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1.
Patterns of variability in soil properties and vegetation cover following abandonment of olive groves in Catalonia (NE Spain) 总被引:2,自引:0,他引:2
Hernando García David Tarrasn Maria Mayol Núria Male-Bascompte Miquel Riba 《Acta Oecologica》2007,31(3):316-324
Understanding patterns and processes involved in changes in soil and vegetation after agricultural abandonment is a key issue for management policies leading to land restoration and reclamation in Mediterranean semiarid environments. We selected a number of active and abandoned fields in two regions of olive groves in Catalonia (NE Spain), in order to analyze changes in certain soil properties and vegetation cover variables, as well as their interrelationships. The soil chemical properties considered, summarized into a single PCA axis, showed significant spatial (regional) differences and no temporal (successional) pattern, indicative of the strong influence of the parent rock material. The soil physical variables examined also showed significant regional variability, but such differences could be partially explained by successional changes. The variability at the landscape level and the observed successional trends for soil physical properties are interpreted as a result of both the influence of the bedrock and contrasting management practices prior to abandonment in each region. Although we did not find significant regional or successional variability in a global measure of plant cover, we did find significant and different patterns of variability for each of the main plant functional groups considered. Regional and post-agricultural variability in soil physical properties seem to be the prime factors determining the abundance of the main plant functional groups. 相似文献
2.
Pueyo E Corrias A Virág L Jost N Szél T Varró A Szentandrássy N Nánási PP Burrage K Rodríguez B 《Biophysical journal》2011,(12):2892-2902
Enhanced temporal and spatial variability in cardiac repolarization has been related to increased arrhythmic risk both clinically and experimentally. Causes and modulators of variability in repolarization and their implications in arrhythmogenesis are however not well understood. At the ionic level, the slow component of the delayed rectifier potassium current (IKs) is an important determinant of ventricular repolarization. In this study, a combination of experimental and computational multiscale studies is used to investigate the role of intrinsic and extrinsic noise in IKs in modulating temporal and spatial variability in ventricular repolarization in human and guinea pig. Results show that under physiological conditions: i), stochastic fluctuations in IKs gating properties (i.e., intrinsic noise) cause significant beat-to-beat variability in action potential duration (APD) in isolated cells, whereas cell-to-cell differences in channel numbers (i.e., extrinsic noise) also contribute to cell-to-cell APD differences; ii), in tissue, electrotonic interactions mask the effect of IKs noise, resulting in a significant decrease in APD temporal and spatial variability compared to isolated cells. Pathological conditions resulting in gap junctional uncoupling or a decrease in repolarization reserve uncover the manifestation of IKs noise at cellular and tissue level, resulting in enhanced ventricular variability and abnormalities in repolarization such as afterdepolarizations and alternans. 相似文献
3.
M.A. Coleman 《Journal of experimental marine biology and ecology》2003,291(1):131-145
Recruitment is often important in structuring patterns of distribution and abundance of algal assemblages. Intertidal and subtidal turfing algal assemblages consistently vary on small spatial scales (tens of centimetres), and this variability may be due to patterns of recruitment varying on similar spatial scales. The validity of this model was evaluated by testing the hypothesis that the numbers and types of taxa recruiting to turfs would vary at small spatial scales within intertidal and within subtidal habitats. Abundances of algal recruits were estimated on sandstone plates that were placed at a number of spatial scales within intertidal and within subtidal habitats (centimetres to tens of metres). Significant differences in entire assemblages were found only between habitats. This was explained by abundances of individual taxa, which generally varied between intertidal and subtidal habitats or between sites within habitats. Only small proportions of the overall spatial variation (dissimilarity) could be explained at the scale of replicate recruitment plates that were centimetres apart. Results indicate that while recruitment may contribute to differences between intertidal and subtidal habitats, it cannot explain the small-scale spatial variability in established turfing algal assemblages within these habitats. There was some evidence to suggest that recruitment may contribute to variability in established turfing algal assemblages but only over longer time scales than examined here. 相似文献
4.
Rapid Change of Chromomeric and Pairing Patterns of Polytene Chromosome Tips in D. MELANOGASTER: Migration of Polytene-Nonpolytene Transition Zone?
