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11.
Nils Chr Stenseth Ottar N. Bj?rnstad Takashi Saitoh 《Researches on Population Ecology》1998,40(1):85-95
We interpret gradients in population dynamics of the gray-sided vole from the southwestern part of the island of Hokkaido
to its northeastern part within the framework of a phenomenological model involving the relative length of summer and winter.
In Hokkaido, as in other northern regions, both spring and fall is considered as short transition periods between the two
main seasons — summer (the primary breeding season) and winter (the non-reproductive or secondary breeding season). We show
that the geographic transition in dynamics may be understood as the combined consequence of different patterns of density-dependence
during summer and winter, and geographically varying season lengths. Differences are shown to exist between summer and winter
with respect to strength of density-dependence. Direct density-dependence, in particular, is stronger during winter than during
summer. A model is presented to show how relative lengths of seasons can induce both stable and periodically fluctuating population
dynamics. The results are compared and contrasted with what is otherwise known about the gradient in rodent dynamics in Fennoscandia. 相似文献
12.
Natural hybridization among wingless carabid beetles of the subgenusOhomopterus (Carabidae, genusCarabus) is reviewed, and its significance in the evolution of this subgenus discussed. Natural hybridization occurs between parapatric
species of similar size. Two case studies of natural hybridization suggest that natural hybridization could have affected
the evolution of this subgenus in different ways. When there is a large difference in genital morphology between hybridizing
species, interspecific copulation often results in genital injuries that causes mortality of copulating individuals, and hence
reduces the fitness of hybridizing individuals greatly. In such a case, hybridization may be effective in maintaining the
parapatric distribution of the two species, and in the long term, may promote reinforcement selection for traits which are
effective in prezygotic reproductive isolation. When the morphological difference in genitalia is not so large as to cause
genital injury, a hybrid population may be established at the intermediate zone between two parental species, provided that
the immigration rates of the two species into the intermediate zone are small. Thus, natural hybridization may have contributed
to both divergence and reticulate evolution in this subgenus. 相似文献
13.
Despite the fact that sickle-cell disease (SCD) is perhaps the most “racialized” medical condition in the USA, very little is known about how “race” impacts public support for health policies related to the condition. We embedded an experiment within the 2011 Cooperative Congressional Election Study in order to assess perceptions about SCD among 1250 participants from diverse backgrounds and evaluate the extent to which these perceptions were associated with support for government spending on SCD-related benefits. We manipulated the racial phenotype of SCD advocates who requested additional government funding and asked participants to indicate how much the government should provide. Overall, participants expressed moderately positive attitudes about SCD, and there were no differences in funding support based on the race of the advocate. However, white participants supported less funding compared to nonwhite participants, even after adjusting for a number of demographic and attitudinal covariates. These findings suggest that a complex relationship between racial identification and implicit racism may shape public perceptions about SCD that negatively influences perceivers’ support for SCD-related policy. 相似文献
14.
Robert?Joseph?TaylorEmail authorView authors OrcID profile Dawne?M.?Mouzon Ann?W.?Nguyen Linda?M.?Chatters 《Race and social problems》2016,8(4):326-339
This study examined reciprocal support networks involving extended family, friends and church members among African Americans. Our analysis examined specific patterns of reciprocal support (i.e., received only, gave only, both gave and received, neither gave or received), as well as network characteristics (i.e., contact and subjective closeness) as correlates of reciprocal support. The analysis is based on the African American subsample of the National Survey of American Life. Overall, our findings indicate that African Americans are very involved in reciprocal support networks with their extended family, friends and church members. Respondents were most extensively involved in reciprocal supports with extended family members, followed closely by friends and church networks. Network characteristics (i.e., contact and subjective closeness) were significantly and consistently associated with involvement with reciprocal support exchanges for all three networks. These and other findings are discussed in detail. This study complements previous work on the complementary roles of family, friend and congregational support networks, as well as studies of racial differences in informal support networks. 相似文献
15.
