Le déclin actuel de la biodiversité a poussé un grand nombre d’études à s’intéresser aux relations entre la biodiversité et le fonctionnement des écosystèmes. La diversité intraspécifique est une facette centrale de la biodiversité qui permet aux espèces de s’adapter aux variations environnementales et dont l’importance écologique est de plus en plus examinée. A l’aide d’une méta-analyse synthétisant des données sur plusieurs espèces et écosystèmes, nous avons démontré qu’un changement de la diversité intraspécifique peut avoir des conséquences écologiques aussi fortes qu’un changement de la diversité spécifique. Ensuite, au travers d’études empiriques nous avons étudié la diversité fonctionnelle et trophique de populations sauvages de vairons (Phoxinus phoxinus), une espèce de poisson abondante en rivière. Une forte variabilité fonctionnelle et trophique a été montrée entre populations de vairons. Cette diversité était structurée de manière complexe du fait de l’action jointe des conditions environnementales, de facteurs évolutifs et des multiples liens existants entre les traits et la niche trophique. Par ailleurs, nous avons montré expérimentalement que les différences fonctionnelles entre populations de vairons pouvaient engendrer des conséquences écologiques aussi fortes qu’une augmentation de la température. De plus, des populations plus diversifiées génétiquement soutenaient des diversités spécifiques élevées puis augmentaient l’intensité des processus écosystémiques. Ces travaux mettent en évidence que la diversité intraspécifique est une composante essentielle de la biodiversité qui doit être considérée comme un facteur majeur affectant la structure des communautés et le fonctionnement des écosystèmes / Current decline of biodiversity has led to many investigations on the relationship between biodiversity and ecosystem functioning. Diversity within species is a pivotal facet of biodiversity that allows species adapting to environmental conditions, and can have ecological effects. Using a meta-analysis synthetizing data across species and ecosystems, we showed that changes in intraspecific diversity can have ecological consequences as strong as changes in species diversity. Then, we empirically studied the functional and trophic diversity among wild populations of European minnows (Phoxinus phoxinus), a highly abundant freshwater species. We observed a high functional and trophic variability among populations, which was shaped by environmental conditions, evolutionary factors, and covariations linking traits and trophic niche among each other. Additionally, we experimentally demonstrated that functional variation among populations led to ecological consequences as strong as those of warming ecosystem. Finally, we uncovered that high genetic diversity within population sustained higher species diversity and higher rates of ecosystem processes. Overall, this thesis reveals that intraspecific diversity is a fundamental component of biodiversity that should be considered as a strong driver of community and ecosystem dynamics.

Drought is one of the most important stress factors affecting plants. Increasing drought resistance via plant breeding is currently the main approach for improvement of plant productivity and reduction of water usage. Plant breeders and scientists search for reliable and easy methods of the determination of drought sensitivity in different genotypes. A precise knowledge about processes underlying plant stress response and defence against limited water availability is necessary for this. The aim of this study was a detailed analysis of photosynthetic processes and changes in leaf proteome (again aimed especially at proteins involved in photosynthesis) during drought stress. This analysis was a part of a complex project focused on the possible causes of genetic variability and drought resistance in agronomically important crops. Another goal was to analyse whether the measurement of selected photosynthetic parameters can be used for the determination of drought sensitivity per se and/or for the prediction of the response of hybrids based on known behaviour of their parents. Young plants of maize inbred lines and their hybrids were used as a model for this analysis, which was made under conditions of moderate and more severe drought. Two inbred lines which were (together with their F1 hybrids) used...

Intraspecific plant-soil feedback is a relationship in which plant affects the composition of the soil and such modified soil affects growth of the same plant species. This relationship and its intensity may be linked with plant dominance and invasiveness. Dominant species can alter the composition of the soil in their favor and thus show positive intraspecific plant-soil feedback. As the invasive species are commonly being dominant in their new environment, it can be expected that intraspecific positive plant-soil feedback could be an important factor allowing the invasive species to achieve their dominant position and become invasive. To test if the existence of positive intraspecific feedback could be a general mechanism underlying plant invasiveness I compared intraspecific plant-soil feedback in a group of invasive and introduced, but non-invasive, plants in the Czech Republic. I did this using a preselected set of 34 species - 17 invasive and 17 non-invasive. For realization of the project I used the method of two-phase experiment. The first phase is called soil conditioning - influencing of soil by the plant. In the second phase the same plant species are planted in conditioned soil from the first phase and in control (unconditioned) soil. Then I compared plant biomass from conditioned and...

