The objective of this thesis was to investigate the effects of mammalian grazers, such as microtine rodents and reindeer, (top-down effects) and nutrient availability (bottom- up effects) on the plant community of a tundra heath. I conducted a large-scale fertilization experiment and studied the impact of grazers using exclosures. I measured the effects of fertilization and grazing on soil microbial activity and nutrient cycling. I investigated the responses to fertilization of the invertebrate community, I studied the effects on the quality of bilberry as food for mammalian herbivores, and I looked at how concentrations of nutrients and carbon-based secondary defences against herbivory fluctuated between seasons in unfertilized and fertilized treatments. The results of my thesis show that the plant community investigated is exposed to a strong top-down control by mammalian herbivores. On the fertilized and grazed areas the aboveground biomass of the vascular plant community did not increase compared to unfertilized areas. However, the productivity of the plant community was clearly nutrient- limited. During the eight years of the experiment, on the fertilized areas plant biomass was significantly increased inside the herbivore exclosures In my study mammalian herbivores at comparatively low densities and grazing outside the growing season were sufficient to control the biomass of a heterogeneous plant community. Microtine rodents (Norwegian lemmings and grey-sided voles) preferred the fertilized areas for overwintering. The food plant quality of bilberry for grey-sided voles was improved on the fertilized areas throughout the year. Grazing decreased the nitrogen storage in the aboveground plant biomass. Reindeer and rodents had also important indirect effects on the plant community by decelerating soil nutrient cycling and soil microbial activity. This effect may be accelerated by the impact of herbivore on plant species composition. Graminoids, which contained the highest nitrogen concentrations in their tissues, increased rapidly on the fertilized areas, but their abundance was significantly lower on grazed fertilized areas. The invertebrate community was detritus-based and received their energy indirectly from the litter via soil microbes and detritivores. Fertilization increased the biomass of invertebrate carnivores, but had no effect on the biomass of invertebrate herbivores. Apparent competition between detritivores and invertebrate herbivores, mediated by carnivorous invertebrates predating on both of them, is supposed to keep the densities and grazing pressure of invertebrate herbivores low. Grazing damage by invertebrates was very low and only 0.021 % of the total vascular plant biomass was removed. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 2001, härtill 6 uppsstser.</p> / digitalisering@umu

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2002. / Härtill 6 uppsatser.

Thesis (M.S.)--Miami University, Dept. of Zoology, 2007. / Title from first page of PDF document. Includes bibliographical references (p. 20-26).