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Paul A. Roberts 《Genetics》1979,92(3):861-878
The high variability of chromomeric patterns in near-terminal regions of polytene chromosome arms has been explored in a number of races, strains and hybrids of Drosophila melanogaster. Traditional explanations for tip differences between strains (differential compaction of chromatin, somatic or germinal deletion) are examined and, in the light of the reported observations, rejected. The range of polytene tip variability and rates of change in wild races are greater than has been supposed: strains formerly considered to be terminally deleted appear to gain terminal bands; others, formerly considered normal, appear to have lost them. Strains with high cell-to-cell tip variability are also described. Cell-to-cell variations, as well as much of the observed rapid changes in tip appearance, are probably due to heritable differences in the location of an abrupt transition zone between polytene and nonpolytene chromatin. A quantitative relationship between the amount of certain subterminal bands present and the frequency of tip association of nonhomologous chromosomes is shown and its possible significance for chromosome is shown and its possible for chromosome pairing discussed. 相似文献
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To test the hypothesis that actA allelic variation contributes to virulence differences among Listeria monocytogenes strains, cell-to-cell spread and intracellular ActA phosphorylation patterns were characterized for 14 wild-type isolates and selected isogenic mutants. Our data show that (i) while actA allelic variation is not responsible for enhanced cell-to-cell spread observed in epidemic clone I strains, actA allelic variation may contribute to reduced plaque size observed in some isolates, (ii) actA sequence alone determines phosphorylation-dependent ActA banding patterns, and (iii) sequence variation at the positively selected ActA residue 498 does not contribute to ActA phosphorylation patterns or to differences in cell-to-cell spread. 相似文献
8.
Elizabeth R. Selig Kenneth S. Casey John F. Bruno 《Global Ecology and Biogeography》2010,19(3):397-411
Aim Coral reefs are widely considered to be particularly vulnerable to changes in ocean temperatures, yet we understand little about the broad‐scale spatio‐temporal patterns that may cause coral mortality from bleaching and disease. Our study aimed to characterize these ocean temperature patterns at biologically relevant scales. Location Global, with a focus on coral reefs. Methods We created a 4‐km resolution, 21‐year global ocean temperature anomaly (deviations from long‐term means) database to quantify the spatial and temporal characteristics of temperature anomalies related to both coral bleaching and disease. Then we tested how patterns varied in several key metrics of disturbance severity, including anomaly frequency, magnitude, duration and size. Results Our analyses found both global variation in temperature anomalies and fine‐grained spatial variability in the frequency, duration and magnitude of temperature anomalies. However, we discovered that even during major climatic events with strong spatial signatures, like the El Niño–Southern Oscillation, areas that had high numbers of anomalies varied between years. In addition, we found that 48% of bleaching‐related anomalies and 44% of disease‐related anomalies were less than 50 km2, much smaller than the resolution of most models used to forecast climate changes. Main conclusions The fine‐scale variability in temperature anomalies has several key implications for understanding spatial patterns in coral bleaching‐ and disease‐related anomalies as well as for designing protected areas to conserve coral reefs in a changing climate. Spatial heterogeneity in temperature anomalies suggests that certain reefs could be targeted for protection because they exhibit differences in thermal stress. However, temporal variability in anomalies could complicate efforts to protect reefs, because high anomalies in one year are not necessarily predictive of future patterns of stress. Together, our results suggest that temperature anomalies related to coral bleaching and disease are likely to be highly heterogeneous and could produce more localized impacts of climate change. 相似文献
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The viscoelastic properties of cells are important in predicting cell deformation under mechanical loading and may reflect cell phenotype or pathological transition. Previous studies have demonstrated that viscoelastic parameters estimated by finite element (FE) analyses of micropipette aspiration (MA) data differ from those estimated by the analytical half-space model. However, it is unclear whether these differences are statistically significant, as previous studies have been based on average cell properties or parametric analyses that do not reflect the inherent experimental and biological variability of real experimental data. To determine whether cell material parameters estimated by the half-space model are significantly different from those predicted by the FE method, we implemented an inverse FE method to estimate the viscoelastic parameters of a population of primary porcine aortic valve interstitial cells tested by MA. We found that inherent differences between the analytical and inverse FE estimation methods resulted in statistically significant differences in individual cell properties. However, in cases with small pipette to cell radius ratios and short loading periods, model-dependent differences were masked by experimental and cell-to-cell variability. Analytical models that account for finite cell-size and loading rate further relaxed the experimental conditions for which accurate cell material parameter estimates could be obtained. These data provide practical guidelines for analysis of MA data that account for the wide range of conditions encountered in typical experiments. 相似文献
11.
