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Natural Variability (natural + variability)

Distribution by Scientific Domains

Earth and Environmental Science	50%
Life Sciences	35%
Medical Sciences	10%

Selected Abstracts

Natural variability of fisheries and lunar illumination: a hypothesis

FISH AND FISHERIES, Issue 2 2008
Santiago Hernández-León
Abstract Long-term synchronous trends in small pelagic fisheries catches around the world suggest that fish populations are governed by the same global climate forcings. Recent findings regarding the population dynamics of zooplankton during the lunar cycle in sub-tropical waters may shed light on the influence of the lunar cycle on fish spawning and mortality. Here I hypothesize that, in the short-term, observed changes in zooplankton abundance during the lunar cycle promote periods of enhanced feeding by adult fish and lower mortality (and increased growth) in their early planktonic stages. Furthermore, a striking 9-year periodicity in sardine and anchovy mortality was inferred in four major upwelling areas, coinciding with the long-term variability in lunar illumination. It is suggested that both short- and long-term changes in lunar illumination should be considered when modelling the effect of climate on the natural variability of fisheries. [source]

Ecological effects of regime shifts in the Bering Sea and eastern North Pacific Ocean

FISH AND FISHERIES, Issue 2 2002
Ashleen J Benson
Abstract Large-scale shifts occurred in climatic and oceanic conditions in 1925, 1947, 1977, 1989 and possibly 1998. These shifts affected the mix and abundance of suites of coexisting species during each period of relative environmental stability,from primary producers to apex predators. However, the 1989 regime shift was not a simple reversal of the 1977 shift. The regime shifts occurred abruptly and were neither random variations nor simple reversals to the previous conditions. Timing of these anomalous environmental events in the North Pacific Ocean appears to be linked to physical and biological responses in other oceanic regions of the world. Changes in the atmospheric pressure can alter wind patterns that affect oceanic circulation and physical properties such as salinity and depth of the thermocline. This, in turn, affects primary and secondary production. Data from the North Pacific indicate that regime shifts can have opposite effects on species living in different domains, or can affect similar species living within a single domain in opposite ways. Climatic forcing appears to indirectly affect fish and marine mammal populations through changes in the distribution and abundance of their predators and prey. Effects of regime shifts on marine ecosystems are also manifested faster at lower trophic levels. Natural variability in the productivity of fish stocks in association with regime shifts indicates that new approaches to managing fisheries should incorporate climatic as well as fisheries effects. [source]

A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajarvi, central Finland

BOREAS, Issue 4 2003
MIA TILJANDER
High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajarvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajarvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980,1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580,1630 and AD 1650,1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago. [source]

Potential Effects of Passenger Pigeon Flocks on the Structure and Composition of Presettlement Forests of Eastern North America

CONSERVATION BIOLOGY, Issue 6 2003
JOSHUA W. ELLSWORTH
We suggest that the activities of roosting and nesting Passenger Pigeons caused widespread, frequent disturbances in presettlement eastern forests through tree limb and stem breakage and nutrient deposition from pigeon excrement. We suspect that the deposition of fine fuels resulting from such disturbances may have influenced fire intensity and frequency in presettlement forests. Further, we propose that consumption of vast quantities of acorns by pigeons during the spring breeding season may partially explain the dominance of white oak (Quercus alba) throughout much of the presettlement north-central hardwoods region. Consequently, the pigeon's extinction may have facilitated the increase and expansion of northern red oak (Quercus rubra) during the twentieth century. Although it is difficult to accurately quantify how physical and chemical disturbances and mast consumption by Passenger Pigeon flocks affected forest ecology, we suspect they shaped landscape structure and species composition in eastern forests prior to the twentieth century. We believe their impact should be accounted for in estimates of the range of natural variability of conditions in eastern hardwood forests. Resumen:,Consideramos los posibles efectos que pudieron haber tenido parvadas de Palomas Migratorias (Ectopistes migratorius) sobre el régimen de perturbación y la composición de especies de bosques en Norte América oriental antes de la colonización. Sugerimos que las actividades de perchado y anidación de las palomas causaron perturbaciones frecuentes y extensas en los bosques orientales antes de la colonización por medio de la ruptura de ramas y tallos de árboles y la deposición de nutrientes del excremento de las palomas. Sospechamos que la deposición de combustibles resultantes de tales perturbaciones pudo haber influido en la intensidad y frecuencia de incendios forestales. Más aún, proponemos que el consumo de grandes cantidades de bellotas por las palomas en la primavera puede parcialmente explicar la dominancia de roble blanco (Quercus alba) en muchos de los bosques nor-orientales. En consecuencia, la extinción de la paloma pudo haber facilitado el incremento y expansión del roble rojo (Quercus rubra) durante el siglo veinte. Aunque es difícil cuantificar con precisión como las perturbaciones físicas y químicas y el consumo masivo por parvadas de palomas migratorias afectaron a la ecología forestal, sospechamos que modelaron la estructura del paisaje y la composición de especies en los bosques orientales antes del siglo veinte. Creemos que su impacto debería ser considerado cuando se hacen estimaciones del rango de variabilidad natural de las condiciones en bosques orientales de maderas duras. [source]

