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Few Kilometres (few + kilometre)
Selected AbstractsFault slip controlled by gouge rheology: a model for slow earthquakesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2004A. Amoruso SUMMARY During 1997 several slow earthquakes have been recorded by a geodetic interferometer located beneath Gran Sasso, central Italy. The strain rise times of the events range from tens to thousands of seconds and strain amplitudes are of the order of 10,9. Amplitudes scale with the square root of the rise time and this suggests a diffusive behaviour of the slip propagation along the fault. In this work, we develop a model in which slip diffusion is the result of the presence of a gouge layer between fault faces, with a viscoplastic rheology. The fluid velocity field in the gouge layer diffuses in the directions of fault length and fault thickness, with different characteristic times. This model reproduces the relation between amplitude and rise time of measured strain signals. Synthetic straingrams, obtained for a horizontally layered, flat Earth and a source located a few kilometres from the instrument, are in agreement with observed signals. [source] The cation and silica chemistry of a Subandean river basin in western AmazoniaHYDROLOGICAL PROCESSES, Issue 7 2002J. A. Sobieraj Abstract We sampled river water at 13 locations in the Pichis basin, a 10 500 km2 large rainforest-covered drainage basin in Peru, to assess the influence of lithological variability and seasonality on water chemistry. The concentrations of major cations and silica show a strong seasonal dependence and a remarkable variability over short distances that is only weakly reduced in the wet season; cation concentrations in streams differ by up to 100% within a few kilometres. The lowest cation concentrations were associated with relatively cation-depleted upper Tertiary and lower Quaternary formations, whereas relatively cation-rich lower Tertiary and Jurassic formations left a clear calcium and sodium signal in the respective rivers. Cluster analysis, in conjunction with boxplots, suggests that the sampling locations can be segregated into three groups based on similarities of their geochemical signals. According to the previously defined criteria, one river is classified as a Group 2 river with 200 < TZ+ < 450 µeq/L, whereas all other rivers fall into Group 3 with 450 < TZ+ < 3000 µeq/L (where TZ+ refers to the total cation charge). Based on a comparison with other studies at different sections of the Amazon mainstem, the river chemistry of our study area is relatively enriched in K+, Mg2+ and Ca2+, and, consequently, has a higher TZ+ value, while being relatively depleted in silica. The influence of lithological variability on water chemistry must be considered in land-use change studies even at watershed areas of 26,3382 km2. Copyright © 2002 John Wiley & Sons, Ltd. [source] Gene movement and genetic association with regional climate gradients in California valley oak (Quercus lobata Née) in the face of climate changeMOLECULAR ECOLOGY, Issue 17 2010VICTORIA L. SORK Abstract Rapid climate change jeopardizes tree populations by shifting current climate zones. To avoid extinction, tree populations must tolerate, adapt, or migrate. Here we investigate geographic patterns of genetic variation in valley oak, Quercus lobata Née, to assess how underlying genetic structure of populations might influence this species' ability to survive climate change. First, to understand how genetic lineages shape spatial genetic patterns, we examine historical patterns of colonization. Second, we examine the correlation between multivariate nuclear genetic variation and climatic variation. Third, to illustrate how geographic genetic variation could interact with regional patterns of 21st Century climate change, we produce region-specific bioclimatic distributions of valley oak using Maximum Entropy (MAXENT) models based on downscaled historical (1971,2000) and future (2070,2100) climate grids. Future climatologies are based on a moderate-high (A2) carbon emission scenario and two different global climate models. Chloroplast markers indicate historical range-wide connectivity via colonization, especially in the north. Multivariate nuclear genotypes show a strong association with climate variation that provides opportunity for local adaptation to the conditions within their climatic envelope. Comparison of regional current and projected patterns of climate suitability indicates that valley oaks grow in distinctly different climate conditions in different parts of their range. Our models predict widely different regional outcomes from local displacement of a few kilometres to hundreds of kilometres. We conclude that the relative importance of migration, adaptation, and tolerance are likely to vary widely for populations among regions, and that late 21st Century conditions could lead to regional extinctions. [source] Microsatellite markers reveal shallow genetic differentiation between cohorts of the common sea urchin Paracentrotus lividus (Lamarck) in northwest MediterraneanMOLECULAR ECOLOGY, Issue 14 2009I. CALDERÓN Abstract Temporal variability was studied in the common sea urchin Paracentrotus lividus through the analysis of the genetic composition of three yearly cohorts sampled over two consecutive springs in a locality in northwestern Mediterranean. Individuals were aged using growth ring patterns observed in tests and samples were genotyped for five microsatellite loci. No reduction of genetic diversity was observed relative to a sample of the adult population from the same location or within cohorts across years. FST and amova results indicated that the differentiation between cohorts is rather shallow and not significant, as most variability is found within cohorts and within individuals. This mild differentiation translated into estimates of effective population size of 90,100 individuals. When the observed excess of homozygotes was taken into account, the estimate of the average number of breeders increased to c. 300 individuals. Given our restricted sampling area and the known small-scale heterogeneity in recruitment in this species, our results suggest that at stretches of a few kilometres of shoreline, large numbers of progenitors are likely to contribute to the larval pool at each reproduction event. Intercohort variation in our samples is six times smaller than spatial variation between adults of four localities in the western Mediterranean. Our results indicate that, notwithstanding the stochastic events that take place during the long planktonic phase and during the settlement and recruitment