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Dynamics Underlying (dynamics + underlying)
Selected AbstractsThe role of Late Holocene climate variability in the expansion of yellow birch in the western Great Lakes regionDIVERSITY AND DISTRIBUTIONS, Issue 5 2002Stephen T. Jackson Abstract. Pollen records from the western Great Lakes region of North America show substantial increases in birch pollen percentages during the late Holocene. The vegetational and population dynamics underlying the birch increase have received little attention, in part because of the inability to discriminate among species of birch based on pollen morphology. We used analyses of pollen and plant macrofossils from four lakes in the Upper Peninsula of Michigan to document that the birch pollen increase represents a regional expansion of yellow birch (Betula alleghaniensis) populations, which was initiated c. 4500 years ago. Whether yellow birch invaded the region at this time or simply expanded from small, previously established populations is not clear, although it probably did not grow near our study sites before the expansion. The initial expansion occurred during an independently documented period of high moisture and high water levels in Lake Michigan. A subsequent expansion in yellow birch abundance and distribution occurred c. 3000 years ago, coinciding with a second period of increased moisture and high lake-levels. The yellow birch expansion may have been modulated by millennial-scale climate variability, with most rapid expansion occurring during relatively wet periods. [source] Invasion impacts local species turnover in a successional systemECOLOGY LETTERS, Issue 9 2004Kathryn A. Yurkonis Abstract Exotic plant invasions are often associated with declines in diversity within invaded communities. However, few studies have examined the local community dynamics underlying these impacts. Changes in species richness associated with plant invasions must occur through local changes in extinction and/or colonization rates within the community. We used long-term, permanent plot data to evaluate the impacts of the exotic vine Lonicera japonica. Over time, species richness declined with increasing L. japonica cover. L. japonica reduced local colonization rates but had no effect on extinction rates. Furthermore, we detected significant reductions in the immigration of individual species as invasion severity increased, showing that some species are more susceptible to invasion than others. These findings suggest that declines in species richness associated with L. japonica invasion resulted from effects on local colonization rates only and not through the competitive displacement of established species. [source] Invasion impacts diversity through altered community dynamicsJOURNAL OF ECOLOGY, Issue 6 2005KATHRYN A. YURKONIS Summary 1Invading plant species often alter community structure, composition and, in some instances, reduce local diversity. However, the community dynamics underlying these impacts are relatively unknown. 2Declines in species richness with invasion may occur via displacement of resident species and/or reduction of seedling establishment by the invader. These two mechanisms differ in the demographic stage of the interaction. 3We document turnover dynamics using long-term permanent plot data to assess the mechanism(s) of invasion impacts of four exotic species on a mixed community of native and exotic species. These mechanisms were evaluated at both the neighbourhood (1-m2 plot) and population (individual species) scales. 4During invasion, species richness declined with increasing invader cover for three of the four invaders. All invaders reduced colonization rates, but had no effect on extinction rates at the neighbourhood scale. Populations differed in their susceptibility to invasion impacts, with significant reductions in colonization for 10 of 25 (40%) species and increases in extinction for only 4 of 29 (14%) species. 5At neighbourhood and population scales, influences of invasion on community dynamics were essentially the same for all invaders regardless of life-form. While individual resident species had some increase in extinction probability, community richness impacts were largely driven by colonization limitation. 6The consistency of invasion impacts across life-forms suggests establishment limitation as a general mechanism of invasion impact. This common causal mechanism should be explored in other systems to determine the extent of its generality. [source] Bayesian geoadditive sample selection modelsJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES C (APPLIED STATISTICS), Issue 3 2010Manuel Wiesenfarth Summary., Sample selection models attempt to correct for non-randomly selected data in a two-model hierarchy where, on the first level, a binary selection equation determines whether a particular observation will be available for the second level, i.e. in the outcome equation. Ignoring the non-random selection mechanism that is induced by the selection equation may result in biased estimation of the coefficients in the outcome equation. In the application that motivated this research, we analyse relief supply in earthquake-affected communities in Pakistan, where the decision to deliver goods represents the dependent variable in the selection equation whereas factors that determine the amount of goods supplied are analysed in the outcome equation. In this application, the inclusion of spatial effects is necessary since the available covariate information on the community level is rather scarce. Moreover, the high temporal dynamics underlying the immediate delivery of relief supply after a natural disaster calls for non-linear, time varying effects. We propose a geoadditive sample selection model that allows us to address these issues in a general Bayesian framework with inference being based on Markov chain Monte Carlo simulation techniques. The model proposed is studied in simulations and applied to the relief supply data from Pakistan. [source] Identifying challenges in supervising school psychologists,PSYCHOLOGY IN THE SCHOOLS, Issue 6 2010Virginia Smith Harvey Previous studies suggest that the majority of school psychologists do not believe they receive sufficient supervision, despite a growing body of research providing empirical support for supervision to maintain and improve skills. This study explores the dynamics underlying the challenges of providing adequate supervision to school psychologists. Findings suggest that supervision of school psychologists is characterized by challenges that extend beyond the traditional demarcations of clinical and administrative supervision typical in clinical settings. Supervisors of school psychologists encounter systemic challenges, unique to school settings, which must be addressed for their supervisees to be able to function successfully. The findings suggest that a clinical,administrative,systemic model of supervision is most appropriate in the supervision of school psychologists. © 2010 Wiley Periodicals, Inc. [source] The acute,aged care interface: Exploring the dynamics of ,bed blocking'AUSTRALASIAN JOURNAL ON AGEING, Issue 3 2008Catherine M Travers Objective: To understand the dynamics underlying ,bed-blocking' in Australian public hospitals that is frequently blamed on older patients. Methods: Analysis of primary and secondary data of utilisation patterns of hospital and aged care services by older Australians. Results: A model of the dynamics at the acute,aged care interface was developed, in which the pathway into permanent high-care Residential Aged Care (RAC) is conceptualised as competing queues for available places by applicants from the hospital, the community and from within RAC facilities. The hospital effectively becomes a safety net to accommodate people with high-care needs who cannot be admitted into RAC in a timely manner. Conclusion: The model provides a useful tool to explore some of the issues that give rise to access-block within the public hospital system. Access-block cannot be understood by viewing the hospital system in isolation from other sectors that support the health and well-being of older Australians. [source] | ||||||||||