Are major canadian city-regions monocentric,polycentric, or dispersed?

Relatively little research has explored spatial structure in modern major Canadian regions. Three common models are monocentricity, polycentricity, and dispersion, but these are not always mutually exclusive in the complex spatial structures of contemporary city-regions. Shifts between these models are discussed in the context of three explanations of economic growth and restructuring: accessibility, municipal competition, and globalization. All three explanations suggest a trend away from monocentricity. While this appears clearly in US cities, disagreement surrounds whether Canadian cities are following the same path. This study uses cross-sectional data from InfoGroup in 2011 to estimate the relative strengths of monocentricity, polycentricity, and dispersion for characterizing eight major regions. Results indicate that elements of each model are evident in all eight study regions, but each tends to dominate in different contexts. When focusing on Montreal, Toronto, and Vancouver, results imply that all three forces which guide spatial structure play a role and that job centers appear to play a particularly important structural role in larger regions.     

Factors explaining the dispersal of Hendra virus disease in South-East Queensland

Hendra virus (HeV) was first described in 1994 following the outbreak of a new disease fatally affecting horses and humans in South-east Queensland. The disease kills 70% of the infected horses and under some circumstances the virus is spread to humans who have had close contact with the infected horses. Fruit bats (Pteropus spp.) commonly known as flying foxes have been identified as the natural host of the virus. A preliminary analysis of the incidents and the flying fox roosting sites revealed a strong relationship between the temporary and seasonal roosting sites in the South-east Queensland. The aim of this paper is to determine the potential factors that can explain the dispersal of HeV incidents in the study area. Based on the preliminary results, a further analysis was done on the roosting sites by considering factors such as the species of flying foxes, foraging range and pregnancy period. Spatial autocorrelation (Global Moran’s I) revealed significant clustering of P. alecto and P. scapulatus species. Kernel density estimation analysis helped in identifying a strong relationship between P. alecto & P. scapulatus species density and the outbreak events in the study area. Buffer analysis established an initial relationship between P. alecto & P. poliocephalus species birth periods and the incidents. Ordinary least-squares regression identified P. poliocephalus species as statistically significant at a global context across the study area. Geographically weighted regression analysis was performed to study the local spatial variations of the explanatory variables. P. alecto & P. poliocephalus species exhibited a significant positive relationship in most of the regions where as pregnancy period variable exhibited a significant negative relationship to the HeV incidents in the study area.     

环境过滤和扩散限制对库姆塔格沙漠南缘植物群落β-多样性的影响

β-多样性反映群落之间的物种组成差异,群落β-多样性的形成和维持一直是生态学研究的核心问题.通过对库姆塔格沙漠南缘60个植物群落的调查,结合环境因素和空间距离,通过Mantel分析以及基于距离的多元回归(MRM),分析了环境过滤和扩散限制对研究区植物群落β-多样性及组分的影响.结果表明:库姆塔格沙漠南缘植物群落存在明显...     

What Determines the Distribution of Coastal Hydrobiid Mudsnails Within North-Western Europe?

The three north-west European species of Hydrobia are often partially segregated along salinity gradients and/or sympatric in the nontidal eastern Danish waters and Baltic Sea, but are rarely sympatric and are confined either to nontidal coastal lagoons ( Hydrobia ventrosa and Hydrobia neglecta ) or to the marine/estuarine intertidal zone ( Hydrobia ulvae ) along the macrotidal Atlantic and North Sea coasts. Significant interspecific competition has been found in Danish waters but not elsewhere in the Atlantic and North-Sea Europe. The two nontidal species and H. ulvae also possess contrasting reproductive strategies. The roles of life-history strategy, interspecific competition and between-habitat dispersal in restricting these mudsnails to their differing habitats are evaluated in the light of these and other findings. It is concluded that all are likely to be relevant, especially dispersal in maintaining and interspecific competition in opposing, mixed populations in the Kattegat-Baltic, and life-history strategy in maintaining the lagoonal versus intertidal dichotomy in the rest of north-west Europe. This dichotomy prevents segregation of species along common salinity gradients outside the Baltic region and restricts potential interspecific competition to within lagoons, where H. ulvae is at a recruitment disadvantage.     

