Global ETD Search

1	Variation Among Fish Species in the Stoichiometry of Nutrient Excretion Torres, Lisette E. 05 August 2005 (has links) No description available. ecological stoichiometry nutrient cycling species identity ecosystem functioning reservoir fish biodiversity
2	Biotic resistance in freshwater fish communities Henriksson, Anna January 2015 (has links) Invasions of non-native species cause problems in ecosystems worldwide, and despite the extensive effort that has been put into research about invasions, we still lack a good understanding for why some, but not other, communities resist these invasions. In this doctoral thesis I test hypotheses on biotic resistance using a large dataset of more than 1000 both failed and successful introductions of freshwater fish into Swedish lakes. We have found that the classic species richness hypothesis is a poor descriptor of introduction success because it fails to acknowledge that resident species contribute to the resistance in different ways. We developed a new measure of biotic resistance, the weighted species richness, which takes into account that the resident species contributes to the resistance with different strength and sign. Further, we correlated performance traits of species in their role as an invader and as a resident species to predict how the biotic resistance of these communities would develop over time. We found a positive correlation between performance traits: Some species have high introduction success, they make a large contribution to the resistance, and they cause extinctions when introduced but do not go extinct themselves when other species establishes, whereas other species are weak performers in these respects. Thus, the biotic resistance of these communities should grow stronger as non-native species accumulates. These results give us clues about what type of communities that should be most sensitive to further invasions, i.e., communities harboring species weak performers. My results show that the biotic resistance of communities is an important factor in determining invasibility of a community. They also show that methods for quantifying resistance must take into account how interactions are structured in nature. What determine the biotic resistance of a community is the type of interactions that the resident species have with the invader and not the species richness of the community. biotic resistance freshwater fish introductions invasions invasion success invasibility invasiveness species richness saturation species identity weighted species richness
3	Species identity and the functioning of ecosystems: the role of detritivore traits and trophic interactions in connecting of multiple ecosystem responses Hines, Jes, Eisenhauer, Nico 05 April 2023 (has links) Ecosystems world-wide experience changes in species composition in response to natural and anthropogenic changes in environmental conditions. Research to date has greatly improved our understanding of how species affect focal ecosystem functions. However, because measurements of multiple ecosystem functions have not been consistently justified for any given trophic group, it is unclear whether interpretations of research syntheses adequately reflect the contributions of consumers to ecosystems. Using model communities assembled in experimental microcosms, we examined the relationship between four numerically dominant detritivore species and six ecosystem functions that underpin fundamental aspects of carbon and nitrogen cycling aboveand below-ground. We tested whether ecosystem responses to changes in detritivore identity depended upon species trait dissimilarity, food web compartment (aboveground, belowground, mixed) or number of responses considered (one to six). We found little influence of detritivore species identity on brown (i.e. soil-based) processes. Only one of four detritivore species uniquely influenced decomposition, and detritivore species did not vary in their influence on soil nitrogen pools (NO3 − and NH4 +), or root biomass. However, changes in detritivore identity influenced multiple aboveground ecosystem functions. That is, by serving as prey, ecosystem engineers and occasionally also as herbivores as well as detritivores, these species altered the strength of aboveground predator–herbivore interactions and plant–shoot biomass. Yet, dissimilarity of detritivore functional traits was not associated with dissimilarity of ecosystem functioning. These results serve as an important reminder that consumers influence ecosystem processes via multiple energy channels and that food web interactions set important context for consumer-mediated effects on multiple ecosystem functions. Given that species are being lost, gained and redistributed at unprecedented rates, we can anticipate that changes in species identity will have additional ecosystem consequences beyond those predicted by species’ primary functional role. info:eu-repo/classification/ddc/570 ddc:570