La variabilité intraspécifique fait partie intégrante de la réponse à court et à long terme des organismes vivants aux fluctuations environnementales. Cette variabilité, exprimée au travers de différents traits des individus, peut potentiellement influencer la sensibilité des espèces à une contamination chimique. La variabilité intraspécifique n'est pas, à l'heure actuelle, prise en compte en évaluation des risques écotoxicologiques, alors même qu'elle pourrait en biaiser les résultats. Pour examiner cette hypothèse, l'importance de la variabilité intraspécifique dans la réponse au cuivre (Cu) a été quantifiée en conditions contrôlées pour trois espèces de macrophytes aquatiques, Lemna minor, Myriophyllum spicatum et Ceratophyllum demersum. Les variations entre génotypes de chacune de ces 3 espèces ont été comparées à la variabilité interspécifique. Les résultats ont mis en évidence une variabilité génotypique significative, dont l'importance dépend de l'espèce considérée. En effet, L. minor a montré une faible variabilité, au contraire de M. spicatum dont la variabilité de l'inhibition de croissance par le Cu est supérieure aux différences interspécifiques. Afin de préciser l'étendue et les mécanismes de la variabilité génotypique chez M. spicatum, d'autres expériences impliquant des mesures de traits d'histoire de vie ont été réalisées sur 7 génotypes exposés au Cu. Les résultats ont montré que certains génotypes étaient jusqu'à 8 fois plus sensibles au Cu à des concentrations allant de 0.15 à 0.5 mg/L). Ces différences de sensibilité sont en partie expliquées par les traits mesurés, mais des mesures physiologiques et/ou des approches en transcriptomique devraient pouvoir expliquer de façon plus consistante la source de ces différences de sensibilité. Enfin, 3 expériences faisant varier respectivement la teneur en nutriments, l'intensité lumineuse et la préexposition au Cu, ont démontré que la plasticité phénotypique joue un rôle majeur dans la sensibilité au Cu chez L. minor. En effet, l'affaiblissement des individus, résultant des conditions environnementales défavorables, peut conduire au doublement de la sensibilité de L. minor au Cu. [...] / Intraspecific variability plays a pivotal role in short and long term responses of species to environmental fluctuations. This variability, expressed through different traits of individuals, can potentially influence species sensitivity to chemical contamination. This intraspecific variability is currently not taken into account in ecotoxicological risk assessment, whereas it can mislead its results. To examine this hypothesis, the importance of intraspecific variability in the response to copper (Cu) was quantified in controlled conditions for three aquatic macrophyte species, Lemna minor, Myriophyllum spicatum and Ceratophyllum demersum. Variations among genotypes of each of these 3 species were compared to interspecific variability. Results have highlighted a significant genotypic variability, whose importance depends on the species considered. Indeed, L. minor demonstrated a low variability, contrarily to M. spicatum whose variability in growth inhibition by Cu was higher than interspecific differences. In order to specify the extent and the mechanisms of genotypic variability in M. spicatum, other experiments involving measurements of life-history traits have been conducted on 7 genotypes exposed to Cu. Results showed that some genotypes were up to eightfold more sensitive to Cu than others (at concentrations ranging between 0.15 and 0.5 mg/L). These differences in sensitivity were partly explained by the traits measured, but physiological or transcriptomic endpoints may explain more precisely the source of these differences in sensitivity. Finally, 3 experiments with fluctuations in nutrient concentrations, light intensity and Cu pre-exposure have demonstrated that phenotypic plasticity plays an important role in L. minor sensitivity to Cu. Indeed, the weakening of individuals, as a result of unfavorable environmental conditions, can lead to a two-fold increase in sensitivity to Cu.[...]