DWEPP: a dynamic soil erosion model based on WEPP source terms

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2007
N. S. Bulygina
Abstract A new rangeland overland-flow erosion model was developed based on Water Erosion Prediction Project (WEPP) sediment source and sink terms. Total sediment yield was estimated for rainfall simulation plots from the WEPP field experiments as well as for a small watershed without a well developed channel network. Both WEPP and DWEPP gave a similar level of prediction accuracy for total event soil losses measured from both rainfall simulation and small watershed experiments. Predictions for plot and hillslope scale erosion simulations were in the range of expected natural variability. Sediment yield dynamics were plotted and compared with experimental results for plots and hillslope, and the results were satisfactory. Effects of cover and canopy on the predicted sediment yields were well represented by the model. DWEPP provides a new tool for assessing erosion rates and dynamics, has physically based erosion mechanics descriptions, is sensitive to treatment differences on the experimental plots and has a well developed parameter database inherited from WEPP. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Insect community organisation in estuaries: the role of the physical environment

ECOGRAPHY, Issue 3 2002
D. Dudley Williams
Insects are reportedly uncommon in marine habitats and, from a spatial/temporal intercomparison perspective, estuaries are among the least studied. We examined the natural variability seen among insect community organisation in estuaries on both sides of the North Atlantic, and evaluated the role of their physical environments. Community composition was found to be strongly influenced by three physical factors: estuary size, the degree of inundation by incoming tides, and substrate size/stability. Insects formed a significant proportion (17,54%, by numbers) of the benthic community of coarse-grained-substratum estuaries, and species richness increased with estuary size. Nymphs/larvae of mayflies, stoneflies, caddisflies, elmid beetles and chironomids dominated channel sites inundated by up to 25% of all incoming tides, but a gradual loss in species richness occurred downstream. However, even the most seaward sites supported high insect densities (up to 25,016 and 5433 m,2, supporting 26 and 4 species, at sites inundated by 75 and 100% of all incoming tides, respectively). Sites covered by tides for between 3 and 5 h twice daily were dominated by orthocladine chironomids, especially of the genus Orthocladius. Chironomid larvae contribute significantly to the diets of some coastal fish species, particularly juvenile flounder and sticklebacks. We present a schematic model summarising the relationships between estuary size, degree of inundation by salt water and insect community structure. [source]

Rhodomyrtophyllum reticulosum (Rossm.) Knobloch & Z. Kva,ek , ein bedeutendes eozänes Florenelement im Tertiär Mitteleuropas

FEDDES REPERTORIUM, Issue 1-2 2003
U. Glinka Dipl.-Biol.
Nach kritischer Überprüfung blattepidermaler und blattmorphologischer Merkmalskomplexe an Blättern und Blattresten von RhodomyrtophyllumRüffle & Jähnichen aus dem Weißelster-Becken und seiner Randgebiete in Mitteldeutschland (Raum Halle,Leipzig,Borna,Altenburg,Zeitz,Zwickau und Ostthüringen) wird nachgewiesen, dass es sich bei den Blattresten um Vertreter einer einzigen Art handelt. Die Untersuchungen stützen sich auf 465 Fossilien aus meist kohlig- oder tonig-schluffiger Facies. In einer erweiterten Diagnose wird neben Grundformen mit typischen Charakteristiken die morphologische und blattanatomische Variationsbreite angeführt, die in den natürlichen Grenzen einer Species liegt. Untersuchungen an Blättern weiterer Fundorte in Europa kommen zum gleichen Ergebnis. An Arten von 21 Gattungen rezenter Myrtaceae erfolgen detaillierte Untersuchungen der Blattmorphologie und vor allem der Epidermisstruktur, die markante Ähnlichkeiten zur fossilen Sippe zeigen, was besonders bei Arten der Gattungen SyzygiumGaertn. und Eugenia L. erkennbar ist. Rhodomyrtophyllum reticulosum (Rossm.) Knobloch & Z. Kva,ek , a significant Eocene floral element in the Tertiary of Central Europe The leaf remains of RhodomyrtophyllumRüffle & Jähnichen from the Eocene occurring in the Weißelster Basin in central Germany (area Halle,Leipzig,Borna,Altenburg,Zeitz,Zwickau and Eastern Thuringia) have been proven to belong to a single species. This has been documented by analysing gross morphology and epidermical structure of 465 fossil leaves and leaf fragments from coal sand coal-silt facies. An emended diagnosis characterises besides basic forms with typical gross morphology and leaf anatomy, also extreme specimens within the limits of natural variability of Rhodomyrtophyllumreticulosum. These results correspond with studies from other European localities. Furthermore, detailed analyses of leaf morphology and epidermal structure of 21 recent species of the Myrtaceae are given. These demonstrate analogies of the fossil taxon studied especially among representatives of SyzygiumGaertn. and Eugenia L. [source]

