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Longitudinal Gradient (longitudinal + gradient)
Selected AbstractsRelative influences of catchment- and reach-scale abiotic factors on freshwater fish communities in rivers of northeastern MesoamericaECOLOGY OF FRESHWATER FISH, Issue 3 2010P. C. Esselman Esselman PC, Allan JD. Relative influences of catchment- and reach-scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica. Ecology of Freshwater Fish 2010: 19: 439,454. © 2010 John Wiley & Sons A/S Abstract,,, While the abiotic factors important to freshwater fish assemblages at a reach scale are well understood, studies of larger scale constraints have yielded variable conclusions, spurring a need for further studies in new biogeographic contexts. This study investigated the importance of catchment- and reach-scale abiotic factors to variation in freshwater fish assemblages in rivers of northeastern Mesoamerica. Abiotic variables and fish data from 72 sampling sites on main stem rivers of Belize were used with partial constrained ordination to determine the proportion of spatially structured and unstructured variation in fish presence and absence, relative abundance, and community metrics explained by catchment- and reach-scale environmental factors. Results showed that, combined, catchment and reach variables explained a large portion of the total variation in the fish assemblage data (54,75%), and that catchment environment explained a greater portion of variation (42,63%) than reach environment (34,50%). Variables representing landscape position (local elevation, watershed area) and their reach-level correlates (channel width, depth variation, and substrate) correlated strongly to the fish assemblage data. Our results suggest that landscape-scale factors have a stronger relative influence on assemblages than environmental conditions at the reach scale within our study area. These results contrast with past findings that showed greater local scale influence in landscapes with low anthropogenic disturbance levels. Our findings suggest that biodiversity conservation efforts should consider assemblage variation across a longitudinal gradient, and that a multi-catchment region is a biologically relevant scale for fish conservation planning and coordination in northeastern Mesoamerica. [source] Feeding, growth and nutritional status of restocked salmon parr along the longitudinal gradient of a large European river: the AllierECOLOGY OF FRESHWATER FISH, Issue 2 2009A. Descroix Abstract,,, The feeding, growth and nutritional status of salmon parr (0+) released at fry stage in different riffles were studied in a large temperate river (Allier, France) throughout the active feeding period. Significant differences were observed along the upstream,downstream gradient. Parr growth performance and energy storage were higher in downstream riffles and low in the most upstream one. These longitudinal growth variations are discussed in the context of diet and food availability differences, habitat variables and intra- and inter-species competition. The most favourable site for optimum growth and nutritional status appeared to be the intermediary riffle located in the grayling zone. [source] The effects of temporal and spatial patterns of Holocene erosion and alluviation on the archaeological record of the Central and Eastern Great Plains, U.S.A.GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 2 2002E. Arthur Bettis III Patterns of erosion and deposition act as a filter that strongly influences the disposition of the archaeological record of the Central and Eastern Plains of the North American Midcontinent. Detailed studies of alluvial valley stratigraphy in four drainage basins in the region reveal temporal and spatial patterns of fluvial system behavior that control the preservation and visibility of past human activity. These basins are located on a 600-km-long longitudinal gradient extending from semiarid southwestern Kansas to moist-subhumid central Iowa. Despite significant environmental variability along this transect, basin-wide patterns of Holocene erosion and deposition are similar across the study area. From ca. 11,000 to 8000 yr B.P., aggradation, punctuated by slow alluviation and/or stability around 10,000 yr B.P., was the dominant process in large and some small valleys. The early and middle Holocene (ca. 8000,5000 yr B.P.) was a period of net erosion and sediment movement in small valleys, sediment storage in large valleys, and episodic aggradation on alluvial fans. During the late Holocene (post-5000 yr B.P.), alluvial fans stabilized, small valleys became zones of net sediment storage, and aggradation slowed in large valleys. Basin-wide aggradation followed by entrenchment and channel migration characterizes fluvial activity during the Historic period. Consideration of the effects of these temporal and spatial patterns of Holocene erosion and alluviation on the archaeological record is crucial for developing efficient cultural resource sampling strategies and for accurately interpreting the archaeological record. © 2002 John Wiley & Sons, Inc. [source] Global climate patterns explain range-wide synchronicity in survival of a migratory seabirdGLOBAL CHANGE BIOLOGY, Issue 1 2009STEPHANIE JENOUVRIER Abstract To predict the impact of climate change over the whole species distribution range, comparison of adult survival variations over large spatial scale is of primary concern for long-lived species populations that are particularly susceptible to decline if adult survival is reduced. In this study, we estimated and compared