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Mitchell, Edward

Nom
Mitchell, Edward
Affiliation principale
Site web
Fonction
Professeur ordinaire
Email
edward.mitchell@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/357
_
0000-0003-0358-506X

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  • Publication
    Accès libre
    Ecology of testate amoebae (Protista) in south-central Alaska peatlands: building transfer-function models for palaeoenvironmental studies
    (2006)
    Payne, Richard J.
    ;
    Kishaba, Keiko
    ;
    Blackford, Jeff J.
    ;
    Mitchell, Edward 
    Testate amoebae are valuable indicators of peatland hydrology and have been used in many palaeoclimatic studies in peatlands. Because the species' ecological optima may vary around the globe, the development of transfer function models is an essential prerequisite for regional palaeoclimatic studies using testate amoebae. We investigated testate amoebae ecology in nine peatlands covering a 250-km north-south transect in south-central Alaska. Redundancy analysis and Mantel tests were used to establish the relationship between the measured environmental variables (water-table depth and pH) and testate amoebae communities. Transfer-function models were developed using weighted averaging, weighted average partial least squares and maximum likelihood techniques. Model prediction error was initially 15.8 cm for water-table depth and 0.3 for pH but this was reduced to 9.7 cm and 0.2 by selective data exclusion. The relatively poor model performance compared with previous studies may be explained by the limitations of one-off water-table measurements, the very large environmental gradients covered and by recent climatic change in the study area. The environmental preferences of testate amoebae species agree well with previous studies in other regions. This study supports the use of testate amoebae in palaeoclimate studies and provides the first testate amoebae transfer function from Alaska.
  • Publication
    Accès libre
    Changes in testate amoebae (Protists) communities in a small raised bog. A 40-year study
    (2005)
    Kishaba, Keiko
    ;
    Mitchell, Edward 
    We analyzed the testate amoebae communities from two sets of moss samples taken forty years apart ( 1961 and 2001) in the same locations of a peat bog of the Swiss Jura Mountains. Peat Cutting and lateral drainage of Le Cachot bog have caused a clear increase in tree cover, especially near the edges. Changes affecting herbaceous plants, mosses. or soil organisms can be subtle, and may easily be overlooked. We hypothesized that we would see changes in the dominant Sphagnum species and the structure of testate amoebae communities living in the mosses. More specifically, we hypothesized that the frequency of bryophyte and testate amoebae species indicative for dry conditions Would increase and that the frequency of species indicative for wet conditions would decrease. The mean testate amoebae species richness per sample decreased from 11.9 to 9.6, but the overall species richness was identical (33 species) in both years. Three species increased significantly in mean relative abundance: Nebela tincta s.l. (+97 %), Bullinularia indica (+ 810 %), and Cyclopyxis eurystoma (+ 100 %; absent in 1961), while two species decreased significantly: Assulina muscorum (- 63 %) and Euglypha compressa (-93 %). The testate amoebae communities clearly differed among microhabitat types (hummocks, lawns, hollows), but no overall significant change in the community was detectable between the two sampling dates (Mantel test). These results could signify that changes at the microscopic level had already taken place by 1961 and no further overall significant changes in micro-enviromental conditions took place during the 40-year period of this Study. This Would agree with the faster response time usually attributed to microorganisms and would also imply that the bushes and trees may be poor predictors of the response of microorganisms if they are themselves in a non-equilibrium stage. Other possible causes for the lack of overall differences are discussed.
  • Publication
    Accès libre
    Changes in Testate Amoebae (Protists) Communities in a Small Raised Bog. A 40-year Study
    (2005)
    Kishaba, Keiko
    ;
    Mitchell, Edward 
    We analysed the testate amoebae communities from two sets of moss samples taken forty years apart (1961 and 2001) in the same locations of a peat bog of the Swiss Jura Mountains. Peat cutting and lateral drainage of Le Cachot bog have caused a clear increase in tree cover, especially near the edges. Changes affecting herbaceous plants, mosses, or soil organisms can be subtle, and may easily be overlooked. We hypothesized that we would see changes in the dominant Sphagnum species and the structure of testate amoebae communities living in the mosses. More specifically, we hypothesized that the frequency of bryophyte and testate amoebae species indicative for dry conditions would increase and that the frequency of species indicative for wet conditions would decrease. The mean testate amoebae species richness per sample decreased from 11.9 to 9.6, but the overall species richness was identical (33 species) in both years. Three species increased significantly in mean relative abundance: Nebela tincta s. l. (+97%), Bullinularia indica (+810%), and Cyclopyxis eurystoma (+100%; absent in 1961), while two species decreased significantly: Assulina muscorum (-63%) and Euglypha compressa (-93%). The testate amoebae communities clearly differed among microhabitat types (hummocks, lawns, hollows), but no overall significant change in the community was detectable between the two sampling dates (Mantel test). These results could signify that changes at the microscopic level had already taken place by 1961 and no further overall significant changes in micro-environmental conditions took place during the 40-year period of this study. This would agree with the faster response time usually attributed to microorganisms and would also imply that the bushes and trees may be poor predictors of the response of microorganisms if they are themselves in a non-equilibrium stage. Other possible causes for the lack of overall differences are discussed.