Les communautés microbiennes benthiques participent activement au recyclage de la matière organique et de fait au fonctionnement biogéochimique des écosystèmes lacustres. Ces communautés comportent de nombreux phyla mais leur diversité fonctionnelle est encore incomplètement connue. Ce travail vise à appréhender les modifications de structure et d'abondance des gènes fonctionnels en lien avec la distribution spatiale verticale (liée au gradient d'oxydoréduction), la variabilité spatiale horizontale (zone côtière vs pélagique) et la dynamique saisonnière liée au brassage de la colonne d'eau (ré-oxygénation des interfaces benthiques), de même que l'identification de la diversité des méthanotrophes et des méthanogènes.Pour cette étude, des carottes sédimentaires ont été prélevées sur un transect zone côtière – zone pélagique, à différentes dates au cours d'un cycle annuel. Chaque carotte sédimentaire a été analysée dans la verticalité entre l'interface eau-sédiment et 20 cm. Les communautés microbiennes participant au cycle du méthane ont été ciblées par 2 gènes de fonction et étudiées en termes de structure, de diversité et d'abondance; par ailleurs, des marqueurs phylogénétiques ont été utilisés pour caractériser les communautés bactériennes et archéennes totales.Les résultats de l'étude spatiale montrent que, si à l'échelle locale (station d'échantillonnage) une relative homogénéité des communautés microbiennes (totales et fonctionnelles) est observée, des variabilités fortes sont détectées d'une part à l'échelle des transects horizontaux en lien avec des changements de conditions environnementales et d'autre part dans la verticalité des sédiments sous l'effet des conditions d'oxydoréduction. La communauté bactérienne étant la plus affectée dans la verticalité, avec des changements de structure entre toutes les strates étudiées. Dans cette même étude, une analyse comparative de la structure des communautés (totales et fonctionelles) a démontré que l'analyse d'échantillons individuels permettait d'obtenir un plus grand nombre d'OTU que l'analyse des mêmes échantillons regroupés en pools.Les résultats de l'étude de la dynamique temporelle des communautés méthanogènes et méthanotrophes révèlent des changements de structure et abondance, principalement à l'interface eau - sédiment en lien avec la dynamique d'oxygénation du lac. Quant à l'analyse de la diversité, elle montre une dominance des Methanomicrobiales (Methanoregula principalement) pour les méthanogènes, mais les Methanosarcinales (Methanosarcina) et les Methanobacteriales (Methanobacterium) ont également été identifiés. Pour les méthanotrophes, la diversité est dominée par Methylobacter en zone profonde et par Methylococcus en zone côtière, les méthanotrophes de Type II (Methylosinus et Methylocystis) ont aussi été identifiés.L'ensemble de ces travaux souligne l'importance de prendre en compte, à la fois la variabilité spatiale (horizontale et verticale) et la variabilité temporelle, des communautés méthanogènes et méthanotrophes lors de l'étude de ces communautés. Les changements quant à leurs structures et leurs abondances sont des paramètres non négligeables pour comprendre les processus impliqués dans le cycle du méthane. / Benthic microbial communities are actively involved in organic matter recycling and fact biogeochemical functioning of lake ecosystems. These communities comprise many phyla but their functional diversity is still incompletely known. This study is focused on the benthic microbial communities involved in the methane cycle in lacsutrine suystems. We aimed understanding the structural and abundance changes of functional genes related to the vertical distribution (redox gradient in sediment), the horizontal variability (coastal vs. pelagic benthic zone) and seasonal dynamics related to mixing of the water column (re-oxygenation of benthic interface). The composition of methanotrophic and methanogenic communities was characterized by sequencing analyses.For this study, sedimentary cores were sampled along a transect from coastal to pelagic zone, at different times during an annual cycle. In addition, each sediment core was analyzed in its verticality from the water-sediment interface to 20 cm depth. Microbial communities involved in the cycle of methane (methanogenesis and methanotrophy) were targeted by 2 functional genes (mcrA and pmoA). Furthermore, phylogenetic markers were used to characterize the total bacterial and archaeal communities. These communities are studied in terms of structure (genotyping), diversity (sequencing) and abundance (qPCR, DNA) of their functional genes.The results of the study showed that, on a spatial scale, a low heterogeneity was detected for a given sampling station in terms of structure of microbial communities (total and functional), however, a high variability was detected both at an horizontal scale along a transect (costal vs. pelagic zone), due to contrasted environmental conditions, and at a vertical scale (upper to deeper layers in the core) under the effect of redox conditions. The bacterial community being the most affected in the verticality, with structural changes among all strata studied. In the same study, a comparative analysis of the structure (for all of the communities), between pooled samples and individual samples, demonstrated that the analysis of individual samples provided a greater number of OTU for the majority of microbial communities.Moreover the study of the temporal dynamic of methanogen and methanotroph communities revealed changes in the structure and abundance, mainly at the water - sediment interface, according to the oxygenation levels that varied through time. The analysis of diversity showed a dominance of Methanomicrobiales (Methanoregula mainly) for methanogens, but Methanosarcinales (Methanosarcina) and Methanobacteriales (Methanobacterium) were also identified. The methanotrophs' community was dominated by Methylobacter on deeper stations and by Methylococcus in coastal station. Type II methanotrophs (Methylosinus and Methylocystis) were also identified.This work highlights the importance of taking into account both the spatial variability (horizontal and vertical) and the temporal variability of methanogen and methanotroph communities. Changes on their structures and abundances are significant parameters for understanding the processes involved in the methane cycle.

