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Projection Models (projection + models)

Distribution by Scientific Domains
Life Sciences62%

Kinds of Projection Models

  • population projection models
    		•

    Selected Abstracts

    Demographic analysis of continuous-time life-history models

    ECOLOGY LETTERS, Issue 1 2008
    André M. De Roos
    Abstract I present a computational approach to calculate the population growth rate, its sensitivity to life-history parameters and associated statistics like the stable population distribution and the reproductive value for exponentially growing populations, in which individual life history is described as a continuous development through time. The method is generally applicable to analyse population growth and performance for a wide range of individual life-history models, including cases in which the population consists of different types of individuals or in which the environment is fluctuating periodically. It complements comparable methods developed for discrete-time dynamics modelled with matrix or integral projection models. The basic idea behind the method is to use Lotka's integral equation for the population growth rate and compute the integral occurring in that equation by integrating an ordinary differential equation, analogous to recently derived methods to compute steady-states of physiologically structured population models. I illustrate application of the method using a number of published life-history models. [source]

    Projected population-level effects of thiobencarb exposure on the mysid, Americamysis bahia, and extinction probability in a concentration-decay exposure system

    ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2005
    Sandy Raimondo
    Abstract Population-level effects of the mysid, Americamysis bahia, exposed to varying thiobencarb concentrations were estimated using stage-structured matrix models. A deterministic density-independent matrix model estimated the decrease in population growth rate (,) with increasing thiobencarb concentration. An elasticity analysis determined that survival of middle stages provided the largest contribution to ,. Decomposing the effects of , in terms of changes in the matrix components determined that reduced reproduction had a large influence on population dynamics at lower thiobencarb concentrations, whereas reduced survivorship had the largest impact on populations at higher concentrations. A simulation model of a concentration-decay system was developed to demonstrate the importance of integrating chemical half-life and management practices in determining population viability. In this model, mysids were originally exposed to a high thiobencarb concentration (300 ,g/L) that decayed an order of magnitude in the number of mysid generations corresponding to thiobencarb half-life values under three different exposure regimes. Environmental stochasticity was added to the model to estimate the cumulative extinction probability of mysids exposed to fluctuating concentrations of thiobencarb in random environments. The cumulative extinction probability increased with thiobencarb half-life, stochasticity, and concentration present at the time of a new exposure. The model demonstrated the expansion of population projection models in determining the ecological impact of a population exposed to pesticides. [source]

    Matrix models for a changeable world: the importance of transient dynamics in population management

    JOURNAL OF APPLIED ECOLOGY, Issue 3 2010
    Thomas 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]

    Population responses to natural and human-mediated disturbances: assessing the vulnerability of the common hippopotamus (Hippopotamus amphibius)

    AFRICAN JOURNAL OF ECOLOGY, Issue 3 2007
    Rebecca Lewison
    Abstract Vulnerable wildlife populations can face a suite of anthropogenic activities that may threaten their persistence. However, human-mediated disturbances are likely to be coincident with natural disturbances that also influence a population. This synergism is often neglected in population projection models. Here I evaluate the effects of natural (rainfall fluctuation) and human disturbances (habitat loss and unregulated hunting) using a multi-matrix environmental state population model for the common hippopotamus (Hippopotamus amphibius). By evaluating each disturbance type (natural and human) alone and then together, I explicitly consider the importance of incorporating realistic environmental variability into population projection models. The model population was most strongly affected by moderate habitat loss, which yielded the highest probability of crossing the risk thresholds over the 60 year time period, although these probabilities were relatively low (,0.31). However, the likelihood of crossing the risk thresholds were two to five times as high when human-mediated and natural disturbances were considered together. When these probabilities were calculated per year of the simulation, the results suggested that even relatively mild human disturbances, when considered in conjunction with realistic natural disturbance, resulted in a high probability (>0.50) of substantial declines within decades. The model highlights the importance of integrating realistic natural disturbances into population models, and suggests that, despite locally abundant populations, protected hippopotamus populations may decline over the next 60 years in response to a combination of environmental fluctuations and human-mediated threats. Résumé Les populations sauvages vulnérables peuvent être confrontées à une suite d'activités humaines qui risquent de menacer leur persistance. Cependant, les perturbations causées par l'homme sont susceptibles de coïncider avec des perturbations naturelles qui influencent aussi une population. Cette synergie est souvent négligée dans les modèles de projection des populations. Ici, j'évalue les effets des perturbations naturelles (fluctuations des chutes de pluie) et humaines (perte d'habitat et chasse non réglementée) en utilisant une chaîne de matrices aléatoires pour l'état environnemental d'une population d'hippopotames (Hippopotamus amphibius). En évaluant chaque type de perturbation (naturelle et humaine) seul et ensemble, je considère explicitement l'importance qu'il y a d'intégrer une variabilité environnementale réaliste dans les modèles de projection des populations. La population modèle était surtout affectée par une perte d'habitat modérée, qui réunissait la plus grande probabilité de dépasser les seuils de risque en une période de 60 ans, même si cette probabilitéétait relativement faible (,0,31). Cependant, la probabilité de franchir les seuils de risque était 2 à 5 fois plus grande lorsque les perturbations d'origine humaine et naturelle étaient considérées ensemble. Lorsque ces probabilités étaient calculées par année, les résultats de la simulation suggéraient que même des perturbations humaines faibles, quand on les considérait en conjonction avec une perturbation naturelle réaliste, résultaient en une forte probabilité (>0,50) de déclin substantiel en quelques décennies. Le modèle souligne l'importance qu'il y a d'intégrer les perturbations naturelles réalistes dans les modèles de population et suggère que, malgré des populations localement abondantes, les populations protégées d'hippopotames peuvent décliner au cours des 60 prochaines années en réaction à une combinaison de fluctuations environnementales et de menaces d'origine humaine. [source]

