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Various Temporal (various + temporal)
Selected AbstractsGenetic estimates of contemporary effective population size in an endangered butterfly indicate a possible role for genetic compensationEVOLUTIONARY APPLICATIONS (ELECTRONIC), Issue 1 2010Emily V. Saarinen Abstract The effective population size (Ne) is a critical evolutionary and conservation parameter that can indicate the adaptive potential of populations. Robust estimates of Ne of endangered taxa have been previously hampered by estimators that are sensitive to sample size. We estimated Ne on two remaining populations of the endangered Miami blue butterfly, a formerly widespread taxon in Florida. Our goal was to determine the consistency of various temporal and point estimators on inferring Ne and to determine the utility of this information for understanding the role of genetic stochasticity. We found that recently developed ,unbiased estimators' generally performed better than some older methods in that the former had more realistic Ne estimates and were more consistent with what is known about adult population size. Overall, Ne/N ratios based on census point counts were high. We suggest that this pattern may reflect genetic compensation caused by reduced reproductive variance due to breeding population size not being limited by resources. Assuming Ne and N are not heavily biased, it appears that the lack of gene flow between distant populations may be a greater genetic threat in the short term than the loss of heterozygosity due to inbreeding. [source] Establishing climate,growth relationships for yelloweye rockfish (Sebastes ruberrimus) in the northeast Pacific using a dendrochronological approachFISHERIES OCEANOGRAPHY, Issue 5 2008BRYAN A. BLACK Abstract We applied dendrochronology (tree-ring) methods to develop multidecadal growth chronologies from the increment widths of yelloweye rockfish (Sebastes ruberrimus) otoliths. Chronologies were developed for the central California coast, a site just north of Vancouver Island, British Columbia, and at Bowie Seamount west of the Queen Charlotte Islands, British Columbia. At each site, synchronous growth patterns were matched among otoliths via the process of cross-dating, ensuring that the correct calendar year was assigned to all increments. Each time series of growth-increment measurements was divided by the values predicted by a best-fit negative exponential function, thereby removing age-related trends. These detrended time series were averaged into a master chronology for each site, and chronologies were correlated with monthly averages of sea surface temperatures, upwelling, the Northern Oscillation Index, and the Pacific Decadal Oscillation. The two northern growth chronologies positively correlated with indices of warm ocean conditions, especially from the prior summer through the spring of the current year. During the same period, the California chronology positively correlated with indices of cool ocean conditions, indicating an opposing productivity regime for yelloweye rockfish between the California Current and the Gulf of Alaska. Overall, this study demonstrates how tree-ring techniques can be applied to quickly develop annually resolved chronologies and establish climate,growth relationships across various temporal and spatial scales. [source] Vegetation dynamics on rangelands: a critique of the current paradigmsJOURNAL OF APPLIED ECOLOGY, Issue 4 2003D. D. Briske Summary 1Rangeland ecologists have been debating the validity of two current paradigms for the evaluation of vegetation dynamics on rangelands. This debate frequently contrasts the conventional model of continuous and reversible vegetation dynamics (range model) with a more contemporary model that can accommodate discontinuous and non-reversible vegetation change (state-and-transition model). 2The range and the state-and-transition models are conceptually related to the equilibrium and non-equilibrium paradigms within ecology, respectively. The methodological dichotomy that has developed between the range and the state-and-transition models has fostered the perception that these two ecological paradigms are mutually exclusive. We challenge this perception and contend that both methodologies and their corresponding paradigms are non-exclusive. 3Equilibrium and non-equilibrium ecosystems are not distinguished on the basis of unique processes or functions, but rather by the evaluation of system dynamics at various temporal and spatial scales. Consequently, ecosystems may express both equilibrium and non-equilibrium dynamics. This confirms early interpretations that ecosystems are distributed along a continuum from equilibrium to non-equilibrium states. 