Le but de cette thèse était de comprendre les liens entre deux processus de dégradation de la matière organique : la digestibilité du fourrage par les herbivores domestiques et la décomposabilité de la litière par la microfaune du sol. Nous avons fait les hypothèses suivantes : (i) les pratiques de gestion affectent la digestibilité et la décomposabilité des espèces, et (ii) en accord avec l’hypothèse de dominance, celles des communautés via des changements de leur structure fonctionnelle ; (iii) digestibilité et décomposabilité peuvent être estimées par un même « marqueur fonctionnel » facile à mesurer aux niveaux d’organisation de l’espèce et de la communauté. Ce travail a été réalisé dans des parcours du domaine expérimental de La Fage situés sur le Causse du Larzac (Aveyron). Nos résultats ont montré un effet des pratiques de gestion sur la digestibilité et la décomposabilité des différents organes (feuille, tige, partie reproductrice) : les espèces de parcours pâturés et fertilisés ont présenté une digestibilité et décomposabilité supérieures à celles des espèces de parcours uniquement pâturés. Des mesures effectuées à deux dates de récolte ont permis de mettre en évidence une baisse de digestibilité au cours du printemps dans les différents organes, principalement causée par une augmentation de leur teneur en fibre. Une relation positive entre digestibilité et décomposabilité a été montrée pour les feuilles et les tiges dans les deux types de parcours. Cette relation était fortement dépendante de la teneur en fibres des organes, qui peut être estimée de façon fiable par la teneur en matière sèche de ceux-ci : plus la teneur en fibres était élevée, plus la teneur en matière sèche était forte, induisant une faible digestibilité et une faible décomposabilité. Ces résultats ont également été démontrés à l’échelle des communautés pour la digestibilité et la décomposabilité, confirmant l’hypothèse de dominance : les propriétés des écosystèmes peuvent être prédites à partir de traits des espèces dominantes des différents parcours, et en particulier de leur teneur en matière sèche. La teneur en matière sèche est donc un marqueur puissant et facile à mesurer pour estimer la digestibilité et la décomposabilité de systèmes complexes. L’approche fonctionnelle de la diversité biologique basée sur les traits peut donc être utilisée comme un outil de diagnostic du fonctionnement des prairies permanentes afin d’adapter les pratiques de gestion selon les objectifs des éleveurs. / The aim of this thesis was to understand links between two degradation processes of organic matter: the forage digestibility by domestic herbivores and the decomposability of litter by soil microfauna. We hypothesized that: (i) management regimes influenced species digestibility and decomposability, and (ii) in agreement with the dominance hypothesis, those of communities through changes in their functional structure; (iii) digestibility and decomposability can be estimated by the same “functional marker” both at the species and community levels. This study was conducted in rangelands from the La Fage research station located on the Larzac Causse (Aveyron). Our results showed an effect of management regimes on the digestibility and decomposability of different organs (leaf, stem, reproductive part): species from grazed and fertilized grasslands had higher digestibility and decomposability than those from grasslands solely grazed. Measurements conducted at two harvest dates showed a decrease of digestibility of the different organs during spring, mostly due to an increase in fibre concentration. A positive relationship between digestibility and decomposability was found for leaves and stems in both management regimes. This relationship was strongly dependent on organ fibre content, which could be safely estimated by the dry matter content of these different organs: the higher their concentration in structural tissues, the higher their dry matter content, and the lower their digestibility and decomposability. These results were also found at the community level for both properties, thereby validating the dominance hypothesis: the digestibility and decomposability of communities could be predicted from the traits of dominant species found in each management regime, in particular their dry matter content. Dry matter content therefore appears as a powerful and easy to measure marker to estimate the digestibility and decomposability of complex systems. The trait-based approach to plant functional diversity can be used as a diagnostic tool to assess rangeland functioning, so as to modulate management practices according to farmer’s objectives.

Les mesures de végétalisation ou de restauration écologique nécessitent de comprendre les mécanismes qui sous-tendent les changements de composition et de structure de la végétation au cours de la succession écologique. Des perturbations, d’intensité et fréquence variables, naturelles ou causées par l’Homme, agissent souvent en interaction sur la dynamique temporelle de la végétation. Cependant, l’influence d’une perturbation récurrente combinée aux changements écologiques au cours de la succession est restée peu étudiée jusqu’à présent.Les communautés végétales de talus routiers représentent un modèle pertinent pour étudier cette problématique. L’historique d’aménagement et de gestion des talus est particulièrement bien renseigné ; on a donc une connaissance précise de l’âge des communautés et de leur régime de perturbation par la fauche. Les talus routiers fournissent ainsi un plan quasi-expérimental in situ permettant l’étude des processus qui affectent l’assemblage des communautés au cours de la succession sous l’influence d’une perturbation récurrente.L’objectif principal de cette étude est de caractériser la dynamique successionnelle initiée par la mise en place d’un talus routier en région méditerranéenne et de déterminer les processus écologiques et les facteurs environnementaux influençant cette dynamique. On s’intéresse en particulier à l’influence de la fauche récurrente sur cette dynamique.Pour cela, nous avons étudié la composition floristique et la diversité des traits fonctionnels (traits foliaires et de phénologie de floraison principalement) de la végétation de talus routiers de l’Hérault (France). Chaque talus inclut une partie fauchée et une partie non fauchée, l’ensemble formant une chronoséquence sur près de 70 ans.L’analyse des variations taxonomiques entre les communautés végétales de talus routiers montre un large remplacement des espèces au cours de la succession. Ce turnover floristique est associé à des changements fonctionnels au sein des communautés. Ces derniers sont structurés par des filtres environnementaux qui influent (1) sur la synchronie de floraison entre espèces au sein des communautés au cours du temps et (2) sur la diversité de combinaisons de traits fonctionnels entre communautés d’âge similaire. Ces changements de filtres environnementaux au cours du temps semblent liés à des changements pédologiques et à l’augmentation de l’hétérogénéité spatiale des conditions de lumière et de température (avec la fermeture progressive de canopée). La fauche altère les trajectoires floristiques et fonctionnelles, notamment en provoquant un ralentissement du changement de stratégie d’utilisation des ressources au cours de la succession par rapport à la trajectoire naturelle, sans fauche. De plus, cette perturbation récurrente induit une augmentation de la diversité taxonomique et fonctionnelle au sein des communautés alors qu’elle la réduit entre communautés d’âge similaire. Finalement, la fauche agit comme un filtre environnemental supplémentaire sur l’assemblage des communautés au cours de la succession et induit une homogénéisation de la végétation entre communautés d’âge similaire.Les conclusions de cette étude contribuent à la connaissance écologique fondamentale. En termes d’implications pour la gestion des communautés végétales de talus routiers, nos conclusions suggèrent, entre autres, que l’association de végétation fauchée et non fauchée au sein des mêmes sites pourrait servir d’habitat pour une plus grande diversité de faune associée. Cette association permettrait de plus d’avoir un rendu paysager agréable aux usagers de la route, tout en garantissant une bonne visibilité pour la sécurité routière. / The success of revegetation or ecological restauration highly depends on our knowledge of mechanisms underlying changes in composition and structure of the vegetation along the ecological succession. Natural or human-induced disturbances of varying intensity and frequency often occur simultaneously to influence vegetation temporal dynamics. However, the influence of a recurrent disturbance combined with ecological changes along plant succession remains poorly documented.Plant communities growing on road slopes are particularly appropriate to study this issue. Construction work and management history are well documented, so that the age of the vegetation and its disturbance regime by mowing can be precisely informed. Thus, road slopes plant communities represent an in situ quasi-experimental framework particularly adapted to study processes affecting community assembly along the ecological succession under the influence of a recurrent disturbance.The principal objective of this study is to characterise the successional dynamic initiated after road slope construction in the Mediterranean area, and to identify the ecological processes and environmental factors influencing this dynamic. We particularly focused on the influence of recurrent mowing on this dynamic.We studied the floristic composition and the diversity of functional traits (mainly leaf traits and flowering phenology traits) in a 70-year long chronosequence of French Mediterranean (Hérault, France) road slopes, each including both mown and unmown vegetation.The analysis of taxonomical variations between road slopes plant communities reveals a large species turnover along the ecological succession. This floristic turnover relates with functional changes within communities. These functional changes are structured by environmental filters influencing flowering synchrony within communities on one hand, and the diversity of a combination of functional traits between communities of similar age on the other hand. These environmental filters changing along the succession relate with changing soil parameters and increasing spatial heterogeneity of light and temperature conditions with canopy closure.Mowing alters floristic and functional trajectories along the succession, notably through the decrease of speed in resource-use strategy changes along the succession in mown communities compared to unmown communities. In addition, this recurrent disturbance increases taxonomic and functional diversity within communities, while it decreases taxonomic and functional turnover between communities of the same age. Finally, mowing acts as an additional environmental filter on community assembly along the succession and homogenises vegetation between communities of the same age.The conclusions of this study provide basic knowledge in ecology. It also has implications for the management of road slopes plant communities in the perspective of their revegetation after construction work. Our conclusions suggest, amongst others, that combining mown and unmown vegetation could provide habitats for a higher diversity of associated fauna. In addition, it would allow vegetation to be pleasant to road users, while still ensuring a good visibility for road safety.

