Current Populations (current + population)

Distribution by Scientific Domains

Terms modified by Current Populations

  • current population size
  • current population survey
  • current population survey data

  • Selected Abstracts


    ,Thawing' of ,frozen' variation in an adventive, facultatively apomictic, clonal weed

    PLANT SPECIES BIOLOGY, Issue 2 2001
    Hazel Chapman
    Abstract Radiation of adventive, sexually reproducing organisms into a new environment has been well documented, but less is understood about the patterns and processes of geographical radiation in adventive species with uniparental reproduction (parthenogenesis or apomixis), usually associated with ,frozen' variation within maternal lineages. In this study we have used Pilosella officinarum to test the hypothesis that sexual reproduction becomes important in the radiation of adventive facultatively apomictic species. Within its native Europe P. officinarum is an extremely variable species, with eight subspecies and a range of ploidy levels. Pentaploids are always apomictic. However, early chromosome analyses of New Zealand adventive populations, carried out during the 1980s, discovered only pentaploid, apomictic clones. Similar observations were made in an early 1990s study of the same sites. Since then, a range of ploidy levels, including aneuploids, and a plethora of morphological variation, has been recorded. In this paper, we use a combination of image analysis and chromosome counts to show that sexual reproduction has become an important avenue for adaptive radiation in New Zealand populations of P. officinarum. Current populations probably comprise complex among-subspecies hybrids, and possibly among-species hybrids, which are at least partially capable of sexual reproduction and various forms of back-crossing. Somatic mutation may also play an important role in creating morphological variation. DNA fingerprinting did not contribute to this study because this technique failed to distinguish between morphological types observed in the field. [source]


    Density effects on life-history traits in a wild population of the great tit Parus major: analyses of long-term data with GIS techniques

    JOURNAL OF ANIMAL ECOLOGY, Issue 2 2006
    TEDDY A. WILKIN
    Summary 1Population density often has strong effects on the population dynamics and reproductive processes of territorial animals. However, most estimates of density-dependent effects use the number of breeding pairs per unit area in a given season and look for correlations across seasons, a technique that assigns the same density score to each breeding pair, irrespective of local spatial variation. 2In this study, we employed GIS techniques to estimate individual breeding densities for great tits breeding in Wytham Woods UK, between 1965 and 1996. We then used linear mixed modelling to analyse the effect of density on reproductive processes. 3The areas of Thiessen polygons formed around occupied nestboxes were used to approximate territory size (necessarily inverse of breeding density). There were significant, independent and positive relationships between clutch size, fledging mass and the number of offspring recruited to the population, and territory size (all P < 0·001), but no effect of territory size on lay-date or egg mass. 4Thiessen polygons are contiguous and cover all of the available area. Therefore, at low nest densities territory polygons were excessively oversized. Using a novel procedure to address this limitation, territory sizes were systematically capped through a range of maxima, with the greatest effect in the models when territories were capped at 0·9,2·3 ha. This figure approximates to the maximum effective territory size in our population and is in close agreement with several field-based studies. This capping refinement also revealed a significant negative relationship between lay-date and territory size capped at 0·9 ha (P < 0·001). 5These density-dependent effects were also detected when analyses were restricted to changes within individual females, suggesting that density effects do not merely result from either increased proportions of low-quality individuals, or increased occupation of poor sites, when population density is high. 6Overall, these results suggest that, in the current population, great tits with territories smaller than c. 2 ha independently lay smaller and later clutches, have lighter fledglings, and recruit fewer offspring to the breeding population. These analyses thus suggest a pervasive and causal role of local population density in explaining individual reproductive processes. [source]


    Population fragmentation leads to spatial and temporal genetic structure in the endangered Spanish imperial eagle

