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Mitchell, Edward
Nom
Mitchell, Edward
Affiliation principale
Fonction
Professeur ordinaire
Email
edward.mitchell@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 10 sur 19
- PublicationMétadonnées seulementResponse of forest soil euglyphid testate amoebae (Rhizaria: Cercozoa) to pig cadavers assessed by high-throughput sequencing(2016-3-1)
; ; ; ; ; Decomposing cadavers modify the soil environment, but the effect on soil organisms and especially on soil protists is still poorly documented. We conducted a 35-month experiment in a deciduous forest where soil samples were taken under pig cadavers, control plots and fake pigs (bags of similar volume as the pigs). We extracted total soil DNA, amplified the SSU ribosomal RNA (rRNA) gene V9 region and sequenced it by Illumina technology and analysed the data for euglyphid testate amoebae (Rhizaria: Euglyphida), a common group of protozoa known to respond to micro- environmental changes. We found 51 euglyphid operational taxonomic units (OTUs), 45 of which did not match any known sequence. Most OTUs decreased in abundance underneath cadavers between days 0 and 309, but some responded positively after a time lag. We sequenced the full-length SSU rRNA gene of two common OTUs that responded positively to cadavers; a phylogenetic analysis showed that they did not belong to any known euglyphid family. This study confirmed the existence of an unknown diversity of euglyphids and that they react to cadavers. Results suggest that metabarcoding of soil euglyphids could be used as a forensic tool to estimate the post-mortem interval (PMI) particularly for long-term (>2 months) PMI, for which no reliable tool exists. - PublicationAccès librePatterns of earthworm, enchytraeid and nematode diversity and community structure in urban soils of different ages(2016-1-9)
; ; ; Annelids (Lumbricidae and Enchytraeidae) and nematodes are common soil organisms and play important roles in organic matter decomposition, nutrient cycling and creation of soil structure and porosity. However, these three groups have rarely been studied together and only few studies exist for urban soils. We studied the diversity and community composition of annelids and nematodes in soils spanning more than two centuries of urban soil development in Neuch^atel (Switzerland) and assessed the relationships 1) among these three groups and 2) between each group and environmental (physical, chemical and functional) characteristics of soils and soil age. While the groups of environmental variables were correlated (Mantel tests) no correlation was found between pairs of soil fauna groups and between each soil fauna group and environmental variables. More specifically, redundancy analyses showed that earthworm assemblages were best correlated with soil bulk density and with soil depth, the latter being positively correlated with soil age. Enchytraeid assemblages and the proportion of enchytraeid r-strategists were respectively best correlated with soil carbonate content and negatively correlated with soil age. Nematodes assemblages were best correlated with soil water content. Moreover, relationships between pairs of soil biota groups, and between each group and environmental (physical, chemical and functional) variables, varied along the soil age gradient (moving window analysis). This study provides new knowledge on urban soil biodiversity and how environmental conditions can influence soil diversity and community patterns in the urban context. The contrasted community patterns of earthworms, enchytraeids and nematodes in urban soils of different ages and their different ecological roles suggest that they represent potential complementary indicators of soil quality and functioning such as soil formation and organic matter dynamics. - PublicationAccès libreFunctional responses of multi-taxa communities to disturbance and stress gradients in a restored floodplain(2015-1-1)
; ; ; ; Moretti, Marco1. Trait-based approaches can reveal the mechanisms through which disturbances or stress impact communities, allowing comparisons of the role of different mechanisms in shaping communities among taxonomic groups. Such information can lead to higher comparability, transferability and predictability of the outcome of restoration projects. However, multitaxa trait-based approaches were rarely used in the context of ecosystem restoration. 2. We investigated the responses to environmental gradients of seven taxa (vascular plants, staphylinid and carabid beetles, spiders, isopods, diplopods and earthworms) in a restored floodplain using a species traits approach. We assessed the impact of flood disturbances and soil hydric stress on the functional diversity (FD) and community-weighted mean (CWM) response of traits for each taxon. 3. Ordination of hydrological variables revealed two main gradients. The first was related to the spatiotemporal dynamics of flood disturbances and the second to the average changes in soil hydric conditions. 4. The analysis of CWM revealed that larger, poorly mobile species with narrow ecological tolerances were filtered by regular floods and/or changes in soil hydric conditions. 5. Functional diversity patterns differed between the two gradients: decreasing with increasing flood disturbance, but increasing along the soil hydric stress gradient. This suggests that the mechanisms shaping community composition differ between the two gradients with environmental filtering being dominant with increasing flood disturbances and competition decreasing with more soil hydric stress. 6. Synthesis and applications. Our study shows that the impact of restored flood disturbances and soil hydric stress on plant and invertebrate functional diversity and community- weighted mean can be positive, negative or more complex depending on the taxonomic group and environmental gradient considered. The patterns can to some extent be explained by the specific characteristics of each group. Larger, poorly mobile species with narrow ecological tolerances were particularly vulnerable to changes in disturbance and stress regime following floodplain restoration. These species may therefore be lost in the initial phases of restoration projects, but other more characteristic species of dynamic floodplains will be favoured. Understanding the consequences of these contrasted responses for biodiversity conservation and ecosystem functioning constitutes the next challenge for ecosystem restoration. - PublicationAccès libreResponse of Sphagnum Peatland Testate Amoebae to a 1-Year Transplantation Experiment Along an Artificial Hydrological Gradient(2014-2-1)
; - PublicationMétadonnées seulementCan soil testate amoebae be used for estimating the time since death? A field experiment in a deciduous forest(2014)
; ; ; - PublicationMétadonnées seulementSpatio-temporal heterogeneity of riparian soil morphology in a restored floodplain(2013)
; - PublicationMétadonnées seulementRelationships between testate amoeba communities and water quality in Lake Donghu, a large alkaline lake in Wuhan, China(2013)
; ; ; - PublicationAccès libreAbove- and below-ground aspects of floodplain restoration: from biodiversity to ecosystem functions(2013)
; La biodiversité est le moteur du fonctionnement des écosystèmes. Elle est directement responsable des services fournis par les écosystèmes aux sociétés humaines. Cependant, la diversité de certains taxa dont beaucoup d'organismes du sol reste peu connue; et les processus qui créent, maintiennent et détruisent cette biodiversité ne sont que très partiellement compris. De ce fait, il est extrêmement difficile de restaurer la biodiversité dans les écosystèmes perturbés.
