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Demographic Models (demographic + models)
Selected AbstractsDemographic models and the management of endangered species: a case study of the critically endangered Seychelles magpie robinJOURNAL OF APPLIED ECOLOGY, Issue 5 2003Ken Norris Summary 1Demographic models are assuming an important role in management decisions for endangered species. Elasticity analysis and scope for management analysis are two such applications. Elasticity analysis determines the vital rates that have the greatest impact on population growth. Scope for management analysis examines the effects that feasible management might have on vital rates and population growth. Both methods target management in an attempt to maximize population growth. 2The Seychelles magpie robin Copsychus sechellarum is a critically endangered island endemic, the population of which underwent significant growth in the early 1990s following the implementation of a recovery programme. We examined how the formal use of elasticity and scope for management analyses might have shaped management in the recovery programme, and assessed their effectiveness by comparison with the actual population growth achieved. 3The magpie robin population doubled from about 25 birds in 1990 to more than 50 by 1995. A simple two-stage demographic model showed that this growth was driven primarily by a significant increase in the annual survival probability of first-year birds and an increase in the birth rate. Neither the annual survival probability of adults nor the probability of a female breeding at age 1 changed significantly over time. 4Elasticity analysis showed that the annual survival probability of adults had the greatest impact on population growth. There was some scope to use management to increase survival, but because survival rates were already high (> 0·9) this had a negligible effect on population growth. Scope for management analysis showed that significant population growth could have been achieved by targeting management measures at the birth rate and survival probability of first-year birds, although predicted growth rates were lower than those achieved by the recovery programme when all management measures were in place (i.e. 1992,95). 5Synthesis and applications. We argue that scope for management analysis can provide a useful basis for management but will inevitably be limited to some extent by a lack of data, as our study shows. This means that identifying perceived ecological problems and designing management to alleviate them must be an important component of endangered species management. The corollary of this is that it will not be possible or wise to consider only management options for which there is a demonstrable ecological benefit. Given these constraints, we see little role for elasticity analysis because, when data are available, a scope for management analysis will always be of greater practical value and, when data are lacking, precautionary management demands that as many perceived ecological problems as possible are tackled. [source] Migratory connectivity in a declining bird species: using feather isotopes to inform demographic modellingDIVERSITY AND DISTRIBUTIONS, Issue 4 2010Thomas S. Reichlin Abstract Aim, Conservation programmes for endangered migratory species or populations require locating and evaluating breeding, stopover and wintering areas. We used multiple stable isotopes in two endangered European populations of wrynecks, Jynx torquilla L., to locate wintering regions and assess the degree of migratory connectivity between breeding and wintering populations. Location, Switzerland and Germany. Methods, We analysed stable nitrogen (,15N), carbon (,13C) and hydrogen (,D) isotopes from wing feathers from two populations of wrynecks to infer their wintering origins and to assess the strength of migratory connectivity. We tested whether variation in feather isotopic values within the Swiss population was affected by bird age and collection year and then considered differences in isotopic values between the two breeding populations. We used isotopic values of summer- and winter-grown feathers to estimate seasonal distributions. Finally, we calculated a species-specific ,D discrimination factor between feathers and mean annual ,D values to assign winter-grown feathers to origin. Results, Bird age and collection year caused substantial isotopic variation in winter-grown feathers, which may be because of annually variable weather conditions, movements of birds among wintering sites and/or reflect asynchronous moulting or selection pressure. The large isotopic variance in winter-grown feathers nevertheless suggested low migratory connectivity for each breeding population, with partially overlapping wintering regions for the two populations. Main conclusions, Isotopic variance in winter-grown feathers of two breeding populations of wrynecks and their geographical assignment point to defined, albeit overlapping, wintering areas, suggesting both leapfrog migration and low migratory connectivity. On this basis, integrative demographic models can be built looking at seasonal survival patterns with links to local environmental conditions on both breeding and wintering grounds, which may elucidate causes of declines in migratory bird species. [source] Mortality differences by APOE genotype estimated from demographic synthesisGENETIC EPIDEMIOLOGY, Issue 2 2002Douglas C. EwbankArticle first published online: 10 JAN 200 Abstract The 4 allele of apolipoprotein E (APOE) is associated with increased risk of two major causes of death in low-mortality populations: ischemic heart disease and Alzheimer's disease. It is less common among centenarians than at younger ages. Therefore, it is likely that it is associated with excess risk of death. This article extends demographic models that estimate relative mortality risks from changes in gene frequencies with age. The resulting demographic synthesis combines gene frequencies with data on mortality by genotype from cohort studies. The model was applied to data from Denmark, Finland, France, Italy, Sweden, and the United States. Near age 50, the 3/4 genotype is associated with a risk of death of 1.34 times that of the 3/3 (95% CI 1.18,1.67). The relative risk for 4/4 is the square of the relative risk for 3/4, 1.81. The 2/3 genotype is protective with a relative risk of 0.84 (0.68,0.93) near age 50. These relative risks move toward 1.0 at the oldest ages and APOE genotype is associated with little variation in mortality over age 100. There are no significant differences in the relative risks by sex. There is little evidence of differences within Europe in the effects of APOE. This approach can be generalized to combine data on genetic risk factors for disease from a wide variety of study designs and sample characteristics. Genet. Epidemiol. 