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41.
Urbanisation is widely considered to promote the establishment of non-native species, but there is limited empirical evidence of the ecological factors driving their responses. The grey squirrel Sciurus carolinensis (Gmelin 1788) is native to North America, but is widespread in the UK and is starting to spread across Europe. It is regarded as one of the world’s worst invasive animals due to its adverse impacts on native biodiversity. We use the non-native grey squirrel population in Sheffield (UK) as a case study to assess which factors limit its distribution and abundance in urban environments. In 2010 the city-wide population of adult squirrels peaked at an estimated 6539 in autumn (0.46 squirrels/ha), with maximum local densities of 8.29/ha. These densities appear to be slightly lower than those recorded in urban environments in the species’ native range. Grey squirrels occurred more frequently at urban sites with larger amounts of green-space in the surrounding region. Local habitat characteristics were, however, more powerful predictors of urban grey squirrel occurrence and abundance than regional availability of green space. Canopy cover, seed bearing trees and supplementary feeders, provided for garden birds, positively influenced grey squirrels. The potential for grey squirrels to connect city dwellers with nature thus appears to be highest in urban locations that have considerable capacity to support native biodiversity. The beneficial impacts of supplementary feeding on grey squirrel populations is notable given concerns that squirrels can adversely influence bird populations. These habitat associations also imply that grey squirrels typically respond negatively to urbanisation, which challenges arguments that urbanisation favours exotic species. 相似文献
42.
Colin J. Beck 《Theory and Society》2014,43(2):197-223
The “Arab Spring” was a surprising event not just because predicting revolutions is a difficult task, but because current theories of revolution are ill equipped to explain revolutionary waves where interactive causal mechanisms at different levels of analysis and interactions between the units of analysis predominate. To account for such dynamics, a multidimensional social science of revolution is required. Accordingly, a meta-framework for revolutionary theory that combines multiple levels of analysis, multiple units of analysis, and their interactions is offered. A structured example of theory building is then given by detailing how the development of world cultural models and practices challenge existing political structures, affect mobilization processes, and make diffusion more likely. A structured example of study design using qualitative comparative analysis of 16 Middle Eastern and North African countries provides support for the interaction of subnational conditions for mobilization, state-centered causes, and transnational factors, including a country’s linkage to world society, as one explanation of the Revolutions of 2011. 相似文献
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Colin Mackerras 《Asian Ethnicity》2011,12(1):121-122
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Colin Chen 《统计学通讯:理论与方法》2013,42(5-6):1257-1271
Following the extension from linear mixed models to additive mixed models, extension from generalized linear mixed models to generalized additive mixed models is made, Algorithms are developed to compute the MLE's of the nonlinear effects and the covariance structures based on the penalized marginal likelihood. Convergence of the algorithms and selection of the smooth param¬eters are discussed. 相似文献
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Colin Cannonier 《Journal of Labor Research》2014,35(2):105-132
The Family and Medical Leave Act (FMLA), implemented in August 1993, grants job-protected leave to any employee satisfying the eligibility criteria. One of the provisions of the FMLA is to allow women to stay at home for a maximum period of 12 weeks to give care to the newborn. The effect of this legislation on the fertility response of eligible women has received little attention by researchers. This study analyzes whether the FMLA has influenced birth outcomes in the U.S. Specifically, I evaluate the effect of the FMLA by comparing the changes in the birth hazard profiles of women who became eligible for FMLA benefits such as maternity leave, to the changes in the control group who were not eligible for such leave. Using a discrete-time hazard model, results from the difference-in-differences estimation indicate that eligible women increase the probability of having a first and second birth by about 1.5 and 0.6 % per annum, respectively. Compared to other women, eligible women are giving birth to the first child a year earlier and about 8.5 months earlier for the second child. 相似文献
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David L. Tschirley Colin Poulton Nicholas Gergely Patrick Labaste John Baffes Duncan Boughton Grald Estur 《Development policy review : the journal of the Overseas Development Institute》2010,28(3):295-323
This article analyses the performance of cotton sectors across East, Southern, and West Africa, paying particular attention to the wide diversity of institutional arrangements that they now exhibit. It finds strong support for earlier contentions regarding trade‐offs between competition and coordination, and between the roles of public and private sectors. New insights provide concrete and context‐specific guidance to policy‐makers and stakeholders regarding the key challenges they will face and the risks they will need to manage as they work to improve productivity and ensure an equitable division of benefits within cotton sectors. 相似文献
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