    MOLECULAR ECOLOGY, Issue 3 2007
    B. MARTÍNEZ-CRUZ
    Abstract The fragmentation of a population may have important consequences for population genetic diversity and structure due to the effects of genetic drift and reduced gene flow. We studied the genetic consequences of the fragmentation of the Spanish imperial eagle (Aquila adalberti) population into small patches through a temporal analysis. Thirty-four museum individuals representing the population predating the fragmentation were analysed for a 345-bp segment of the mitochondrial control region and a set of 10 nuclear microsatellite loci. Data from a previous study on the current population (N = 79) were re-analysed for this subset of 10 microsatellite markers and results compared to those obtained from the historical sample. Three shared mitochondrial haplotypes were found in both populations, although fluctuations in haplotype frequencies and the occurrence of a fourth haplotype in the historical population resulted in lower current levels of haplotype and nucleotide diversity. However, microsatellite markers revealed undiminished levels of nuclear diversity. No evidence for genetic structure was observed for the historical Spanish imperial eagle population, suggesting that the current pattern of structure is the direct consequence of population fragmentation. Temporal fluctuations in mitochondrial and microsatellite allelic frequencies were found between the historical and the current population as well as for each pairwise comparison between historical and current Centro and historical and current Parque Nacional de Doñana nuclei. Our results indicate an ancestral panmictic situation for the species that management policies should aim to restore. A historical analysis like the one taken here provides the baseline upon which the relative role of recent drift in shaping current genetic patterns in endangered species can be evaluated and this knowledge is used to guide conservation actions. [source]


    Where Is the Future in Public Health?

    THE MILBANK QUARTERLY, Issue 2 2010
    HILARY GRAHAM
    Context: Today's societies have far-reaching impacts on future conditions for health. Against this backdrop, this article explores how the future is represented in contemporary public health, examining both its conceptual base and influential approaches through which evidence is generated for policy. Methods: Mission statements and official reviews provide insight into how the future is represented in public health's conceptual and ethical foundations. For its research practices, the article takes examples from epidemiological, intervention, and economic research, selecting risk-factor epidemiology, randomized controlled trials, and economic evaluation as exemplars. Findings: Concepts and ethics suggest that public health research and policy will be concerned with protecting both today's and tomorrow's populations from conditions that threaten their health. But rather than facilitating sustained engagement with future conditions and future health, exemplary approaches to gathering evidence focus on today's population. Thus, risk-factor epidemiology pinpoints risks in temporal proximity to the individual; controlled trials track short-term effects of interventions on the participants' health; and economic evaluations weigh policies according to their value to the current population. While their orientation to the present and near future aligns well with the compressed timescales for policy delivery on which democratic governments tend to work, it makes it difficult for the public health community to direct attention to conditions for future health. Conclusions: This article points to the need for research perspectives and practices that, consistent with public health's conceptual and ethical foundations, represent the interests of both tomorrow's and today's populations. [source]


    Estimation of genetic variability of the founder population in a conservation scheme using microsatellites

    ANIMAL GENETICS, Issue 3 2003
    M. A. Toro
    Summary In a conservation programme with genealogical records it is possible to estimate the amount of variability of the founder population from a measure of the similarity among the individuals in the current population based on microsatellite markers. Here we compare three available methods and we shown that the one based on the molecular coancestry coefficient should be preferred. [source]


    Population Structure in Contemporary Sweden,A Y-Chromosomal and Mitochondrial DNA Analysis

    ANNALS OF HUMAN GENETICS, Issue 1 2009
    T. Lappalainen
    Summary A population sample representing the current Swedish population was analysed for maternally and paternally inherited markers with the aim of characterizing genetic variation and population structure. The sample set of 820 females and 883 males were extracted and amplified from Guthrie cards of all the children born in Sweden during one week in 2003. 14 Y-chromosomal and 34 mitochondrial DNA SNPs were genotyped. The haplogroup frequencies of the counties closest to Finland, Norway, Denmark and the Saami region in the north exhibited similarities to the neighbouring populations, resulting from the formation of the Swedish nation during the past millennium. Moreover, the recent immigration waves of the 20th century are visible in haplogroup frequencies, and have led to increased diversity and divergence of the major cities. Signs of genetic drift can be detected in several counties in northern as well as in southern Sweden. With the exception of the most drifted subpopulations, the population structure in Sweden appears mostly clinal. In conclusion, our study yielded valuable information of the structure of the Swedish population, and demonstrated the usefulness of biobanks as a source of population genetic research. Our sampling strategy, nonselective on the current population rather than stratified according to ancestry, is informative for capturing the contemporary variation in the increasingly panmictic populations of the world. [source]