4	Revégétalisation de sols mis à nu : un outil pour limiter les espèces indésirables Trejo Pérez, Rolando 04 1900 (has links) Les couvertures végétales herbacées peuvent être utilisées non seulement pour revégétaliser les sols mis à nu, mais aussi pour contrer l’établissement d’arbres dans des écosystèmes naturels et semi-naturels. Cependant, la sélection des espèces permettant de composer des mélanges efficaces soulève des difficultés importantes encore aujourd’hui. De plus, garantir que les mélanges herbacés les plus efficaces dans une expérience de diversité peuvent être transposés dans des conditions réelles est un autre défi soulevant de l’incertitude lors de la mise en œuvre d’un plan de revégétalisation. La prise en compte des mécanismes spatiaux, abiotiques et biotiques est également cruciale pour comprendre comment les couvertures herbacées et les espèces ligneuses interagissent. Dans ce contexte, l'objectif principal de cette thèse fut d'améliorer le choix des espèces herbacées et d'approfondir notre compréhension des mécanismes biotiques, abiotiques et spatiaux impliqués dans l'inhibition des espèces ligneuses. Le premier objectif de cette thèse fut d'examiner la contribution de la composition et de la diversité (taxonomique et fonctionnelle) des espèces herbacées à l'établissement de deux espèces ligneuses indigènes, Acer rubrum et Betula populifolia, sur une période de trois ans. Le deuxième objectif fut d'évaluer l'efficacité de mélanges herbacés contenant Achillea millefolium et Solidago canadensis dans des conditions réelles de terrain pour contrer l'établissement d'espèces ligneuses (Acer negundo, Robinia pseudoacacia et Rhamnus cathartica), tout en tenant compte de facteurs locaux tels que les propriétés du sol, l'espace et la diversité alpha (taxonomique, fonctionnelle et phylogénétique) de la communauté herbacée résidente. Le troisième objectif fut d'élucider la relation entre les mycorhizes à arbuscules (MA) et le fitness des semis d'Acer rubrum. Ce dernier objectif comprenait également l'évaluation de l'influence sur le fitness des semis d'Acer rubrum de plusieurs facteurs, tels que les mélanges d’herbacées initiaux, l'abondance de la couverture, les propriétés du sol, ainsi que la densité et la richesse des couvertures végétales au sol et en surface. Pour atteindre ces objectifs, nous avons réalisé trois expériences : une expérience de diversité en conditions contrôlées dans une friche régulièrement fauché, une expérience de diversité en conditions de terrain et une expérience de rétroaction plante-sol en serre. Nos résultats ont mis en évidence que, dans des conditions contrôlées, les mélanges diversifiés et certaines espèces telles que Achillea millefolium et Solidago canadensis sont les moteurs d'une plus grande efficacité dans la prévention de l'établissement des arbres (c'est-à-dire Acer rubrum et Betula populifolia). Cependant, dans des conditions réelles de terrain et sur différentes espèces ligneuses colonisatrices (Acer negundo, Robinia pseudoacacia et Rhamnus cathartica), une revégétalisation réussie nécessite de prendre en compte à la fois l'efficacité des mélanges dans des conditions idéales et leur polyvalence écologique. Nos principales conclusions ont également mis en évidence que l'abondance relative des champignons mycorhiziens influençant la performance des semis d’Acer ne peut pas être prédite ni par les propriétés du sol ni par la structure de la communauté herbacée sur le terrain. En plus, certains mycorhizes à arbuscules (Dominikia sp. et Ambispora sp.) peuvent être liées à des effets négatifs sur les espèces ligneuses (Acer rubrum). En résumé, les trois projets de recherche présentés dans cette thèse ont permis d'identifier des mécanismes écologiques pertinents affectant les espèces ligneuses tels que l'identité des espèces herbacées considérées dans les mélanges, le rôle de la versatilité écologique des espèces herbacées, l'influence de mécanismes multiples, ainsi que le rôle des champignons mycorhiziens. Les résultats de cette thèse sont sujet, évidemment, à certaines limitations expérimentales et méthodologiques à prendre en compte dans l’éventualité d’une utilisation en conditions réelles ou lors de travaux de recherche futures. Les recherches futures pourraient par exemple explorer ces limites et identifier des mécanismes supplémentaires pour améliorer l'efficacité des efforts de revégétalisation dans des contextes de revégétalisation écologique. / Herbaceous plant covers can be used not only to revegetate bare soil but also to inhibit tree encroachment in many managed and semi-natural grasslands. However, selecting the right species to build effective mixtures has posed challenges until now. Defining if the most effective herbaceous mixtures in diversity experiments can be applied in real field conditions and over different woody species is even another challenge posing incertitude in a revegetation plan. Addressing spatial, abiotic, and biotic mechanisms is also crucial to understanding how herbaceous covers and woody species interact. Taking this into account, the main objective of this thesis was to improve the choice of herbaceous species and to deepen our understanding of the biotic, abiotic and spatial mechanisms involved in the inhibition of woody species. The first objective of this thesis was to examine the contribution of herbaceous species composition and diversity (taxonomic and functional) against the establishment of two native woody species, Acer rubrum and Betula populifolia, over 3 years. The second objective was to evaluate the efficacy of herbaceous mixtures containing Achillea millefolium and Solidago canadensis under real field conditions to suppress woody establishment (Acer negundo, Robinia pseudoacacia and Rhamnus cathartica), while considering local factors such as soil properties, space and alpha diversity (taxonomic, functional and phylogenetic) of the resident herbaceous community. The third objective was to unravel the relationship between arbuscular mycorrhiza fungi (AMF) and Acer rubrum seedling fitness. This objective also included the evaluation