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Classic Model (classic + model)
Selected AbstractsDo biotic interactions shape both sides of the humped-back model of species richness in plant communities?ECOLOGY LETTERS, Issue 7 2006Richard Michalet Abstract A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity,diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity. [source] Achievement orientations from subjective histories of success: Promotion pride versus prevention prideEUROPEAN JOURNAL OF SOCIAL PSYCHOLOGY, Issue 1 2001E. Tory Higgins A new task goal elicits a feeling of pride in individuals with a subjective history of success, and this achievment pride produces anticipatory goal reactions that energize and direct behavior to approach the task goal. By distinguishing between promotion pride and prevention pride, the present paper extends this classic model of achievement motivation. Regulatory focus theory (Higgins, 1997) distinguishes between a promotion focus on hopes and accomplishments (gains) and a prevention focus on safety and responsibilities (non-losses). We propose that a subjective history of success with promotion-related eagerness (promotion pride) orients individuals toward using eagerness means to approach a new task goal, whereas a subjective history of success with prevention-related vigilance (prevention pride) orients individuals toward using vigilance means to approach a new task goal. Studies 1,3 tested this proposal by examining the relations between a new measure of participants' subjective histories of promotion success and prevention success (the Regulatory Focus Questionnaire (RFQ)) and their achievement strategies in different tasks. Study 4 examined the relation between participants' RFQ responses and their reported frequency of feeling eager or vigilant in past task engagements. Study 5 used an experimental priming technique to make participants temporarily experience either a subjective history of promotion success or a subjective history of prevention success. For both chronic and situationally induced achievement pride, these studies found that when approaching task goals individuals with promotion pride use eagerness means whereas individuals with prevention pride use vigilance means. Copyright © 2001 John Wiley & Sons, Ltd. [source] Further understanding of the ,-globin locus regulation at the molecular level: looping or linking models?GENES TO CELLS, Issue 9 2002Yi Tang The human ,-globin locus is a classic model of the eukaryotic multigene family with tissue- and temporally specific expression. Over the past few years, great advances have been achieved in studies of ,-globin locus regulation. The dominant role of the ,-globin locus control region (LCR) in chromatin opening and developmental switching has been challenged, and elements beyond the LCR have been studied in depth. More recently, the fields of research have been expanded to intergenic transcription, nuclear localization and histone modification. Several models have been proposed to elucidate the regulation mechanism; among them, the looping and linking models are the most prevalent. Different models are the summarization of the observations made at different times and a persuasive model must be based on a systematic understanding of the numerous observations. The objective of this review is to provide an overview of progress in the area of ,-globin regulation and then to discuss models for it. [source] A new shallow water model with polynomial dependence on depthMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 5 2008José M. Rodríguez Abstract In this paper, we study two-dimensional Euler equations in a domain with small depth. With this aim, we introduce a small non-dimensional parameter , related to the depth and we use asymptotic analysis to study what happens when , becomes small. We obtain a model for , small that, after coming back to the original domain, gives us a shallow water model that considers the possibility of a non-constant bottom, and the horizontal velocity has a dependence on z introduced by the vorticity when it is not zero. This represents an interesting novelty with respect to shallow water models found in the literature. We stand out that we do not need to make a priori assumptions about velocity or pressure behaviour to obtain the model. The new model is able to approximate the solutions to Euler equations with dependence on z (reobtaining the same velocities profile), whereas the classic model just obtains the average velocity. Copyright © 2007 John Wiley & Sons, Ltd. [source] Histological and Ultrastructural Characterization of Developing Miniature Pig Salivary Glands,THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 7 2010Jian Zhou Abstract Salivary glands are a classic model of organ development and differentiation. Miniature pigs are considered as a unique animal model for salivary gland researchers in the fields of gene transfer, radiation damage, and functional reconstruction. However, there is little information about the development of miniature pig salivary glands. The present article was designed to study the developmental stages of salivary glands in miniature pigs using histological and ultrastructural methods. Sections from E40, E60, E80, E95 embryos, and P0 pups were stained with hematoxylin,eosin, Alcian blue, or periodic acid-schiff. Selected specimens were also processed for electron microscopy. The development of the miniature pig salivary glands can be divided into five different stages that refer to the stages of the developing mouse submandibular gland. The histological characteristics of the miniature pig salivary glands at different developmental stages were synchronously verified at the ultrastructural level. Interestingly, the development of the miniature pig parotid gland trailed that of the submandibular gland by ,15 days. Our study provides first-hand data regarding the morphological organogenesis of salivary glands in the miniature pig and provides a foundation for further research on this model. Anat Rec 293:1227,1239, 2010. © 2010 Wiley-Liss, Inc. [source] Regenerated synapses in lamprey spinal cord are sparse and small even after functional recovery from injuryTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 14 2010Paul A. Oliphint Abstract Despite the potential importance that synapse regeneration plays in restoring neuronal function after spinal cord injury (SCI), even the most basic questions about the morphology of regenerated synapses remain unanswered. Therefore, we set out to gain a better understanding of central synapse regeneration by examining the number, distribution, molecular composition, and ultrastructure of regenerated synapses under conditions in which behavioral recovery from SCI was robust. To do so, we used the giant reticulospinal (RS) neurons of lamprey spinal cord because they readily regenerate, are easily identifiable, and contain large synapses that serve as a classic model for vertebrate excitatory neurotransmission. Using a combination of light and electron microscopy, we found that regenerated giant RS synapses regained the basic structures and presynaptic organization observed at control giant RS synapses at a time when behavioral recovery was nearly complete. However, several obvious differences remained. Most strikingly, regenerated giant RS axons produced very few synapses. In addition, presynaptic sites within regenerated axons were less complex, had fewer vesicles, and had smaller active zones than normal. In contrast, the densities of presynapses and docked vesicles were nearly restored to control values. Thus, robust functional recovery from SCI can occur even when the structures of regenerated synapses are sparse and small, suggesting that functional recovery is due to a more complex set of compensatory changes throughout the spinal network. J. Comp. Neurol. 518:2854,2872, 2010. © 2010 Wiley-Liss, Inc. [source] Revisiting the neighbor exclusion model and its applicationsBIOPOLYMERS, Issue 1 2010Marcio S. Rocha Abstract We review the neighbor exclusion model and some of its applications to analyze the binding data of DNA-ligand complexes. We revisit the closed form of the model developed by McGhee and von Hippel in 1974, showing that this classic model can be used to help studying the behavior of DNA contour and persistence lengths when interacting with intercalating ligands. We present methods to quantitatively analyze the variation of these two quantities, allowing one to determine important parameters of the interaction such as the intrinsic binding constant and the exclusion number of the ligand. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 1,7, 2010. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||