<p>U radu je izvr&scaron;ena podela 572 registrovane vrste osolikih muva sa područja jugoistočne Evrope na funkcionalne grupe, na osnovu registrovanih funkcionalnih karaktera. Za<br />odabrane 44 endemske i nativne ne-endemske vrste koje su svojim klimatskim ni&scaron;ama ograničene na istraživani prostor, kreirane su mape sada&scaron;nje i buduće potencijalne distribucije (za dva perioda, 2041 -2060 i 2061-2080) upotrebom MAXENT algoritma. Na osnovu dobijenih mapa, izračunata je potenijalna promena areala za odabrane vrste, čime je procenjen efekat klimatskih promena na distribuciju vrsta sirfida. Detektovane su vrste koje će najvi&scaron;e biti pogođene klimatskim promenama, kao i prostori sa najvećim potencijalnim bogatstvom vrsta u budućnosti i područja predviđena da će izgubiti deo diverziteta sirfida. Pokazano je da vrste sa ograničenim arealom neće u budućnosti iskusiti veće smanjenje areala u odnosu na &scaron;iroko rasprostranjene vrste. Takođe, na osnovu mapa potenicijalne sada&scaron;nje distribucije i procenjene retkosti vrsta, izvr&scaron;ena je prioretizacija područja značajnih za opstanak osolikih muva u jugoistočnoj Evropi. Primenom linearnih regresionih i linearnih modela sa me&scaron;ovitim efektom ispitana je međuzavisnost&nbsp; funkcionalnih karaktera vrsta i procenjene promene veličine areala. Definisani su&nbsp; funkcionalni karakteri koji utiču na promenu veličine areala osolikih muva. Ustanovljeni koncept može biti upotrebljen za detekciju vrsta koje se jo&scaron; uvek ne smatraju ugroženim, ali zbog svojih biolo&scaron;ko-ekolo&scaron;kih karakteristika imaju potencijal da to postanu, te stoga zaslužuju pažnju konzervacionista. Dobijeni rezultati mogu u velikoj meri poslužiti za kreiranje sistematskog konzervacionog plana za očuvanje osolikih muva na teritoriji jugoistočne Evrope.</p> / <p>In this paper, the division of 572 species of hoverflies registered in Southeast Europe into functional groups was conducted, based on their functional traits. For 44 selected&nbsp; endemic and native non-endemic species that have their climatic niches limited in the study area, maps of current and future potential distributions were created (for the periods, 2041-2060 and 2061-2080) using MAXENT algorithm. Based on the obtained &nbsp; maps, changes in potential area of occupancy were calculated, in order to estimate the &nbsp; effect of climate change on the distribution of hoverfly species. Species that will be most affected by climate change were detected, as well as the areas with the greatest potential species richness in the future and areas predicted to lose part of the diversity of hoverflies. It is shown that species with limited distribution in the future will not experience a greater reduction of its area in relation to the widespread species. Also, based on the current maps of potential distribution and assessed rarity of species,priority areas important for the survival of hoverflies in Southeast Europe were established. By using linear regression and linear mixed effect models, the interdependence between functional traits and the estimated changes in the range size was tested. Traits affecting the changes in range size of hoverflies were determined. The established concept can be used for the detection of species that are not yet considered endangered, but because of their biological and ecological traits have the potential to become threatened, and therefore deserve the attention of conservationists.&nbsp; This results can largely be used to create a systematic conservation plan for the preservation of hoverflies in Southeast Europe.</p>

Diversos estudos teóricos, experimentais e observacionais têm demonstrado que as relações entre a biodiversidade e as funções ecossistêmicas (BEF) são determinadas pela estrutura funcional da comunidade (ou seja, pela distribuição dos atributos das suas espécies constituintes). Isso pode ocorrer por meio de dois mecanismos mutuamente não exclusivos: (1) a hipótese de dominância (também denominada de efeito de relação de massa), na qual os processos ecossistêmicos são influenciados pela média ponderada na comunidade de um dado atributo funcional (CWM) considerado relevante; (2) a hipótese de complementaridade, na qual a maior variabilidade de um atributo funcional na comunidade (FD) é uma expressão da complementariedade de nicho, o que beneficia o desempenho dos processos ecossistêmicos. Embora ambos os mecanismos já tenham sido amplamente estudados em comunidades de plantas em pequenas escalas espaciais, análises globais considerando distintos biomas ainda são necessárias. Neste estudo, a relação entre biodiversidade e funcionamento dos ecossistemas foi avaliada com base na integração entre uma base de dados global de parcelas de vegetação (sPlot), uma base de dados de atributos de espécies de plantas (TRY) e dados do Índice de Vegetação por Diferença Normalizada (NDVI) obtidos por sensoriamento remoto. O objetivo foi verificar, simultaneamente, os efeitos de dominância e de complementaridade sobre a produção de biomassa vegetal em ecossistemas campestres em todo o mundo. Os dados sobre a estrutura funcional das comunidades (CWM e FD) foram obtidos a partir da base de dados sPLOT e TRY, utilizando para isso atributos funcionais de plantas ecologicamente relevantes. O NDVI, considerado como aproximação da produtividade da vegetação, representa uma medida do funcionamento do ecossistema e foi obtido a partir do produto MOD13Q do sensor MODIS, com resolução espacial de 250m. Para garantir que as medidas de NDVI fossem derivadas apenas de ecossistemas campestres, sem a interferência de outras fisionomias vegetais, foram descartadas as parcelas do sPlot com presença de paisagens heterogêneas no seu entorno mediante consulta a um mapa global de cobertura e uso da terra (Globcover2009). Para quantificar os efeitos independentes da dominância e da complementariedade sobre as variações no NDVI , com controle das variáveis climáticas, foi utilizada uma análise de regressão múltipla do tipo commonality. Os resultados demonstraram que o principal preditor da variação no NDVI correspondeu a um conjunto de atributos funcionais das espécies dominantes relacionados com o espectro de economia da comunidade vegetal (atributos fast-slow), indicando a prevalência da hipótese de dominância (R2 ajustado = 0,65). Os efeitos evidentes da dominância e os efeitos potenciais da complementariedade são discutidos no contexto da sua relação com os fatores abióticos, sendo que a precipitação pluviométrica, em particular, parece ter maior influência tanto sobre a composição de atributos quanto sobre a produtividade. Apesar de algumas limitações metodológicas, a abordagem inovadora utilizada neste trabalho pode ajudar a esclarecer as relações entre biodiversidade e funções ecossistêmicas em escala global, dentro de uma perspectiva integradora e baseada em dados. / Theoretical, experimental and observational studies show that biodiversity ecosystem functioning (BEF) relationships are determined by functional community structure (i.e. trait distributions in a community) through two mutually non-exclusive mechanisms: (1) The dominance hypothesis (a.k.a. mass ratio effect) links ecosystem processes to the community weighted mean (CWM) of a relevant effect trait. (2) The complementarity hypothesis states that higher variability of a trait value within a community (FD) reflects niche complementarity enhancing ecosystem processes. While both mechanisms have been extensively studied in plant communities at small spatial scales, there is a need for global analyses across biomes. Here, a data driven approach to the BEF question is presented integrating a global vegetation plot database with a trait database and remotely sensed NDVI. The objective of this study was to simultaneously evaluate dominance and complementarity effects in grassland systems worldwide. Data on functional community structure (CWM and FD) were obtained from the global vegetation plot database sPlot in combination with the plant trait database TRY using 18 ecologically relevant plant traits. Ecosystem functioning at the selected sPlot sites (n = 2941) was measured as NDVI at a spatial resolution of 250m using the MODIS product MOD13Q (annual peak NDVI being a proxy of productivity). The landcover map Globcover2009 was used for characterization of landscape heterogeneity and landcover at each site, and plots in heterogeneous non-grassland pixels were discarded. Multiple regression commonality analysis was used to disentangle the contributions of complementarity and dominance effects to the variation in NDVI, while controlling for climate variables (adjusted R2 = 0.65). The results show that a plant community economics spectrum referring to the “fast-slow traits” of the dominant species in the community was the strongest predictor of the NDVI values in the grassland systems (dominance effect). Both, evident dominance and potential complementarity effects are discussed against the background of their interplay with abiotic factors and it is noted that especially precipitation seems to drive trait composition and productivity. Despite methodological shortcomings, the novel approach presented in this paper is considered a step towards a more integrative data-driven BEF debate at the global scale

Les stratégies alimentaires peuvent être définies comme la mise en place d'ensembles cohérents de réponses morphologiques, physiologiques, écologiques ou comportementales permettant d’optimiser le succès alimentaire d’une espèce. Le présent travail s'est proposé d'aller au-delà de la simple analyse taxonomique des régimes alimentaires en utilisant les caractéristiques des proies pour explorer certains aspects des stratégies alimentaires et de l’énergétique de la prédation chez les mammifères marins de l’atlantique nord-est. L'objectif majeur était de contribuer à une meilleure compréhension du "pourquoi une proie est une proie ?" La valeur énergétique des proies est apparue comme un élément central des stratégies de prédation. Il en résulte que des coûts d'existence importants chez les mammifères marins doivent être soutenus par une alimentation de qualité élevée et ne peuvent pas être satisfaits simplement par une plus grande quantité de proies de qualité moyenne ou faible. Les résultats obtenus lors de cette thèse ont ainsi permis de progresser de la description des régimes alimentaires vers la compréhension de certaines relations fonctionnelles entre proies et prédateurs. Ainsi, les traits descriptifs de la qualité des proies, comme la teneur en lipides et la valeur énergétique, et les traits descriptifs des coûts d’existence des mammifères marins, comme l’indice mitochondrial et la teneur en lipides des muscles, sont significativement corrélés. Enfin, ce travail souligne que pour comprendre l'écologie alimentaire d'un prédateur, il faut surtout bien connaitre les caractéristiques de ses proies. / Foraging strategies can be defined as the establishment of a consistent set of morphological, physiological, ecological and behavioural responses allowing the optimization of foraging success. Beyond the simple description of the diet, the present work attempted to explore some aspects of foraging strategies and of the energetic of predation among northeast Atlantic marine mammals. The main goal of the study was to contribute to a better understanding of "why a prey is a prey?" Prey energy density appeared to be a key point of predation strategies. Hence, marine mammal species with high existence costs would need high quality prey items, and cannot fulfil their energy requirement just by ingesting more prey items of low to medium quality. The results of this thesis permitted to progress from a taxonomic description of marine mammal diets to the identification of functional relationships between prey and predators. Hence, traits of prey quality such as lipid content or energy density, and traits of predator cost of existence such as muscle mitochondrial density or muscle lipid content, were significantly correlated. Finally, this work underlines that in order to understand the foraging ecology of a predator, its prey characteristics have to be known.

<p>U&nbsp; radu&nbsp; je&nbsp; analizirano&nbsp; gazdovanje&nbsp; &scaron;umama&nbsp; u&nbsp; za&scaron;tićenim&nbsp; područjima&nbsp; u&nbsp; Srbiji,<br />posmatrajući:&nbsp; 1)&nbsp; ekolo&scaron;ke&nbsp; efekte&nbsp; gazdovanja,&nbsp; i&nbsp; 2)&nbsp; procese&nbsp; prilagođavanja&nbsp; gazdovanja&nbsp; konzervacionim&nbsp; potrebama.&nbsp; Povr&scaron;ina&nbsp; za&scaron;tićenih&nbsp; područja&nbsp; je&nbsp; značajno&nbsp; porasla,&nbsp; ali&nbsp; ima malo&nbsp; informacija o njihovom doprinosu u realizaciji konzervacionih&nbsp; ciljeva. Po&scaron;to se u većini za&scaron;tićenih &scaron;umskih područja u Evropi aktivno gazduje, i dozvoljeno je kori&scaron;ćenje drvne&nbsp; biomase,&nbsp; informacije&nbsp; o&nbsp; efektima&nbsp; gazdovanja&nbsp; su&nbsp; neophodne.&nbsp; Glavna&nbsp; barijera&nbsp; u ekolo&scaron;kim&nbsp; evaluacijama&nbsp; gazdovanja&nbsp; je&nbsp; nepostojanje&nbsp; indikatora&nbsp; kojima&nbsp; bi&nbsp; se&nbsp; mogle izmeriti promene u ekosistemu, a&nbsp; koje&nbsp; nastaju kao rezultat primenjenih mera&nbsp; gazdovanja. Poslednjih&nbsp; godina&nbsp; se&nbsp; sve&nbsp; vi&scaron;e&nbsp; ističe&nbsp; potencijal&nbsp; primene&nbsp; funkcionalnih&nbsp; indikatora,&nbsp; tj. indikatora&nbsp; koji&nbsp; se&nbsp; oslanjaju&nbsp; na&nbsp; informacije&nbsp; o&nbsp; funkcionalnim&nbsp; karakteristikama&nbsp; vrsta.&nbsp; U radu je stoga primenjen funkcionalni pristup za analizu ekolo&scaron;kog efekta gazdovanja. U te&nbsp; svrhe&nbsp; su&nbsp; odabrane&nbsp; karakteristike&nbsp; koje&nbsp; se&nbsp; povezuju&nbsp; sa&nbsp; sposobno&scaron;ću&nbsp; vrsta&nbsp; za&nbsp; brzo<br />usvajanje&nbsp; ili konzervisanje resursa, tj.