    ADAPTIVE MULTI-OBJECTIVE OPTIMIZATION BASED ON NONDOMINATED SOLUTIONS

    COMPUTATIONAL INTELLIGENCE, Issue 2 2009
    Dongdong Yang
    An adaptive hybrid model (AHM) based on nondominated solutions is presented in this study for multi-objective optimization problems (MOPs). In this model, three search phases are devised according to the number of nondominated solutions in the current population: 1) emphasizing the dominated solutions when the population contains very few nondominated solutions; 2) maintaining the balance between nondominated and dominated solutions when nondominated ones become more; 3) when the population consists of adequate nondominated solutions, dominated ones could be ignored and the isolated nondominated ones are allocated more computational budget by their crowding distance values for heuristic search. To exploit local information efficiently, a local incremental search algorithm, LISA, is proposed and merged into the model. This model maintains the adaptive mechanism between the optimization process by the online discovered nondominated solutions. The proposed model is validated using five ZDT and five DTLZ problems. Compared with three other state-of-the-art multi-objective algorithms, namely NSGA-II, SPEA2, and PESA-II, AHM achieves comparable results in terms of convergence and diversity metrics. Finally, the sensitivity of introduced parameters and scalability to the number of objectives are investigated. [source]


    RECENT ECOLOGICAL DIVERGENCE DESPITE MIGRATION IN SOCKEYE SALMON (ONCORHYNCHUS NERKA)

    EVOLUTION, Issue 6 2010
    Scott A. Pavey
    Ecological divergence may result when populations experience different selection regimes, but there is considerable discussion about the role of migration at the beginning stages of divergence before reproductive isolating mechanisms have evolved. However, detection of past migration is difficult in current populations and tools to differentiate genetic similarities due to migration versus recent common ancestry are only recently available. Using past volcanic eruption times as a framework, we combine morphological analyses of traits important to reproduction with a coalescent-based genetic analysis of two proximate sockeye salmon (Oncorhynchus nerka) populations. We find that this is the most recent (,500 years, 100 generations) natural ecological divergence recorded in a fish species, and report that this divergence is occurring despite migration. Although studies of fish divergence following the retreat of glaciers (10,000,15,000 years ago) have contributed extensively to our understanding of speciation, the Aniakchak system of sockeye salmon provides a rare example of the initial stages of ecological divergence following natural colonization. Our results show that even in the face of continued migration, populations may diverge in the absence of a physical barrier. [source]


    Genetic maladaptation of coastal Douglas-fir seedlings to future climates

    GLOBAL CHANGE BIOLOGY, Issue 7 2007
    J. BRADLEY ST CLAIR
    Abstract Climates are expected to warm considerably over the next century, resulting in expectations that plant populations will not be adapted to future climates. We estimated the risk of maladaptation of current populations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) to future climates as the proportion of nonoverlap between two normal distributions where the means and genetic variances of current and future populations are determined from genecological models derived from seedling common garden studies. The risk of maladaptation was large for most traits when compared with the risk associated with current transfers within seed zones, particularly for the more drastic climate change scenario. For example, the proportion of nonoverlap for a composite trait representing bud set, emergence, growth, and root : shoot ratio was as high as 0.90. We recommend augmenting within-population variation by mixing local populations with some proportion of populations from lower elevations and further south. Populations expected to be adapted to climates a century from now come from locations as far down in elevation as 450,1130 m and as far south in latitude as 1.8,4.9°. [source]


    Abundance of Snowy and Wilson's Plovers in the lower Laguna Madre region of Texas

