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1.
Marine organisms with a pelagic stage are often assumed to display minor population structure given their extended larval development and subsequent high long‐distance dispersal ability. Nonetheless, considerable population structure might still occur in species with high dispersal ability due to current oceanographic and/or historical processes. Specifically, for the wider Caribbean and Gulf of Mexico, theoretical and empirical considerations suggest that populations inhabiting each of the following areas should be genetically distinct: Panama, Belize, Southwest Florida (Tampa), and Southeast Florida (Fort Pierce). This study tests the hypothesis of significant genetic differentiation in Palaemon floridanus populations across the wider Caribbean and Gulf of Mexico. Population level comparisons were conducted using sequences of the mtDNA COI. In agreement with predictions, AMOVA and pairwise FST values demonstrated population differentiation among most pairs of the studied populations. Only Panama and East Florida populations were genetically similar. An isolation‐with‐migration population divergence model (implemented in IMA2) indicated that population divergence with incomplete lineage sorting can be invoked as the single mechanism explaining genetic dissimilarity between populations from the east and west coast of Florida. Historical demographic analyses indicated demographic expansion of P. floridanus in some localities [recent in Panama and ancient in East Florida and the wider Caribbean (entire dataset)] but constant population in other localities (in Belize and West Florida). This study rejects the idea of panmixia in marine species with high long‐distance dispersal ability. Contemporary and historical processes might interact in a complex manner to determine current phylogeographic patterns. 相似文献
2.
A GIS-Based Multivariate Statistical Analysis for Shallow Landslide Susceptibility Mapping in La Pobla de Lillet Area (Eastern Pyrenees,Spain) 总被引：22，自引：0，他引：22
Santacana Núria Baeza Baeza Corominas Jordi De Paz Ana Marturiá Jordi 《Natural Hazards》2003,30(3):281-295
This paper presents a GIS-aided procedure for shallow landslide susceptibility mapping at a regional scale. Most of the input data for the susceptibility assessment have been captured automatically. A total of 13 parameters, related to the slope geometry, have been derived from the digital elevation model (DEM) while vegetation cover and thickness of superficial formations have been obtained from photointerpretation and field work. The susceptibility assessment is based on multivariate statistical techniques (discriminant analysis), which hasbeen tested in a pilot area in La Pobla de Lillet (Eastern Pyreenes, Spain). Theresults obtained using a random sample show that 82% of all the cells, and 90% of cells including slope failures, have been properly classified. A susceptibility map based on the discriminant function has given consistent results. The susceptibilityassessment is very sensitive to the parameters selected. Compared to thetraditional methods, the main advantage of the GIS-aided procedure is the rapidityprovided by the automatic capture of parameters. It also has the capability of coveringlarge areas, and the objectivity and reproducibility of the results. The main drawbackis that, at present, not all regions have DEM accurate enough to cope with small landslides. 相似文献
3.
Influence of sample and terrain unit on landslide susceptibility assessment at La Pobla de Lillet,Eastern Pyrenees,Spain 总被引：2，自引：2，他引：0
The reliability of susceptibility maps depends largely on the quality of the information used for its evaluation. This study
seeks to analyze the influence of sample size and type on the results of discriminant analysis applied to shallow landslide
susceptibility assessment. The study also assesses the role of the terrain unit in discriminant analysis. To this end, two
databases based on fieldwork (slope unit) and GIS with 15- and 45-m grid cells (grid cell-based unit), were compared in the
same zone at La Pobla de Lillet, Spanish Eastern Pyrenees. The results show that although there is no significant influence
of the type of sample, it is necessary to use at least half of the individuals of the sample in order to obtain good results
from discriminant analysis. It is the terrain unit that exerts the biggest influence on the result of susceptibility. Some
morphometric parameters related to landslides were compared in the databases. The slope unit of the fieldwork database better
reflects the land characteristics than the regular grid used by GIS. The values of the variables obtained by GIS procedures
are smooth, obtaining mean errors for the slope angle variable of 19.5 and 33.5% for the grids of 15 and 45 m, respectively,
in the study area. One-way and T tests demonstrate that the smoothness of the values exerts a decisive influence on the discriminant results. Kappa’s analysis
shows that there is no significant equivalence between some of the categorical variables used in both databases. The use of
these variables demand the application of clearly defined criteria. The cell size should match the dimensions of the phenomenon
analyzed given the unsuitability of the grid of 45 m in this study. 相似文献
4.