processes, reproductive success in this species is high enough to produce cohorts genetically diverse and with little differentiation between them. Further research is needed before the link between genetic structure and underlying physical and biological processes can be well established. [source] Fine-scale population structure and dispersal in Biomphalaria glabrata, the intermediate snail host of Schistosoma mansoni, in VenezuelaMOLECULAR ECOLOGY, Issue 5 2002J. Mavárez Abstract Biomphalaria glabrata is the main intermediate host of Schistosoma mansoni in America and one of the most intensely studied species of freshwater snails, yet very little is known about its population biology. Here, we used seven highly polymorphic microsatellite loci to analyse genetic diversity in the Valencia lake basin, which represents the core of the endemic area for schistosomiasis in Venezuela. Populations were sampled at short spatial scale (a few kilometres), both inside the lake and in ponds or rivers near the lake. Our results indicate that B. glabrata essentially cross-fertilizes, with little variation in selfing rates among populations. Our markers detected considerable genetic variation, with an average heterozygosity of 0.60. More diversity per population was found within than outside the lake, suggesting an influence of connectivity among populations on the levels of genetic diversity. A marked population structure was detected and lake populations were less structured than other populations. Most individuals were assigned to their population of origin using an assignment test. No strong demographic signal (e.g. bottleneck) was detected, though lake populations are likely to experience bottlenecks more frequently than the other populations analysed. Differences in gene flow therefore seem to play an important role in population differentiation and in the restoring of genetic diversity in demographically unstable populations. [source] A new method for estimating insolation based on PV-module currents in a cluster of stand-alone solar systemsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 5 2007Frans Nieuwenhout Abstract In order to evaluate the performance of solar home systems (SHSs), data on local insolation is a prerequisite. We present a new method to estimate insolation if direct measurements are unavailable. This method comprises estimation of daily irradiation by correlating photovoltaic (PV) module currents from a number of SHSs, located a few kilometres apart. The method was tested with a 3-year time series for nine SHS in a remote area in Indonesia. Verification with reference cell measurements over a 2-month period showed that our method could determine average daily irradiation with a mean bias error of 1·3%. Daily irradiation figures showed a standard error of 5%. The systematic error in this method is estimated to be around 10%. Especially if calibration with measurements during a short period is possible, the proposed method provides more accurate monthly insolation figures compared with the readily available satellite data from the NASA SSE database. An advantage of the proposed method over satellite data is that irradiation figures can be calculated on a daily basis, while the SSE database only provides monthly averages. It is concluded that the new method is a valuable tool to obtain information on insolation when long-term measurements are absent. Copyright © 2007 John Wiley & Sons, Ltd. [source] Deep, hierarchical divergence of mitochondrial DNA in Amplirhagada land snails (Gastropoda: Camaenidae) from the Bonaparte Archipelago, Western AustraliaBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010MICHAEL S. JOHNSON Continental islands have experienced cycles of isolation and connection. Although complex genetic patterns have been described for mainland species affected by glacial cycles of isolation, island biotas have received little attention. We examined mitochondrial DNA in Amplirhagada land snails from 16 islands and two adjacent mainland areas of the Bonaparte Archipelago, in the Kimberley region of northern Western Australia. Four major clades, with sequence divergence of 16,27% in the 16S ribosomal RNA gene, correspond to the major geographic groupings, separated by 10,160 km. Distinct lineages also characterize islands that are only a few kilometres apart. The large differences indicate that the lineages are much older than the islands themselves, and show no evidence of geologically recent connection. Three of the major clades match the morphological description of Amplirhagada alta. Either this named species comprises several morphologically cryptic species, or it is a single, genetically very diverse species, distributed over much of the Bonaparte Archipelago. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 141,153. [source] Neutral markers mirror small-scale quantitative genetic differentiation in an avian island populationBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009ERIK POSTMA We still know remarkably little about the extent to which neutral markers can provide a biologically relevant description of population structure. In the present study, we address this question, and quantify microsatellite differentiation among a small, structured island population of great tits (Parus major), and a large mainland population 150 km away. Although only a few kilometres apart, we found small but statistically significant levels of differentiation between the eastern and the western part of the island. On the other hand, there was no differentiation between the western part of the island and the mainland population, whereas the eastern part and the mainland did differ significantly. This initially counterintuitive result provides powerful support for the hypothesis that the large genetic difference in clutch size between both parts of the island found earlier is maintained by different levels of gene flow into both parts of the island, and illustrates the capacity of microsatellites to provide a meaningful description of population structure. Importantly, because the level of microsatellite differentiation is very low, we were unable to infer any population structure without grouping individuals a priori. Hence, these low levels of differentiation in neutral markers could easily remain undetected, or incorrectly be dismissed as biologically irrelevant. Thus, although microsatellites can provide a powerful tool to study genetic structure in wild populations, they should be used in conjunction with a range of other sources of information, rather than as a replacement. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 867,875. [source] | |||||||||||||