Home About us Contact
|
Home About us Contact | ||
|
|
||
Main Gradients (main + gradient)
Selected AbstractsThe inselberg flora of Atlantic Central Africa.JOURNAL OF BIOGEOGRAPHY, Issue 4 2005Abstract Aims, To identify the relative contributions of environmental determinism, dispersal limitation and historical factors in the spatial structure of the floristic data of inselbergs at the local and regional scales, and to test if the extent of species spatial aggregation is related to dispersal abilities. Location, Rain forest inselbergs of Equatorial Guinea, northern Gabon and southern Cameroon (western central Africa). Methods, We use phytosociological relevés and herbarium collections obtained from 27 inselbergs using a stratified sampling scheme considering six plant formations. Data analysis focused on Rubiaceae, Orchidaceae, Melastomataceae, Poaceae, Commelinaceae, Acanthaceae, Begoniaceae and Pteridophytes. Data were investigated using ordination methods (detrended correspondence analysis, DCA; canonical correspondence analysis, CCA), Sřrensen's coefficient of similarity and spatial autocorrelation statistics. Comparisons were made at the local and regional scales using ordinations of life-form spectra and ordinations of species data. Results, At the local scale, the forest-inselberg ecotone is the main gradient structuring the floristic data. At the regional scale, this is still the main gradient in the ordination of life-form spectra, but other factors become predominant in analyses of species assemblages. CCA identified three environmental variables explaining a significant part of the variation in floristic data. Spatial autocorrelation analyses showed that both the flora and the environmental factors are spatially autocorrelated: the similarity of species compositions within plant formations decreasing approximately linearly with the logarithm of the spatial distance. The extent of species distribution was correlated with their a priori dispersal abilities as assessed by their diaspore types. Main conclusions, At a local scale, species composition is best explained by a continuous cline of edaphic conditions along the forest-inselberg ecotone, generating a wide array of ecological niches. At a regional scale, these ecological niches are occupied by different species depending on the available local species pool. These subregional species pools probably result from varying environmental conditions, dispersal limitation and the history of past vegetation changes due to climatic fluctuations. [source] The influence of hydrological regime and grazing management on the plant communities of a karst wetland (Skealoghan turlough) in IrelandAPPLIED VEGETATION SCIENCE, Issue 1 2008J. Moran Abstract Question: What is the influence of hydrological regime, soils and management on the plant community composition and species richness of Skealoghan turlough (groundwater dependent calcareous wetland). Location: Skealoghan turlough, County Mayo, Ireland. Methods: Percentage cover of vascular plants and bryophytes were recorded, and data on hydrological regimes, soils and management were collected. Data were analysed using multivariate statistical techniques. Results: A total of 69 species of vascular plants and mosses were recorded. Cluster analysis grouped the samples into two separate communities, the Cirsio-Molinietum and the Ranunculo-Potentilletum anserinae plant communities. The plant community composition and species richness followed a main gradient down into the turlough basin, but also varied with microtopography, resulting in a mosaic of vegetation types. Conclusions: The biodiversity and conservation value of the site is linked to the heterogeneity in its physical environment in which hydrology, soils and grazing management all play critical roles. [source] Vegetation gradients in Atlantic Europe: the use of existing phytosociological data in preliminary investigations on the potential effects of climate change on British vegetationGLOBAL ECOLOGY, Issue 3 2000J. C. Duckworth Abstract 1This paper aims to demonstrate the use of available vegetation data from the phytosociological literature in preliminary analyses to generate hypotheses regarding vegetation and climate change. 2Data for over 3000 samples of calcareous grassland, mesotrophic grassland, heath and woodland vegetation were taken from the literature for a region in the west of Atlantic Europe and subjected to ordination by detrended correspondence analysis in order to identify the main gradients present. 3Climate data were obtained at a resolution of 0.5° from an existing database. The relationship between vegetation composition and climate was investigated by the correlation of the mean scores for the first two ordination axes for each 0.5° cell with the climate and location variables. 4The ordinations resulted in clear geographical gradients for calcareous grasslands, heaths and woodlands but not for mesotrophic grasslands. Significant correlations were shown between some of the vegetation gradients and the climate variables, with the strongest relationships occurring between the calcareous grassland gradients and July temperature, latitude and oceanicity. Some of the vegetation gradients were also inferred to reflect edaphic factors, management and vegetation history. 5Those gradients that were related to temperature were hypothesized to reflect the influence of a progressively warmer climate on species composition, providing a baseline for further studies on the influence of climate change on species composition. 