Les zones alluviales cristallisent ces problèmes. Elles accueillent une extraordinaire biodiversité qui est souvent mal caractèrisée; elles sont mondialement menacées; et il n'y a que peu de consensus en ce qui concerne les méthodes pour revitaliser leur biodiversité
Dans le but d'améliorer notre compréhension des écosystèmes dynamiques et de la multitude d'interactions écologiques qu'ils hébergent, cette thèse se concentre sur trois aspects des zones alluviales: les sols alluviaux, la biodiversité hébergée par ces sols et les changements de biodiversité entre les différents groupes étudiés le long des gradients environnementaux.
Les résultats obtenus lors de cette thèse comblent plusieurs lacunes dans la connaissance écosystémique des zones alluviales et fournissent des perspectives pour améliorer la gestion de ces écosystèmes. En effet, l'hétérogénéité spatio-temporelle de la morphologie des sols fournit des informations structurelles et fonctionnelles sur les zones alluviales qui peuvent être inclues dans les protocoles des projets de revitalisation. De plus, les conditions environnementales influencent fortement les caractéristiques fonctionnelles des communautés. Ces caractéristiques peuvent donc être exploitées comme outil de bioindication. Finalement, les résultats du présent travail ont démontré le rôle de la diversité en tant qu'assurance pour le maintient du fonctionnement des communautés dans les écosystèmes récemment revitalisés.
Les prochains défis à relever consistent à adopter une approche holistique des réseaux trophiques du sol, et définir l'importance des processus écologiques dans la structuration de la biodiversité des écosystèmes dynamiques., Biodiversity sustains ecosytem functioning and services to human societies. However, the diversity of certain taxa including many soil organisms remains poorly known and the processes creating, sustaining, and destroying biodiversity are only partially understood. As a result, restoring diversity in disturbed ecosystem remains a challenging task.
Floodplains cristallize these issues. They host an extraordinary biodiversity that is often poorly charaterized, they are threathen worldwide, and there is little agreement about the ways to restore their biodiversity.
Aiming at improving our understanding of disturbed ecosystems and the many ecological interactions they host, this PhD thesis focuses on three aspects of floodplain ecosystems: floodplain soils, below-ground biodiversity, and the changes in biodiversity among taxonomic groups and along environmental gradients.
With this respect, the results obtained during this PhD thesis fulfil several gaps in the knowledge of riparian ecosystems and provide perspectives for improved management of floodplains and riverine ecosystems. For instance, the spatio-temporal heterogeneity of soil morphology provides structural and functional information on floodplain ecosystems that can be included into restoration project protocols. Moreover, the strong impacts of environmental conditions on community functional characteristics can be developed into bioindication tools. Finally, the results of this PhD thesis revealed the role of diversity as an insurance to community functioning in recently restored ecosystems.
Future challenges include using holistic approaches for the study of the diversity and the functioning of the soil foodwebs, and disentangling the importance of assembly processes in structuring biodiversity patterns in disturbed ecosystems. - PublicationAccès librePatterns of earthworm communities and species traits in relation to the perturbation gradient of a restored floodplain(2012-3-29)
; ; ; Little is known about the diversity and ecology of earthworms in floodplains, as well as their response to natural and anthropic perturbations (e.g. floods, river channelisation, floodplain restoration). We characterised the patterns of earthworm communities and species traits in the different habitats of a lowland restored floodplain in Switzerland. In addition to classical species-based metrics, such as species richness and Shannon diversity, species traits were used to calculate the community weighted means (CWMs) of traits and functional dispersion (FDis). We hypothesised that trait-based metrics would reveal clearer patterns than classical approaches. The distribution of earthworm traits varied among habitats in relation to changes in flooding frequency: poorly developed gravel bar soils most exposed to flooding were characterised by high abundance of small epigeic species and low abundance of large anecic species. Differences in anecic and endogeic earthworm community structure matched flood frequency. In agreement with our hypothesis, CWMs were more strongly correlated to environmental variables than species composition, diversity, or functional diversity. Based on these results, the ratio of the relative abundances of epigeic and anecic species, and the differences in species composition within anecic and endogeic ecological types of earthworms were identified as indicators of soil development in floodplains. - PublicationAccès libreToward the use of testate amoeba functional traits as indicator of floodplain restoration success(2012)
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