of the influence of several factors on Acer rubrum seedling fitness, such as initial treatments, cover abundances, soil properties, as well as the density and richness of ground and surface vegetation covers. To tackle these objectives, we carried out three experiments: a diversity experiment under controlled conditions in a regularly mown old field, a diversity experiment under field conditions, and a greenhouse plant-soil feedback experiment. Our results highlighted that, in controlled conditions, diversified mixtures and certain species such as Achillea millefolium and Solidago canadensis as drivers of higher efficiency in preventing tree establishment (i.e. Acer rubrum and Betula populifolia). Yet, in real field conditions and over different woody species colonizers (i.e., Acer negundo, Robinia pseudoacacia and Rhamnus cathartica), successful revegetation requires considering both mixture effectiveness in ideal conditions and their ecological versatility. Our key findings also highlighted that the relative abundance of mycorrhizal fungi influencing the performance of Acer seedlings cannot be predicted by either soil properties or the structure of the herbaceous community in the field. Additionally, certain arbuscular mycorrhiza (i.e., Dominikia sp. and Ambispora sp.) can be linked to negative effects on woody species (i.e., Acer rubrum). In summary, the three research projects presented in this thesis allowed the identification of relevant ecological mechanisms affecting woody species such as the identity of the herbaceous species considered in the mixtures, the role of the ecological versatility of herbaceous species, the influence of multiple mechanisms, as well as the role of mycorrhizal fungi. The results of this thesis have experimental and methodological limitations that must be considered when used in real-life conditions or future research. Further research could explore these limitations and identify additional mechanisms to improve the effectiveness of revegetation efforts in ecological contexts. Revégétalisation Mélange de graines d’herbacées Couverture végétale sol mis à nu Arbres indésirables Identité de l'espèce Versatilité écologique Traits fonctionnels des plantes Champignon mycorhizien à arbuscules Revegetation Herbaceous seed mixture Herbaceous cover Bare soil Unwanted trees Species identity Ecological versatility Plant traits Arbuscular mycorrhizal fungi Ecology / Écologie (UMI : 0329)
5	Birds, bats and arthropods in tropical agroforestry landscapes: Functional diversity, multitrophic interactions and crop yield Maas, Bea 20 November 2013 (has links) No description available. 630 birds bats arthropods multitrophic interactions agroforestry tropical landscape forest margin landscape functional diversity crop yield exclosure experiments experimental exclusion arthropod suppression avian predation ecosystem services mist netting point counts artificial plasticine caterpillar dummy experiment biological control monitoring mapping Lemon-bellied White-eye Grosbeak Starling Zosterops chloris Scissiostrum dubium Theobroma cacao cacao agroforestry cacao diseases cacao harvest cacao pests flying vertebrates aerial insectivores volant vertebrates logging breeding colony flower herbivory mesopredator release predatory insects ants spiders aphids Lepidoptera Coleoptera Lepidopteran larvae sustainable agriculture sustainable agroforestry management implications management recommendations applied managament extensive land use management landscape management conservation biodiversity-friendly dbh distance to forest forest proximity habitat conversion herbivory Indonesia insectivorous bats insectivorous birds invertebrates Central Sulawesi Napu valley leaf gleaning leaf herbivory pests insects phytophagous insects plant productivity remnant forest trees shade tree managament South-east Asia Paleotropics tropical landscape tree height landscape gradient local shade management Cacao Pod Borer Cherelle Wilt fruit abortion Helopeltis sulawesi deforestation habitat fragmentation land use intensification forest margin species critical decline predation experiment species-specific functions Southeast Asia biodiversity conservation mesopredators food security human welfare human well-being poverty alleviation poverty reduction smallholder cacao smallholder plantation cacao farmers sustainable cacao management landscape perspective landscape scale large scale field experiment long term field experiment human wellbeing economic importance economic value valuation ecosystem services landscape matrix yield quality yield quantity fruit productivity species identity species diversity species richness ecosystem functioning pesticide use chemical compounds complex food web tritrophic interactions wildlife-friendly rural livelihoods endangered bird species endangered bat species endemic endemic birds endemic bats beneficial impact IUCN Lore Lindu National Park bioindicator indicator species forest margin agricultural habitat agroforestry systems population density predation activity species activity cacao flower cacao pod Orthoptera linear mixed effect models Tukey Post Hoc Test AICc model selection generalized least squares restricted maximum likelihood model simplification species richness estimator species accumulation linear mixed-effects models Likelihood Ratio Test Maximum Likelihood nocturnal insects diurnal arthropods nocturnal arthropods diurnal insects landscape context Land- und Forstwirtschaft (PPN621302791)

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