Natural variability of fisheries and lunar illumination: a hypothesis

Short-term climatic trends affect the temporal variability of macroinvertebrates in California ,Mediterranean' streams

FRESHWATER BIOLOGY, Issue 12 2007
LEAH A. BÊCHE
Summary 1. Long-term studies in ecology are essential for understanding natural variability and in interpreting responses to disturbances and human perturbations. We assessed the long-term variability, stability and persistence of macroinvertebrate communities by analysing data from three regions in northern California with a mediterranean-climate. During the study period, precipitation either increased or decreased, and extreme drought events occurred in each region. 2. Temporal trends in precipitation resulted in shifts from ,dry-year' communities, dominated by taxa adapted to no or low flow, to ,wet-year' communities dominated by taxa adapted to high flows. The abundance of chironomid larvae was an important driver of community change. Directional change in community composition occurred at all sites and was correlated with precipitation patterns, with more dramatic change occurring in smaller streams. 3. All communities exhibited high to moderate persistence (defined by the presence/absence of a species) and moderate to low stability (defined by changes in abundance) over the study period. Stability and persistence were correlated with climatic variation (precipitation and El Niño Southern Oscillation) and stream size. Stability and persistence increased as a result of drought in small streams (first-order) but decreased in larger streams (second- and third-order). Communities from the dry season were less stable than those from the wet-season. 4. This study demonstrates the importance of long-term studies in capturing the effects of and recovery from rare events, such as the prolonged and extreme droughts considered here. [source]

Modelling the hydraulic preferences of benthic macroinvertebrates in small European streams

FRESHWATER BIOLOGY, Issue 1 2007
SYLVAIN DOLÉDEC
Summary 1. Relating processes occurring at a local scale to the natural variability of ecosystems at a larger scale requires the design of predictive models both to orientate stream management and to predict the effects of larger scale disturbances such as climate changes. Our study contributes to this effort by providing detailed models of the hydraulic preferences of 151 invertebrate taxa, mostly identified at the species level. We used an extensive data set comprising 580 invertebrate samples collected using a Surber net from nine sites of second and third order streams during one, two or three surveys at each site. We used nested non-linear mixed models to relate taxon local densities to bed shear stresses estimated from FliesswasserStammTisch hemisphere numbers. 2. An average model by taxon, i.e. independent from surveys, globally explained 25% of the density variations of taxa within surveys. A quadratic relationship existed between the average preferences and the niche breadth of taxa, indicating that taxa preferring extreme hemisphere numbers had a reduced hydraulic niche breadth. A more complete model, where taxa preferences vary across surveys, globally explained 38% of the variation of taxa densities within surveys. Variations in preferences across surveys were weak for taxa preferring extreme hemisphere numbers. 3. There was a significant taxonomic effect on preferences computed from the complete model. By contrast, season, site, average hemisphere number within a survey and average density of taxa within a survey used as covariates did not consistently explain shifts in taxon hydraulic preferences across surveys. 4. The average hydraulic preferences of taxa obtained from the extensive data set were well correlated to those obtained from two additional independent data sets collected in other regions. The consistency of taxon preferences across regions supports the use of regional preference curves for estimating the impact of river management on invertebrate communities. By contrast, the hydraulic niche breadths of taxa computed from the different data sets were not related. [source]

Functional biodiversity of macroinvertebrate assemblages along major ecological gradients of boreal headwater streams

FRESHWATER BIOLOGY, Issue 9 2005
JANI HEINOArticle first published online: 3 AUG 200
Summary 1. Biodiversity,environment relationships are increasingly well-understood in the context of species richness and species composition, whereas other aspects of biodiversity, including variability in functional diversity (FD), have received rather little rigorous attention. For streams, most studies to date have examined either taxonomic assemblage patterns or have experimentally addressed the importance of species richness for ecosystem functioning. 2. I examined the relationships of the functional biodiversity of stream macroinvertebrates to major environmental and spatial gradients across 111 boreal headwater streams in Finland. Functional biodiversity encompassed functional richness (FR , the number of functional groups derived from a combination of functional feeding groups and habit trait groups), FD , the number of functional groups and division of individuals among these groups, and functional evenness (FE , the division of individuals among functional groups). Furthermore, functional structure (FS) comprised the composition and abundance of functional groups at each site. 3. FR increased with increasing pH, with additional variation related to moss cover, total nitrogen, water colour and substratum particle size. FD similarly increased with increasing pH and decreased with increasing canopy cover. FE decreased with increasing canopy cover and water colour. Significant variation in FS was attributable to pH, stream width, moss cover, substratum particle size, nitrogen, water colour with the dominant pattern in FS being related to the increase of shredder-sprawlers and the decrease of scraper-swimmers in acidic conditions. 4. In regression analysis and redundancy analysis, variation in functional biodiversity was not only related to local environmental factors, but a considerable proportion of variability was also attributable to spatial patterning of environmental variables and pure spatial gradients. For FR, 23.4% was related to pure environmental effects, 15.0% to shared environmental and spatial effects and 8.0% to spatial trends. For FD, 13.8% was attributable to environmental effects, 15.2% to shared environmental and spatial effects and 5% to spatial trends. For FE, 9.0% was related to environmental variables, 12.7% to shared effects of environmental and spatial variables and 4.5% to spatial variables. For FS, 13.5% was related to environmental effects, 16.9% to shared environmental and spatial effects and 15.4% to spatial trends. 5. Given that functional biodiversity should portray variability in ecosystem functioning, one might expect to find functionally rather differing ecosystems at the opposite ends of major environmental gradients (e.g. acidity, stream size). However, the degree to which variation in the functional biodiversity of stream macroinvertebrates truly portrays variability in ecosystem functioning is difficult to judge because species traits, such as feeding roles and habit traits, are themselves strongly affected by the habitat template. 6. If functional characteristics show strong responses to natural environmental gradients, they also are likely to do so to anthropogenic environmental changes, including changes in habitat structure, organic inputs and acidifying elements. However, given the considerable degree of spatial structure in functional biodiversity, one should not expect that only the local environment and anthropogenic changes therein are responsible for this variability. Rather, the spatial context, as well as natural variability along environmental gradients, should also be explicitly considered in applied research. [source]

