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Internal Variation (internal + variation)
Selected AbstractsThe riverscape of Western Amazonia , a quantitative approach to the fluvial biogeography of the regionJOURNAL OF BIOGEOGRAPHY, Issue 8 2007Tuuli Toivonen Abstract Aim, To provide a quantitative spatial analysis of the riverscape (open-water bodies and their surrounding areas) of the Western Amazonian lowlands using a consistent surface of remotely sensed imagery. Taking into account the essential significance of fluvial environments for the Amazonian biota, we propose that an enhanced understanding of the Amazonian riverscape will provide new insight for biogeographical studies in the region and contribute to the understanding of these megadiverse tropical lowlands. Location, An area of 2.2 million km2 covering the Western Amazonian lowlands of the Andean foreland region, i.e. the upper reaches of the Amazon river system. Areas in Colombia, Venezuela, Ecuador, Peru, Brazil and Bolivia between longitudes 83 °W and 65 °W and latitudes 5 °N and 12 °S are included. Methods, A mosaic of 120 Landsat TM satellite images was created with 100-m resolution, and water areas of over 1 ha in size or c. 60 m in width were extracted using a simple ratio threshold applicable to a large set of data. With this method, 99.1% of the water areas present in 30-m imagery were mapped with images with 100-m resolution. Water pixels of distinct river segments were assigned to river classes on the basis of their channel properties, and islands and lakes were distinguished separately and classified. Measures of water patterns such as structure, composition, richness and remoteness were provided for various spatial units. Riverine corridors were computed from the open-water mask by outer limits of active channels and floodplain lakes. Analytical results are shown as both thematic maps and statistics. Results, A total of 1.1% of Western Amazonia is covered by open-water bodies over 1 ha in size or 60 m in width. River-bound waters comprise 98% of the total water surface. Whilst isolated lakes are scarce, river-bound oxbow and backchannel lakes are plentiful, comprising 17.5% of all waters. They are particularly frequent along meandering channels, which dominate both in area and length. The riverine corridors including active channels and floodplain lakes cover 17% of the land area. The average distance from any point of land to the nearest water is 12 km. Geographically speaking, the distribution of waters is uneven across the region, and the detailed characteristics of the riverscape are geographically highly variable. Three major, fluvially distinct regions can be identified: central Western Amazonia, the south, and the north-east. The proportional surface areas of the riverine corridors, numbers of lakes, sizes of islands and their distributions depend largely on the types and sizes of the rivers. Main conclusions, Our results support the notion of Western Amazonia as a dynamic, highly fluvial environment, highlighting and quantifying considerable internal variation within the region in terms of fluvial patterns and the processes that they reflect and control. Biogeographically, the variety of types of fluvial environments and their characteristics are important constituents of what influences the distribution of species and dynamics of terrestrial habitats. Spatially consistent riverscape data can serve as a consistent and scalable source of relevant information for other biogeographical approaches in the region. [source] Mesoscale distribution patterns of Amazonian understorey herbs in relation to topography, soil and watershedsJOURNAL OF ECOLOGY, Issue 5 2005FLÁVIA R. C. COSTA Summary 1Many authors have suggested that topography and soils are the major determinants of species distributions and community patterns at small or regional scales, but few studies addressed the patterns at mesoscales. We used Reserva Ducke (100 km2) as a model to analyse the effects of soil, topography and watersheds on the variation of the herb community composition, and to determine the relative importance of the environmental factors on species composition. 2Taxonomic groups are frequently used as surrogates in studies of biodiversity distribution and complementarity, but their efficacy is controversial. We therefore studied the correlations between the distributional patterns of three different herb groups (Marantaceae, pteridophytes and ,others') and their responses to environmental predictors. 3Terrestrial herbs were sampled in 59 plots of 250 × 2 m, systematically distributed over the reserve. Plots followed isoclines of altitude, to minimize the internal variation of soil. Composition of the total herb community and of the three herb groups was summarized with PCoA. 4Soil structure, represented by PCA axes, was the main determinant of the variation in herb composition for all groups, but slope affected only pteridophytes. Soil and topography explained less than one-third of the variance in community data. Herb composition was significantly different between watersheds, but watersheds differ only slightly in soil parameters. Our results indicate high turnover in species composition, on spatial scales of 5,10 km in central Amazonia, which is not necessarily associated with soil change. 5Compositional patterns of the three groups analysed were significantly correlated, but with low values for the correlation coefficient. Although composition was correlated, the responses to environmental predictors differed among groups, and the use of one group as a surrogate will miss around 50% of the variation in other groups. 