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Transient Dynamics (transient + dynamics)
Selected AbstractsSensitivity analysis of transient population dynamicsECOLOGY LETTERS, Issue 1 2007Hal Caswell Abstract Short-term, transient population dynamics can differ in important ways from long-term asymptotic dynamics. Just as perturbation analysis (sensitivity and elasticity) of the asymptotic growth rate reveals the effects of the vital rates on long-term growth, the perturbation analysis of transient dynamics can reveal the determinants of short-term patterns. In this article, I present a completely new approach to transient sensitivity and elasticity analysis, using methods from matrix calculus. Unlike previous methods, this approach applies not only to linear time-invariant models but also to time-varying, subsidized, stochastic, nonlinear and spatial models. It is computationally simple, and does not require calculation of eigenvalues or eigenvectors. The method is presented along with applications to plant and animal populations. [source] Computational significance of transient dynamics in cortical networksEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2008Daniel Durstewitz Abstract Neural responses are most often characterized in terms of the sets of environmental or internal conditions or stimuli with which their firing rate are correlated increases or decreases. Their transient (nonstationary) temporal profiles of activity have received comparatively less attention. Similarly, the computational framework of attractor neural networks puts most emphasis on the representational or computational properties of the stable states of a neural system. Here we review a couple of neurophysiological observations and computational ideas that shift the focus to the transient dynamics of neural systems. We argue that there are many situations in which the transient neural behaviour, while hopping between different attractor states or moving along ,attractor ruins', carries most of the computational and/or behavioural significance, rather than the attractor states eventually reached. Such transients may be related to the computation of temporally precise predictions or the probabilistic transitions among choice options, accounting for Weber's law in decision-making tasks. Finally, we conclude with a more general perspective on the role of transient dynamics in the brain, promoting the view that brain activity is characterized by a high-dimensional chaotic ground state from which transient spatiotemporal patterns (metastable states) briefly emerge. Neural computation has to exploit the itinerant dynamics between these states. [source] Resident and transient dynamics, site fidelity and survival in wintering Blackcaps Sylvia atricapilla: evidence from capture,recapture analysesIBIS, Issue 2 2007EDUARDO J. BELDA In their winter quarters, migrant birds may either remain within a small area (resident strategy) or move frequently over a large area looking for locally abundant food (transient strategy). It has been suggested that both strategies could simultaneously occur in the same population. We used time-since-marking capture,recapture models to infer the coexistence of these two behavioural strategies (transient and resident) among wintering Blackcaps Sylvia atricapilla using weekly recapture data over a 7-year period. A related question is whether Blackcaps, if surviving to the next winter, always return to the same wintering area, so we also used this approach to analyse winter site fidelity and to estimate annual survival probabilities. Model selection supported the existence of heterogeneity in survival estimates for both the within-season and the interannual survival probabilities, i.e. there was evidence for the existence of transients. It was estimated that 26% of the Blackcaps were resident during the winter. Mean apparent annual survival probability was 0.46 (se = ±0.11). However, there was some evidence suggesting that not all individuals showed winter site fidelity. The estimated proportion of individuals that, if alive, returned to the wintering area was 28%. This is the first study to show the existence of these two behavioural strategies (residence and transience) among wintering Blackcaps, and the first confirming this pattern using capture,recapture models. These models considering transient and resident dynamics may become an important tool with which to analyse wintering strategies. [source] A new computational method for transient dynamics including the low- and the medium-frequency rangesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005Pierre Ladevèze Abstract This paper deals with a new computational method for transient dynamic analysis which enables one to cover both the low- and medium-frequency ranges. This is a frequency approach in which the low-frequency part is obtained through a classical technique while the medium-frequency part is handled through the variational theory of complex rays (VTCR) initially introduced for vibrations. Preliminary examples are shown. Copyright © 2005 John Wiley & Sons, Ltd. [source] 3D dynamics of discrete element systems comprising irregular discrete elements,integration solution for finite rotations in 3DINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2003A. Munjiza Abstract An algorithm for transient dynamics of discrete element systems comprising a large number of irregular discrete elements in 3D is presented. The algorithm is a natural extension of contact detection, contact interaction and transient dynamics algorithms developed in recent years in the context of discrete element methods and also the combined finite-discrete element method. It complements the existing algorithmic procedures enabling transient motion including finite rotations of irregular discrete elements in 3D space to be accurately integrated. Copyright © 2002 John Wiley & Sons, Ltd. [source] Matrix models for a changeable world: the importance of transient dynamics in population managementJOURNAL OF APPLIED ECOLOGY, Issue 3 2010Thomas H. G. Ezard Summary 1.,Matrix population models are tools for elucidating the association between demographic processes and population dynamics. A large amount of useful theory pivots on the assumption of equilibrium dynamics. The preceding transient is, however, of genuine conservation concern as it encompasses the short-term impact of natural or anthropogenic disturbance on the population. 2.,We review recent theoretical advances in deterministic transient analysis of matrix projection models, considering how disturbance can alter population dynamics by provoking a new population trajectory. 3.,We illustrate these impacts using plant and vertebrate systems across contiguous and fragmented landscapes. 4.,Short-term responses are of fundamental relevance for applied ecology, because the time-scale of transient effects is often similar to the length of many conservation projects. Investigation of the immediate, post-disturbance phase is vital for understanding how population processes respond to widespread disturbance in the short- and into the long term. 5.,Synthesis and applications.,Transient analysis is critical for understanding and predicting the consequences of management activities. By considering short-term population responses to perturbations, especially in long-lived species, managers can develop more informed strategies for species harvesting or controlling of invasive species. [source] What happens if density increases?ANIMAL CONSERVATION, Issue 4 2007Conservation implications of population influx into refuges Abstract Sudden catastrophic events like fires, hurricanes, tsunamis, landslides and deforestation increase population densities in habitat fragments, as fleeing animals encroach into these refuges. Such sudden overcrowding will trigger transient fluctuations in population size in the refuges, which may expose refuge populations to an increased risk of extinction. Until recently, detailed information about the operation of density dependence in stage-structured populations, and tools for quantifying the effects of transient dynamics, have not been available, so that exploring the extinction risk of such transient fluctuations has been intractable. Here, we use such recently developed tools to show that extinction triggered by overcrowding can threaten populations in refuges. Apart from situations where density dependence acts on survival, our results indicate that short-lived species may be more at risk than longer-lived species. Because dynamics in local populations may be critical for the preservation of metapopulations and rare species, we argue that this aspect warrants further attention from conservation biologists. [source] Savanna dynamics in central Texas: just succession?APPLIED VEGETATION SCIENCE, Issue 1 2009Norma L. Fowler Abstract Question: What is the best way to model savanna dynamics? Specifically, under what conditions is a traditional succession model, i.e., a model of ordered, uni-directional change in the plant community, better than a state-and-transition model? Location: Central Texas savannas. Methods: We describe three examples of successional processes in central Texas savannas: (a) woody plant encroachment, (b) invasion by a non-native grass, and (c) establishment of different grass species in highly disturbed sites. Results and Conclusions: Savanna dynamics are now commonly conceptualized with state-and-transition models. However, in some situations a traditional succession model may be more appropriate or more useful. Succession models may better fit current ecological reality, as found in central Texas. Succession models emphasize transient dynamics rather than an (often unknown) endpoint, and direct us towards relevant literature from non-savanna ecosystems. Succession models may be particularly useful for land management and restoration, and where woody plant encroachment and/or invasions by non-native species control vegetation dynamics. [source] | ||||||||||