundant in the Acadian Province. Tidal range, sea surface temperature (SST), and sea surface salinity (SSS) are statistically significant parameters influencing cyst assemblages. Samples from the same type of estuary cluster together in canonical correspondence analysis when the estuaries are within the same biogeographic province. The large geographic extent of this study, encompassing four main estuary types (riverine, lagoon, coastal embayment, and fjord), allowed us to determine that the type of estuary has an important influence on cyst assemblages. Due to greater seasonal variations in SSTs and SSSs in estuaries compared to the open ocean, cyst assemblages show distinct latitudinal trends. The estuarine context is important for understanding present‐day species distribution, the factors controlling them, and to better predict how they may change in the future. 相似文献
78.
中国水域瓶鼻海豚的mtDNA控制区序列变异性分析 总被引:8,自引:0,他引:8
测定了30头中国水域瓶鼻海豚(Tursiops sp.)mtDNA控制区5′端424bp的序列,结合已发表的中国水域其它瓶鼻海豚的mtDNA控制区序列,共发现54个变异位点,定义了37种单元型。中国水域瓶鼻海豚的两个形态型之间没有共享单元型,且具有8个鉴别位点。基于最大似然法和邻接法的系统发生分析均把单元型聚类为分别代表两个形态型的支系。形态型之间的核苷酸歧异度为5.58%,超过了其它海豚类种间的序列歧异水平,支持把这两个形态型划分为两个独立的种,即T.truncatus和T.aduncus的观点。虽然两种瓶鼻海豚的分布区在台湾海峡一带出现重叠,但相互之间缺乏基因流动,提示两者可能已出现了显著的生殖隔离。 相似文献
79.
在水培条件下,研究了2种柳树(Salix integra)无性系(“一支笔”和“微山湖”)对模拟富营养化水体中氮素的吸收状况,并采用常规耗竭法探讨了柳树幼苗根系对NH4+-N、NO3--N的吸收动力学特征.结果表明:2种柳树无性系对低浓度模拟富营养化水体中总氮的去除率均达90%以上,是高浓度情况下的2倍;对低浓度模拟污水中总磷的去除率达80%,高浓度下则达92%,且“一支笔”对总氮、总磷的吸收效果优于“微山湖”;2种柳树无性系对氮素的吸收均表现为水体中营养物质浓度越高,去除效果越好;只有NH4+-N或NO3--N存在时,“微山湖”的最大吸收速率和亲和力高于“一支笔”;当有其他氮源影响时,2种柳树无性系对NH4+-N和NO3--N的吸收效率则下降至50%;研究表明,柳树对富营养化水体的生态修复作用较强,是进行面源污染生态修复的优良树种. 相似文献
80.