Genetic variation in Avicennia marina in three estuaries of Sydney (Australia) and implications for rehabilitation and management     

Melville F  Burchett M 《Marine pollution bulletin》2002,44(6):469-479

In order to ensure conservation of mangroves, genetic diversity in remaining populations must be explored. Both morphological and isozyme analyses were used and compared in investigating the intra- and inter-estuarine variation in Avicennia marina in Sydney, the most urbanised area in Australia. Sediment characteristics, metal levels, tree attributes, leaf morphology and isozyme/allozyme analyses were conducted. Tree characteristics did not prove to be adequate genetic markers, but leaf morphology may be of use in this species. Isozyme/allozyme analyses indicated that genetic distance corresponded with geographic distance, although habitat metal levels may indicate local selection pressures. High levels of heterozygote deficiencies were displayed in each estuary, which could threaten future viability. The results hold implications for management as periodic isozyme analysis may be useful in indicating management needs. The identification of metal-tolerant types may also be useful. Transplantation among estuaries may assist in increasing genetic diversity, if considered desirable. Whatever the management aims, isozyme/allozyme analyses are shown to be useful for revealing genetic diversity in this species.  相似文献   

新疆人口分布和地震分布的关系初探     

李胜年 《内陆地震》1988,(4)

本文在分析新疆人口分布和强地震地理分布特点的基础上,得出人口在地震活动带上相对集中的结论。并根据新疆构造地貌特点和气候水文条件,对这一现象的产生作了初步探讨。  相似文献   

广州经济发展与城市化的协调     

李文翎 《热带地理》1995,15(3):210-217

本文通过分析广州经济自改革开放以来以较快速度持续向前发展的现状以及广州人口的变化与迁移趋势，指出了广州人口呈分散性聚集的逆城市化现象与其经济发展趋势相一致，论证了广州城市群体形成的必然性。  相似文献   

迁移八律与中国人口迁移   总被引：3，自引：0，他引：3  

胡兆量 《云南地理环境研究》1994,6(1):45-53

中国人口迁移具有下列八个特征：１，提高生活质量是经济目的迁移的主要原因，非经济目的迁移违反经济规律时不能巩固；２，在城市化过程中，乡村迁往城市是主要迁移方向；３，整体男性迁移多，轻工劳务和婚姻迁移突出地区女性迁移多；４，独身青年迁移多；５，短距离迁移多，高素质人口迁移距离较长；６，迁移有圈层递补现象；７，强迁移方向必然带来较弱的迁移回流，当两地经济势能接近和递转时，回流加强；８，城市化过程中大城市迁入人口比重大，吸引迁移的范围广。可见，列文斯坦提出的人口迁移规律基本上适合中国的实际，中国人口迁移的实际又丰富了列文斯坦的人口迁移规律。  相似文献   

Estimation of a continuous spatio-temporal population model     

Javier Alvarez  Pascal Mossay 《Journal of Geographical Systems》2006,8(3):307-316

In this paper we propose a continuous spatio-temporal model that describes population change in a region in terms of population growth, migration drift towards regions with better economic or climate conditions, and population diffusion from more populated to less populated areas. Finite-differences are used to approximate the space and time derivatives. The model is estimated by using population data from the US census corresponding to the period 1790–1910. People tend to migrate from east to west, and to relocate towards regions with lower precipitation levels and more abundant coal and iron resources. Also population growth tends to be larger in zones with higher precipitation levels and higher temperatures.  相似文献   

Distribution and abundance of Daphnia pulicaria, a large Daphnia of the “pulex group”, in Lake Constance (Lower Lake)     

Hans Bernd Stich  Gerhard Maier   《Limnologica》2007,37(4):303-310

The population dynamics and distribution of Daphnia pulicaria were studied in Lake Constance (Lower Lake). This Daphnia was absent in the year 2004, absent during most part of the year 2005 and absent in spring 2007 but present from November 2005 to July 2006. Abundance was high from January to late May of the year 2006; maximum abundance was 95,000 ind. m⁻² (30 May). Males and ephippial females were observed in January and late May. Ovigerous females constituted between 30% and 70% of adult females from November 2005 to April 2006; in June and July their percentage decreased to <20%. Mean number of eggs per egg-bearing female ranged between 2 (in November 2005) and 9.8 (in April 2006) and maximum egg number was 20. Birth and growth rates were low (generally <0.15); death rate was highest in June (0.275). Females of D. pulicaria were larger than females of Daphnia galeata/hyalina but carried somewhat fewer eggs. D. pulicaria generally preferred the deep cool water layers. The species was abundant in the northern parts of the Lower Lake (Gnadensee and Zeller See), rare in the southern parts (Rheinsee) and absent in the Upper Lake. We conclude that the life history and occurrence of large-bodied D. pulicaria in Lake Constance can be governed by fish predation pressure. This suggestion is supported by analyses of stomach contents from Coregonus lavaretus; stomachs contained high proportions of D. pulicaria in the first half of the year 2006. The disappearance of D. pulicaria in early summer and the comparatively low proportion of adults for most part of the investigation period also indicate that fish predation is involved in the dynamics of this Daphnia. The preference for deep cool water can be strategy to reduce predation risk. The low density of D. pulicaria in the southern basin of Lower Lake (Rheinsee) may be explained by the influence of the Rhine River which flows through this basin.  相似文献   