Vivian?ViallonEmail author Sophie?Lambert-Lacroix H?lger?Hoefling Franck?Picard 《Statistics and Computing》2016,26(1-2):285-301
Using networks as prior knowledge to guide model selection is a way to reach structured sparsity. In particular, the fused lasso that was originally designed to penalize differences of coefficients corresponding to successive features has been generalized to handle features whose effects are structured according to a given network. As any prior information, the network provided in the penalty may contain misleading edges that connect coefficients whose difference is not zero, and the extent to which the performance of the method depend on the suitability of the graph has never been clearly assessed. In this work we investigate the theoretical and empirical properties of the adaptive generalized fused lasso in the context of generalized linear models. In the fixed \(p\) setting, we show that, asymptotically, adding misleading edges in the graph does not prevent the adaptive generalized fused lasso from enjoying asymptotic oracle properties, while forgetting suitable edges can be more problematic. These theoretical results are complemented by an extensive simulation study that assesses the robustness of the adaptive generalized fused lasso against misspecification of the network as well as its applicability when theoretical coefficients are not exactly equal. Our contribution is also to evaluate the applicability of the generalized fused lasso for the joint modeling of multiple sparse regression functions. Illustrations are provided on two real data examples. 相似文献
16.
The article discusses the nature of the tangled interaction between the ex-Soviet Central Asian republics and the outside
great powers – Russia, the United States and China. Although the so-called Great Game model is often used to explain the geopolitical
rivalry in the region, the current pattern of relations between various international actors is much more complex than a traditional
tug-of-war between the old colonial empires. While Russia's strategic role in Central Asia appears to be on the rise, the
capacity of the West to influence political developments in the region has diminished. However, the overall situation in Central
Asia remains volatile and its geopolitical landscape is far from being settled. 相似文献
17.
Upon reviewing the extant literature on determinants of unionism, it becomes clear that many areas that have had a plethora
of research attention do not converge upon singularly directional findings. This study explores a potential cause of such
an apparent anomaly: nonlinearity of data. An exploratory examination of correlation coefficients among typical union determinant
variables seems to show different patterns of relationships at different levels of union demand. Thus, a break from traditional
linear data analysis techniques is explored in the interest of explaining more variance with typical, theoretically derived
variables by using neural network analysis. Results of analyses on industry level data reveal that using neural network analysis
to model union demand explained over four times as much variance as multiple regression analysis. 相似文献
18.
This paper studies natives’ economically motivated preferences over different levels of immigration of low-income earners. Immigration affects natives through both intra- and intergenerational redistribution programmes and in the labour market. Our analysis suggests, in a welfare state that looks after the poor and the aged, economic motivation does not necessarily lead a native to have an extreme opinion on the preferable level of immigration, although it causes disagreement among natives. We find, regardless of parameter values, high-income earners prefer at least as much immigration as low-income earners who, in turn, prefer at least as much immigration as pensioners. The median voter is then likely to be a low-income native.
相似文献
Yuji TamuraEmail: Fax: +44-24-76523032 |
19.
John‐Michael Davis Yaakov Garb 《Development policy review : the journal of the Overseas Development Institute》2019,37(1):67-89
This article describes an unconventional participatory development approach carried out in an informal e‐waste hub in South‐West Hebron, an area that has collected and processed the bulk of Israeli e‐waste for over a decade. Our approach contributes to the critique and recovery of community representation in participatory development and the search for ways to facilitate representative community engagement. Specifically, we describe our use of a novel Delphi‐like method that allowed us to facilitate a broadly endorsed development trajectory within a heterogeneous and conflicted community. We show how the results yielded by this approach diverged from those that were likely to emerge from more facile forms of participation in ways that are important for other similar e‐waste hubs internationally, which face a destructive status quo on the one hand, or the economically ruinous international policies that ban e‐waste trade from “developed” to “developing” countries on the other. Despite real tensions and cleavages within the affected communities, the process described facilitated a shift from deadlocked environmental versus livelihood positions towards building capacity and regulating existing informal e‐waste trades to preserve livelihoods dependent on these. 相似文献
20.
本文是对清华大学教授葛兆光新著《中国思想史》第一卷的学术评论。文章认为 ,葛先生“重写”思想史的基本路子即以论带史、以今视昔、以文领义 ,而“基本路子只有一条 ,一分为三 ,乃是方便说法”。事实上 ,思想史领域本来就别有洞天 ,“葛先生自许的突破之处 ,不过是划地为牢 ,然后纵身一跃 ,作突破状而已。”文章还批评了《中国思想史》中存在的理路不清、用词不当的一些“大议论”。本文作者总结道 :如果要我用一句话来评论这本书 ,我将说 :“在这本号称‘思想史’的书里 ,我看不到历史上的思想和知识 ,我只看到现在一位中国人葛兆光的‘思想’”。 相似文献