4Although both equilibrium and non-equilibrium dynamics occur in numerous ecosystems, the empirical evidence is frequently confounded by (i) uncertainty regarding the appropriate evidence necessary to distinguish between paradigms; (ii) disproportionate responses among vegetation attributes to climate and grazing; (iii) comparisons among systems with varying degrees of managerial involvement; and (iv) the evaluation of vegetation dynamics at various spatial and temporal scales. 5Synthesis and applications. This critique supports the conclusion that a paradigm shift has not taken place in rangeland ecology, but rather, the debate has forced a more comprehensive interpretation of vegetation dynamics along the entirety of the equilibrium,non-equilibrium continuum. Therefore, the rangeland debate should be redirected from the dichotomy between paradigms to one of paradigm integration. [source] Removing undersampling artifacts in DCE-MRI studies using independent components analysisMAGNETIC RESONANCE IN MEDICINE, Issue 4 2008A.L. Martel Abstract In breast MRI mammography both high temporal resolution and high spatial resolution have been shown to be important in improving specificity. Adaptive methods such as projection reconstruction time-resolved imaging of contrast kinetics (PR-TRICKS) allow images to be reconstructed at various temporal and spatial resolutions from the same data set. The main disadvantage is that the undersampling, which is necessary to produce high temporal resolution images, leads to the presence of streak artifacts in the images. We present a novel method of removing these artifacts using independent components analysis (ICA) and demonstrate that this results in a significant improvement in image quality for both simulation studies and for patient dynamic contrast-enhanced (DCE)-MRI images. We also investigate the effect of artifacts on two quantitative measures of contrast enhancement. Using simulation studies we demonstrate that streak artifacts lead to pronounced periodic oscillations in pixel concentration curves which, in turn, lead to increased errors and introduce bias into heuristic measurements. ICA filtering significantly reduces this bias and improves accuracy. Pharmacokinetic modeling was more robust and there was no evidence of bias due to the presence of streak artifacts. ICA filtering did not significantly reduce the errors in the estimated pharmacokinetic parameters; however, the chi-squared error was greatly reduced after ICA filtering. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc. [source] Herbaceous vegetation change in variable rangeland environments: The relative contribution of grazing and climatic variabilityAPPLIED VEGETATION SCIENCE, Issue 2 2001Samuel D. Fuhlendorf Hatch et al. (1990) Abstract. A 44-yr record of herbaceous vegetation change was analysed for three contrasting grazing regimes within a semi-arid savanna to evaluate the relative contribution of confined livestock grazing and climatic variability as agents of vegetation change. Grazing intensity had a significant, directional effect on the relative composition of short- and mid-grass response groups; their composition was significantly correlated with time since the grazing regimes were established. Interannual precipitation was not significantly correlated with response group composition. However, interannual precipitation was significantly correlated with total plant basal area while time since imposition of grazing regimes was not, but both interannual precipitation and time since the grazing regimes were established were significantly correlated with total plant density. Vegetation change was reversible even though the herbaceous community had been maintained in an altered state for ca. 60 yr by intensive livestock grazing. However, ca. 25 yr were required for the mid-grass response group to recover following the elimination of grazing and recovery occurred intermittently. The increase in mid-grass composition was associated with a significant decrease in total plant density and an increase in mean individual plant basal area. Therefore, we failed to reject the hypotheses based on the proportional change in relative response group composition with grazing intensity and the distinct effects of grazing and climatic variability on response group composition, total basal area and plant density. Long-term vegetation change indicates that grazing intensity established the long-term directional change in response group composition, but that episodic climate events defined the short-term rate and trajectory of this change and determines the upper limit on total basal area. The occurrence of both directional and non-directional vegetation responses were largely a function of (1) the unique responses of the various community attributes monitored and (2) the distinct temporal responses of these community attributes to grazing and climatic variation. This interpretation supports previous conclusions that individual ecosystems may exist in equilibrial and non-equilibrial states at various temporal and spatial scales. 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