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Matrix Population Models (matrix + population_models)
Selected AbstractsMatrix 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] Partial life cycle analysis: a model for pre-breeding census dataOIKOS, Issue 3 2001Madan K. Oli Matrix population models have become popular tools in research areas as diverse as population dynamics, life history theory, wildlife management, and conservation biology. Two classes of matrix models are commonly used for demographic analysis of age-structured populations: age-structured (Leslie) matrix models, which require age-specific demographic data, and partial life cycle models, which can be parameterized with partial demographic data. Partial life cycle models are easier to parameterize because data needed to estimate parameters for these models are collected much more easily than those needed to estimate age-specific demographic parameters. Partial life cycle models also allow evaluation of the sensitivity of population growth rate to changes in ages at first and last reproduction, which cannot be done with age-structured models. Timing of censuses relative to the birth-pulse is an important consideration in discrete-time population models but most existing partial life cycle models do not address this issue, nor do they allow fractional values of variables such as ages at first and last reproduction. Here, we fully develop a partial life cycle model appropriate for situations in which demographic data are collected immediately before the birth-pulse (pre-breeding census). Our pre-breeding census partial life cycle model can be fully parameterized with five variables (age at maturity, age at last reproduction, juvenile survival rate, adult survival rate, and fertility), and it has some important applications even when age-specific demographic data are available (e.g., perturbation analysis involving ages at first and last reproduction). We have extended the model to allow non-integer values of ages at first and last reproduction, derived formulae for sensitivity analyses, and presented methods for estimating parameters for our pre-breeding census partial life cycle model. We applied the age-structured Leslie matrix model and our pre-breeding census partial life cycle model to demographic data for several species of mammals. Our results suggest that dynamical properties of the age-structured model are generally retained in our partial life cycle model, and that our pre-breeding census partial life cycle model is an excellent proxy for the age-structured Leslie matrix model. [source] Modelling life history strategies with capture,recapture data: Evolutionary demography of the water skink Eulamprus tympanumAUSTRAL ECOLOGY, Issue 4 2001Simon P. Blomberg Abstract Matrix population models, elasticity analysis and loop analysis can potentially provide powerful techniques for the analysis of life histories. Data from a capture,recapture study on a population of southern highland water skinks (Eulamprus tympanum) were used to construct a matrix population model. Errors in elasticities were calculated by using the parametric bootstrap technique. Elasticity and loop analyses were then conducted to identify the life history stages most important to fitness. The same techniques were used to investigate the relative importance of fast versus slow growth, and rapid versus delayed reproduction. Mature water skinks were long-lived, but there was high immature mortality. The most sensitive life history stage was the subadult stage. It is suggested that life history evolution in E. tympanum may be strongly affected by predation, particularly by birds. Because our population declined over the study, slow growth and delayed reproduction were the optimal life history strategies over this period. Although the techniques of evolutionary demography provide a powerful approach for the analysis of life histories, there are formidable logistical obstacles in gathering enough high-quality data for robust estimates of the critical parameters. [source] General guidelines for invasive plant management based on comparative demography of invasive and native plant populationsJOURNAL OF APPLIED ECOLOGY, Issue 4 2008Satu Ramula Summary 1General guidelines for invasive plant management are currently lacking. Population declines may be achieved by focusing control on demographic processes (survival, growth, fecundity) with the greatest impact on population growth rate. However, we often have little demographic information on populations in the early stages of an invasion when control can be most effective. Here we determine whether synthesis of existing demographic data on invasive and native plant populations can address this knowledge problem. 2We compared population dynamics between invasive and native species using published matrix population models for 21 invasive and 179 native plant species. We examined whether the population growth rate responsiveness to survival, growth and fecundity perturbations varied between invasive and native species, and determined which demographic processes of invaders to target for reductions in population growth rate. 3Invaders had higher population growth rates (,) than natives, resulting in differences in demographic processes. Perturbations of growth and fecundity transitions (elasticities) were more important for population growth of invaders, whereas perturbations of survival had greater importance for population growth of natives. 4For both invasive and native species, elasticities of , to survival increased with life span and decreased with ,; while elasticities to growth and fecundity decreased with life span and increased with ,. 