&nbsp; određuju odgovor vrsta na promene u dostupnim resursima, a koje, na primer,&nbsp; nastaju usled uklanjanja drvne biomase: visina, specifična povr&scaron;ina lista, sadržaj suve materije lista, sadržaj ukupnog azota i ukupnog fosfora. Iste se&nbsp; dovode&nbsp; i&nbsp; u&nbsp; vezu&nbsp; sa&nbsp; primarnom&nbsp; produktivno&scaron;ću&nbsp; i&nbsp; dekompozicijom,&nbsp; procesima&nbsp; od značaja&nbsp; za&nbsp; očuvanje&nbsp; integriteta&nbsp; ekosistema.&nbsp; Po&scaron;to&nbsp; analiza&nbsp; odgovora&nbsp; funkcionalnih indikatora&nbsp; zahteva&nbsp; duži&nbsp; vremenski&nbsp; period&nbsp; posmatranja,&nbsp; u&nbsp; radu&nbsp; je&nbsp; osmi&scaron;ljen&nbsp; drugačiji pristup za izvođenje eksperimenta. U te svrhe su iskori&scaron;ćeni Landsat satelitski snimci, tj. tri snimka sa vremenskim razmakom od 10 godina: 1994.,&nbsp; 2005. i 2015. godina. Izvr&scaron;ena je&nbsp; digitalna&nbsp; klasifikacija&nbsp; snimaka&nbsp; prema&nbsp; sastavu&nbsp; &scaron;uma,&nbsp; nakon&nbsp; čega&nbsp; su&nbsp; detektovane promene&nbsp; u&nbsp; sastavu&nbsp; &scaron;uma&nbsp; za&nbsp; period&nbsp; od&nbsp; ukupno&nbsp; 20&nbsp; godina.&nbsp; Ovi&nbsp; podaci&nbsp; su&nbsp; spojeni&nbsp; sa podacima&nbsp; o&nbsp;&nbsp; funkcionalnim&nbsp; karakteristikama&nbsp; vrsta,&nbsp; kako&nbsp; bi&nbsp; se&nbsp; utvrdile&nbsp; promene&nbsp; u funkcionalnoj kompoziciji. Poslednji korak je bio formiranje modela &scaron;umske krune, kroz koji&nbsp; je&nbsp; određen&nbsp; intenzitet&nbsp; seče.&nbsp; Koristeći&nbsp; podatke&nbsp; o&nbsp; promenama&nbsp; u&nbsp; gustini&nbsp; krune&nbsp; i<br />promenama&nbsp; u&nbsp; funkcionalnoj&nbsp; kompoziciji,&nbsp; sproveden&nbsp; je&nbsp; eksperiment,&nbsp; tj.&nbsp; analiza&nbsp; efekta različitih&nbsp; nivoa&nbsp; intenziteta&nbsp; seče&nbsp; na&nbsp; promene&nbsp; u&nbsp; funkcionisanju&nbsp; &scaron;umskog&nbsp; ekosistema.&nbsp; Za sprovođenje ovog eksperimenta je odabran samo jedan deo Fru&scaron;ke gore, jer je cilj bio da se osmisli&nbsp; pristup za evaluaciju, prilagođen trenutnom konceptu gazdovan ja za&scaron;tićenim &scaron;umskim&nbsp; područjima,&nbsp; i&nbsp; ispita&nbsp; njegova&nbsp; praktičnost.&nbsp; Kao&nbsp; propratni&nbsp; podatak&nbsp; ovoj&nbsp; analizi, sprovedena&nbsp; je&nbsp; i&nbsp; komparativna&nbsp; analiza&nbsp; upravljača&nbsp; za&scaron;tićenih&nbsp; &scaron;umskih&nbsp; područja&nbsp; u&nbsp; Srbiji, kako&nbsp; bi&nbsp; se&nbsp; ispitao&nbsp; nivo&nbsp; ulaganja&nbsp; u&nbsp; konzervacione&nbsp; sposobnosti,&nbsp; kao&nbsp; ključnog&nbsp; procesa&nbsp; u implementaciji&nbsp;&nbsp; konzervacionih&nbsp; ciljeva.&nbsp; U&nbsp; digitalnoj&nbsp; klasifikaciji&nbsp; je&nbsp; postignuta&nbsp; visokapreciznost,&nbsp; sa&nbsp; ukupnom&nbsp; precizno&scaron;ću&nbsp; 94,5%&nbsp; i&nbsp; Kapa&nbsp; koeficijentom&nbsp; 0,93.&nbsp; Potpuno spektralno razdvajanje je postignuto samo za&nbsp; <em>Q. petraea&nbsp;</em> od<em> Tilia tomentosa</em>, i&nbsp; sastojina u<br />kojima se kao dominantne pojavljuju <em>F. silvatica i Tilia tomentosa</em>. Utvđeno je prodiranje<em> F.&nbsp; moesiaca&nbsp;&nbsp;&nbsp; </em>u&nbsp; &scaron;ume&nbsp; <em>Q.&nbsp; petraea,&nbsp;</em> i&nbsp; apsolutno&nbsp; &scaron;irenje&nbsp; vrste&nbsp; <em>Tilia&nbsp; tomentosa,</em>&nbsp; posebno&nbsp; u periodu&nbsp; nakon&nbsp; 2005.&nbsp; godine,&nbsp; a&nbsp; koja&nbsp; prema&nbsp; podacima&nbsp; o&nbsp; karakteristikama&nbsp; vrsta&nbsp; ima najveću&nbsp; kompetetivnu&nbsp; sposobnost&nbsp; u&nbsp; odnosu&nbsp; na&nbsp; druge&nbsp; ispitivane&nbsp; vrste&nbsp; drveća.&nbsp; Rezultati modela gustine krune ukazuju na postepeno proređivanje &scaron;ume od 1994. ka 2015. godini, sa&nbsp; potpunim&nbsp; nestankom&nbsp; &scaron;uma&nbsp; guste&nbsp; krune&nbsp; na&nbsp; prelazu&nbsp; između&nbsp; 1994.&nbsp; i&nbsp; 2005.&nbsp; godine. Utvrđen je značajan efekat proređivanja &scaron;ume na promene u funkcionalnoj kompoziciji. Sa&nbsp; vi&scaron;im&nbsp; intenzitetom&nbsp; proređivanja,&nbsp; CWM&nbsp; indikator&nbsp; se&nbsp; pomerio&nbsp; od&nbsp; konzervativnih karakteristika ka onima koje ukazuju na dominaciju vrsta sklonih brzom sticanju resursa. Prelaz&nbsp; koji&nbsp; je&nbsp; imao&nbsp; značajnog&nbsp; efekta&nbsp; na&nbsp; promene&nbsp; je&nbsp; prelaz&nbsp; iz&nbsp; &scaron;ume&nbsp; sa&nbsp; gustinom&nbsp; krune većom&nbsp; od&nbsp; 65%&nbsp; u&nbsp; &scaron;umu&nbsp; gustine&nbsp; krune&nbsp; između&nbsp; 50-65%,&nbsp; a&nbsp; &scaron;to&nbsp; bi&nbsp; moglo&nbsp; ukazivati&nbsp; i&nbsp; na prelaz u drugi režim funkcionisanja&nbsp; ekosistema.&nbsp; Konzervacioni ciljevi su jo&scaron; uvek slabo integrisani u gazdovanje &scaron;umama u za&scaron;tićenim područjima.</p> / <p>In&nbsp; this&nbsp; work,&nbsp; the&nbsp; forest&nbsp; management&nbsp;&nbsp; in&nbsp; protected&nbsp; areas&nbsp; of&nbsp; Serbia&nbsp; was&nbsp; analysed, following:&nbsp; 1)&nbsp; ecologic&nbsp; effects&nbsp; of&nbsp; management&nbsp; and&nbsp; 2)&nbsp; investments&nbsp; in&nbsp; capabilities essential&nbsp; for&nbsp; integration&nbsp; of&nbsp; conservation&nbsp; objectives.&nbsp; The&nbsp; size&nbsp; of&nbsp; protected&nbsp; areas&nbsp; has significantly&nbsp; grown,&nbsp; but&nbsp; there&nbsp; is&nbsp; a&nbsp; little&nbsp; information&nbsp; on&nbsp; their&nbsp; contribution&nbsp; to&nbsp; real conservation&nbsp; goals.&nbsp; Since&nbsp; in&nbsp; most&nbsp; of&nbsp; European&nbsp; protected&nbsp; forest&nbsp; areas&nbsp; is&nbsp; employed active management, the information on ecological&nbsp; effects of management&nbsp; is necessary. The&nbsp; main&nbsp; barrier&nbsp; in&nbsp; ecologic&nbsp; evaluations&nbsp; of&nbsp; managing&nbsp; is&nbsp; the&nbsp; absence&nbsp; of&nbsp; indicators, which&nbsp; could&nbsp; measure&nbsp; the&nbsp; changes&nbsp; in&nbsp; ecosystem,&nbsp; resulting&nbsp; from&nbsp; applied&nbsp; measures. Recently, the potentiality of&nbsp; functional indicators is more&nbsp; emphasized, i.e. indicators, which lean on information about functional traits of species. So, in this work functional approach&nbsp; was&nbsp; taken&nbsp; to&nbsp; analyse&nbsp; ecologic&nbsp; effects&nbsp; of&nbsp; forest&nbsp; management.&nbsp; For&nbsp; this&nbsp; sake were chosen characteristics, which are connected to capabilities of specie s to acquire or&nbsp; conserve&nbsp; resources,&nbsp; i.e.&nbsp; define&nbsp; the&nbsp; answer&nbsp; of&nbsp; the&nbsp; species&nbsp; on&nbsp; changes&nbsp; in&nbsp; available resources,&nbsp; caused&nbsp; by&nbsp; elimination&nbsp; of&nbsp; wooden&nbsp; mass,&nbsp; i.e.&nbsp; logging:&nbsp; height,&nbsp; specific&nbsp; leaf area, leaf dry matter cont ent, nitrogen content and&nbsp; phosphorus&nbsp; content. The same are connected to the processes of significance for conservation of ecosystem integrity&nbsp; (net primary&nbsp; productivity&nbsp; and&nbsp; decomposition).&nbsp; Since&nbsp; the&nbsp; analysis&nbsp; of&nbsp; functional&nbsp; indicators response&nbsp; demands&nbsp; a&nbsp; longer&nbsp; period&nbsp; of&nbsp; observation,&nbsp; another&nbsp; attitude of&nbsp; performing&nbsp; the experiment was conceptualized. For that purpose Landsat&nbsp; satellite&nbsp; image was&nbsp; used,&nbsp; i.e. three&nbsp; images&nbsp; in&nbsp; interval&nbsp; of&nbsp; ten&nbsp; years:&nbsp; 1994,&nbsp; 2005,&nbsp; and&nbsp; 2015.