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排序方式: 共有330条查询结果,搜索用时 271 毫秒
61.
J. W. Durban D. A. Elston D. K. Ellifrit E. Dickson P. S. Hammond P. M. Thompson 《Marine Mammal Science》2005,21(1):80-92
Mark-recapture techniques are widely used to estimate the size of wildlife populations. However, in cetacean photo-identification studies, it is often impractical to sample across the entire range of the population. Consequently, negatively biased population estimates can result when large portions of a population are unavailable for photographic capture. To overcome this problem, we propose that individuals be sampled from a number of discrete sites located throughout the population's range. The recapture of individuals between sites can then be presented in a simple contingency table, where the cells refer to discrete categories formed by combinations of the study sites. We present a Bayesian framework for fitting a suite of log-linear models to these data, with each model representing a different hypothesis about dependence between sites. Modeling dependence facilitates the analysis of opportunistic photo-identification data from study sites located due to convenience rather than by design. Because inference about population size is sensitive to model choice, we use Bayesian Markov chain Monte Carlo approaches to estimate posterior model probabilities, and base inference on a model-averaged estimate of population size. We demonstrate this method in the analysis of photographic mark-recapture data for bottlenose dolphins from three coastal sites around NE Scotland. 相似文献
62.
63.
Question: What are the responses of Racomitrium lanuginosum moss to altered snow‐lie and sheep use? Location: ACarexbigelowii‐Racomitrium lanuginosum heath on a Scottish montane plateau affected since 1986 by a fenced ski corridor. Methods: Permanent quadrats were set up along transects 45 m long perpendicular to the snow‐fence. Cover was assessed over a 12‐year period from 1990. Pellet‐group clearance counts provided data on sheep usage between 1990 and 1996. Snow‐lie was mapped in the springs of 1991–1996. Results: The snow‐fence created a gradient in sheep use and altered the duration of snow‐lie. At the start of monitoring Racomitrium cover was lower immediately adjacent to the fence, and after 12 years its cover was significantly reduced within 10 m of the fence. Further away from the fence Racomitrium cover was relatively stable. The loss of Racomitrium was correlated both with increased snow‐lie and heavier sheep usage. Grass cover increased near the fence and was related to sheep use. Dicranum fuscescens responded differently to Racomitrium, increasing significantly near the fence. Conclusions: We found that changes in snow‐lie and grazing pressure quickly brought about vegetation change in this montane ecosystem. Racomitrium was the most sensitive species to the changes in grazing and snow‐lie caused by the fence, having the biggest initial changes. Loss of Racomitrium permitted increases of species more resistant to grazing including Dicranum fuscescens and grasses. 相似文献
64.
Walter H. Pearson Richard B. Deriso Ralph A. Elston Sharon E. Hook Keith R. Parker Jack W. Anderson 《Reviews in Fish Biology and Fisheries》2012,22(1):95-135
This paper updates previous reviews of the 1993 stock decline of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, and focuses on hypotheses about subsequent poor recovery. Recent age structured assessment
modeling with covariate analysis indicates that the population dynamics of the sound’s herring are influenced by oceanic factors,
nutrition, and, most substantially, hatchery releases of juvenile pink salmon. For the 1993 decline, poor nutrition remains
the most probable cause with disease a secondary response. Concerning poor recovery, we examined 16 potential factors and
found three to be causal: oceanic factors, poor nutrition, and hatchery releases of juvenile pink salmon. Absences of strong
year classes at both Sitka and Prince William Sound after 1993 indicate the action of large-scale ocean processes. Beyond
regional-scale environmental factors, two factors specific to the sound influence the population dynamics of herring and are
likely impeding recovery. First, pink salmon fry releases have increased to about 600 million annually and may disrupt feeding
in young herring, which require adequate nutrition for growth and overwintering survival. Juvenile pink salmon and age-1 herring
co-occur in nearshore areas of bays in late spring and summer, and available data on dietary overlap indicates potential competition
between the age-1 juvenile herring and juvenile pink salmon. Field studies demonstrate that juvenile herring reduce food intake
substantially in the presence of juvenile pink salmon. Second, overwintering humpback whales may consume potentially large
amounts of adult herring, but further studies must confirm to what extent whale predation reduces herring biomass. 相似文献
65.