adult survival rates between 1989 and 1997 of six populations of Cory's shearwater (Calonectris diomedea) spread across 4600 km using capture,recapture models. We showed that mean annual adult survival rates are different among populations along a longitudinal gradient and between sexes. Variation in adult survival is synchronized among populations, with three distinct groups: (1) both females and males of Corsica, Tremiti, and Selvagem (annual survival range 0.88,0.96); (2) both females and males of Frioul and females from Crete (0.82,0.92); and (3) both females and males of Malta and males from Crete (0.74,0.88). The total variation accounted for by the common pattern of variation is on average 71%, suggesting strong environmental forcing. At least 61% of the variation in survival is explained by the Southern Oscillation Index fluctuations. We suggested that Atlantic hurricanes and storms during La Niña years may increase adult mortality for Cory's shearwater during winter months. For long-lived seabird species, variation in adult survival is buffered against environmental variability, although extreme climate conditions such as storms significantly affect adult survival. The effect of climate at large spatial scales on adult survival during the nonbreeding period may lead to synchronization of variation in adult survival over the species' range and has large effects on the meta-population trends. One can thus worry about the future of such long-lived seabirds species under the predictions of higher frequency of extreme large-scale climatic events. [source] National-scale metacommunity dynamics of carabid beetles in UK farmlandJOURNAL OF ANIMAL ECOLOGY, Issue 2 2008David R. Brooks Summary 1Understanding the wide-scale processes controlling communities across multiple sites is a foremost challenge of modern ecology. Here, data from a nation-wide network of field sites are used to describe the metacommunity dynamics of arable carabid beetles. This is done by modelling how communities are structured at a local level, by changes in the environment of the sampled fields and, at a regional level, by fitting spatial parameters describing latitudinal and longitudinal gradients. 2Local and regional processes demonstrated independent and significant capacities for structuring communities. Within the local environment, crop type was found to be the primary determinant of carabid community composition. The regional component included a strong response to a longitudinal gradient, with significant increases in diversity in an east-to-west direction. 3Carabid metacommunities seem to be structured by a combination of species sorting dynamics, operating at two different, but equally important, spatial scales. At a local scale, species are sorted along a resource gradient determined by crop type. At a wider spatial scale species appear to be sorted along a longitudinal gradient. 4Nation-wide trends in communities coincided with known gradients of increased homogeneity of habitat mosaics and agricultural intensification. However, more work is required to understand fully how communities are controlled by the interaction of crops with changes in landscape structure at different spatial scales. 5We conclude that crop type is a powerful determinant of carabid biodiversity, but that it cannot be considered in isolation from other components of the landscape for optimal conservation policy. [source] Distribution patterns of fish biomass by acoustic survey in three Tunisian man-made lakesJOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2010I. Djemali Summary In order to test the hypothesis that fish distribution is related to water depth, three exploited reservoirs were sampled at day and at night using a Simrad EK60 echosounder. Acoustic surveys were carried out between February and June 2008, which focused on the fish size, species density (fish per ha) and biomass (kg ha,1) along vertical and longitudinal gradients. It was evident in the surface layer (0,3 m) during daytime that the larger fish sizes occupy waters near the dam or the middle of Lakhmess and Sejnane reservoirs. In the upper layer at nighttime, a gradient of fish size is shown proportional to the depth at Lakhmess Reservoir and inversely proportional at the man-made Sejnane Lake. At Lakhmess and Laabid reservoirs, fish density was significantly higher in deep water (3926 ± 1409 and 624 ± 258 fish per ha) rather than in the upper layer (988 ± 2 and 8 ± 2 fish per ha in daytime, respectively), while at Sejnane Reservoir the number of fish per area was similar along the vertical gradient. The biomass was significantly higher in waters deeper than 3 m at Sejnane Reservoir whereas at Lakhmess it was higher in the surface layer. Fish biomass increased from upstream (0.16 ± 0.05 kg ha,1) to middle (3.07 ± 2.96 kg ha,1) and downstream (3.82 ± 2.30 kg ha,1 at night) areas in the man-made Laabid Lake while a similar longitudinal gradient occurred in the deepest Sejnane Reservoir. The vertical gradient in fish distribution is discussed. From the dam to the tributary of the entire water column, it was concluded that fish biomass distribution was governed by depth and was most abundant in areas with deep waters. [source] Ecological biogeography of North American mammals: species density and ecological structure in relation to environmental gradientsJOURNAL OF BIOGEOGRAPHY, Issue 6 2000Catherine Badgley Abstract Aim, To evaluate the relationship of climate and physiography to species density and ecological diversity of North American mammals. Location, North America, including Mexico and Central