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Mitchell, Edward
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Mitchell, Edward
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Professeur ordinaire
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edward.mitchell@unine.ch
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Voici les éléments 1 - 3 sur 3
- PublicationAccès libreHorizontal distribution patterns of testate amoebae (Protozoa) in a Sphagnum magellanicum carpet(2000-5-2)
; ;Borcard, D. ;Buttler, Alexandre ;Grosvernier, Philippe ;Gilbert, DanielThe distribution of soil microorganisms is generally believed to be patchy and to reflect habitat heterogeneity. Despite this general rule, the amount of existing data oil species distribution patterns is scarce. Testate amoebae (Protozoa; Rhizopoda) are an important component of soil microbial communities and are increasingly used in ecological and paleoecological studies of Sphagnum-dominated peatlands, but data on the spatial structure of communities are completely lacking. This is an important aspect since quantitative models used for paleoecological reconstruction and monitoring are based on species assemblages. We explored the distribution patterns of testate amoebae distribution in a macroscopically homogeneous Sphagnum carpet, down to a scale of several centimeters. Distributions maps of the species and spatially constrained sample groups were produced. Multivariate and individual spatial autocorrelations were calculated. The importance of spatial structure was quantified by canonical correspondence analysis. Our ultimate goal is to find the finest resolution of environmental monitoring using testate amoebae. The distribution patterns differed among species, resulting in a complex spatial structure of the species assemblage in a whole. Spatial structure accounted for 36% of the total variation of species abundance in a canonical correspondence analysis constrained by spatial variables. This structure was partly correlated to altitude (microtopography) at a very fine scale. These results confirmed the existence of significant broad-and fine-scale spatial structures within restate amoebae communities that could in parr be interpreted as effects of ecological gradients. This shows that, on a surface area of 0.25 m(2), ecological conditions which look uniform from a macroscopic point of view are not perceived as such by Sphagnum-inhabiting organisms. Therefore, restate amoebae could prove very useful to monitor fine-scale ecological processes or disturbances. Studies of the species' spatial distribution patterns in combination with autoecological studies are needed and should be included in the toolbox of biomonitoring itself. - PublicationMétadonnées seulementRelationships among testate amoebae (Protozoa), vegetation and water chemistry in five Sphagnum-dominated peatlands in Europe(2000)
; ;Buttler, Alexandre ;Grosvernier, Philippe ;Rydin, Hakan ;Albinsson, Christer ;Greenup, Alisson ;Heijmans, Monique ;Hoosbeek, MarcelSaarinen, TimoTo study the relationships between groups of organisms and the degree to which these relationships are consistent across major climatic gradients, we analysed the testate amoeba (Protozoa) communities, vegetation and water chemistry of one peatland in five countries: Switzerland, The Netherlands, Great Britain, Sweden and Finland, as part of the BERI (Bog Ecosystem Research Initiative) project. The relationships between the different data sets and subsets were investigated by means of detrended correspondence analysis, canonical correspondence analysis and Mantel permutation tests. The comparison of data on vegetation and testate amoebae showed that inter-site differences are more pronounced for the vegetation than for the testate amoebae species assemblage. Testate amoebae are a useful tool in multi-site studies and in environmental monitoring of peatlands because: (1) the number of species in Sphagnum-dominated peatlands is much higher than for mosses or vascular plants; (2) most peatland species are cosmopolitan in their distributions and therefore less affected than plants by biogeographical distribution patterns, thus differences in testate amoeba assemblages can be interpreted primarily in terms of ecology; (3) they are closely related to the ecological characteristics of the exact spot where they live, therefore they can be used to analyse small-scale gradients that play a major role in the functioning of peatland ecosystems. This study revealed the existence of small-scale vertical gradients within the vegetation and life-form niche separation in response to water chemistry. The deep-rooted plants such as Carex spp. and Eriophorum spp. are related to the chemistry of water sampled at or near the ground water table, whereas the mosses are not. Testate amoebae wereshown to be ecologically more closely related to the chemistry of water sampled at or near the water table level and to the mosses than to the deep-rooted plants. - PublicationMétadonnées seulementEcology of testate amoebae (Protozoa : Rhizopoda) in Sphagnum peatlands in the Jura mountains, Switzerland and France(1999-5-2)
; ;Buttler, Alexandre ;Warner, BarryTestate amoebae (Protozoa) living in Sphagnum peatlands are important environmental and paleoecological indicators. The distribution of these animals is closely related to soil moisture variables. This study examines the ecology of sphagnicolous testate amoebae near the southern limit of bogs in Europe. A total of 64 samples were collected for analysis of testate amoebae from six peatlands in the Jura region of Switzerland and France. Eleven site-specific ecological variables, six of which were soil-moisture related variables, were measured at each site. The data were subjected to weighted averaging, jack-knifing, cluster analysis, canonical correspondence analysis, and the indicator value method to model relationships between testate amoebae distributions and environmental variables. Testate amoebae abundance showed a direct relationship with pear pH and depth to water table. Strong relationships were with sites that had a water table less than 41 cm deep. In drier sites with water table depth greater than 41 cm, other factors such as soil porosity and water holding capacity were more important compared to the wetter sites. Though there was a strong relationship between restate amoebae faunas and soil moisture content and porosity, these two variables could not be confidently predicted. Testate amoebae in peatlands in this region appear to be sensitive to peat pH and water tables. Further work is needed to explore relationships between restate amoebae, soil moisture, and porosity.