5For long-lived invaders, simulated reductions in either survival, growth or fecundity transitions were generally insufficient to produce population declines, whereas multiple reductions in either survival + growth or survival + fecundity were more effective. For short-lived invaders, simulated reductions in growth or fecundity and all pairwise multiple reductions produced population declines. 6Synthesis and applications. Life history and population growth rate of invasive species are important in the selection of control targets. For rapidly growing populations of short-lived invaders, growth and fecundity transitions should be prioritized as control targets over survival transitions. For long-lived invaders, simultaneous reductions in more than one demographic process, preferably survival and growth, are usually required to ensure population decline. These general guidelines can be applied to rapidly growing new plant invasions and at the invasion front where detailed demographic data on invasive species are lacking. [source] Heterogeneous grazing causes local extinction of edible perennial shrubs: a matrix analysisJOURNAL OF APPLIED ECOLOGY, Issue 2 2001L.P. Hunt Summary 1Population modelling and field measurements of births, growth and deaths were used to investigate the long-term change in abundance of Atriplex vesicaria (Chenopodiaceae), a long-lived, palatable, perennial shrub, under sheep grazing. Of particular interest was whether A. vesicaria is at risk of being eliminated throughout grazed paddocks when the recommended practice of continuous grazing at conservative stocking rates is employed. 2Time-invariant matrix population models indicated that the A. vesicaria population was in decline over much of the study paddock, but the rate of decline was greatest nearer to the water point (population growth rate , , 0·8). Time-varying stochastic matrix models projected that the A. vesicaria population would become locally extinct at most sites up to approximately 2200 m from water, occurring first closer to water (within 12,29 years). The population was stable (i.e. , , 1) at sites greater than 2200 m from water over the projection period of 100 years. 3Decreases in adult survival and recruitment made the largest contributions to reductions in the population growth rate. However, there were spatial patterns centred on the water point in the degree to which particular demographic processes contributed to these reductions, because of a grazing gradient and the differential sensitivity of demographic processes to grazing. Thus decreases in recruitment contributed to reductions in the population growth rate at greater distances. Such responses, together with the sensitivity of the population growth rate to these processes, determined the spatial pattern in population growth. 4The results suggest that piospheres (i.e. the zone of impact) continue to expand over many years under set-stocking so that the area around the water point that is devoid of A. vesicaria becomes larger. The process of expansion appears to first involve the inhibition of recruitment, followed by eventual mortality of established shrubs. 5The large contribution of adult survival to the population growth rate in A. vesicaria suggests that minimizing the mortality of established adults should be a priority for management. This is likely to involve resting from grazing at critical times such as during extended dry periods. This may also permit increased levels of recruitment during subsequent moister periods. [source] The accuracy of matrix population model projections for coniferous trees in the Sierra Nevada, CaliforniaJOURNAL OF ECOLOGY, Issue 4 2005PHILLIP 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] Limitation of population recovery: a stochastic approach to the case of the emperor penguinOIKOS, Issue 9 2009Stéphanie Jenouvrier Major population crashes due to natural or human-induced environmental changes may be followed by recoveries. There is a growing interest in the factors governing recovery, in hopes that they might guide population conservation and management, as well as population recovery following a re-introduction program. The emperor penguin Aptenodytes forsteri population in Terre Adélie, Antarctica, declined by 50% during a regime shift in the mid-1970s, when abrupt changes in climate and ocean environment regimes affected the entire Southern Ocean ecosystem. Since then the population has remained stable and has not recovered. To determine the factors limiting recovery, we examined the consequences of changes in survival and breeding success after the regime shift. Adult survival recovered to its pre-regime shift level, but the mean breeding success declined and the variance in breeding success increased after the regime shift. Using stochastic matrix population models, we found that if the distribution of breeding success observed prior to the regime shift had been retained, the emperor penguin population would have recovered, with a median time to recovery of 36 years. The observed distribution of breeding success after the regime shift makes recovery very unlikely. This indicates that the pattern of breeding success is sufficient to have prevented emperor penguin population recovery. The population trajectory predicted on the basis of breeding success agrees with the observed trajectory. This suggests that the net effect of any facors other than breeding success must be small. We found that the probability of recovery and the time to recovery depend on both the mean and variance of breeding success. Increased variance in breeding success increases the probability of recovery when mean success is low, but has the opposite effect when the mean is high. This study shows the important role of breeding success in determining population recovery for a long-lived species and demonstrates that demographic mechanisms causing population crash can be different from those preventing population recovery. [source] | ||||||||||