Bierman SM Fairbairn JP Petty SJ Elston DA Tidhar D Lambin X 《The American naturalist》2006,167(4):583-590
We demonstrate changes over time in the spatial and temporal dynamics of an herbivorous small rodent by analyzing time series of population densities obtained at 21 locations on clear cuts within a coniferous forest in Britain from 1984 to 2004. Changes had taken place in the amplitude, periodicity, and synchrony of cycles and density-dependent feedback on population growth rates. Evidence for the presence of a unidirectional traveling wave in rodent abundance was strong near the beginning of the study but had disappeared near the end. This study provides empirical support for the hypothesis that the temporal (such as delayed density dependence structure) and spatial (such as traveling waves) dynamics of cyclic populations are closely linked. The changes in dynamics were markedly season specific, and changes in overwintering dynamics were most pronounced. Climatic changes, resulting in a less seasonal environment with shorter winters near the end of the study, are likely to have caused the changes in vole dynamics. Similar changes in rodent dynamics and the climate as reported from Fennoscandia indicate the involvement of large-scale climatic variables. 相似文献
66.
Gyungah Jun Hong Guo Barbara E. K. Klein Ronald Klein Jie Jin Wang Paul Mitchell Hui Miao Kristine E. Lee Tripti Joshi Matthias Buck Preeti Chugha David Bardenstein Alison P. Klein Joan E. Bailey-Wilson Xiaohua Gong Tim D. Spector Toby Andrew Christopher J. Hammond Robert C. Elston Sudha K. Iyengar Bingcheng Wang 《PLoS genetics》2009,5(7)
Age-related cataract is a major cause of blindness worldwide, and cortical cataract is the second most prevalent type of age-related cataract. Although a significant fraction of age-related cataract is heritable, the genetic basis remains to be elucidated. We report that homozygous deletion of Epha2 in two independent strains of mice developed progressive cortical cataract. Retroillumination revealed development of cortical vacuoles at one month of age; visible cataract appeared around three months, which progressed to mature cataract by six months. EPHA2 protein expression in the lens is spatially and temporally regulated. It is low in anterior epithelial cells, upregulated as the cells enter differentiation at the equator, strongly expressed in the cortical fiber cells, but absent in the nuclei. Deletion of Epha2 caused a significant increase in the expression of HSP25 (murine homologue of human HSP27) before the onset of cataract. The overexpressed HSP25 was in an underphosphorylated form, indicating excessive cellular stress and protein misfolding. The orthologous human EPHA2 gene on chromosome 1p36 was tested in three independent worldwide Caucasian populations for allelic association with cortical cataract. Common variants in EPHA2 were found that showed significant association with cortical cataract, and rs6678616 was the most significant in meta-analyses. In addition, we sequenced exons of EPHA2 in linked families and identified a new missense mutation, Arg721Gln, in the protein kinase domain that significantly alters EPHA2 functions in cellular and biochemical assays. Thus, converging evidence from humans and mice suggests that EPHA2 is important in maintaining lens clarity with age. 相似文献
67.
Pascal Vittoz Neil Bayfield Rob Brooker David A. Elston Elizabeth I. Duff Jean‐Paul Theurillat Antoine Guisan 《植被学杂志》2010,21(6):1035-1047
Question: When multiple observers record the same spatial units of alpine vegetation, how much variation is there in the records and what are the consequences of this variation for monitoring schemes to detect changes? Location: One test summit in Switzerland (Alps) and one test summit in Scotland (Cairngorm Mountains). Method: Eight observers used the GLORIA protocols for species composition and visual cover estimates in percentages on large summit sections (>100 m2) and species composition and frequency in nested quadrats (1 m2). Results: The multiple records from the same spatial unit for species composition and species cover showed considerable variation in the two countries. Estimates of pseudo‐turnover of composition and coefficients of variation of cover estimates for vascular plant species in 1 m × 1‐m quadrats showed less variation than in previously published reports, whereas our results in larger sections were broadly in line with previous reports. In Scotland, estimates for bryophytes and lichens were more variable than for vascular plants. Conclusions: Statistical power calculations indicated that unless large numbers of plots were used, changes in cover or frequency were only likely to be detected for abundant species (exceeding 10% cover) or if relative changes were large (50% or more). Lower variation could be reached with the point method and with larger numbers of small plots. However, as summits often strongly differ from each other, supplementary summits cannot be considered as a way of increasing statistical power without introducing a supplementary component of variance into the analysis and hence into the power calculations. 相似文献
68.