6The validity of the literature data was assessed by the collection of an original set of field data for calcareous grasslands and the subsequent ordination of a dataset containing samples from both the literature and the field. The considerable overlap between the samples from the literature and the field suggest that literature data can be used, despite certain limitations. Such preliminary analyses, using readily available data, can thus achieve useful results, thereby saving lengthy and costly field visits. [source] Trophic diversity of the otter (Lutra lutra L.) in temperate and Mediterranean freshwater habitatsJOURNAL OF BIOGEOGRAPHY, Issue 5 2003Miguel Clavero Abstract Aim To analyse the geographical patterns in the composition and diversity of otter's (Lutra lutra L.) diet and their relationship with climatic characteristics. Location European freshwater habitats under Mediterranean and temperate climatic regimes. Methods Thirty-seven otter diet studies were reviewed, twenty-one from temperate and sixteen from Mediterranean areas. All studies were based on spraint analysis and their results expressed as relative frequency of occurrence of seven main prey categories. Principal Component Analysis was performed to extract the main gradients of diet composition. Pearson's correlation and t -tests were used to assess the relationship between diet characteristics (composition, diversity and taxonomic richness) and geographical and climatic variables. Results A clear latitudinal gradient in diet composition was observed. Otter diet was more diverse and featured more prey classes in southern localities, while the species was more piscivorous towards the north, where it predated upon a higher number of fish families. This pattern was similar when temperate and Mediterranean localities of Europe were compared. Mediterranean otters behaved as more generalist predators than temperate ones, relying less on fish, and more on aquatic invertebrates and reptiles. Main conclusions Geographical differences in otter feeding ecology in Europe seem to be related with the two contrasted climatic conditions affecting prey populations. The otter can act as a highly specialized piscivorous predator in temperate freshwater ecosystems, which do not suffer a dry season and have a comparatively stable water regime compared to Mediterranean ones. However, the unpredictable prey availability in Mediterranean areas, affected by strong spatial and temporal water shortages, favours a diversification of the otter's diet. [source] Demography and population dynamics of Drosera anglica and D. rotundifoliaJOURNAL OF ECOLOGY, Issue 1 2004J.-F. Nordbakken Summary 1We studied demography and population dynamics of the sympatric perennial herbs Drosera anglica and D. rotundifolia on a boreal bog in SE Norway. Dry mass of 2872 D. anglica plants and 2467 D. rotundifolia plants (estimated from field morphological measurements) was used to classify plants into five species-specific size classes. Demographic changes within these two populations were followed from 1995 to 1999, and within segments (quartiles) along the water table gradient and the peat productivity gradient. 2Mortality was strongly size dependent, and varied between years, for both species; it was high for seedlings, low for the smallest mature rosettes and increased again for the largest mature rosettes. The proportion of fertile rosettes increased with increasing rosette size. Fecundity varied considerably between years, but little relative to gradient position. 3Growth rate (,) was > 1, except in the second year, when it fell to 0.572 for D. anglica and 0.627 for D. rotundifolia . For D. anglica small, but significant, differences were found between the two extremities of the water table gradient, and for D. rotundifolia between the second and the uppermost quartile. There was a tendency for D. anglica populations to have a lower growth rate in the most productive sites, whereas D. rotundifolia grew less on both low and high peat productivity. Elasticity analysis showed that stasis and size increase (primarily within mature stages) made major contributions to , for D. anglica in all years. 4The variance in population growth rate (var ,) was high between years, and higher for D. anglica than for D. rotundifolia , while the variance between quartiles along the two main gradients was low. Life-table response experiment (LTRE) analyses revealed that for both species, differences in probabilities of transitions within mature stages, and in growth to larger stages, contributed most to var ,. 5The effects of global warming are uncertain: drier growing seasons would affect Drosera populations negatively, while initially positive responses to a wetter climate may be balanced by competition from increased Sphagnum growth. [source] Biodiversity conservation in Mediterranean and Black Sea lagoons: a trait-oriented approach to benthic invertebrate guildsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2008A. Basset Abstract 1. The extent to which conservation of biodiversity enforces the protection of ecosystem functioning, goods and services is a key issue in conservation ecology. 2. In order to address this conservation issue, this work focused on community organization, linking community structure, as described both in taxonomic and functional terms, to community functioning and ecosystem processes. 3. Body size is an individual functional trait that is deterministically related to components of ecosystem functioning such as population dynamics and energy flow, and which determines components of community structure. Since body size is an individual trait that reflects numerous factors, it is also exposed to trait selection and the niche filtering underlying the community. 4. An analysis of the relevance of body size to community organization in transitional water ecosystems in the eastern Mediterranean and Black Sea regions is presented, based on field research conducted on a sample of 15 transitional water ecosystems. 5. 250 taxa were identified, clumped in five orders of magnitude of body size. All body size patterns showed triangular distributions with an optimal size range of 0.13 mg to 1.0 mg individual body mass. 6. Deterministic components of size structure were emphasized and a hierarchical organization with dominance of large sizes was demonstrated by the slopes of the body size-abundance distributions, consistently larger than the EER threshold (b=,0.75), and by the direct relationship of energy use to body size for most of the body size range. 7. Consistent variations of body size-related descriptors were observed on three main gradients of environmental stress: eutrophication, confinement and metal pollution. 8. The results support the relevance of constraints imposed by individual body size on community organization in transitional water ecosystems and the adequacy of size patterns as an indicator for ecological conservation of these fragile ecosystems. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||