Rolf Kilian Christoph Schneider Johannes Koch Martinus Fesq-Martin Harald Biester Gino Casassa Marcelo Arvalo Gert Wendt Oscar Baeza Jan Behrmann 《Global and Planetary Change》2007,59(1-4):49
Late Glacial to Holocene ice retreat was investigated along a 120 km long fjord system, reaching from Gran Campo Nevado (GCN) to Seno Skyring in the southernmost Andes (53°S). The aim was to improve the knowledge on regional and global control on glacier recession with special emphasis on latitudinal shifting of the westerlies. The timing of ice retreat was derived from peat and sediment cores, using mineralogical and chemical characteristics, and pollen as proxies. Stratigraphy was based on 14C-AMS ages and tephrochronology. The ice retreat of the Seno Skyring Glacier lobe is marked by an ice rafted debris layer which was formed around 18,300 to 17,500 cal. yr B.P. Subsequently, fast glacier retreat occurred until around 15,000 to 14,000 cal. yr B.P. during which around 84% of Skyring Glacier were lost. This fast recession was probably also triggered by an increase of the Equilibrium Line Altitude (ELA) from 200 to 300 m. Subsequently, the ice surface was lowered below the ELA in an area that previously made up more than 50% of the accumulation area. Much slower retreat and glacier fluctuations of limited extent in the fjord channel system northeast of GCN occurred between around 14,000 to 11,000 cal. yr B.P. during both the Antarctic Cold Reversal and the Younger Dryas. This slow down of retreat indicates a decline in the general warming trend and/or increased precipitation, due to a southward migration of the westerlies. After around 11,000 cal. yr B.P. pollen distribution shows evolved Magellanic Rainforest and similar climate as at present, which lasted throughout most of the Holocene. Only Late Neoglacial moraine systems were formed in the period 1220–1460 AD, and subsequently in the 1620s AD, and between 1870 and 1910 AD. The results indicate that the Gran Campo Nevado ice cap has reacted more sensitive and partly distinct to climate change, compared to the Patagonian Ice Field. 相似文献
5.
The biotic composition, structure, and function of aquatic, wetland, and riparian ecosystem depend largely on the hydrological regime (Poff, N.L., Ward, J.V., 1990. Implications of streamflow variability and predictability for lotic community structure: a regional analysis of streamflow patterns. Can. J. Fisheries Aquat. Sci. 46, 1805–1818; Richter, B.D., Baumgartner, J.V., Wiginton, R., Braun, D.P., 1997 How much water does a river need? Freshwater Biol. 37, 231–249). Available flow data for many rivers in the world can be used to validate these ecological theories. There is a demand for studies that use hydrological indices to establish criteria, which serve to group together regime types at a local level. Once this has been done, these hydrologically similar groups can be used to identify communities of living organisms that are linked to specific aspects of the river's behaviour.
An approach to characterise flow regimes in the river network of the Tagus basin in Spain is presented. The river Tagus (río Tajo) is one of the seven major rivers of the Iberian peninsula. All hydrological data were acquired from the measurements made in the Tagus basin, at 25 gauging stations. Twelve variables were derived for each gauged site to describe variability and predictability of average streamflow conditions, and to describe the frequency, timing and intensity of high flow and low flow extremes.
A hierarchical clustering routine was used to identify similar groups of rivers as defined in terms of similar characteristics of their streamflow regime. The variables were also examined with simple correlations to determine if multicollinearity occurred, in order to reject redundant parameters or to identify similar behaviour trends between pairs of parameters. Some parameters have shown a tendency to increase or decrease along the east–west axis, suggesting that some of the studied characteristics may have a geographical cause.
Cluster analysis, with the values of the 12 parameters, reveals two main groups, each of which splits into two main subdivisions. One of these subgroups contains six rivers with similar characteristics, can be considered to be ‘classic regular rivers’, the stations in this first subgroup are mostly situated geographically close to each other. At the other end, we have found a subgroup, with a high variation of flows over the year and high flood flows; these rivers are highly irregular rivers with great changes. This regular–irregular gradient found between the groups is similar to that observed by others authors (Poff, N.L., Allan J.D., 1995. Functional organization of stream fish assemblages in relation to hydrological variability. Ecology 76, 606–627), and strong associations have been documented with compositions of populations and probably reflect differences in other similar important environmental factors. 相似文献
6.