Dans le contexte des grands bouleversements socio-économiques, technologiques et environnementaux des révolutions agricoles, les zones de montagnes sont souvent considérées comme favorables à la biodiversité et à des pratiques agricoles respectueuses de l'environnement. Pourtant, ces territoires subissent une pression anthropique réelle via l'agriculture ou la sylviculture menant à une des questions fondamentales du siècle à venir sur l'altération des ressources naturelles pas les activités anthropiques. Ces nouveaux systèmes agricoles ont entraîné l'émergence ou l'augmentation d'abondance d'espèces devenues des pestes agricoles. En raison des pertes de productions alimentaires, de la lutte chimique et des dégâts sur la faune non-cible, des réservoirs de zoonoses qu’ils représentent ou comme maillon essentiel des réseaux trophiques, les micro-mammifères et leurs pullulations représentent un domaine d’étude de première importance en écologie. Les politiques agricoles qui ont mené à une spécialisation des pratiques agricoles vers la production herbagère ont contribué à favoriser l’apparition des pullulations de campagnols prairiaux (campagnol terrestre et campagnol des champs) via l’augmentation de la production végétale et une homogénéisation du paysage agricole dans le Massif Jurassien et le Massif Central. Tandis que certains prédateurs comme les petits mustélidés se spécialisent dans la consommation de ces micro-mammifères. D’autres prédateurs, considérés comme généralistes, présentent une réponse fonctionnelle alimentaire en adaptant leur alimentation à la disponibilité de la ressource. Cette réponse fonctionnelle peut être à l’origine d’un report de prédation sur des proies alternatives aux micro-mammifères. Parmi toutes ces espèces, la petite faune chassable et patrimoniale représente à l’heure actuelle des enjeux de gestion et de conservation marqués.Cette thèse a pour but de comparer deux zones géographiques (vallée alpine de la Haute-Romanche et Massif Jurassien) présentant un degré a priori différent de connaissances sur les systèmes de pullulations de campagnols prairiaux. Nous avons, au travers de ce travail, comparé le phénomène de pullulation observé en Haute-Romanche avec les connaissances actuelles du Massif Jurassien. Nous avons également, par l’analyse de données de monitoring à long terme et la mise en place d’expérimentations de terrain, essayé d’apporter des informations quant aux relations entre proies et prédateurs dans un système de pullulation de campagnol prairiaux en milieu tempéré. L’objectif est de tenter une comparaison tant que faire se peut entre les deux zones géographiques pour améliorer la gestion de ces écosystèmes.Notre premier travail fut d’analyser les données récoltées entre 1998 et 2010 pour caractériser le fonctionnement spatio-temporel du campagnol terrestre en Haute-Romanche. Nous avons également confronté ces données à l’histoire agricole de la vallée entre 1810 et 2003 à l’échelle parcellaire. Dans un premier temps, nous avons constaté que le scénario historique agricole était similaire entre cette vallée de la Haute-Romanche et d’autres zones montagnardes européennes, avec une spécialisation sur la production herbagère et comme effet direct la disparition virtuelle des zones labourées, le cantonnement des zones de fauches dans les fonds de vallée et l’extension des zones de pâtures au reste des zones exploitées pour l’agriculture. En se basant sur ces données, nous avons pu mettre en évidence un lien corrélatif à l’échelle parcellaire entre l’occupation du sol actuelle et l’intensité de la pullulation du campagnol terrestre. Les zones pâturées ont présenté une amplitude de l’abondance en campagnol terrestre moins importante que les zones fauchées. L’occupation agricole actuelle étant directement dépendant de l’histoire agricole de la vallée, il apparaît vraisemblable que la spécialisation agricole vers la production herbagère dans cette vallée est, comme dans le Jura, à l’origine / In the context of the great socio-economic, technological and environmental upheavals of agricultural revolutions, mountain areas are often considered as favorable to biodiversity and environmentally friendly agricultural practices. However, these territories are under real anthropic pressure via agriculture or forestry leading to one of the fundamental questions of the coming century on the alteration of natural resources, not human activities. These new farming systems have led to the emergence or increase in abundance of species that have become agricultural pests. Due to loss of food production, chemical control and damage to non-target fauna, reservoirs of zoonoses they represent or as an essential link in food webs, micro-mammals and their outbreaks represent an area of study of primary importance in ecology. Agricultural policies that have led to a specialization of agricultural practices towards grassland production have contributed to the emergence of outbreaks of prairie voles (ground vole and field vole) through increased crop production and homogenization of the agricultural landscape. in the Jurassic Massif and the Massif Central. While some predators like small mustelids specialize in the consumption of these micro-mammals. Other predators, considered as generalists, present a functional food response by adapting their diet to the availability of the resource. This functional response may be at the origin of a postponement of predation on prey alternatives to micro-mammals. Of all these species, hunting and heritage small-scale wildlife presently represent marked management and conservation issues. The purpose of this thesis is to compare two geographical zones (Upper Romans valley and Upper Jurassic mountains) with a priori different degree of knowledge about prairie volcano outbreak systems. Through this work, we compared the phenomenon of outbreaks observed in Haute-Romanche with current knowledge of the Jurassian Massif. We also, through the analysis of long-term monitoring data and the implementation of field experiments, tried to provide information on the relations between prey and predators in a meadow vole breeding system in a temperate environment. . The objective is to try to make a comparison as much as possible between the two geographical areas to improve the management of these ecosystems. Our first work was to analyze the data collected between 1998 and 2010 to characterize the spatio-temporal functioning of the ground vole in Haute-Romanche. We also compared these data to the agricultural history of the valley between 1810 and 2003 at the plot scale. Firstly, we found that the agricultural historical scenario was similar between this valley of Haute-Romanche and other European mountain areas, with a specialization on grassland production and as a direct effect the virtual disappearance of plowed areas, the cantonment of mowing areas in the valley bottoms and extension of grazing areas to the rest of the areas used for agriculture. Based on these data, we were able to highlight a correlative link at the plot scale between the current land use and the intensity of the vole's overgrowth. Grazing areas had a lower vole abundance than mowed areas. The current agricultural occupation being directly dependent on the agricultural history of the valley, it seems likely that the agricultural specialization towards grassland production in this valley is, as in the Jura, the origin