6Although important, soil and topography alone cannot predict herb community structure. Knowledge of geographical, historical or other landscape features, such as watershed morphology, may therefore be necessary to predict the turnover patterns over mesoscales. Moreover, the same factors may not have the same effectiveness as predictors of the structure of seemingly similar biological groups. [source] Eating between the Lines: Mississippian Migration and Stable Carbon Isotope Variation in Fort Ancient PopulationsAMERICAN ANTHROPOLOGIST, Issue 3 2009Robert A. Cook ABSTRACT Appreciating variation along the edges of traditional archaeological Culture Historical boundaries requires close consideration of social contexts associated with culture contact. We focus on dietary variation as a function of these concerns through a case study of Fort Ancient populations who, on average, consumed lower quantities of maize than their Mississippian neighbors as determined by stable carbon isotope ratios of bone collagen. However, this dichotomy is not as rigid as initially thought, with some Fort Ancient burials producing stable carbon isotope ratios similar to Mississippian cases. Detailed investigation of internal variation of carbon isotopes for human burials at the SunWatch site provides evidence that contact included small-scale Mississippian migrations to Fort Ancient sites. The main conclusion is that variation in diet and archaeological context can be a useful approach for examining prehistoric migration. [source] Morphometric and spatial analysis of thaw lakes and drained thaw lake basins in the western Arctic Coastal Plain, AlaskaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 4 2005K. M. Hinkel Abstract Landsat-7 ETM,+ scenes were acquired for the western Arctic Coastal Plain of Alaska extending from 152° to 162° W longitude. A segmentation algorithm was used to classify lakes and drained thaw lake basins (DTLBs) exceeding 1,ha in size. A total of 13,214 lakes and 6539 DTLBs were identified. Several indices were obtained from the image processing software and used for a comparative analysis of lakes and basins including object size, goodness of elliptic fit, shape complexity, shape asymmetry, and orientation of the major axis. Nonparametric statistical analyses indicate that lakes and basins share similar orientation only. Three subregions of the western Arctic Coastal Plain were identified based on landscape age, as demarcated by ancient shorelines. The surfaces become progressively older inland and include the Younger Outer Coastal Plain, the Outer Coastal Plain, and the oldest Inner Coastal Plain. Lakes and basins in all subregions have statistically similar orientation, indicating that summer wind direction has not changed appreciably over the past several thousand years. Basin orientation is less clustered than lake orientation. Lakes are highly elliptical, while basins have more complex shapes. Lake coverage (%) is fairly constant across the three subregions, while DTLB coverage decreases on older surfaces. Lake and basin size decreases on progressively older surfaces, but the number of features per unit area increases. It is uncertain if surface age is responsible for differences in regional metrics as an analysis of the Inner Coastal Plain demonstrates significant internal variation. Distance from the coast, ground ice content, surficial sediments, and local relief may also influence lake morphometry. Copyright © 2005 John Wiley & Sons, Ltd. [source] Spatial patterns and evolutionary processes in southern South America: A study of dental morphometric variationAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010Valeria Bernal Abstract The purpose of this article is to examine the patterns of evolutionary relationships between human populations from the later Late Holocene (1,500,100 years BP) of southern South America on the basis of dental morphometric data. We tested the hypotheses that the variation observed in this region would be explained by the existence of populations with different phylogenetic origin or differential action of gene flow and genetic drift. In this study, we analyzed permanent teeth from 17 samples of male and female adult individuals from throughout southern South America. We measured mesiodistal and buccolingual diameters at the base of the crown, along the cement,enamel junction. The results of multiple regression analysis and a mantel correlogram indicate the existence of spatial structure in dental shape variation, as the D2 Mahalanobis distance between samples increases with increasing geographical distance between them. In addition, the correlation test results show a trend toward reduction of the internal variation of samples with increasing latitude. The detected pattern of dental variation agrees with the one expected as an outcome of founder serial effects related to an expansion of range during the initial occupation of southern South America. Am J Phys Anthropol, 2010. © 2009 Wiley-Liss, Inc. [source] Using historical ecology to understand patterns of biodiversity in fragmented agricultural landscapesJOURNAL OF BIOGEOGRAPHY, Issue 11 2005Ian D. Lunt Abstract Aim, To enhance current attempts to understand biodiversity patterns by using an historical ecology approach to highlight the over-riding influence of land-use history in creating past, current and future patterns of biodiversity in fragmented agricultural landscapes. Methods, We develop an integrative conceptual framework for understanding spatial and temporal variations in landscape patterns in fragmented agricultural landscapes by presenting five postulates (hypotheses) which highlight the important role of historical, anthropogenic disturbance regimes. We then illustrate each of these postulates with examples drawn from fragmented woodlands in agricultural areas of south-eastern Australia, and discuss these findings in an international context. Location examples are drawn from agricultural areas in south-eastern Australia. Results, We conclude that there is limited potential to refine our understanding of patterns of biodiversity in human-modified landscapes based on traditional concepts of island biogeography, or simple assumptions of ongoing destruction and degradation. Instead, we propose that in agricultural landscapes that were largely cleared over a century ago: (1) present-day remnant vegetation patterns are not accidental, but are logically arrayed due to historic land-use decisions, (2) historic anthropogenic disturbances have a major influence on current ecosystem conditions and diversity patterns, and (3) the condition of remnant ecosystems is not necessarily deteriorating rapidly. Main conclusions, An historical ecology approach can enhance our understanding of why different species and ecosystem states occur where they do, and can explain internal variations in ecological conditions within remnant ecosystems, too often casually attributed to the ,mess of history'. This framework emphasizes temporal changes (both past and future) in biotic patterns and processes in fragmented agricultural landscapes. Integration of spatially and temporally explicit historical land-use information into ecological studies can prove extremely useful to test hypotheses of the effects of changes in landscape processes, and to enhance future research, restoration and conservation management activities. [source] | |||||||||||||