Spatial hierarchical approach in community ecology: a way beyond high context-dependency and low predictability in local phenomena 总被引:4,自引:0,他引:4
Takashi Noda 《Population Ecology》2004,46(2):105-117
Patterns and functioning of communities, which are determined by a set of processes operating at a large variety of spatial and temporal scales, exhibit quite high context-dependency and low predictability at the fine spatial scales at which recent studies have concentrated. More attention to broader scale and across-scale phenomena may be useful to search for general patterns and rules in communities. In this context, it is effective to incorporate hierarchical spatial scale explicitly into the experimental and sampling design of field studies, an approach referred to here as the spatial hierarchical approach, focusing on a particular assemblage in which biological interaction and species life history are well known. The spatial hierarchical approach can provide insight into the effects of scale in operating processes and answers to a number of important questions in community ecology such as: (1) detection of patterns and processes in spatiotemporal variability in communities, including how to explain the partitioning of pattern information of species diversity at a broad scale into finer scales, and the pattern of spatial variability of community properties at the finest spatial scale; (2) evaluation of changes in patterns observed in macroecology at finer scales; (3) testing of models explaining the coexistence of competing species; and (4) detection of latitudinal patterns in spatiotemporal variability in communities and their causal processes. 相似文献
12.
Variation in spatial patterns of competing organisms is of fundamental importance for community and population processes. Yet the mechanisms controlling subjects like the degree of spatial aggregation in competing insect larvae across fragmented resources have rarely been addressed. In the present study, we tested for systematic differences in the spatial distribution patterns of Drosophila subobscura in natural fly communities, and found significant differences in two habitats that differ in the availability of breeding substrate types (decaying fruits). Assuming that the spatial egg-laying behaviour of drosophilids is under genetic control, and that different breeding substrates mediate different density-dependent larval fitness consequences, we tested whether adaptive genotypic variability is involved in the local variation of egg distribution patterns. We extracted isofemale lines from both habitats and analysed the spatial distribution of eggs achieved by single female flies under controlled laboratory conditions. This is a reasonable first test, because spatial patterns at the fly population level can be attributed to individual egg-laying behaviour. The degree of individual egg aggregation significantly depended on fly line identity, which indicates the existence of behavioural variants in natural populations. Based on habitat-dependent differences in the degree of spatial aggregation, we discuss to what extent our findings may reflect a behavioural adaptation to local breeding conditions. 相似文献
13.
Joanna Skommer Tom Brittain Subhadip Raychaudhuri 《Apoptosis : an international journal on programmed cell death》2010,15(10):1223-1233
BH3 mimetics have been proposed as new anticancer therapeutics. They target anti-apoptotic Bcl-2 proteins, up-regulation of
which has been implicated in the resistance of many cancer cells, particularly leukemia and lymphoma cells, to apoptosis.
Using probabilistic computational modeling of the mitochondrial pathway of apoptosis, verified by single-cell experimental
observations, we develop a model of Bcl-2 inhibition of apoptosis. Our results clarify how Bcl-2 imparts its anti-apoptotic
role by increasing the time-to-death and cell-to-cell variability. We also show that although the commitment to death is highly
impacted by differences in protein levels at the time of stimulation, inherent stochastic fluctuations in apoptotic signaling
are sufficient to induce cell-to-cell variability and to allow single cells to escape death. This study suggests that intrinsic
cell-to-cell stochastic variability in apoptotic signaling is sufficient to cause fractional killing of cancer cells after
exposure to BH3 mimetics. This is an unanticipated facet of cancer chemoresistance. 相似文献
14.
Jesse A. Gillis Liang Zhang Frances K. Skinner 《Journal of computational neuroscience》2010,29(3):521-532
Local field potential (LFP) multielectrode recordings of spontaneous rhythms in an isolated whole hippocampal preparation
are characterized with respect to their spatial variability within the hippocampus, and their frequency properties. Using
simulated data, we categorize potential relationships between frequency variation over time in LFP recordings and spatial
variability between electrodes. We then use data recorded from the intact preparation to distinguish between our theoretical
categories. We find that the LFP recordings have a close to spatially invariant frequency distribution (not phase) across
the hippocampus, and differ in frequency only in a component that may be seen as physiological noise. From these facts, we
conclude that the isolated hippocampal LFP recordings represent a single signal and may be regarded as a unitary circuitry.