Evans DM Redpath SM Evans SA Elston DA Gardner CJ Dennis P Pakeman RJ 《Biology letters》2006,2(4):636-638
Livestock grazing is a major driver of ecosystem change and has been associated with significant declines in various bird species in Britain and worldwide. However, there is little experimental evidence to show how grazing affects bird populations. We manipulated livestock densities in a replicated field experiment and found that mixed sheep and cattle grazing, at low intensity, improved the breeding abundance of a common upland passerine, the meadow pipit Anthus pratensis, after two years. Plots stocked with sheep alone (at high or low density) or not stocked at all held fewer pipit territories. Despite a year-on-year decline in pairs of meadow pipits in intensively grazed plots, we found no effect of sheep number on breeding abundance. Our results support the hypothesis that mixed species of herbivores generate greater heterogeneity in vegetation structure, which modifies prey availability, resulting in a greater abundance of birds. The results of our study should inform the management of grassland areas and enhance the abundance of some bird species, particularly in areas that have seen significant shifts from mixed livestock grazing to grazing dominated by single species of animals. 相似文献
69.
Jaume?Pons Jaume?Sauleda Verónica?Regueiro Carmen?Santos Meritxell?López Joana?Ferrer Alvar?GN?Agustí José?A?BengoecheaEmail author 《Respiratory research》2006,7(1):64
Background
Chronic obstructive pulmonary disease (COPD) is characterised by pulmonary and systemic inflammation which flare-up during episodes of acute exacerbation (AECOPD). Given the role of Toll-like receptors (TLRs) in the induction of inflammatory responses we investigated the involvement of TLRs in COPD pathogenesis.Methods
The expression of TLR-2, TLR-4 and CD14 in monocytes was analyzed by flow cytometry. To study the functional responses of these receptors, monocytes were stimulated with peptidoglycan or lipopolysaccharide and the amounts of TNFα and IL-6 secreted were determined by ELISA.Results
We found that the expression of TLR-2 was up-regulated in peripheral blood monocytes from COPD patients, either clinically stable or during AECOPD, as compared to never smokers or smokers with normal lung function. Upon stimulation with TLR-2 ligand monocytes from COPD patients secreted increased amounts of cytokines than similarly stimulated monocytes from never smokers and smokers. In contrast, the expressions of TLR-4 and CD14 were not significantly different between groups, and the response to lipopolysaccharide (a TLR-4 ligand) stimulation was not significantly different either. At discharge from hospital TLR-2 expression was down-regulated in peripheral blood monocytes from AECOPD patients. This could be due to the treatment with systemic steroids because, in vitro, steroids down-regulated TLR-2 expression in a dose-dependent manner. Finally, we demonstrated that IL-6, whose plasma levels are elevated in patients, up-regulated in vitro TLR-2 expression in monocytes from never smokers.Conclusion
Our results reveal abnormalities in TLRs expression in COPD patients and highlight its potential relationship with systemic inflammation in these patients.70.
Bukulmez H Matthews AL Sullivan CM Chen C Kraay MJ Elston RC Moskowitz RW Goldberg VM Warman ML 《Arthritis research & therapy》2006,8(1):R25
In order to determine whether there is a genetic component to hip or knee joint failure due to idiopathic osteoarthritis (OA), we invited patients (probands) undergoing hip or knee arthroplasty for management of idiopathic OA to provide detailed family histories regarding the prevalence of idiopathic OA requiring joint replacement in their siblings. We also invited their spouses to provide detailed family histories about their siblings to serve as a control group. In the probands, we confirmed the diagnosis of idiopathic OA using American College of Rheumatology criteria. The cohorts included the siblings of 635 probands undergoing total hip replacement, the siblings of 486 probands undergoing total knee replacement, and the siblings of 787 spouses. We compared the prevalence of arthroplasty for idiopathic OA among the siblings of the probands with that among the siblings of the spouses, and we used logistic regression to identify independent risk factors for hip and knee arthroplasty in the siblings. Familial aggregation for hip arthroplasty, but not for knee arthroplasty, was observed after controlling for age and sex, suggesting a genetic contribution to end-stage hip OA but not to end-stage knee OA. We conclude that attempts to identify genes that predispose to idiopathic OA resulting in joint failure are more likely to be successful in patients with hip OA than in those with knee OA. 相似文献