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International audience; In the sub-Antarctic region, climate change is particularly rapid, while their freshwater ecosystems, such as ponds, host plant species with limited spatial distributions. These particular systems and their plant communities remain however poorly known and the context of their changing habitat calls for deeper insights into these systems. We performed an extensive survey of 45 ponds over three locations of the Iles Kerguelen during the winter and summer seasons of two years, which included the measurement of 12 abiotic parameters and the assessment of the plant community composition. Overall, our results showed that Iles Kerguelen ponds are shallow freshwater ecosystems harbouring species-poor plant communities with high even- ness, of which structure did not vary among the sampled locations. Three different habitats were identified among ponds in relation with nutrient supply by marine animals, which ultimately influenced plant community structure and cover. We highlight that these habitats are mostly determined by water depth, nutrients, and temperature (mean and variance). Present plant community composition was more strongly correlated with plant community composition in the previous year than with abiotic conditions. Overall, this study provides new knowledge on the aquatic plant communities and the functioning of Iles Kerguelen freshwater ecosystems, which can serve as a basis for future studies dealing with the impact of climate change in the sub-Antarctic region.

Le projet consistait à analyser l’évolution des pressions engendrées par les prélèvements agricoles et les dérivations industrielles sur les écoulements naturels dans les trois bassins du site atelier depuis le XIXe siècle (Ardèche, Cèze, Gardons). Si de nombreuses études ont été menées sur les effets environnementaux des grands ouvrages, la connaissance du rôle joué par la « petite hydraulique » sur les écoulements et les milieux est encore assez lacunaire. Jusqu’à présent l’accent a surtout été mis sur les obstacles physiques opposés au transit sédimentaire et aux flux biologiques : chaussées, barrages, prises d’eau (Walter et Merritts, 2008 ; Lespez et al., 2013). Les aspects quantitatifs ont été plus rarement étudiés dans une perspective temporelle longue (Berger, 1998 ; Jacob, 2005, 2015 ; Jacob et al., 2016), alors qu’un des enjeux actuels est de cerner des niveaux de pression acceptables dans des bassins où la ressource est fortement sollicitée ou risque d’être sujette à une raréfaction consécutive aux changements climatiques. Le travail s’est appuyé sur des documents statistiques produits à la fin du XIXe siècle (1862-1899) qui décrivent les pressions industrielles et agricoles soit à l’échelle du réseau hydrographique (prises d’eau), soit à l’échelle du bassin (surfaces irriguées) et sur une base de données hydrologiques contemporaine, le Réseau Hydrographique Théorique (RHT) (Pella et al., 2012). Le traitement de ces informations dans un SIG a permis une comparaison de la pression sur les eaux de surface à la fin du XIXe avec la situation actuelle à l’échelle du sous-bassin et du tronçon ainsi qu’une simulation des effets de ces dérivations sur des débits caractéristiques. La confrontation avec des reconstructions et réanalyses hydrométéorologiques a permis de contraindre les incertitudes concernant les données hydrologiques utilisées pour cette étude. L’information historique a permis également d’orienter le diagnostic écologique basé sur les stratégies biologiques (trait) adoptées par les différentes espèces composant les communautés de macroinvertébrés benthiques de façon à déterminer si les pressions hydrauliques jouent un rôle sur ces communautés et, indirectement, sur les écosystèmes aquatiques.

The rates of species and trait diversification vary across the Tree-of-Life and over time. Whereas species richness and clade age generally are decoupled, the correlation of accumulated trait diversity of clades (trait disparity) with clade age remains poorly explored. Total trait disparity may be coupled with clade age if the growth of disparity (disparification) within and across clades is continuous with time in an additive niche expansion process (linear-cumulative model), or alternatively if the rate of trait disparification varies over time and decreases as ecological space becomes gradually saturated (disparity-dependent model). Using a clock-calibrated phylogenetic tree for 143 freshwater macroinvertebrate families and richness and trait databases covering > 6400 species, we measured trait disparity in 18 independent clades that successively transitioned to freshwater ecosystems and analyzed its relation with clade age. We found a positive correlation between clade age and total disparity within clades, but no relationship for most individual traits. Traits unique to freshwater lifestyle were highly variable within older clades, while disparity in younger clades shifted towards partially terrestrial lifestyles and saline tolerance to occupy habitats previously inaccessible or underutilized. These results argue that constraints from incumbent lineages limit trait disparity in younger clades that evolved for filling unoccupied regions of the trait space, which suggests that trait disparification may follow a disparity-dependent model. Overall, we provide an empirical pattern that reveals the potential of the disparity-dependent model for understanding fundamental processes shaping trait dynamics across the Tree-of-Life., This research received support from grant CGL2007‐60163/BOS funded by the Spanish Ministry of Education and Science/FEDER (Fondo Europeo de Desarrollo Regional). NB acknowledges the BioFresh EU funded project Biodiversity of Freshwater Ecosystems: Status, Trends, Pressures, and Conservation Priorities (7th FWP contract no. 226874). Further funding support was provided by a Beatriu de Pinós postdoctoral fellowship (BP‐DGR‐2011) to CM by the Agència de Gestió d'Ajuts Universitarisi de Recerca, Generalitat de Catalunya.

Assessing how much management of agricultural landscapes, in addition to protected areas, can offset biodiversity erosion in the tropics is a central issue for conservation that still requires cross‐taxonomic and landscape‐scale studies. We measured the effects of Amazonia deforestation and subsequent land‐use intensification in 6 agricultural areas (landscape scale), where we sampled plants and 4 animal groups (birds, earthworms, fruit flies, and moths). We assessed land‐use intensification with a synthetic index based on landscape metrics (total area and relative percentages of land uses, edge density, mean patch density and diversity, and fractal structures at 5 dates from 1990 to 2007). Species richness decreased consistently as agricultural intensification increased despite slight differences in the responses of sampled groups. Globally, in moderately deforested landscapes species richness was relatively stable, and there was a clear threshold in biodiversity loss midway along the intensification gradient, mainly linked to a drop in forest cover and quality. Our results suggest anthropogenic landscapes with high‐quality forest covering >40 % of the surface area may prevent biodiversity loss in Amazonia.