22:146,155, 2002. © 2002 Wiley-Liss, Inc. [source] Predicting time-specific changes in demographic processes using remote-sensing dataJOURNAL OF APPLIED ECOLOGY, Issue 2 2006HENRIK B. RASMUSSEN Summary 1Models of wildlife population dynamics are crucial for sustainable utilization and management strategies. Fluctuating ecological conditions are often key factors influencing both carrying capacity, mortality and reproductive rates in ungulates. To be reliable, demographic models should preferably rely on easily obtainable variables that are directly linked to the ecological processes regulating a population. 2We compared the explanatory power of rainfall, a commonly used proxy for variability in ecological conditions, with normalized differential vegetation index (NDVI), a remote-sensing index value that is a more direct measure of vegetation productivity, to predict time-specific conception rates of an elephant population in northern Kenya. Season-specific conception rates were correlated with both quality measures. However, generalized linear logistic models compared using Akaike's information criteria showed that a model based on the NDVI measure outperformed models based on rainfall measures. 3A predictive model based on coarse demographic data and the maximum seasonal NDVI value was able to trace the large variation in observed season-specific conception rates (Range 0,0·4), with a low median deviation from observed values of 0·07. 4By combining the model of season-specific conception rates with the average seasonal distribution of conception dates, the monthly number of conceptions (range 0,22) could be predicted within ±3 with 80% confidence. 5Synthesis and applications. The strong predictive power of the normalized differential vegetation index on time-specific variation in a demographic variable is likely to be generally applicable to resource-limited ungulate species occurring in ecologically variable ecosystems, and could potentially be a powerful factor in demographic population modelling. [source] Range-wide phylogeography and gene zones in Pinus pinaster Ait. revealed by chloroplast microsatellite markersMOLECULAR ECOLOGY, Issue 10 2007GABRIELE BUCCI Abstract Some 1339 trees from 48 Pinus pinaster stands were characterized by five chloroplast microsatellites, detecting a total of 103 distinct haplotypes. Frequencies for the 16 most abundant haplotypes (pk > 0.01) were spatially interpolated over a lattice made by 430 grid points. Fitting of spatially interpolated values on raw haplotype frequencies at the same geographical location was tested by regression analysis. A range-wide ,diversity map' based on interpolated haplotype frequencies allowed the identification of one ,hotspot' of diversity in central and southeastern Spain, and two areas of low haplotypic diversity located in the western Iberian peninsula and Morocco. Principal component analysis (PCA) carried out on haplotypes frequency surfaces allowed the construction of a colour-based ,synthetic' map of the first three PC components, enabling the detection of the main range-scale genetic trends and the identification of three main ,gene pools' for the species: (i) a ,southeastern' gene pool, including southeastern France, Italy, Corsica, Sardinia, Pantelleria and northern Africa; (ii) an ,Atlantic' gene pool, including all the western areas of the Iberian peninsula; and (iii) a ,central' gene pool, located in southeastern Spain. Multivariate and amova analyses carried out on interpolated grid point frequency values revealed the existence of eight major clusters (,gene zones'), whose genetic relationships were related with the history of the species. In addition, demographic models showed more ancient expansions in the eastern and southern ranges of maritime pine probably associated to early postglacial recolonization. The delineation of the gene zones provides a baseline for designing conservation areas in this key Mediterranean pine. [source] Bayesian inference of evolutionary history from chloroplast microsatellites in the cosmopolitan weed Capsella bursa - pastoris (Brassicaceae)MOLECULAR ECOLOGY, Issue 14 2005ALF CEPLITIS Abstract Besides showing an extraordinary degree of phenotypic variability, Capsella bursa-pastoris (Brassicaceae) is also one of the world's most common plant species and a serious weed in many countries. We have employed a coalescent-based Bayesian analysis of chloroplast microsatellite data to infer demographic and evolutionary parameters of this species. Two different demographic models applied to data from seven chloroplast microsatellite loci among 59 accessions show that the effective population size of C. bursa-pastoris is very small indicating a rapid expansion of the species, a result that is in accordance with fossil and historical data. Against this background, analysis of flowering time variation among accessions suggests that ecotypic differentiation in flowering time has occurred recently in the species' history. Finally, our results also indicate that mononucleotide repeat loci in the chloroplast genome can deteriorate in relatively short periods of evolutionary time. [source] | ||||||||||