We additionally examine phase differences across our recording sites. We use our characterization of the hippocampal isolate’s
properties to predict its spatial coherence in response to high frequency stimulation. We find that there is a finely tuned
inverse relationship between temporal variability in the hippocampal isolate’s LFP recordings and their spatial coherence. 相似文献
15.
Jovic A Wade SM Miyawaki A Neubig RR Linderman JJ Takayama S 《Molecular bioSystems》2011,7(7):2238-2244
Since information in intracellular calcium signaling is often frequency encoded, it is physiologically critical and experimentally useful to have reliable, convenient, and non-invasive methods to entrain it. Because of cell-to-cell variability, synchronization of intracellular signaling across a population of genetically identical cells can still be difficult to achieve. For intrinsically oscillatory signaling pathways, such as calcium, upon continuous stimulation, cell-to-cell variability is manifested as differences in intracellular response frequencies. Even with entrainment using periodic stimulation, cell-to-cell variability is manifested as differences in the fidelity with which extracellular inputs are converted into intracellular signals. Here we present a combined theoretical and experimental analysis that shows how to appropriately balance stimulation strength, duration, and rest intervals to achieve entrainment with high fidelity stimulation-to-response ratios for G-protein-coupled receptor-triggered intracellular calcium oscillations. We further demonstrate that stimulation parameters that give high fidelity entrainment are significantly altered upon changes in intracellular enzyme levels and cell surface receptor levels. Theoretical analysis suggests that, at key threshold values, even small changes in these protein concentrations or activities can result in precipitous changes in entrainment fidelity, with implications for pathophysiology. 相似文献
16.
Scales of spatial patterns of distribution of intertidal invertebrates 总被引:15,自引:0,他引:15
Few comparative studies of spatial patterns at different scales have examined several species in the same habitat or the same species over a range of habitats. Therefore, variability in patterns among species or among habitats has seldom been documented. This study quantifies spatial patterns of a suite of intertidal snails and a species of barnacle using a range of statistical techniques. Variability in densities was quantified from the scale of adjacent quadrats (over a distance of centimeters) to tens of kilometers. Significant differences in abundances occurred primarily at two spatial scales. Small-scale differences were found at the scales of centimeters or 1–2 m and, for many species on many shores, these accounted for most of the variability in abundances from place to place. These are likely to be determined by behavioural responses to small-scale patches of microhabitat. Large-scale differences in abundance were also found in most species at the scale of hundreds of meters alongshore. These are likely to be due to variation in recruitment (and/or mortality) because of limited dispersal by adults of these species. There was little or no additional variation among shores, separated by tens of kilometers, than was shown among patches of shore separated by hundreds of meters. Identification of the scale(s) at which significant differences in abundance are found focus attention on the processes (and the scales at which these processes operate) that influence patterns of distribution and abundance. Some of the advantages and disadvantages of various procedures are discussed. 相似文献
17.
Abstract. Plant species distributions are generally thought to be chiefly under environmental control, although they may be affected by disturbance events or dispersion properties of the species. The relative importance of these different factors is not easy to evaluate because they often share common spatial patterns, such that an inextricable network of relationships occurs between plant distributions, environmental conditions, disturbance events and endogenous factors such as propagule dispersion. In this paper we propose a method for untangling the common spatial component from the relationship between environmental conditions and the distribution of tree species. Using partial Mantel tests and path analysis, we test models of relationships between these data sets. Results show that in our study area, spatial patterns of species associated with hydric conditions remain largely correlated with environmental conditions. However, mesic sites show more complex forest covers, in which a significant spatial component persists when environmental variation is statistically controlled for. This remaining spatial variability suggests that other factors possessing spatial structure partly explain species distributions. 相似文献
18.