&nbsp; A&nbsp; digital&nbsp; image classification of&nbsp; forest composition was&nbsp; performed, after which the&nbsp; changes&nbsp; in&nbsp; forest composition&nbsp; were&nbsp; detected&nbsp; over&nbsp; the&nbsp; period&nbsp; of&nbsp; 20&nbsp; years.&nbsp; These&nbsp; data&nbsp; were&nbsp; then connected with the data on functional characteristics of species to determine changes in functional composition.&nbsp;&nbsp; The last step&nbsp; was forming of forest canopy&nbsp; density model, through&nbsp; which&nbsp; was&nbsp; determined&nbsp; the&nbsp; intensity&nbsp; of&nbsp; logging.&nbsp; Using&nbsp; data&nbsp; on&nbsp; changes&nbsp; of forest&nbsp; canopy&nbsp; density&nbsp; model&nbsp; and&nbsp; changes&nbsp; in&nbsp; functional&nbsp; composition,&nbsp; an&nbsp; experiment was&nbsp; performed,&nbsp; i.e.&nbsp; analysis&nbsp; of&nbsp; effects&nbsp; of&nbsp; different&nbsp; levels&nbsp; of&nbsp; logging&nbsp; intensity&nbsp; on changes&nbsp; in&nbsp; forest&nbsp; ecosystem&nbsp; function.&nbsp; For&nbsp; the&nbsp; performing&nbsp; of&nbsp; this&nbsp; experiment&nbsp; was chosen&nbsp; just&nbsp; a&nbsp; part&nbsp; of&nbsp; Fruska&nbsp; gora,&nbsp; as&nbsp; the&nbsp; goal&nbsp; was&nbsp; to&nbsp;&nbsp; try&nbsp; to&nbsp; construct the&nbsp; evaluation approach,&nbsp; adapted to&nbsp; momentary&nbsp; concept of&nbsp; managing&nbsp; in&nbsp; protected&nbsp; forest&nbsp; areas&nbsp; and inspect&nbsp; its&nbsp; feasibility.&nbsp; As&nbsp; an&nbsp;&nbsp; accompanying&nbsp; data&nbsp; with&nbsp; this&nbsp; analysis&nbsp; was&nbsp; performed&nbsp; a comparative&nbsp; analysis&nbsp; of protected forest area managers&nbsp; in Serbia, to&nbsp; examine&nbsp; the level of&nbsp; investments&nbsp; in&nbsp; conservation&nbsp; capabilities,&nbsp; as&nbsp; the&nbsp; key&nbsp; process&nbsp; in&nbsp; implementing conservation goals.</p>

Les cours d’eau de tête de bassin versant, malgré leurs tailles réduites, jouent des rôles importants pour le fonctionnement des milieux situés en aval, et rendent de nombreux services écologiques. Depuis l’émergence du River Continuum Concept, le fonctionnement de ces cours d’eau est considéré comme reposant principalement sur les apports allochtones de matière organique détritique par opposition aux écosystèmes aval de plus grande taille dans lesquels la production primaire autochtone est considérée comme prépondérante. Bien que les détritus soient, par définition, des ressources de moindre qualité pour leurs consommateurs que les végétaux vivants, le rôle des facteurs qui limitent la production biologique et les processus fonctionnels dans ces écosystèmes détritiques reste encore peu exploré. Par exemple la carence en éléments minéraux essentiels (notamment en azote et en phosphore) dans les détritus peut limiter le développement des organismes vivants dans les cours d’eau. De ce fait, la disponibilité en éléments minéraux dans la colonne d’eau, en stimulant la croissance, l’activité des décomposeurs et la qualité élémentaire des ressources par le processus d’immobilisation microbienne, pourrait contrôler pour partie les processus écologiques en jeu dans ces écosystèmes. En étudiant in situ la réponse des communautés microbiennes aux nutriments le long d’un gradient d’occupation des sols, nos travaux ont mis en évidence un effet positif des éléments dissous (N et P) sur la décomposition des litières et les activités enzymatiques des décomposeurs, et ce même pour les niveaux en nutriments les plus élevés du gradient, pour lesquels des effets inverses étaient attendus. Indépendamment, dans des cours d’eau anciennement soumis à de forts dépôts acidifiants, nous avons pu observer une récupération du processus de décomposition des litières. Néanmoins, cette restauration s’accompagnant d’un appauvrissement marqué en N, des perturbations du fonctionnement de ces cours d’eau pourrait se manifester à terme. Le rôle de la production primaire dans les cours d’eau de tête de bassin versant a ensuite été questionné. En effet, bien qu’étant mineur quantitativement, l’apport de carbone de forte qualité pourrait jouer un rôle non négligeable sur le fonctionnement des cours d’eau de tête de bassin versant. En particulier, l’importance et le rôle des apports en acides gras polyinsaturés (AGPI) via les biofilms phototrophes ont été questionnés. En se basant sur un suivi de terrain sur 15 cours d’eau des Vosges le long d’un gradient d’acidification, nos recherches ont tout d’abord pu mettre en évidence la présence de biofilms diatomiques riches en AGPI, malgré le caractère très forestier de ces cours d’eau. Dans un second temps, une expérience en conditions contrôlées a permis d’observer le rôle positif des apports, mêmes faibles, de ressources diatomiques sur la croissance et la survie du crustacé amphipode Gammarus fossarum. Sans cet apport, ces organismes se sont avérés incapables de maintenir leurs niveaux internes d’AGPI, suggérant qu’une consommation de producteurs primaires autochtones était indispensable à ces organismes détritivores. Nos résultats ont ainsi pu mettre en évidence les rôles fondamentaux que peuvent jouer la disponibilité en éléments dissous (N et P) et la qualité du carbone dans les ressources sur la production biologique et sur le processus de décomposition des litières dans les cours d’eau de tête de bassin versant. Ces résultats appellent désormais à investiguer plus profondément les interactions entre ces deux facteurs limitants, et à comprendre dans quels contextes l’un des facteurs pourrait suppléer l’autre. En particulier, il sera intéressant de rechercher comment diverses perturbations anthropiques (xénobiotiques, réchauffement climatique etc…) pourraient affecter l’intensité ou la nature de ces limitations / Despite their reduced sizes, headwater streams play important roles in the functioning of downstream ecosystems and provide numerous ecological services. Since the River Continuum Concept, the functioning of these streams has been considered as mainly relying on allochthonous supplies of detrital organic matter for their functioning, in contrast with downstream ecosystems of larger size where primary production is considered to be predominant. Despite that detritus represent, by definition, a resource of lower quality for its consumers than living plants, the nature of the factors limiting the biological production and functional processes in these detrital ecosystems remains sparsely explored. First, the lack of essential elements (in particular nitrogen and phosphorus) in detritus could be a major constraint for the development of living organisms in streams. As a result, the availability of mineral elements in the water column, by stimulating the growth and activity of decomposers, but also by increasing the elemental quality of resources through microbial immobilization, could control ecological processes in a