America. Methods, Species density, size structure and trophic structure of mammalian faunas and nine environmental variables were documented for quadrats covering the entire continent. Spatial autocorrelation of species density and the environmental variables illustrated differences in their spatial structure at the continental scale. We used principal component analysis to reduce the dimensionality of the climatic variables, linear multiple regression to determine which environmental variables best predict species density for the continent and several regions of the continent, and canonical ordination to evaluate how well the environmental variables predict ecological structure of mammalian faunas over North America. Results, In the best regression model, five environmental variables, representing seasonal extremes of temperature, annual energy and moisture, and elevation, predicted 88% of the variation in species density for the whole continent. Among different regions of North America, the environmental variables that predicted species density vary. Changes in the size and trophic structure of mammalian faunas accompany changes in species density. Redundancy analysis demonstrated that environmental variables representing winter temperature, frostfree period, potential and actual evapotranspiration, and elevation account for 77% of the variation in ecological structure. Main conclusions, The latitudinal gradient in mammalian species density is strong, but most of it is explained by variation in the environmental variables. Each ecological category peaks in species richness under particular environmental conditions. The changes of greatest magnitude involve the smallest size categories (< 10 g, 11,100 g), aerial insectivores and frugivores. Species in these categories, mostly bats, increase along a gradient of decreasing winter temperature and increasing annual moisture and frostfree period, trends correlated with latitude. At the opposite end of this gradient, species in the largest size category (101,1000 kg) increase in frequency. Species in size categories 3 (101,1000 g), 5 (11,100 kg) and 6 (101,1000 kg), herbivores, and granivores increase along a longitudinal gradient of increasing annual potential evapotranspiration and elevation. Much of the spatial pattern is consistent with ecological sorting of species ranges along environmental gradients, but differential rates of speciation and extinction also may have shaped the ecological diversity of extant North American mammals. [source] Changes of taxonomic and trophic structure of fish assemblages along an environmental gradient in the Upper Beni watershed (Bolivia)JOURNAL OF FISH BIOLOGY, Issue 1 2006M. Pouilly The distribution and the diet of 28 fish species were evaluated, during the dry season, in 12 streams of the Upper Beni watershed (Amazon basin, Bolivia). The 12 streams were of similar size (stream width and water depth) but situated on a gradient of altitude in the Andean and sub-Andean areas. The environmental conditions in the stream changed in relation to the altitude. As altitude decreased, slope and water velocity also decreased, while temperature, conductivity, pH and the proportion of pools increased. Although the diets of the species were mainly based on two aquatic autochthonous food resources, invertebrates and sediment, species were classified into five trophic guilds: detritivores, algivores, piscivores, invertivores-omnivores and aquatic specialist invertivores. In all streams invertivores dominated or co-dominated with detritivores. The trophic structure of the assemblages, however, changed in relation to the environmental gradient. The fish species richness increased and the trophic composition became more diverse at lower altitudes, when slope decreased and temperature increased. At the same time, the relative number of invertivore species decreased, whereas the relative number of detritivore, algivore and piscivore species increased. Decreasing altitude appeared to play a role similar to increasing stream size along the longitudinal gradient. This could be explained by geomorphological and temperature variations that may generate environmental conditions favourable to an increase of productivity. [source] Taxonomic diversity gradients through geological timeDIVERSITY AND DISTRIBUTIONS, Issue 4 2001J. Alistair Crame Abstract., There is evidence from the fossil record to suggest that latitudinal gradients in taxonomic diversity may be time-invariant features, although almost certainly not on the same scale as that seen at the present day. It is now apparent that both latitudinal and longitudinal gradients increased dramatically in strength through the Cenozoic era (i.e. the last 65 my) to become more pronounced today than at any time in the geological past. Present-day taxonomic diversity gradients, in both the marine and terrestrial realms, are underpinned by the tropical radiations of a comparatively small number of species-rich clades. Quite why these particular taxa proliferated through the Cenozoic is uncertain, but it could be that at least part of the explanation involves the phenomenon of evolutionary escalation. This is, in essence, a theory of biological diversification through evolutionary feedback mechanisms between predators and prey; first one develops an adaptive advantage, and then the other. However, there may also have been some form of extrinsic control on the process of tropical diversification, and this was most likely centred on the phenomenon of global climate change. This is especially so over the last 15 my Various Late Cenozoic (Neogene) vicariant events effectively partitioned the tropics into a series of high diversity centres, or foci. It has been suggested that, in the largest of these in the marine realm (the Indo-West Pacific or IWP centre), a critical patterns of islands acted as a template for rapid speciation during glacioeustatic sea level cycles. The same process occurred in the Atlantic, Caribbean and East Pacific (ACEP) centre, though on a lesser scale. Tropical terrestrial diversity may also have been promoted by rapid range expansions and contractions in concert with glacial cycles (a modified refugium hypothesis). We are beginning to appreciate that an integrated sequence of Neogene tectonic and climatic events greatly influenced the formation of contemporary taxonomic diversity patterns. [source] National-scale metacommunity dynamics of carabid beetles in UK farmlandJOURNAL OF ANIMAL ECOLOGY, Issue 2 2008David R. Brooks Summary 1Understanding the wide-scale processes controlling communities across multiple sites is a foremost challenge of modern ecology. Here, data from a nation-wide network of field sites are used to describe the metacommunity dynamics of arable carabid beetles. This is done by modelling how communities are structured at a local level, by changes in the environment of the sampled fields and, at a regional level, by fitting spatial parameters describing latitudinal and longitudinal gradients. 2Local and regional processes demonstrated independent and significant capacities for structuring communities. Within the local environment, crop type was found to be the primary determinant of carabid community composition. The regional component included a strong response to a longitudinal gradient, with significant increases in diversity in an east-to-west direction. 3Carabid metacommunities seem to be structured by a combination of species sorting dynamics, operating at two different, but equally important, spatial scales. At a local scale, species are sorted along a resource gradient determined by crop type. At a wider spatial scale species appear to be sorted along a longitudinal gradient. 4Nation-wide trends in communities coincided with known gradients of increased homogeneity of habitat mosaics and agricultural intensification. However, more work is required to understand fully how communities are controlled by the interaction of crops with changes in landscape structure at different spatial scales. 5We conclude that crop type is a powerful determinant of carabid biodiversity, but that it cannot be considered in isolation from other components of the landscape for optimal conservation policy. [source] Distribution patterns of fish biomass by acoustic survey in three Tunisian man-made lakesJOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2010I. Djemali Summary In order to test the hypothesis that fish distribution is related to water depth, three exploited reservoirs were sampled at day and at night using a Simrad EK60 echosounder. Acoustic surveys were carried out between February and June 2008, which focused on the fish size, species density (fish per ha) and biomass (kg ha,1) along vertical and longitudinal gradients. It was evident in the surface layer (0,3 m) during daytime that the larger fish sizes occupy waters near the dam or the middle of Lakhmess and Sejnane reservoirs. In the upper layer at nighttime, a gradient of fish size is shown proportional to the depth at Lakhmess Reservoir and inversely proportional at the man-made Sejnane Lake. At Lakhmess and Laabid reservoirs, fish density was significantly higher in deep water (3926 ± 1409 and 624 ± 258 fish per ha) rather than in the upper layer (988 ± 2 and 8 ± 2 fish per ha in daytime, respectively), while at Sejnane Reservoir the number of fish per area was similar along the vertical gradient. The biomass was significantly higher in waters deeper than 3 m at Sejnane Reservoir whereas at Lakhmess it was higher in the surface layer. Fish biomass increased from upstream (0.16 ± 0.05 kg ha,1) to middle (3.07 ± 2.96 kg ha,1) and downstream (3.82 ± 2.30 kg ha,1 at night) areas in the man-made Laabid Lake while a similar longitudinal gradient occurred in the deepest Sejnane Reservoir. The vertical gradient in fish distribution is discussed. From the dam to the tributary of the entire water column, it was concluded that fish biomass distribution was governed by depth and was most abundant in areas with deep waters. [source] Spatial patterns of disparity and diversity of the Recent cuttlefishes (Cephalopoda) across the Old WorldJOURNAL OF BIOGEOGRAPHY, Issue 8 2003Pascal Neige Abstract Aim Diversity and disparity metrics of all Recent cuttlefishes are studied at the macroevolutionary scale (1) to establish the geographical biodiversity patterns of these cephalopods at the species level and (2) to explore the relationships between these two metrics. Location Sampling uses what is known about these tropical, subtropical and warm temperate cephalopods of the Old World based on a literature review and on measurements of museum specimens. Some 111 species spread across seventeen biogeographical areas serve as basic units for exploring diversity and disparity metrics in space. Methods Landmarks describe the shape of the cuttlebone (the inner shell of the sepiids) and differences between shapes are quantified using relative warp analyses. Relative warps are thus used as the morphological axis for constructing morphospaces whose characteristics are described by disparity indices: total variance, range, and minimum and maximum of relative warps. These are analysed and then compared with