Orientador: Márcio Silva Araújo / Resumo: A variação individual no uso de recursos alimentares pode depender de fatores ecológicos como a competição intra e interespecífica, predação, além da diversidade e abundância de recursos. O objetivo deste trabalho foi identificar as causas da variação individual no uso de recursos alimentares em populações do peixe Characidium schubarti, conh’ecido como “charutinho” e descrito como insetívoro bentônico. O estudo foi realizado em riachos de Mata Atlântica no Parque Estadual Carlos Botelho, núcleo São Miguel Arcanjo, região sudeste do Estado de São Paulo. Os charutinhos foram coletados ao longo de transectos em 11 riachos diferentes. Foram coletadas amostras da comunidade de invertebrados bentônicos em cada riacho para a obtenção de estimativas da diversidade e abundância de recursos alimentares. Identificamos e quantificamos todas as possíveis espécies de peixes competidoras (insetívoros bentônicos). Nossos resultados sugerem significativa variação na dieta dos indivíduos de todas as populações, porém com baixo grau de especialização individual. Nós não encontramos efeito significativo da oportunidade ecológica (diversidade de recursos), produtividade secundária (biomassa de recursos) e competição (densidade de charutinhos e competidores) sobre o grau de variação na dieta nas populações estudadas. / Abstract: Individual variation in food resource use can depend on ecological factors such as intra and interspecific competition, predation, and the diversity and abundance of resources. Our main goal in this study was to identify the ecological causes of individual variation in the use of food resources in natural populations of the fish Characidium schubarti, part of a group popularly known as “South American darters”, described as benthic insectivores. The study was conducted in Atlantic Forest streams at the Carlos Botelho State Park, at São Miguel Arcanjo, in the southeast of the state of São Paulo. Specimens were collected along transects in 11 streams. We collected samples from the benthic invertebrate community in each stream to estimate the diversity and abundance of food resources. We identified and quantified all possible competing species of fishes (benthic insectivores). Our results suggest significant variation in the diet of individuals from all populations, however, with a low degree of individual specialization. We found no significant effect of ecological opportunity (resource diversity), secondary productivity (resource biomass) and competition (density of charutinhos and competitors) on the degree of dietary variation in the studied populations. / Mestre

No description available.

Invasive plants can displace native species, deteriorate native forest, and change plant communities and ecosystem functions. Native plant populations are fundamentally impacted by invasive species because of the interactions between invasive species and native plants. This study focuses on understanding the extent, mechanisms and consequences of interaction between a non-indigenous invader Ailanthus altissima and its functionally similar native species Robinia pseudoacacia in the Mid-Appalachian region, from an individual scale to a regional scale. These two subject species are common and coexist in early-successional eastern deciduous forest. The interactions between these two common species are important to community structure and canopy tree regeneration. To address the type and extent of interactions of these two species, a greenhouse experiment utilizing various species proportions, nutrient levels and seed sources was performed. In addition, a common-garden experiment with various species densities and proportions over three consecutive growing seasons was performed in a more natural condition than that of the greenhouse experiment. We found at the seedling stage, the dominant interaction was competition, and R. pseudoacacia was the winner both above- and belowground. The allelopathic compounds of A. altissima may have inhibited nodulation of R. pseudoacacia. Ailanthus altissima seedlings from its native region had slightly stronger competitive abilities compared with the seedlings from its invaded range. In the common garden experiment, R. pseudoacacia plants grew quicker than A. altissima, but A. altissima inhibited the growth of R. pseudoacacia by interspecific competition. The negative impact of A. altissima on R. pseudoacacia became larger as time progressed. To assess the community-level consequences of the two species, we conducted a forest mapping and a complete target-tree-based forest survey, and analyzed regional-scale data from the Forest Inventory Analysis Data Base. The two target species were significantly associated with themselves and with each other. Community species composition and diversity were significantly different across sites. A negative impact of both species on the understory community diversity and tree regeneration at the neighborhood scale was detected; while at a regional level, tree diversity in the FIA plots with either A. altissima or R. pseudoacacia was higher than the reference plots. / Ph. D.