higher extent than previously believed in these ecosystems. By studying in situ, the response of microorganisms to nutrients availability along a land-use gradient, our results have shown a positive effect of the dissolved elements (N and P) on the decomposition of leaf litters and the enzymatic activities of the decomposers, even for the highest nutrient levels of the gradient, for which adverse effects were expected. Independently, in streams formerly subjected to acidification, we observed a recovery of the process of leaf litter decomposition. Nevertheless, this recovery was accompanied by a marked N reduction in the ecosystem, huge changes in stream functioning might be expected in the medium to long term. The role of autochthonous primary production was then questioned. Indeed, while being quantitatively minor, this contribution of high quality carbon may play a significant role in the functioning of headwater streams. In particular, the importance and role of polyunsaturated fatty acid (PUFA) intakes via phototrophic biofilms was questioned. Based on a field survey of 15 rivers in the Vosges Mountains along an acidification gradient, our results first showed the presence of diatomic biofilms rich in PUFA, despite these streams are clearly in a forested context. In a second step, an experimentation carried out under controlled conditions permitted to observe the positive role of diatomic resources, even in low concentrations, on the growth and survival of the crustacean amphipod Gammarus fossarum. Without this input, these organisms were unable to maintain their internal levels of PUFAs, suggesting that the consumption of autochthonous primary producers might be essential for these detritivore organisms. All our results permit to highlight the fundamental roles that can be played by the availability of dissolved elements (N and P) and the carbon quality of the resources on the biological production and on leaf litter decomposition in headwater streams. These results stress the need for more profound investigation of the interactions between these two limiting factors, and for understanding in which contexts one factor could supplement the other. In particular, it will be interesting to investigate to what extent various anthropogenic disturbances (xenobiotics, global warming, etc...) could affect the intensity or the nature of these limitations

Les prairies subalpines abritent de grandes populations d’herbivores sauvages et sont souvent soumises au pâturage domestique. Le but de cette thèse est d’analyser la réponse métabolique des plantes subalpines à l’herbivorie, et d’identifier les conséquences fonctionnelles sur l’écosystème via la décomposabilité des litières. Pour cela, nous avons établi un dispositif d’exclusion des herbivores sur l’alpage d’Armenaz dans le massif des Bauges, dans deux contextes de pâturage différents : extensif par des herbivores sauvages (chamois, Rupicapra rupicapra) et intensif par des herbivores domestiques (génisses, Bos taurus). Nous avons caractérisé une vingtaine d’espèces végétales par des traits fonctionnels foliaires reflétant leur métabolisme de croissance et de défense, en présence ou en absence d’herbivores, et avons estimé la décomposabilité des litières de certaines d’entre elles. Contrairement à l’hypothèse du compromis entre croissance et défense, nos résultats montrent que la présence de composés de défense (polyphénols et lignine) chez les plantes n’est pas reliée à leur stratégie d’acquisition des ressources. Dans notre étude, la réponse des plantes à l’exclusion des herbivores dépend essentiellement : (1) du contexte d’herbivorie, la réponse étant d’avantage marquée dans le contexte du pâturage intensif par les génisses qu’extensif par les chamois, (2) des espèces végétales, suggérant l’existence de différentes stratégies de défense, (3) des conditions environnementales, pouvant être le reflet d’effets d’interaction avec le traitement d’herbivorie. Parmi les réponses observées, l’exclusion des herbivores entraîne chez certaines espèces une diminution de la teneur en composés phénoliques, et plus particulièrement en flavonoïdes, pouvant refléter la relaxation de la synthèse de ces composés de résistance en absence d’herbivores. L’exclusion des chamois n’influence pas la composition chimique des litières ni leur décomposabilité. Cette dernière, parmi les composés étudiés, dépend majoritairement de sa composition en polyphénols. L’identification d’effets contrastés de différents contextes d’herbivorie sur la réponse des plantes et des fonctions écosystémiques qui en découlent nous permet d’améliorer notre compréhension du fonctionnement des prairies subalpines. Ce sont autant d’éléments pour nous aider à mieux appréhender les effets sur l’environnement d’éventuels changements démographiques des populations de grands herbivores. / Alpine grasslands are home to large populations of wild herbivores and are often exposed to additional grazing by domestic herbivores. This study aims to investigate the metabolic response of subalpine plant species to herbivory and to identify the ecosystem functional consequences via the alteration of litter decomposability. For this purpose, we set up a two-year experimental design using exclosures on the Armenaz subalpine grassland from the Bauges massif, under two mammalian herbivory regimes: intensive grazing by domestic heifers (Bos taurus) and extensive grazing by wild chamois (Rupicapra rupicapra). We measured leaf functional traits representative of growth and defense metabolisms on about twenty plant species grown in presence or absence of herbivores, and estimated litter decomposability of some of these species. Contrary to the hypothesis of a growth/defense tradeoff, our results show that the allocation of defensive compounds (polyphenols and lignin) in plants is not related to their nutrient acquisition strategy. In our study, plant responses to grazing exclusion vary according to: (1) herbivory context, plant response being more pronounced in the case of intensive grazing by heifers than extensive grazing by chamois, (2) plant species, suggesting that they rely on different defensive strategies, (3) environmental conditions, which may reflect the interactive effects with grazing treatment. One of the observed responses of plants to grazing exclusion is the decrease of their phenolic content, and more specifically flavonoids, which can be explained by the relaxation of the production of plant defenses when herbivores are no longer present. Chamois exclusion has no influence on chemical composition and decomposability of litters, the latter being best explained by its phenolic content. Revealing the contrasted effects of wild and domestic mammalian herbivores on vegetation and related soil processes allow us to improve our understanding of subalpine grasslands functioning. This should help us to better predict the effects of potential demographic variations of herbivore populations on environment.