Assessment of shallow landslide susceptibility by means of multivariate statistical techniques 总被引：1，自引：0，他引：1
Several multivariate statistical analyses have been performed to identify the most influential geological and geomorphological parameters on shallow landsliding and to quantify their relative contribution. A data set was first prepared including more than 30 attributes of 230 failed and unfailed slopes. The performance of principal component analysis, t‐test and one‐way test, allowed a preliminary selection of the most significant variables, which were used as input variables for the discriminant analysis. The function obtained has classified successfully 88·5 per cent of the overall slope population and 95·6 per cent of the failed slopes. Slope gradient, watershed area and land‐use appeared as the most powerful discriminant factors. A landslide susceptibility map, based on the scores of the discriminant function, has been prepared for Ensija range in the Eastern Pyrenees. An index of relative landslide density shows that the results of the map are consistent. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
7.
J. A. Cuchí-Oterino J. Baeza Rodríguez-Caro C. García de la Noceda-Márquez 《Environmental Geology》2000,39(5):482-487
Hydrothermic features in Spain have been used since ancient times for therapeutic purposes. At present, the number of spas
has decreased notably, although some of them have been restored for aesthetic reasons. From 1970 onwards hydrogeothermic energy
started to be used. There are some boreholes and small facilities at several places in Spain, mostly on the Mediterranean
coast and near Madrid. The hydrochemistry of spanish thermal groundwaters is directly related to the geological nature of
granite and limestones where most important springs are located.
Received: 9 November 1998 · Accepted: 11 May 1999 相似文献
8.
B.?Caba?asEmail author M.?T.?Baeza P.?Martín S.?Salgado F.?Villanueva E.?Monedero K.?Wirtz 《Journal of Atmospheric Chemistry》2005,51(3):317-335
Products of the gas-phase reaction of the NO3 radical with thiophene have been investigated using different experimental systems. On the one hand, experiments have been conducted in our laboratory using two different methods, a Teflon static reactor coupled to a gas chromatograph combined with mass-spectrometry (GC-MS) and a discharge flow tube with direct MS spectroscopic detection. A qualitative analysis in these cases indicates that possible products for the reaction of thiophene+NO3 at room temperature include: sulphur dioxide, acetic and formic acids, a short-chain aldehyde, 2-nitrothiophene and 3-nitrothiophene. On the other hand, quantitative experiments have been performed in the European Photoreactor (EUPHORE) in Valencia, Spain. In this case, the major products were: HNO3 (≈80%), nitrothiophenes (≈30%), SO2 (≈20%), propanal (3%) and a fraction of particles (≈10%). The results obtained indicate that at least 70% of the reaction of NO3 with thiophene proceeds by an H-abstraction process at room temperature. The mechanism of the reaction studied is proposed on the basis of experimental results. 相似文献
9.
10.
This paper deals with the quality of two multivariate statistical models based on the Geographical Information System for
shallow landslide susceptibility assessment in a test area at La Pobla de Lillet (Eastern Pyrenees, Spain). The quality, which
was guaranteed by a rigorous methodology based on a suitable diagnosis, validation, and evaluation of the models, ensured
a reliable contrast of the final susceptibility maps. This enables us to transfer the best results to the end user. Landslide
susceptibility models were carried out by logistic regression and discriminant analysis of the significant conditioning factors
related to the characteristics of the slope and the upslope contributing area captured from the digital elevation model and
landslide distribution. The explanatory variables were tested (KS test, principal components and one-way and T-test) to select the most statistically significant ones before being introduced into the logistic and discriminant analyses.
Accuracy statistics and the receiver operating characteristic curve used for diagnosis and validation showed similar prediction
skills and a good fit to the data with more than 85% of unfailed cells properly classified for the two models. The evaluation
of the study area and the correlation function (R
2 = 0.83) between the models revealed that the discriminant model overestimated the susceptibility of the most stable zones
with respect to the logistic model. Different methods of producing susceptibility maps showed marked differences in matching
the models. Substantial spatial agreement (Kappa = 0.741) between binary maps produced by the standard cut-off value descended
moderately (Kappa = 0.540) as a result of superimposing maps with five susceptibility levels defined by landslide percentage.
Despite the fact that the two statistical models are similar in assessing susceptibility in the study area, the implications
for hazard and risk management can be different because of the conservative nature of the discriminant model. 相似文献