the diversity (species richness) metric. Results Results show no significant latitudinal or longitudinal gradients either for diversity or for disparity. Around the coast of southern Africa, disparity is high regardless of whether diversity (species richness) is high or low. In the ,East Indies' area disparity is low despite the high diversity. Main conclusions The relationship between diversity and disparity is clearly not linear and no simple adjustment models seem to fit. The number of species in a given area does not predict its disparity level. The particular pattern of southern Africa may be the result of paleogeographical changes since the Eocene, whereas that of the ,East Indies' may indicate that this area could act as a centre of origin. However, the lack of any clear phylogenetical hypothesis precludes the study from providing any explanation of the observed patterns. [source] Regional variability of climate,growth relationships in Pinus cembra high elevation forests in the AlpsJOURNAL OF ECOLOGY, Issue 5 2007MARCO CARRER Summary 1The tree-ring growth response of stone pine (Pinus cembra L.) to climatic variability was studied in the Alps. The aims were (i) to assess tree-ring growth patterns at different spatial-temporal scales; (ii) to identify the climate parameters that explain most of the variability in radial growth at different time domains; and (iii) to study past and current trends in radial growth and climate,growth relationships at different locations. 2High- and low-frequency stone pine chronologies were compiled for 30 treeline sites on the French and Italian Alps. We used gridded climate data computed from 200 years of instrumental records from an extensive Alpine network. Climate,growth relationships were computed with bootstrap correlation functions and their stationarity and consistency over time assessed with moving correlation. 3No spatial patterns were detected in stone pine chronology statistics despite the regional clustering observed in tree-ring series and climate responses. This can be attributed to (i) local weather variability; (ii) different biophysical conditions caused by soil moisture, solar radiation, snowmelt dynamics and growing season length; and (iii) forest stand history and age structure, the expression of long-term land use and disturbances. 4The exceptionally long-term climate records allowed significant stone pine growth response changes to be assessed at both annual and decadal time scales. Winter conditions and spring,summer temperatures mainly affected the growing season length, in addition to site carbon and water balance. Most of these limiting factors varied spatially and temporally along the latitudinal and longitudinal gradients in response to the corresponding changes in local conditions. 5Our results show evidence of a clear response variability of Pinus cembra to climate limiting factors, at both spatial and temporal scale. Such knowledge extended to other species and regions will provide better estimates of the effect of climate variability on species distribution and dynamics within global change scenarios and more accurate past climate reconstruction and forest ecosystem modelling. [source] The seasonal phenology of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) in QueenslandAUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 3 2010Sakuntala Muthuthantri Abstract Bactrocera tryoni is a polyphagous fruit fly, originally endemic to tropical and subtropical coastal eastern Australia, but now also widely distributed in temperate eastern Australia. In temperate parts of its range, B. tryoni populations show distinct seasonal peaks driven by changing seasonal climates, especially changing temperature. In contrast to temperate areas, the seasonal phenology of B. tryoni in subtropical and tropical parts of its range is poorly documented and the role of climate unknown. Using a large, historical (1940s and 1950s) fruit fly trapping dataset, we present the seasonal phenology of B. tryoni at nine sites across Queensland for multiple (two to seven) years per site. We correlate monthly trap data for each site with monthly weather averages (temperature, rainfall and relative humidity) to investigate climatic influences. We also correlate observed population data with predicted population data generated by an existing B. tryoni population model. Supporting predictions from climate driven models, B. tryoni did show year-round breeding at most Queensland sites. However, contrary to predictions, there was a common pattern of a significant population decline in autumn and winter, followed by a rapid population increase in August and then one or more distinct peaks of abundance in spring and summer. Mean monthly fly abundance was significantly different across sites, but was not correlated with altitudinal, latitudinal or longitudinal gradients. There were very few significant correlations between monthly fly population size and weather variables (either for the corresponding month or for up to 3 months previously) for eight of the nine sites. For the southern site of Gatton fly population abundance was correlated with temperature. Results suggest that although climate factors may be influencing patterns of B. tryoni population abundance in southern subtropical Queensland, they are not explaining patterns of abundance in northern subtropical and tropical Queensland. In the discussion we focus on the role of other factors, particularly larval host plant availability, as likely drivers of B. tryoni abundance in tropical and subtropical parts of its range. [source] | |||||||||||||