Diversos estudos teóricos, experimentais e observacionais têm demonstrado que as relações entre a biodiversidade e as funções ecossistêmicas (BEF) são determinadas pela estrutura funcional da comunidade (ou seja, pela distribuição dos atributos das suas espécies constituintes). Isso pode ocorrer por meio de dois mecanismos mutuamente não exclusivos: (1) a hipótese de dominância (também denominada de efeito de relação de massa), na qual os processos ecossistêmicos são influenciados pela média ponderada na comunidade de um dado atributo funcional (CWM) considerado relevante; (2) a hipótese de complementaridade, na qual a maior variabilidade de um atributo funcional na comunidade (FD) é uma expressão da complementariedade de nicho, o que beneficia o desempenho dos processos ecossistêmicos. Embora ambos os mecanismos já tenham sido amplamente estudados em comunidades de plantas em pequenas escalas espaciais, análises globais considerando distintos biomas ainda são necessárias. Neste estudo, a relação entre biodiversidade e funcionamento dos ecossistemas foi avaliada com base na integração entre uma base de dados global de parcelas de vegetação (sPlot), uma base de dados de atributos de espécies de plantas (TRY) e dados do Índice de Vegetação por Diferença Normalizada (NDVI) obtidos por sensoriamento remoto. O objetivo foi verificar, simultaneamente, os efeitos de dominância e de complementaridade sobre a produção de biomassa vegetal em ecossistemas campestres em todo o mundo. Os dados sobre a estrutura funcional das comunidades (CWM e FD) foram obtidos a partir da base de dados sPLOT e TRY, utilizando para isso atributos funcionais de plantas ecologicamente relevantes. O NDVI, considerado como aproximação da produtividade da vegetação, representa uma medida do funcionamento do ecossistema e foi obtido a partir do produto MOD13Q do sensor MODIS, com resolução espacial de 250m. Para garantir que as medidas de NDVI fossem derivadas apenas de ecossistemas campestres, sem a interferência de outras fisionomias vegetais, foram descartadas as parcelas do sPlot com presença de paisagens heterogêneas no seu entorno mediante consulta a um mapa global de cobertura e uso da terra (Globcover2009). Para quantificar os efeitos independentes da dominância e da complementariedade sobre as variações no NDVI , com controle das variáveis climáticas, foi utilizada uma análise de regressão múltipla do tipo commonality. Os resultados demonstraram que o principal preditor da variação no NDVI correspondeu a um conjunto de atributos funcionais das espécies dominantes relacionados com o espectro de economia da comunidade vegetal (atributos fast-slow), indicando a prevalência da hipótese de dominância (R2 ajustado = 0,65). Os efeitos evidentes da dominância e os efeitos potenciais da complementariedade são discutidos no contexto da sua relação com os fatores abióticos, sendo que a precipitação pluviométrica, em particular, parece ter maior influência tanto sobre a composição de atributos quanto sobre a produtividade. Apesar de algumas limitações metodológicas, a abordagem inovadora utilizada neste trabalho pode ajudar a esclarecer as relações entre biodiversidade e funções ecossistêmicas em escala global, dentro de uma perspectiva integradora e baseada em dados. / Theoretical, experimental and observational studies show that biodiversity ecosystem functioning (BEF) relationships are determined by functional community structure (i.e. trait distributions in a community) through two mutually non-exclusive mechanisms: (1) The dominance hypothesis (a.k.a. mass ratio effect) links ecosystem processes to the community weighted mean (CWM) of a relevant effect trait. (2) The complementarity hypothesis states that higher variability of a trait value within a community (FD) reflects niche complementarity enhancing ecosystem processes. While both mechanisms have been extensively studied in plant communities at small spatial scales, there is a need for global analyses across biomes. Here, a data driven approach to the BEF question is presented integrating a global vegetation plot database with a trait database and remotely sensed NDVI. The objective of this study was to simultaneously evaluate dominance and complementarity effects in grassland systems worldwide. Data on functional community structure (CWM and FD) were obtained from the global vegetation plot database sPlot in combination with the plant trait database TRY using 18 ecologically relevant plant traits. Ecosystem functioning at the selected sPlot sites (n = 2941) was measured as NDVI at a spatial resolution of 250m using the MODIS product MOD13Q (annual peak NDVI being a proxy of productivity). The landcover map Globcover2009 was used for characterization of landscape heterogeneity and landcover at each site, and plots in heterogeneous non-grassland pixels were discarded. Multiple regression commonality analysis was used to disentangle the contributions of complementarity and dominance effects to the variation in NDVI, while controlling for climate variables (adjusted R2 = 0.65). The results show that a plant community economics spectrum referring to the “fast-slow traits” of the dominant species in the community was the strongest predictor of the NDVI values in the grassland systems (dominance effect). Both, evident dominance and potential complementarity effects are discussed against the background of their interplay with abiotic factors and it is noted that especially precipitation seems to drive trait composition and productivity. Despite methodological shortcomings, the novel approach presented in this paper is considered a step towards a more integrative data-driven BEF debate at the global scale