    JOURNAL OF FIELD ORNITHOLOGY, Issue 4 2007
    Sharyn L. Hood
    ABSTRACT Snowy Plovers (Charadrius alexandrinus) and Wilson's Plovers (C. wilsonia) are shorebird species of increasing conservation concern, with populations apparently declining in North America. However, estimates of current populations are needed before initiating long-term monitoring or planning. In 2004, we estimated abundance of breeding Snowy and Wilson's plovers in the lower Laguna Madre region of Texas using occupancy abundance estimation. We made repeated visits to survey plots from April to June, recording the number of adults of both species observed and the amount of suitable breeding habitat within each plot. We considered Bayesian occupancy abundance models with and without habitat covariates to explain the abundance of both species. For both Snowy and Wilson's plovers, the number of birds counted in each plot was influenced by the amount of suitable breeding habitat within the plot (Snowy Plover ,habitat= 0.52, SD = 0.10, 95% CI = 0.33,0.71; Wilson's Plover ,habitat= 0.48, SD = 0.12, 95% CI = 0.24,0.71). Using the habitat covariate models for each species, we estimated that 416 adult Snowy Plovers (95% CI = 394,438) and 279 adult Wilson's Plovers (95% CI = 262,296) were present in our study area. Our results illustrate the use of a relatively new method for abundance estimation, and indicate that the lower Laguna Madre region of Texas is an important breeding area for both Snowy and Wilson's plovers. Given the documented and suspected population declines for Snowy and Wilson's plovers, we recommend protection of their breeding habitats along the coast of Texas from development and degradation resulting from unregulated use. SINOPSIS Charadrius alexandrinus y C. wilsonia son dos especies de playeros que son objeto de preocupación porque sus poblaciones parecen estar disminuyendo en Norte América. Sin embargo, se necesitan estimados poblacionales antes de se comience con su monitoreos a largo alcance o la planificación de su conservación. En el 2004, estimamos la abundancia de ambas especies en la parte baja de la Laguna Madre en Texas utilizando estimados de abundancia. Hicimos visitas repetidas para hacer encuestas en parcelas de abril a junio, contando el número de adultos de ambas especies y la cantidad de hábitat adecuado para cada especie entre cada parcela. Consideramos un modelo de abundancia Bayesiano con y sin covariantes de hábitat para explicar la abundancia de ambas especies. Para ambas especies el número de aves contadas en cada parcela fue influenciado por la cantidad de hábitat reproductivo apropiado dentro de la parcela (C. alexandrinus,habitat= 0.52, SD = 0.10, 95% CI = 0.33 , 0.71; C. wilsonia,habitat= 0.48, SD = 0.12, 95% CI = 0.24 , 0.71). Utilizando el modelo de covarianza para cada especie, estimamos un total de 416 individuos de C. alexandrinus (95% CI = 394 , 438) y de 279 adultos de C. wilsonia (95% CI = 262 , 296) en nuestra área de estudio. Nuestros resultados ilustran el uso de un método relativamente nuevo para estimar la abundancia. Este indica que la región estudiada en Laguna Madre es de importancia para la reproducción de ambas especies. Dada la documentación y la sospecha fundamentada de la reducción en número de ambas especies, recomendamos la protección de su hábitat reproductivo, del desarrollo urbano y de la degradación resultante del uso sin regulación de la costa en Texas. [source]


    Rarity and decline in palaeoendemic Martino's vole Dinaromys bogdanovi

    MAMMAL REVIEW, Issue 4 2008
    BORIS KRY, TUFEK
    ABSTRACT 1Martino's vole Dinaromys bogdanovi is the only living member of the Tertiary genus Dinaromys, and probably also the only surviving member of the Pliomys lineage. The range of the genus Dinaromys has historically been small and its rate of evolution has been low. 2Martino's vole shows all three attributes of rarity in accordance with Rabinowitz's ,seven forms of rarity' model: (i) its range is estimated at 43 545 km2 but the area of occupancy is <5200 km2; (ii) its habitat requirements are narrow and the species is strictly tied to exposed, karstified bedrock; and (iii) current populations are invariably small and frequently isolated. 3The Pleistocene range of Martino's vole exceeded the recent one, at least in the north-western part of the Balkans, and its shrinkage continued into the Holocene. 4Martino's vole may be in competition with the European snow vole Chionomys nivalis, which has a very similar morphology and presumably identical habitat requirements, but is shifted towards an r-selected life-history strategy. Long-term sympatry of these voles has probably resulted in competitive exclusion of the relatively K-selected Martino's vole by the relatively r-selected European snow vole. 5Martino's vole consists of two deeply divergent (about one million years ago) phylogeographical lineages, which may represent distinct cryptic species. Rarity is particularly pronounced in the north-western lineage to the west of the Neretva River, where rocky habitats are largely occupied by the European snow vole. 6In the IUCN Red List of Threatened Animals, Martino's vole is classified as ,near threatened'. However, the north-western lineage, which is phylogeographically most divergent and has the greatest genetic diversity, is classed as a ,vulnerable' evolutionary significant unit on the basis of its small area of occupancy (<2000 km2). Long-term population monitoring is an essential step in evaluating the conservation needs of Martino's vole. [source]