Parasiten können den Energietransfer in Lebensgemeinschaften über trophische Kaskaden beeinflussen, indem sie Änderungen in den Konsumenten-Ressourcen-Interaktionen induzieren. In der vorliegenden Arbeit wurde die Rolle von Trematoden auf das Freßverhalten ihrer Wirte auf zwei trophischen Ebenen untersucht. Vier verschiedene Süßwasserschnecken-Trematoden-Systeme wurden verwendet, um zu testen, ob ein allgemeines Muster für die Auswirkung von Infektionen auf die Grazingaktivität von Schnecken auf das Periphyton nachgewiesen werden kann. Die Grazingraten auf Periphyton bei infizierten Schnecken entweder höher, niedriger oder ähnlich denen derjenigen von nicht infizierten Artgenossen. Augenparasiten können die Leistungsfähigkeit ihres Wirtes beeinträchtigen, was die Auswirkungen auf das Erkennen von Beutetieren, Raubtieren und Artgenossen hat. Mit Tylodelphys clavata experimentell infizierte Flussbarsche wurden mit zwei verschiedenen Beutetierarten eingesetzt, um das Fraßverhalten in Konkurrenz mit nicht infizierten Artgenossen zu untersuchen. Die Entfernung, aus der infizierte Fische die beiden Beutetierarten attackierten, war im Vergleich zu nicht infizierten Artgenossen signifikant kürzer. Die Tendenz war, dass nicht infizierte Fische mehr von den verfügbaren Beutetieren verzehrten. Um zu prüfen, ob der Fisch als Kompensation seine Beutepräferenz verändert, wurde die Beutezusammensetzung von Flussbarschen aus dem Müggelsees mittels Mageninhalts- und Stabilisotopenanalysen untersucht. Beide Methoden ergaben, dass sich die Fische mit zunehmender Intensität der Infektion selektiver ernährten, während sich geringer infizierte Fische Generalisten herausstellten. Die Ergebnisse dieser Studie bestätigen, dass Trematoden eine wichtige Rolle in Nahrungsnetzen spielen können, indem sie das Freßverhalten ihres Wirtes verändern. Darüber hinaus können Trematoden so die Stärke der Interaktion ihrer Wirte mit anderen Arten auf verschiedenen trophischen Ebenen beeinflussen. / Parasites can influence energy transfer through communities via trophic cascades by inducing alterations on consumer-resource interactions. This study evaluated the role of trematodes on their host’s feeding behaviour at two trophic levels. Four different freshwater snail–trematode systems were used to test whether a general pattern can be detected for the impact of infections on snail periphyton grazing activity. Mass-specific periphyton grazing rates of infected snails were higher, lower, or similar to rates of non-infected conspecifics. The variation across systems may result from differences on how the parasites use the resources of the snail and thus affect its energy budget. Eye parasites can impair their host’s sensory performance with important consequences for the detection of prey, predators and conspecifics. European perch experimentally infected with Tylodelphys clavata were used to evaluate their feeding behaviour under competition with non-infected conspecifics, for two different prey species (Asellus aquaticus and Daphnia magna). The distance at which infected fish attacked both prey species was significantly shorter in comparison to non-infected conspecifics. Additionally, infected fish had more unsuccessful attacks and there was a general tendency that non-infected fish consumed more of the available prey. To evaluate whether fish alter their prey preference as a compensatory mechanism, perch from Lake Müggelsee were sampled and their diet was evaluated using both stomach content and stable isotope analyses. Both methods indicated that with increasing infection intensity fish had a more selective diet, while less intensively infected fish appeared to be generalist feeders. The results from this study confirm that trematodes can play a relevant role within food webs by altering their hosts’ feeding behaviour. Furthermore, in this way trematodes can affect the interaction strengths of their hosts with other species at various trophic levels.

Plant-soil feedback is an important mechanism in plant communities affecting their species composition. Understanding plant-soil feedback is crucial for describing the interactions between plant communities and their soil communities. The effects of plant-soil feedback can be positive, negative or neutral and because of these changes plants are either coexisting or competing. Plant-soil feedback is often studied within plant succession, plant invasion and plant dominance in a plant community. In these cases, the nature and strength of influence of each species is studied. Despite the large number of previous studies on plant-soil feedback, very little is known about the temporal and spatial changes of the intensity of plant-soil feedback and the intraspecific variability in plant-soil feedback. The aim of my work was to observe the temporal changes in the plant-soil feedback of a species growing in soil which was conditioned by the same or other plant species. Another goal was to explore spatial changes in plant-soil feedback. The last objective was to test differences in the intensity of plant-soil feedback among different genotypes of one species. The results of my work demonstrated that the intensity of intraspecific plant-soil feedback of Rorippa austriaca is negative and increases with...

The observational study on natural regeneration of Norway spruce (Picea abies) was provided during seasons 2010 and 2011 in the windthrow area of High Tatra National Park. The main aim of this master thesis was to describe the distribution pattern in Norway spruce regeneration as well as to estimate the spatial scale, which most preciselly describes the differences in its phenotypic variability. Following step was to determine the relative influence of abiotic and stand factors on the growth characteristics and abundance of spruce seedlings. The Main focus lied on stressing the role of biotic interactions, like intraspecific and interspecific competition, leading to certain discrepancies in the phenotype, as well as in abundance of spruce seedlings.The reponse in variability in spruce traits was recognized at each spatial level. The results showed clear causality between soil moisture and vegetation composition, which both directly modified not only the phenotype of spruce seedlings and plants, but have even influenced their counts on particular stands.