    The accuracy of matrix population model projections for coniferous trees in the Sierra Nevada, California

    JOURNAL OF ECOLOGY, Issue 4 2005
    PHILLIP J. VAN MANTGEM
    Summary 1We assess the use of simple, size-based matrix population models for projecting population trends for six coniferous tree species in the Sierra Nevada, California. We used demographic data from 16 673 trees in 15 permanent plots to create 17 separate time-invariant, density-independent population projection models, and determined differences between trends projected from initial surveys with a 5-year interval and observed data during two subsequent 5-year time steps. 2We detected departures from the assumptions of the matrix modelling approach in terms of strong growth autocorrelations. We also found evidence of observation errors for measurements of tree growth and, to a more limited degree, recruitment. Loglinear analysis provided evidence of significant temporal variation in demographic rates for only two of the 17 populations. 3Total population sizes were strongly predicted by model projections, although population dynamics were dominated by carryover from the previous 5-year time step (i.e. there were few cases of recruitment or death). Fractional changes to overall population sizes were less well predicted. Compared with a null model and a simple demographic model lacking size structure, matrix model projections were better able to predict total population sizes, although the differences were not statistically significant. Matrix model projections were also able to predict short-term rates of survival, growth and recruitment. Mortality frequencies were not well predicted. 4Our results suggest that simple size-structured models can accurately project future short-term changes for some tree populations. However, not all populations were well predicted and these simple models would probably become more inaccurate over longer projection intervals. The predictive ability of these models would also be limited by disturbance or other events that destabilize demographic rates. [source]

    A long-term study of neighbour-regulated demography during a decline in forest species diversity

    JOURNAL OF VEGETATION SCIENCE, Issue 1 2006
    Lin Yi-ching
    Abstract Question: Did disturbance, no density-dependence of the dominant species, and negative neighbourhood interactions on rare species affect tree demography during a decline in species diversity associated with the increase of Acer saccharum from 1939,2001? Hypotheses: 1. The rise in dominance of A. saccharum was because of its advantage in disturbances and lack of density-dependence of its demography. 2. Rare species were not favoured by disturbances, including those from Dutch elm disease, and demonstrated negative neighbourhood interactions with A. saccharum. Location: Brownfield Woods in Illinois, USA. Methods: Historical maps of trees (, 7.6 cm DBH) from 1939, 1951, 1988, and 2001 in 16 quadrats (48 m × 68 m) were used to compare demography of eight tree species. Effects of disturbances, density-dependence, and neighbourhood interactions on mortality and recruitment of tree species within a 6-m radius of individual target trees were studied. Results: A. saccharum demonstrated a demographic advantage over rare species. It had lower mortality and higher recruitment rates. Disturbances facilitated recruitment of A. saccharum, but did not enhance rare species. Density-dependence of both mortality and recruitment of A. saccharum occurred, but population projection models indicated that ecological conditions became more favourable for A. saccharum in the past 62 years. Furthermore, negative neighbourhood interactions were detected between rare species and A. saccharum. The increase in neighbouring A. saccharum significantly increased mortality and reduced recruitment of the rare species. Conclusions: The general disturbance regime, enhanced by Dutch elm disease, in Brownfield Woods facilitated the rise of dominance of A. saccharum. Meanwhile, rare species declined as a result of their disadvantage in disturbance and negative neighbourhood interactions with A. saccharum. [source]

    Recommendations to improve space projection models and university space usage

    NEW DIRECTIONS FOR INSTITUTIONAL RESEARCH, Issue 135 2007
    Sam W. StigallArticle first published online: 24 SEP 200
    This chapter reviews the current space projection model for the State of Texas Higher Education Coordinating Board (THECB) and compares this methodology to other select states. [source]

    DIPKIP: A CONNECTIONIST KNOWLEDGE MANAGEMENT SYSTEM TO IDENTIFY KNOWLEDGE DEFICITS IN PRACTICAL CASES

    COMPUTATIONAL INTELLIGENCE, Issue 1 2010
    Álvaro Herrero
    This study presents a novel, multidisciplinary research project entitled DIPKIP (data acquisition, intelligent processing, knowledge identification and proposal), which is a Knowledge Management (KM) system that profiles the KM status of a company. Qualitative data is fed into the system that allows it not only to assess the KM situation in the company in a straightforward and intuitive manner, but also to propose corrective actions to improve that situation. DIPKIP is based on four separate steps. An initial "Data Acquisition" step, in which key data is captured, is followed by an "Intelligent Processing" step, using neural projection architectures. Subsequently, the "Knowledge Identification" step catalogues the company into three categories, which define a set of possible theoretical strategic knowledge situations: knowledge deficit, partial knowledge deficit, and no knowledge deficit. Finally, a "Proposal" step is performed, in which the "knowledge processes",creation/acquisition, transference/distribution, and putting into practice/updating,are appraised to arrive at a coherent recommendation. The knowledge updating process (increasing the knowledge held and removing obsolete knowledge) is in itself a novel contribution. DIPKIP may be applied as a decision support system, which, under the supervision of a KM expert, can provide useful and practical proposals to senior management for the improvement of KM, leading to flexibility, cost savings, and greater competitiveness. The research also analyses the future for powerful neural projection models in the emerging field of KM by reviewing a variety of robust unsupervised projection architectures, all of which are used to visualize the intrinsic structure of high-dimensional data sets. The main projection architecture in this research, known as Cooperative Maximum-Likelihood Hebbian Learning (CMLHL), manages to capture a degree of KM topological ordering based on the application of cooperative lateral connections. The results of two real-life case studies in very different industrial sectors corroborated the relevance and viability of the DIPKIP system and the concepts upon which it is founded. [source]