12 research outputs found

    Impacts des feux anthropogéniques et des fourmis invasives sur la diversité des fourmis natives de Nouvelle-Calédonie : des gènes aux communautés

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    La destruction de l'habitat, les invasions biologiques et leur interaction sont des menaces majeures pour la biodiversité. La Nouvelle-Calédonie est menacée à la fois par des feux d'origine humaine, et par des fourmis invasives : il est important de comprendre leur impact sur ce biotope unique. Pour ce faire, une approche hiérarchique intégrant différents aspects de la biodiversité (composition, structure et fonction) a été adoptée. Les fourmis ont une grande importance écologique, en particulier en milieu tropical, et leur classification en groupes fonctionnels facilite l'interprétation de leur réponse aux perturbations environnementales. Les objectifs de cette étude étaient donc d'évaluer les impacts des feux, des fourmis invasives, et de leur interaction, sur les fourmis natives de Nouvelle-Calédonie, et ce à différentes échelles spatiales (globale, régionale, locale) et temporelles (court et long terme), ainsi qu'à divers niveaux d'organisation biologique (communautés, espèces, gènes). L'étude contribue à une meilleure connaissance de la myrmécofaune calédonienne, en révélant l'absence de fourmis souterraines spécialisées, et en documentant la distribution et composition des communautés de fourmis à l'échelle de l'île, en lien avec l'habitat et les fourmis exotiques. Les mécanismes par lesquels les feux impactent les fourmis natives, y compris en association avec les fourmis invasives, sont révélés. Le feu, en créant les conditions de micro- et macrohabitat favorisées par les fourmis invasives, facilite l'invasion, qui cause ensuite d'avantage de perte de diversité, soit quelques années après un incendie ou dans le contexte de la fragmentation à long terme. L'approche hiérarchique a permis de détecter des réponses contrastées au niveau des espèces et de la génétique, liées à différents traits d'histoire de vie, en plus des réponses mesurées au niveau des communautés. Cette étude souligne l'avantage d'une approche holistique pour adresser des problèmes liés à la biodiversité.Habitat destruction, biological invasions and their interaction are global drivers of biodiversity loss. The New Caledonian hotspot of biodiversity is threatened by both anthropogenic fires and invasive ants: it is important to understand their impacts on its biota. Because biodiversity spans several levels of organisation (from genes to communities) and relates to different attributes (compositional, structural and functional), this thesis takes a hierarchical approach to address this issue. Ants are of great ecological importance, especially in tropical biomes, and their classification into functional groups provides a global framework for analysing their response to disturbance. My aims were therefore to investigate the impacts of anthropogenic fires and invasive ants, and their interaction, on the native New Caledonian ant fauna at different spatial (global, regional, local) and temporal (short and long term) scales, and at different levels of biological organisation (community, species, genes). The study contributes to an improved knowledge of the New Caledonian ants, by revealing the lack of specialised subterranean species, and by investigating island-scale patterns of ant communities, in relation to habitat and invasion. The mechanisms by which fire impacts native ants, either as a standalone process or in association with invasion could be identified. In particular, I show that fire, by creating macro- and microhabitats favoured by invasive ants, facilitates invasion, which then causes further diversity declines, either in the short- (post-burning) or long-term (forest fragmentation). The hierarchical approach used enabled the detection of contrasting trait-derived responses at the species and genetic level, in addition to responses measured at the community level. This study highlights the advantage of a holistic approach to investigating biodiversity-related issues

    Species scores on the first two CCA components (explaining 88% and 11% of variance, respectively).

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    <p>Species scores on the first two CCA components (explaining 88% and 11% of variance, respectively).</p

    Ant species collected and percentage of sites occupied per habitat type.

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    <p>FVS: rainforest on volcano-sedimentary soils (13 sites); FUM: rainforest on ultramafic soils (15); MAQ: maquis shrubland (15); SAV: savanna (11) and GAI: gaiac thicket (2).</p><p>An asterisk indicates an introduced species.</p><p>See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067245#pone.0067245.s003" target="_blank">Table S2</a> for the functional group classification.</p

    Relationship between habitat variables and the five most abundant exotic species.

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    <p>Canonical Correspondence Analysis triplot of the habitat variables in relation to sites [FVS: rainforests on volcano-sedimentary substrate (10); FUM: rainforests on ultramafic substrate (12); MAQ: maquis-shrubland (14); SAV: savannas (11); GAI: gaiac thickets (2)] and exotic species (AG: <i>A. gracilipes</i>; WA: <i>W. auropunctata</i>; BO: <i>B.</i> cf. <i>obscurior</i>; NV: <i>N. vaga</i>; PM: <i>P. megacephala</i>). Proportion explained by each eigenvalues is reported next to the axis label. The right- and upper axes relate to the environmental variables constraints.</p

    Contribution of native ants to the dissimilarity between ‘pristine’ rainforest sites and rainforest sites dominated by exotic species, with exotic species excluded from the dataset.

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    <p>Contributions up to a 70% cumulative cut-off value are indicated, using the SIMPER procedure.</p><p>GM: generalised myrmicinae, FOP: forest opportunists, CG: cryptic generalists.</p

    Distribution maps of sampling sites and species collected in New Caledonia.

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    <p>Location of sampling sites in relation to habitat and substrate type (white areas: volcano-sedimentary V; shaded areas: ultramafic U) (a), and proportional frequency (as measured by occurrence in traps) of native ant species, Dominant Opportunists, and exotic Weedy Opportunists (b).</p

    Functional group composition of each habitat type.

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    <p>Values are proportions of total species records. FVS: rainforest on volcano-sedimentary substrate; FUM: rainforest on ultramafic substrate; MAQ: maquis shrubland; SAV: savanna; GAI: gaiac thicket. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067245#pone.0067245.s003" target="_blank">Table S2</a> for the functional group classification.</p

    MDS ordinations of sites using different levels of ant community organisation.

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    <p>The significant groups identified by CLUSTER analysis are overlaid: (a) at the species level, (b) at the genus level, (c) at the functional group level. Group 1 (incl. 1a, 1b and 1c): ‘pristine’ forest sites; group 2: forest sites dominated by <i>Solenopsis</i> sp. B; group 3: sites dominated by exotic ants (3a: <i>P. megacephala</i>; 3b: <i>A. gracilipes</i>; 3c: <i>B.</i> cf. <i>obscurior</i> and 3d: <i>W. auropunctata</i>). DO: Dominant Opportunists and WO: Weedy Opportunists. Sites are displayed according to habitat type [FVS: rainforest on volcano-sedimentary substrate (13); FUM: rainforest on ultramafic substrate (15); MAQ: maquis shrubland (15); SAV: savanna (11); GAI: gaiac thicket (2)]. Stress values <0.2 indicate a good 2-D summary of the sample relationships.</p

    MDS ordination of rainforest sites based on native ants only, at the species level.

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    <p>The significant difference identified by ANOSIM between invaded and non-invaded sites is indicated by a line. FVS: rainforest on volcano sedimentary substrate; FUM: rainforest on ultramafic substrate. Stress values <0.2 indicate a good 2-D summary of the sample relationships.</p

    Relative abundance of the five most abundant exotic species according to habitat type.

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    <p>Values are proportions of total records of the five species per habitat type (total records in brackets). FVS: rainforest on volcano-sedimentary substrate; FUM: rainforest on ultramafic substrate; MAQ: maquis shrubland; SAV: savanna; GAI: gaiac thicket.</p
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