An application of canonical correspondence analysis for developing ecological quality assessment metrics for river macrophytes

FRESHWATER BIOLOGY, Issue 5 2005
IAN DODKINS
Summary 1. Aquatic macrophyte composition and abundance is required by the European Union's Water Framework Directive for determining ecological status. Five metrics were produced that can be combined to determine the deviation of aquatic macrophytes from reference conditions in Northern Ireland's rivers. 2. Species optima and niche breadths along silt, nitrate, pH, conductivity and dissolved oxygen gradients were generated from aquatic macrophyte and water quality surveys conducted at 273 sites throughout Northern Ireland using Canonical Correspondence Analysis (CCA). Five metric scores based on these environmental gradients were determined at new monitoring sites using the mean optima of the species occurring at the site, weighted by percentage cover and niche breadth of each species. 3. A preliminary reference network of 32 sites of high physico-chemical and hydromorphological quality, and representative of the range of river types in Northern Ireland, enabled reference metric scores to be produced for each river type. Five unimpacted and twenty impacted sites were used for testing the performance of the metrics. By subtracting reference metric scores from metric scores at a monitoring site measures of ecological impact could be determined along five different impact gradients. Metrics were also combined to give a measure of total ecological change. 4. The metrics system distinguished unimpacted from impacted sites and correctly identified 77% of the known impacts. The metrics distinguished different types of impact, e.g. silt and nitrate. 5. Aquatic macrophyte occurrence and abundance has high natural variability at a site, both temporally and spatially. This method was designed to be sensitive to ecological change whilst reducing noise caused by natural variation. [source]

Uncertainties in early Central England temperatures

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2010
David E. Parker
Abstract Uncertainties in historical climate records constrain our understanding of natural variability of climate, but estimation of these uncertainties enables us to place recent climate events and extremes into a realistic historical perspective. Uncertainties in Central England temperature (CET) since 1878 have already been estimated; here we estimate uncertainties back to the start of the record in 1659, using Manley's publications and more recently developed techniques for estimating spatial sampling errors. Estimated monthly standard errors are of the order of 0.5 °C up to the 1720s, but 0.3 °C subsequently when more observing sites were used. Corresponding annual standard errors are up to nearly 0.4 °C in the earliest years but around 0.15 °C after the 1720s. Daily standard errors from 1772, when the daily series begins, up to 1877 are of the order of 1 °C because only a single site was used at any one time. Inter-diurnal variability in the daily CET record appears greater before 1878 than subsequently, partly because the sites were in the Midlands or southern England where day-to-day temperature variability exceeds that in the Lancashire part of Manley's CET. Copyright © 2009 Royal Meteorological Society [source]

An Arctic and antarctic perspective on recent climate change

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2007
John Turner
Abstract We contrast recent climatic and environmental changes and their causes in the Arctic and the Antarctic. There are continuing increases in surface temperatures, losses of sea ice and tundra, and warming of permafrost over broad areas of the Arctic, while most of the major increase in Antarctic temperatures is on the Antarctic Peninsula associated with sea ice loss in the Bellingshausen,Amundsen Seas sector. While both natural atmospheric and oceanic variability, and changes in external forcing including increased greenhouse gas concentrations, must be considered in the quest for understanding such changes, the interactions and feedbacks between system components are particularly strong at high latitudes. For the 1950s to date in the Arctic and for 1957 to date in the Antarctic, positive trends in large-scale atmospheric circulation represented by the Arctic oscillation (AO) and Antarctic oscillations (AAO) and the Pacific North American (PNA) pattern contribute to the long-term temperature trends. However, continuing Arctic trends during the last decade of near neutral AO will require alternate explanations. The trend in the AAO since 1950 is larger than expected from natural variability and may be associated with the decrease in stratospheric ozone over Antarctic. The persistence shown in many Arctic and Antarctic Peninsula components of climate and their influence through possible feedback supports continuation of current trends over the next decade. One can expect large spatial and temporal differences, however, from the relative contributions of intrinsic variability, external forcing, and internal feedback/amplifications. It is particularly important to resolve regional feedback processes in future projections based on modeling scenarios. Copyright © 2006 Royal Meteorological Society. [source]