    Population genetics of Galápagos land iguana (genus Conolophus) remnant populations

    MOLECULAR ECOLOGY, Issue 23 2008
    ATHANASIA C. TZIKA
    Abstract The Galápagos land iguanas (genus Conolophus) have faced significant anthropogenic disturbances since the 17th century, leading to severe reduction of some populations and the extinction of others. Conservation activities, including the repatriation of captive-bred animals to depleted areas, have been ongoing since the late 1970s, but genetic information has not been extensively incorporated. Here we use nine species-specific microsatellite loci of 703 land iguanas from the six islands where the species occur today to characterize the genetic diversity within, and the levels of genetic differentiation among, current populations as well as test previous hypotheses about accidental translocations associated with early conservation efforts. Our analyses indicate that (i) five populations of iguanas represent distinct conservation units (one of them being the recently discovered rosada form) and could warrant species status, (ii) some individuals from North Seymour previously assumed to be from the natural Baltra population appear related to both Isabela and Santa Cruz populations, and (iii) the five different management units exhibit considerably different levels of intrapopulation genetic diversity, with the Plaza Sur and Santa Fe populations particularly low. Although the initial captive breeding programmes, coupled with intensive efforts to eradicate introduced species, saved several land iguana populations from extinction, our molecular results provide objective data for improving continuing in situ species survival plans and population management for this spectacular and emblematic reptile. [source]


    Conserving the evolutionary potential of California valley oak (Quercus lobata Née): a multivariate genetic approach to conservation planning

    MOLECULAR ECOLOGY, Issue 1 2008
    DELPHINE GRIVET
    Abstract California valley oak (Quercus lobata Née) is a seriously threatened endemic oak species in California and a keystone species for foothill oak ecosystems. Urban and agricultural development affects a significant fraction of the species' range and predicted climate change is likely to dislocate many current populations. Here, we explore spatial patterns of multivariate genotypes and genetic diversity throughout the range of valley oak to determine whether ongoing and future patterns of habitat loss could threaten the evolutionary potential of the species by eradicating populations of distinctive genetic composition. This manuscript will address three specific questions: (i) What is the spatial genetic structure of the chloroplast and nuclear genetic markers? (ii) What are the geographical trends in the distribution of chloroplast and nuclear genotypes? (iii) Is there any part of the species' range where allelic diversity in either the chloroplast or nuclear genomes is particularly high? We analysed six chloroplast and seven nuclear microsatellite genetic markers of individuals widespread across the valley oak range. We then used a multivariate approach correlating genetic markers and geographical variables through a canonical trend surface analysis, followed by GIS mapping of the significant axes. We visualized population allelic richness spatially with GIS tools to identify regions of high diversity. Our findings, based on the distribution of multivariate genotypes and allelic richness, identify areas with distinctive histories and genetic composition that should be given priority in reserve network design, especially because these areas also overlap with landscape change and little degree of protection. Thus, without a careful preservation plan, valuable evolutionary information will be lost for valley oak. [source]


    Genetic evaluation of a proposed introduction: the case of the greater prairie chicken and the extinct heath hen