Plinian fall deposits from Vulsini Volcanic District (Central Italy)

Stratigraphic investigations of the Vulsini Volcanic District indicate the existence of five prominent plinian fall deposits, deposited over a period of about 0.34 Ma. The oldest deposit (Basal pumices) crops out mainly in the peripheral areas and is one of the largest plinian events in the Vulsini District, with a volume of about 9 km³ and a calculated column height exceeding 30 km. Subcircular patterns of isopachs and isopleths around the Bolsena lake indicate emplacement in wind-free conditions and suggest a source vent location in the northernmost sector of the present Bolsena lake, where it is possible that an older central volcanic structure existed. The four younger plinian fall deposits are related to Bolsena activity. The oldest of these, named the Ponticello and Orvieto-Bagnoregio pumices, are mainly distributed on the north-eastern sector of the Vulsini District. Their volumes are an order of magnitude lower than that of the basal unit, and the estimated column heights do not exceed 20 km. The younger Ospedaletto pumice deposit has a NE-SW dispersal axis, whereas the youngest Casetta pumice deposit is found only in the north-eastern sector of the district. Their estimated volumes are respectively 1.2 and 0.1 km³, whereas the inferred vent areas appear to be located slightly to the east of the Ponticello and Orvieto-Bagnoregio pumice deposit source areas. The chronology of the Ospedaletto and Casetta pumices indicates that the final plinian activity from the Bolsena complex is contemporaneous with the Latera activity. The decreasing volumes from the oldest to the youngest units, together with the progressive shifting northeastwards of the source vents, may be related to the volcano-tectonic subsidence of the Bolsena area. The source vents for the post-Basal pumices events are mainly clustered just north of Bolsena village where the greatest displacement during subsidence occurred. Accordingly, source vent shifting appears to be related to the progressive opening of normal faults from the inner to the outer margin of the Bolsena depression.     

西北地区一次人工消雨试验效果分析

通过利用人工消雨作业目标区和对比区降水量资料,研究了作业前后降水量的时间变化和空间变化。开展作业后作业区出现了显著的降水低值区,作业影响区出现了延迟降水。说明集中过量播撒作业对抑制云团的发展起到了积极的作用,消雨作业实施后1~3 h内有一定的作业效果。消雨作业实施后,目标区(影响区)的降水量要明显小于对比区的降水量。     

中国种子植物特有科属的分布型

中国种子植物特有属有２６８属，归７８科，其中有８个单种属中国特有科。本文根据特有属的地理分布及与环境的关系，区分为９个分布型和２３个亚型（包括本分布型），对各分布型和亚型进行了统计分析和详细阐述，讨论了分布区的间断和替代现象。提出特有科属分布型的主要特点。     

超大陆旋回与成矿作用

世界上绝大多数大矿床都是超级地质作用导致矿石异常集中的结果,一般多发生于一个地质作用结束的时期.地壳形成作用和板块构造、地幔柱模型已经成为如何认识矿床形成的关键所在,现代矿床成功的探索实践历史就是对大陆和海洋的深人认识进程.因此,矿床形成与全球构造和大陆的演化关系是研究成矿动力学的基础.本文以全球活动构造的视角,从超大陆聚散的历史纪录角度,对活动的地球演化环境下的成矿作用进行总结探索,以图激发对该领域更为深入的研究和思考.     

Assessment of the effectiveness of natural coral fragmentation as a dispersal mechanism for coral reef‐boring sponges

Eastern Pacific reefs are mostly made up of interlocking coral branches of Pocillopora, which are easily broken by physical forces associated with heavy swells and winds. In this study we investigated the potential of these coral fragments to enable propagation of boring sponges. For this, we quantified the frequency of occurrence and diversity of boring sponges in fragments of corals recently trapped among the branches of live colonies, and later tested the hypothesis that these sponges colonize new branches of corals. Nearly 80% of the coral colonies investigated had coral fragments among their branches, and 69% of these coral fragments contained boring sponges (11 species), some of these sponges in reproduction (23% of them carried oocytes). To test whether sponges inhabiting coral fragments could colonize new branching corals we transplanted them to healthy branches, and to branches whose living tissue was mechanically eliminated to simulate damage produced by grazing and death after bleaching and other causes of coral tissue mortality. All the transplanted coral fragments cemented to each new colony by means of calcification, and of the three sponge species tested (Cliona vermifera, Cliona tropicalis and Thoosa mismalolli) only C. vermifera was able to colonize both new living branches (26.9%) and cleaned branches (65.5%). The apparent capability of C. vermifera to colonize by direct contact may be another key ability of this species to maintain high frequency of occurrence in Pacific coral reefs. However, although C. tropicalis and T. mismalolli were not able to colonize new coral substrata by direct contact, coral fragments have the potential to contribute to local persistence of these sponges and to their dispersal, both by asexual (fragments) and sexual means (transport of sexual products). The present findings may partly explain the current increase of excavating sponges on deteriorating reefs with a large availability of dead branching corals.