Features of cross-Pacific climate shown in the variability of China and US precipitation

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2005
Q. Li
Abstract In this study, we have analyzed the climate features of China and the United States with a focus on the differences, similarities, connectivity, and predictability of precipitation and the relationships between precipitation and large-scale patterns of natural variability. China precipitation is characterized by large seasonality, with a maximum in summer and a minimum in winter. The seasonality of precipitation shows an increasing linear tendency in northwest China, with a change of about 20% from 1901 to 1998. A relatively weaker increasing tendency also appears in the Big Bend of Yellow River (BBYR) and the Tibetan Plateau, while southwest China experiences a decreasing tendency. Furthermore, the seasonality in the BBYR shows particularly significant interdecadal variability, while that of southern and eastern China has decreased slightly in the recent decades. Compared to China, the United States as a whole has less precipitation in summer but more precipitation in other seasons. Here, the seasonality of precipitation is only about 24% of that in China. The annual mean precipitation is 64.1 mm per month in the United States, compared to 54.6 mm per month in China. The seasonality of precipitation exhibits a decreasing tendency in the southeast, Pacific Northwest, and Gulf Coast and an increasing tendency in the Great Lakes. The seasonality in the Great Plains exhibits large interdecadal variability. The long-term variations of precipitation are highly seasonally dependent. In summer, a decreasing trend is observed in north China and an increasing trend is found in eastern-central China. However, these trends are almost opposite in spring. In addition, the fall precipitation decreases with time nearly everywhere in China except for the middle and lower reaches of the Yangtze River Valley. Results also indicate that the El Niño/Southern Oscillation (ENSO), the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the North Pacific (NP) fluctuation affect strongly the variations of China and US precipitation. Although these influences vary with regions and seasons, we in particular emphasize the importance of AO and NAO for China precipitation and NP and PDO for US precipitation. In fall, ENSO and PDO are the two phenomena that influence predominantly precipitation variability in both China and the United States We also identify the common phenomena that influence China and US regional precipitation and provide a better understanding of the physical mechanism for precipitation variability through the associated changes in atmospheric and oceanic conditions. Furthermore, we develop a linear regression model, based on multiple regression method by combining the regionally and seasonally varying impacts, to increase the skill of precipitation prediction. Copyright © 2005 Royal Meteorological Society [source]

Signals of anthropogenic influence on European warming as seen in the trend patterns of daily temperature variance

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2005
A. M. G. Klein Tank
Abstract Signals of anthropogenic warming over Europe are searched for in the spatial trend patterns for the variance and skewness (expressed by the 10th and 90th percentiles) of the distribution of daily mean temperature. Comparisons are made between these patterns in the station records of the European Climate Assessment dataset for the 1976,99 period, the patterns associated with natural variability in the observations (which were empirically derived from the observations in the 1946,75 period), and the patterns of future warming and natural variability as simulated by the National Center for Atmospheric Research Community Climate System Model in the Challenge ensemble experiment. The results indicate that, on the basis of the patterns for the variance, a distinction can be made between temperature change due to natural variability and temperature change due to changes in external forcing. The observed variance trend patterns for the spring (March,May) and summer (June,August) warming 1976,99 are clearly different from the patterns for the change in variance associated with a warming due to natural variability in the observations. This led us to conclude that a change in an external forcing has to be invoked to explain the observed spring and summer warming. From the evaluation of the greenhouse and natural variability patterns in the climate model simulations, we infer that the observed spring and summer variance trend patterns contain imprints consistent with anthropogenic warming. The analysis of the variance trend patterns for the winter (December,February) season is inconclusive about identifying causes of the observed warming for that season. Unlike the other three seasons, the autumn (September,November) is for Europe a period of cooling in recent decades. The observed variance trend pattern for this season closely resembles the estimated pattern for the change in variance associated with a cooling due to natural variability, indicating that the observed autumn cooling can be ascribed to random weather variations in the period under consideration. Copyright © 2005 Royal Meteorological Society [source]

Homeostasis and Gauss statistics: barriers to understanding natural variability

JOURNAL OF EVALUATION IN CLINICAL PRACTICE, Issue 3 2010
Bruce J. West PhD
Abstract Rationale, In this paper, the concept of knowledge is argued to be the top of a three-tiered system of science. Aims and objectives, The first tier is that of measurement and data, followed by information consisting of the patterns within the data, and ending with theory that interprets the patterns and yields knowledge. Thus, when a scientific theory ceases to be consistent with the database the knowledge based on that theory must be re-examined and potentially modified. Results, Consequently, all knowledge, like glory, is transient. Methods, Herein we focus on the non-normal statistics of physiologic time series and conclude that the empirical inverse power-law statistics and long-time correlations are inconsistent with the theoretical notion of homeostasis. Conclusions, We suggest replacing the notion of homeostasis with that of Fractal Physiology. [source]