    MOLECULAR ECOLOGY, Issue 7 2004
    Eric P. Palkovacs
    Abstract Population introduction is an important tool for ecosystem restoration. However, before introductions should be conducted, it is important to evaluate the genetic, phenotypic and ecological suitability of possible replacement populations. Careful genetic analysis is particularly important if it is suspected that the extirpated population was unique or genetically divergent. On the island of Martha's Vineyard, Massachusetts, the introduction of greater prairie chickens (Tympanuchus cupido pinnatus) to replace the extinct heath hen (T. cupido cupido) is being considered as part of an ecosystem restoration project. Martha's Vineyard was home to the last remaining heath hen population until its extinction in 1932. We conducted this study to aid in determining the suitability of greater prairie chickens as a possible replacement for the heath hen. We examined mitochondrial control region sequences from extant populations of all prairie grouse species (Tympanuchus) and from museum skin heath hen specimens. Our data suggest that the Martha's Vineyard heath hen population represents a divergent mitochondrial lineage. This result is attributable either to a long period of geographical isolation from other prairie grouse populations or to a population bottleneck resulting from human disturbance. The mtDNA diagnosability of the heath hen contrasts with the network of mtDNA haplotypes of other prairie grouse (T. cupido attwateri, T. pallidicinctus and T. phasianellus), which do not form distinguishable mtDNA groupings. Our findings suggest that the Martha's Vineyard heath hen was more genetically isolated than are current populations of prairie grouse and place the emphasis for future research on examining prairie grouse adaptations to different habitat types to assess ecological exchangeability between heath hens and greater prairie chickens. [source]


    Contrasting patterns of mitochondrial and microsatellite population structure in fragmented populations of greater prairie-chickens

    MOLECULAR ECOLOGY, Issue 12 2003
    Jeff A. Johnson
    Abstract Greater prairie-chickens (Tympanuchus cupido pinnatus) were once found throughout the tallgrass prairie of midwestern North America but over the last century these prairies have been lost or fragmented by human land use. As a consequence, many current populations of prairie-chickens have become isolated and small. This fragmentation of populations is expected to lead to reductions in genetic variation as a result of random genetic drift and a decrease in gene flow. As expected, we found that genetic variation at both microsatellite DNA and mitochondrial DNA (mtDNA) markers was reduced in smaller populations, particularly in Wisconsin. There was relatively little range-wide geographical structure (FST) when we examined mtDNA haplotypes but there was a significant positive relationship between genetic (FST) and geographical distance (isolation by distance). In contrast, microsatellite DNA loci revealed significant geographical structure (FST) and a weak effect of isolation by distance throughout the range. These patterns were much stronger when populations with reduced levels of genetic variability (Wisconsin) were removed from the analyses. This suggests that the effects of genetic drift were stronger than gene flow at microsatellite loci, whereas these forces were in range-wide equilibrium at mtDNA markers. These differences between the two molecular markers may be explained by a larger effective population size (Ne) for mtDNA, which is expected in species such as prairie-chickens that have female-biased dispersal and high levels of polygyny. Our results suggest that historic populations of prairie-chickens were once interconnected by gene flow but current populations are now isolated. Thus, maintaining gene flow may be important for the long-term persistence of prairie-chicken populations. [source]


    An unexpected wide population variation of the G1733A polymorphism of the androgen receptor gene: Data on the Mediterranean region

    AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 6 2005
    E. Esteban
    The androgen receptor (AR) has been proposed as a candidate gene for several cancers (breast, prostate, uterine endometrium, colon, and esophagus). Ethnicity is considered an associated risk factor for some of these cancers. Several case-control genetic studies have been focused in samples of the main ethnic groups, but little is known about the distribution of risk polymorphisms in current populations with accurate ethnic and/or geographic origins. The A allele of the G1733A polymorphism of the AR gene has been associated with increased risk of prostate cancer. We provide data from this marker in 12 samples from 7 Mediterranean countries such as Spain, Italy (Sardinia), Greece, Turkey, Morocco, Algeria, and Egypt. A sample from Ivory Coast has also been analyzed. The A allele distribution shows a frequency in the Ivory Coast population (65.17%) that contrasts with the low values found in Northern Mediterraneans (mean average value of 13.98%). North African populations present two-times higher frequencies (average value of 27.19%) than Europeans. The wide population variation range found for the A allele strengthens the potential interest of further screening as a baseline to the design of future preventive and population health programs. Am. J. Hum. Biol. 17:690,695, 2005. © 2005 Wiley-Liss, Inc. [source]