Fernando Tuya Rubén Ramírez Pablo Sánchez–Jerez R.J. Haroun Antonio J. González-Ramos Josep Coca 《Hydrobiologia》2006,553(1):337-344
We describe the spatial distribution patterns of rocky intertidal Patella spp. limpets (heavily collected by shellfishers) and top-shell snails belonging to the genus Osilinus (comparatively slightly harvested) through a multiscaled sampling design spanning five orders of magnitude of spatial variability
(from 10s of m to 100s of km) throughout the Canarian Archipelago (eastern Atlantic); where rocky intertidal assemblages on
opposite sides of the Archipelago (western vs. eastern islands) are subjected to different regimes of bottom-up effects, as
large spatial variation in oceanographic conditions is recorded across an east–west gradient. We tested the hypothesis that
the response of rocky intertidal populations to mesoscale oceanographic bottom-up variability (quantified using differences
in Chlorophyll-a concentration among islands as an approximation to bottom-up effects) depends on the exploitation status of coastal resources,
by means of a correlative approach. Our study represent another case in which mesoscale shore-associated physical processes
seem to be correlated to large-scale differences (variability among islands, 10s to 100s of km apart) in the abundance of
slightly harvested intertidal grazers (topshell snails). In contrast, we did not observe large-scale spatial differences for
heavily collected grazers (limpets). In conclusion, our study suggests that the signal of bottom-up processes in coastal populations
may be difficult to demonstrate under intense human exploitation. 相似文献
19.
The effects of land-cover change on soil properties have reached regional proportions in the southwestern Amazon, and can be detected in their patterns at the scale of hundreds of thousands of square kilometers. Spatial analysis of an extensive soil profile database revealed four nested spatial scales at which different patterns in soil properties occur: <3, <10, <68, and >68 km. The shortest scales account for the majority of the spatial variability in the biogeochemically important properties (phosphorus, nitrogen, organic carbon), while the longest scales explain the most for pedologic properties (pH, aluminum, percent clay and sand). The magnitude and sign of correlations among soil properties changed with scale, indicating major shifts in distribution and soil dynamics depending on the scale of observation and analysis. Precipitation, substrate composition, topography, and biological influences vary over large areas, leading to variable distribution of soil properties, and complicating the evaluation of the effect of deforestation on biogeochemical cycling. We modeled the relationships among scale-specific patterns in soil properties and the soil forming state factors to tease out the relative impact of changing land cover. Soil property short-scale variability corresponded with the distribution of land cover and terrain attributes, medium scale variation with geology and state soil map classifications, and long scale with geology and precipitation. The strength of these relationships may be partially attributable to the resolution of the maps used as proxies for the soil forming factors. Land-cover change has already left a discernable imprint on broad-scale soil nutrient patterns, although it is still not the dominant process. 相似文献
20.
Marti J. Anderson Carol E. Diebel Wilma M. Blom 《Journal of experimental marine biology and ecology》2005,320(1):35-56
The focus of this study was to measure natural spatial variability in the biodiversity of fauna inhabiting kelp holdfasts in northeastern New Zealand at several spatial scales: from meters up to hundreds of kilometers. We wished to test the hypothesis that multivariate variation and biodiversity would vary significantly at different spatial scales in different ways for the major phyla in the holdfast community (Arthropoda, Annelida, Mollusca and Bryozoa). Biodiversity was considered in terms of richness, total abundance, structural composition (as measured by the Bray-Curtis dissimilarity measure) and taxonomic breadth for each major phylum and for the assemblage as a whole. We also examined the effect of taxonomic resolution on multivariate patterns. Species richness and total abundance increased with increases in holdfast volume. Multivariate variation was greatest at the smallest spatial scale for all phyla, but different phyla showed different patterns of multivariate variation at different spatial scales. Variations among locations at the largest spatial scale were primarily due to differences in the composition and richness of bryozoans and molluscs. Location effects became less and less distinct with decreases in taxonomic resolution. There were very few significant differences in richness or abundance for holdfasts of a given volume, taxonomic breadth did not vary significantly across locations, nor did the proportional abundances of phyla. These consistencies across large spatial scales in the absence of environmental impacts and results from other studies suggest that holdfast communities in New Zealand systems would provide a useful model assemblage against which future impacts may be detected as changes in proportions of component phyla. In addition, high variability detected at small and large scales at the species level, especially for bryozoans and molluscs, suggest that these communities may also provide unique opportunities for studying and understanding sources and functions of marine biodiversity. 相似文献