Instream Flow Science For Sustainable River Management,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2009
Geoffrey E Petts
Abstract:, Concerns for water resources have inspired research developments to determine the ecological effects of water withdrawals from rivers and flow regulation below dams, and to advance tools for determining the flows required to sustain healthy riverine ecosystems. This paper reviews the advances of this environmental flows science over the past 30 years since the introduction of the Instream Flow Incremental Methodology. Its central component, Physical HABitat SIMulation, has had a global impact, internationalizing the e-flows agenda and promoting new science. A global imperative to set e-flows, including an emerging trend to set standards at the regional scale, has led to developments of hydrological and hydraulic approaches but expert judgment remains a critical element of the complex decision-making process around water allocations. It is widely accepted that river ecosystems are dependent upon the natural variability of flow (the flow regime) that is typical of each hydro-climatic region and upon the range of habitats found within each channel type within each region. But as the sophistication of physical (hydrological and hydraulic) models has advanced emerging biological evidence to support those assumptions has been limited. Empirical studies have been important to validate instream flow recommendations but they have not generated transferable relationships because of the complex nature of biological responses to hydrological change that must be evaluated over decadal time-scales. New models are needed to incorporate our evolving knowledge of climate cycles and morphological sequences of channel development but most importantly we need long-term research involving both physical scientists and biologists to develop new models of population dynamics that will advance the biological basis for 21st Century e-flow science. [source]

Vegetation, environment, and time: The origination and termination of ecosystems

JOURNAL OF VEGETATION SCIENCE, Issue 5 2006
Stephen T. Jackson
Abstract Terrestrial ecosystems originate when particular plant species attain dominance at specific locations under specific environmental regimes. Ecosystems terminate, gradually or abruptly, when the dominant species or functional types are replaced by others, usually owing to environmental change or severe and irreversible disturbance. Assessing whether current ecosystems are sustainable in the face of future environmental change can be aided by examining the range of environmental variation those ecosystems have experienced in the past, and by determining the environmental conditions under which those ecosystems arose. The range of environmental variation depends on the time scale at which it is assessed. A narrow time span (e.g. 200,300 years) may underestimate the range of variation within which an ecosystem is sustainable, and it may also underestimate the risk of major transformation or disruption of that ecosystem by environmental change. Longer time spans (e.g. 1000,2000 years) increase the range of variation, by encompassing a larger sample of natural variability as well as non-stationary variability in the earth system. Most modern ecosystems disappear when the time span is expanded to 10000,15 000 years owing to secular changes in earth's climate system. Paleo-ecological records can pinpoint the time of origination of specific ecosystems, and paleo-environmental records can reveal the specific environmental changes that led to development of those ecosystems and the range of environmental variation under which those ecosystems have maintained themselves in the past. This information can help identify critical environmental thresholds beyond which specific modern ecosystems can no longer be sustained. [source]

Use of evans blue dye to compare limb muscles in exercised young and old mdx mice

MUSCLE AND NERVE, Issue 4 2010
Christine I. Wooddell PhD
Abstract Evans blue dye (EBD) is used to mark damaged and permeable muscle fibers in mouse models of muscular dystrophy and as an endpoint in therapeutic trials. We counted EBD-positive muscle fibers and extracted EBD from muscles sampled throughout the hindlimbs in young adult and old mdx mice to determine if the natural variability in morphology would allow measurement of a functional improvement in one limb compared to the contralateral limb. Following one bout of rotarod or treadmill exercise that greatly increased serum creatine kinase levels, the number of EBD+ muscle fibers in 12,19-month-old mdx mice increased 3-fold, EBD in the muscles increased, and, importantly, contralateral pairs of muscles contained similar amounts of EBD. In contrast, the intra- and interlimb amounts of EBD in 2,7-month-old mdx mice were much too variable. A therapeutic effect can more readily be measured in old mdx mice. These results will be useful in the design of therapy protocols using the mdx mouse. Muscle Nerve, 2010 [source]

Passive microwave radiometer channel selection basedoncloudandprecipitation information content

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 617 2006
Sabatino Di Michele
Abstract The information content of microwave frequencies between 5 and 200 GHz for rain, snow and cloud water retrievals over ocean and land surfaces was evaluated using optimal estimation theory. The study was based on large datasets representative of summer and winter meteorological conditions over North America, Europe, Central Africa, South America and the Atlantic obtained from short-range forecasts with the operational ECMWF model. The information content of rain, snow and cloud water was traded off against the uncertainties due to the natural variability of other variables that microwave observations are sensitive to. These are surface emissivity, land surface skin temperature, atmospheric temperature and moisture. The estimation of the underlying error statistics was based on ECMWF model forecast error statistics. The results suggest that a number of frequency bands are most suited for the retrieval of (i) rain over oceans: 15,18, 35,40, 80, 145, 118.75±10,14 GHz; rain over land: 85,100, 135,140 GHz, (ii) snow over land and oceans: 95,100, 140,150, 187 GHz, (iii) clouds over oceans: 40, 80,85 GHz; clouds over land: 90,100, 135,140 GHz. For radiometers designed for global and multi-season applications, several channels in all of the above frequency ranges would be desirable for optimizing channel usage in hydrometeor retrievals depending on the observed situation. Copyright © 2006 Royal Meteorological Society. [source]