基于改进灰狼算法的岩石声发射定位研究     

王桂林  欧阳啸天  梁锋  张亮 《工程地质学报》2022,30(1):234-241

针对岩石力学试验中传统的声发射定位算法存在局限性,将灰狼算法(GWO)引入声发射定位研究中,该算法模仿了狼群的领导阶层与狩猎机制,用α、β、δ和ω 4种灰狼来模拟头狼领导,通过搜寻猎物、包围猎物和攻击猎物3个步骤实现目标的发现到捕获的全过程。在原始灰狼算法的基础上,针对其局部搜索能力欠佳的缺陷,修改收敛因子递减方式和淘汰最劣个体,提出基于种群记忆淘汰制的改进灰狼算法(BGWO)。基于预制裂隙岩石试件单轴压缩声发射试验结果,对比分析BGWO、GWO、引力搜索法(GSA)、Geiger算法、最小二乘法(LS)算法等5种定位算法的性能,发现改进后的BGWO算法在声发射定位搜索效率、搜索精度、稳定性和试验结果模拟方面效果优于其他算法。  相似文献   

The Demographic Constraints on Future Population Growth in Regional Australia     

Tom Wilson 《The Australian geographer》2015,46(1):91-111

Concern about rapid population growth in Australia's large cities and slower growth in many non-metropolitan areas has stimulated a range of government policies attempting to lift non-metropolitan growth rates. However, there is relatively little research on which to base these policies. It would be helpful to understand more about the consequences of current demographic trends continuing and the effects of alternative migration patterns. This paper presents sub-national population projections for Australia over the horizon 2011–2041, basing the projections on more socially meaningful Remoteness Areas instead of common statistical geographies. Three sets of projections were generated: a Current Direction scenario in which recent demographic trends are maintained, a Regional Immigration scenario in which more immigrants settle in regional and remote areas, and a Metro Exodus scenario in which there is increased internal migration from metropolitan to non-metropolitan areas. The future of Australia's population geography is shown to be one of spatially varying growth and population ageing, and continued metropolitanisation. In regional areas rapid population ageing will lower natural increase rates and thus reduce overall growth, resulting in a falling share of the national population. Policy measures attempting to increase the share of growth in regional areas will struggle against natural demographic forces operating in the opposite direction.  相似文献   

Automated egg counting and sizing from scanned images: Rapid sample processing and large data volumes for fecundity estimates   总被引：1，自引：0，他引：1  

K.D. Friedland  D. Ama-Abasi  M. Manning  L. Clarke  G. Kligys  R.C. Chambers 《Journal of Sea Research》2005,54(4):307-316

The production of eggs in a fish population is a fundamental parameter in fisheries management and ecology. Management decisions are based largely on the abundance and composition of the spawning stock; hence it is essential to estimate the contribution of viable eggs by females of various ages, which may depend on the size and maturation schedules in females of younger ages, and the size and reproductive senescence of older ones. The level of recruitment may also be influenced by the size and quality of eggs. Egg quality can be characterised in a number of ways; however, the most useful methods are those that are efficient and widely available. Estimating potential fecundity and egg size in fish and invertebrate populations has been hindered by the processing time, toxicity, and resources required by traditional methods. We have developed an imaging-based technique that counts and measures oocytes from a gravimetric gonadal sub-sample in relatively little time and at low cost. Sub-samples were preserved in a non-toxic formulation of Gilson's solution, which offers an alternative to other preservatives commonly used in fecundity studies. The technique uses high-resolution optical scans of plated oocytes, imaging software, and user-defined object classifications to separate oocyte from ancillary material likely to be present in a processed sample. Estimates of misclassification are as low as 1% (false-negatives) in automated counts.  相似文献   

Small-scale distribution characteristics of Munida spp. populations (Decapoda: Anomura) off the Catalan coasts (western Mediterranean)     

Carme Huguet  Francesc Maynou  Pere Abell 《Journal of Sea Research》2005,53(4):283

The small-scale distribution characteristics of three species of the anomuran genus Munida, namely Munida rutllanti, Munida intermedia and Munida tenuimana, have been studied on the lower shelf and upper-middle continental slope near the coasts of Tarragona and the Ebro delta region in the western Mediterranean. The differential bathymetric distribution showed that a fair degree of overlap exists between M. rutllanti and M. intermedia, with the former being mainly found at shallower depths. The size population structure of the three species showed that polymodality, as indicative of a longer life-span and of a higher degree of population structuring was more evident in the deeper-living species, whereas unimodality, as an indication of a recruitment dependent population, was more evident in the shallowest-occurring species. Geostatistics have been applied to determine the degree of spatial variability occurring in M. intermedia abundance, the better-sampled species. The Mantel test has been used to assess the significance of the overlap between the three species distributions as well as the relation between certain population parameters. A discussion on the population characteristics of M. rutllanti is made in relation with its expansion along the western Mediterranean in the last decades.  相似文献