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Likely Contributions (likely + contribution)
Selected AbstractsLocal environmental effects and spatial effects in macroecological studies using mapped abundance classes: the case of the rook Corvus frugilegus in ScotlandJOURNAL OF ANIMAL ECOLOGY, Issue 5 2006A. GIMONA Summary 1The study of the spatial pattern of species abundance is complicated by statistical problems, such as spatial autocorrelation of the abundance data, which lead to the confusion of environmental effects and dispersal. 2Atlas-derived data for the rook in Scotland are used as a case study to propose an approach for assessing the likely contribution of dispersal and local environmental effects, based on a Bayesian Conditional Autoregressive (CAR) approach. 3The availability of moist grasslands is a key factor explaining the spatial pattern of abundance. This is influenced by a combination of climatic and soil-related factors. A direct link to soil properties is for the first time reported for the wide-scale distribution of a bird species. In addition, for this species, dispersal seems to contribute significantly to the spatial pattern and produces a smoother than expected decline in abundance at the north-western edge of its distribution range. Areas where dispersal is most likely to be important are highlighted. 4The approach described can help ecologists make more efficient use of atlas data for the investigation of the structure of species abundance, and can highlight potential sink areas at the landscape and regional scale. 5Bayesian spatial models can deal with data autocorrelation in atlas-type data, while clearly communicating uncertainty through the estimation of the full posterior probability distribution of all parameters. [source] Towards integrating tracer studies in conceptual rainfall-runoff models: recent insights from a sub-arctic catchment in the Cairngorm Mountains, ScotlandHYDROLOGICAL PROCESSES, Issue 2 2003Chris Soulsby Abstract Hydrochemical tracers (alkalinity and silica) were used in an end-member mixing analysis (EMMA) of runoff sources in the 10 km2 Allt a' Mharcaidh catchment. A three-component mixing model was used to separate the hydrograph and estimate, to a first approximation, the range of likely contributions of overland flow, shallow subsurface storm flow, and groundwater to the annual hydrograph. A conceptual, catchment-scale rainfall-runoff model (DIY) was also used to separate the annual hydrograph in an equivalent set of flow paths. The two approaches produced independent representations of catchment hydrology that exhibited reasonable agreement. This showed the dominance of overland flow in generating storm runoff and the important role of groundwater inputs throughout the hydrological year. Moreover, DIY was successfully adapted to simulate stream chemistry (alkalinity) at daily time steps. Sensitivity analysis showed that whilst a distinct groundwater source at the catchment scale could be identified, there was considerable uncertainty in differentiating between overland flow and subsurface storm flow in both the EMMA and DIY applications. Nevertheless, the study indicated that the complementary use of tracer analysis in EMMA can increase the confidence in conceptual model structure. However, conclusions are restricted to the specific spatial and temporal scales examined. Copyright © 2003 John Wiley & Sons, Ltd. [source] Demographic factors and genetic variation influence population persistence under environmental changeJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2009YVONNE WILLI Abstract Population persistence has been studied in a conservation context to predict the fate of small or declining populations. Persistence models have explored effects on extinction of random demographic and environmental fluctuations, but in the face of directional environmental change they should also integrate factors affecting whether a population can adapt. Here, we examine the population-size dependence of demographic and genetic factors and their likely contributions to extinction time under scenarios of environmental change. Parameter estimates were derived from experimental populations of the rainforest species, Drosophila birchii, held in the lab for 10 generations at census sizes of 20, 100 and 1000, and later exposed to five generations of heat-knockdown selection. Under a model of directional change in the thermal environment, rapid extinction of populations of size 20 was caused by a combination of low growth rate (r) and high stochasticity in r. Populations of 100 had significantly higher reproductive output, lower stochasticity in r and more additive genetic variance (VA) than populations of 20, but they were predicted to persist less well than the largest size class. Even populations of 1000 persisted only a few hundred generations under realistic estimates of environmental change because of low VA for heat-knockdown resistance. The experimental results document population-size dependence of demographic and adaptability factors. The simulations illustrate a threshold influence of demographic factors on population persistence, while genetic variance has a more elastic impact on persistence under environmental change. [source] Paradoxical aspects of parkinsonian tremorMOVEMENT DISORDERS, Issue 2 2008Paul S. Fishman MD Abstract Although resting tremor is the most identifiable sign of Parkinson's disease, its underlying basis appears to be the most complex of the cardinal signs. The variable relationship of resting tremor to other symptoms of PD has implications for diagnosis, prognosis, medical and surgical treatment. Structural lesions very rarely cause classic resting tremor, with likely contributions to tremor by a network of neurons both within and outside the basal ganglia. Patients with only resting tremor show dopaminergic deficits with radioligand imaging, but severity of tremor correlates poorly in such dopamine imaging studies. Correlation of tremor severity to changes in radioligand studies is also limited by the use of mostly qualitative measures of tremor severity. A complex pharmacologic basis of parkinsonian resting tremor is supported by treatment studies. Although levodopa is clearly effective for resting tremor, several agents have shown efficacy that appears to be superior or additive to that of levodopa including anticholinergics, clozapine, pramipexole, and budipine. Although the thalamus has the greatest body of evidence supporting its role as an effective target for surgical treatment of tremor, recent studies suggest that the subthalamic nucleus may be a reasonable alternative target for patients with Parkinson's disease and severe tremor as the predominant symptom. © 2007 Movement Disorder Society [source] | ||||||||||