Atlantic air,sea interaction and seasonal predictability

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 583 2002
M. J. Rodwell
Abstract We analyse patterns of North Atlantic air,sea interaction in observations and model output throughout the annual cycle with the dual aims of validating natural variability in climate models, and quantifying seasonal predictability of the atmosphere and of ocean surface temperatures. The Met Office's HadCM3 coupled ocean,atmosphere model is shown to represent well the atmospheric forcing of sea surface temperature (SST) in the North Atlantic region through the action of latent-heat fluxes. Winter ocean temperature anomalies in both observations and model appear to be preserved below the shallow summer mixed layer and to re-emerge in the following autumn. We find observational evidence from the last half of the twentieth century for SST forcing of the atmospheric circulation in the North Atlantic region. Results validate our atmospheric model (HadAM2b) and confirm the levels of potential predictability of the North Atlantic Oscillation (NAO) that have been found in recent modelling studies. We suggest that the ultimate correlation skill of a winter NAO hindcast in this period is in the range 0.45 to 0.63. Analysis of observational and atmospheric model data from the first half of the twentieth century identifies very little predictability of the winter NAO. We suggest that the change in seasonal predictability is genuine and may be related to the strength of decadal oscillations. The ocean,atmosphere model, which incorporates a different atmospheric component (HadAM3), fails to show a causal link between North Atlantic temperatures and the atmospheric circulation even during periods where low-frequency variability is as strong as in the recent observations. A brief observational investigation suggests that any implied predictability of the winter NAO based on a knowledge of South Atlantic SSTs depends on the existence of secular trends in the data. Tropical Pacific SSTs appear to influence the winter climate of the North Atlantic region, but not via trends in the NAO. © Crown copyright, 2002. [source]

A baseline biological survey of the proposed Taputeranga Marine Reserve (Wellington, New Zealand): spatial and temporal variability along a natural environmental gradient

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2009
Anjali Pande
Abstract 1.Four macroalgal, four macroinvertebrate and eight fish species were surveyed at eight sites (three inside, five outside the proposed reserve) over three years before the establishment of the Taputeranga Marine Reserve (MR) on Cook Strait (Wellington, New Zealand). This baseline data set was used to estimate temporal and spatial variability in size and abundance of these taxa, and will be used to quantify taxon-specific changes in size and abundance once the MR is established. 2.Statistically significant differences in size and/or abundance were observed for many taxa among the sites. These differences are consistent with the existence of a natural environmental gradient from the west (entrance to Cook Strait) to the east (Wellington Harbour). This gradient highlights the importance of conducting a pre-reserve baseline survey at multiple sites and over multiple years to better understand the conservation or fisheries benefits that MRs are expected to deliver. 3.Two macroalgal, one macroinvertebrate, and six fish species showed statistically significant seasonal variation in abundance. Subsequent multi-taxa monitoring needs to include a seasonal component to capture this natural variability. 4.This multi-site and multi-year data set represents one of the most comprehensive and robust baseline data sets available anywhere in the world. It will be used to quantify the ecological changes associated with a newly established full no-take marine reserve. Ongoing monitoring will enhance understanding of the sizes and abundances of key taxa, allow a detailed determination of the conservation effects of reserve establishment, and inform management decisions for Wellington's south coast. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Conservation importance of semi-arid streams in north-eastern Brazil: implications of hydrological disturbance and species diversity

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2006
L. Maltchik
Abstract 1.Intermittent streams in the semi-arid region of Brazil are distinctive landscape features existing as dry watercourses for most of the time. It has been recognized that the extremes of flooding and total absence of water flow are the principal hydrological characteristics of rivers and streams in this region. This is a consequence of complex climatic patterns that lead to an irregular distribution of the small amount of rainfall and low thermal amplitude. The latter is the main climatic difference between the Brazilian semi-arid region and other semi-arid lands. 2.The expansion of water resource development has been a threat to the natural flow regime and the ecological integrity of rivers and streams in semi-arid Brazil. Efforts to manage and conserve the natural flow regime of these systems are hampered by limited scientific information on the ecological processes driving their flora and fauna and the responses of biota to the high natural variability in flow regime. 3.The most important issues in the conservation of streams in semi-arid Brazil are the need for their recognition as important sites of biodiversity and that this diversity is closely associated with natural patterns of flow and the hydrological disturbances. Without the understanding of how the extremes of flooding and drought affect the aquatic fauna, the conservation strategies for Brazilian semi-arid streams and their fauna will not be effective. 4.Therefore, conservation efforts in semi-arid Brazil must ensure that the processes sustaining biodiversity are maintained at multiple-scale and landscape levels and that the natural integrity of the riparian zone is maintained Copyright © 2006 John Wiley & Sons, Ltd. [source]

Change in the dominant decadal patterns and the late 1980s abrupt warming in the extratropical Northern Hemisphere

ATMOSPHERIC SCIENCE LETTERS, Issue 3 2010
Tzu-Ting Lo
Abstract Widespread abrupt warming in the extratropical Northern Hemisphere (NH) occurred in the late 1980s. This warming was associated with a change in the relative influence of the Pacific Decadal Oscillation (PDO)-like pattern and the Arctic Oscillation (AO)-like pattern. The AO-like pattern has had a dominant influence on the NH-mean temperature since the late 1980s, whereas the influence of the PDO has weakened. The AO-like mode appears as part of natural variability in the pre-industrial simulations of the CMIP3/IPCC climate models. However, its emergence in the late 1980s was not simulated by most models with or without the observed increasing greenhouse effect in the 20th century. Copyright © 2010 Royal Meteorological Society [source]

Radiative cooling effect of Hurricane Florence in 2006 and precipitation of Typhoon Matsa in 2005

ATMOSPHERIC SCIENCE LETTERS, Issue 2 2009
Quanhua Liu
Abstract The increasing strength of tropical cyclones may be a response of the Earth's interaction between natural variability and human activities. Negative effects of the severe storms, such as flooding, landslides, damage to properties, and even a number of human casualties, have been reported many times. This study reported other aspects on Hurricanes and Typhoons, which may be beneficial to the world. We found that Hurricane Florence in 2006 decreased radiation energy by , 0.5 × 1020 J to the Earth-atmospheric system, about 10% of the annual global energy consumption. If the amount of energy uniformly distributes over the whole Earth surface and over 1-year time, it corresponds to a power of , 0.003 W m,2 The total forcing power on climate change is 0.24 W m,2, if we only take account for the stored fluxes in water, atmosphere, continents, and heat required to melt glaciers and sea ice. Thus, the shielding effect of solar radiation by tropical storms could contribute to ease global warming. In addition, hurricane and typhoon can ease drought sometimes. This study found that the total rainwater carried by Typhoon Matsa in August 2005 into China's inland amounts to about 135 billion tons. The rainfall over the northern China eased severe drought in summer 2005. Copyright © 2009 Royal Meteorological Society [source]

Maternal serum activin, inhibin, human chorionic gonadotrophin and ,-fetoprotein as second trimester predictors of pre-eclampsia

BJOG : AN INTERNATIONAL JOURNAL OF OBSTETRICS & GYNAECOLOGY, Issue 1 2003
Emma J. Davidson
Objective To compare the serum levels of human chorionic gonadotrophin (hCG), ,-fetoprotein, activin A, inhibin A and inhibin isoforms containing pro and ,C in the second trimester serum of women who subsequently developed hypertensive disorders of pregnancy with those who remained normotensive throughout pregnancy. Design Retrospective case,control study of 15,20 week serum samples matched for duration of storage at ,20°C. Setting Antenatal clinics at a teaching hospital in Scotland. Sample Second trimester serum samples of 39 women who subsequently developed pre-eclampsia, 31 who subsequently developed pregnancy-induced hypertension and 155 women who remained normotensive throughout pregnancy. Main outcome measures hCG, ,-fetoprotein, activin A, inhibin A and inhibin pro,,C serum levels. Results Activin A levels in serum were significantly elevated in women who later developed pregnancy-induced hypertension (26% increase compared with controls) and hCG levels were significantly elevated in women who later developed pre-eclampsia (24% increase compared with controls). ,-Fetoprotein, inhibin A and inhibin pro,,C levels were not significantly elevated in the patient groups compared with their controls. Conclusions A combination of analyses including second trimester serum activin A and hCG may yet prove to be helpful predictors of women at risk of hypertensive disorders of pregnancy. While the results proved significant, the effects reported in this study are too modest compared with natural variability to be useful as screening tools on their own. [source]

Developmental craniofacial anthropometry: Assessment of race effects

CLINICAL ANATOMY, Issue 7 2009
Reid B. Durtschi
Abstract Differences in craniofacial anatomy among racial groups have been documented in a variety of structures, but the oral and maxillofacial regions have been shown to be a particularly defining region of variability between different racial/ethnic groups. Such comparisons are informative, but they neither address developmental changes of the craniofacial anatomy nor do they assess or take into account the natural variability within individual races that may account for similar reported, across-group variations. The purpose of this report was to compare,using medical imaging studies,the growth trend of select race-sensitive craniofacial variables in the oral and pharyngeal regions when all races [White, Asian, Black, and Hispanic (AR)] are included versus only a single race category [White (WR)]. Race effect was tested by comparing sex-specific growth fits (fourth degree polynomial model) for AR versus WR data. Findings indicate that the inclusion of all races versus a single race did not significantly alter the growth model fits. Thus, the inclusion of all races permits the advancement of general growth models; however, methodologically, it is best to treat the race variable as a covariate in all future analysis to test for both potential all race effects or individual race effects, on general growth models. Clin. Anat. 22:800,808, 2009. © 2009 Wiley-Liss, Inc. [source]