No description available.

The object of this thesis was to study plant community structure, especially in relation to vertebrate herbivory, in an altitudinal gradient in the Fennoscandian mountain chain. A sowing experiment in a high alpine Ranunculus glacialis population showed that seeds germinated better in cleared microsites than under established individuals. This is contrasted with a hypothesis that predicts positive plant-plant interactions in high alpine environments. It was concluded that plant-plant interactions in die studied population varied from neutral to negative, whereas no indications for positive interactions were found. An exclosure experiment in a snow-bed showed that a lemming population consumed 33 % of the available graminoids and 66 % of the mosses from August to June during a population peak. The results shows that grazing needs to be considered as a structuring factor in snow-bed vegetation. The vegetation in exclosures in another snow-bed changed from a graminoid-dominated to a herb-dominated plant community during a long-term (six years) experiment No changes of the same magnitude were seen in a tall herb meadow on a lower altitude. Survival of transplanted adult shoots from the tall herb meadow was equally high in the snow-bed as on the meadow, and germination was also high on bare ground in the snow-bed. Grazing seemed to be a more important structuring factor in the snow-bed than in the more productive tall herb meadow. Raising the grazing pressure during one growing season by introducing microtine rodents into enclosures did not cause any large short-term effects on plant community structure in a tall hob meadow or in a snow-bed. Marked shoots showed that some preferred plant species had a high shoot mortality, but biomass for pooled categories of plants was not significantly affected. It was predicted that the tall herb meadow would be more grazing sensitive than die snow-bed, but productivity on the meadow seemed to be sufficiently high for the plants to compensate for the grazing during the growing season. A greenhouse experiment showed that voles, when grazing freely, have the potential to deplete productive field layer vegetation contrary to predictions from plant defence theories. A nitrogen-based defence did not prevent heavy shoot mortality for toxic tall herbs. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1993, härtill 5 uppsatser.</p> / digitalisering@umu.se

Toxoplasma gondii ist ein weltweit verbreiteter Parasit. In Europa ernährt sich der Endwirt (Katzen) hauptsächlich von kleinen Säugetieren wie Myodes glareolus und Microtus spp. (Wühlmäusen) und Apodemus spp., seltener von Mus spp. Erstere zeigen gegenüber Mus spp. erhöhte Prävalenzen von T. gondii und überleben diese eher als Mus spp. Daher wird vermutet, dass Wühlmäusen und Apodemus spp. eine größere Rolle als Zwischenwirte besitzen, als Mus spp. Der Schutz wird auf das IFN-γ-induzierte IRGb2-b1 zurückgeführt, die den zentralen parasitären Virulenzfaktor ROP5 inhibiert. Daher liegt der Fokus meiner Arbeit auf der protektiven Rolle von IRGb2-b1 bei der Infektion mit T. gondii in Wühlmäusen und Apodemus spp. Mit dieser Arbeit trage ich nützliche Werkzeuge zur Erforschung von Wühlmäusen bei, wie ein rekombinantes M. glareolus IFN-γ Zytokin und neuartige Zellsysteme. Alle untersuchten Wühlmaus-Systeme besaßen einen Phänotyp bei Infektion mit in vivo Resistenz beschrieben wurde: einem IFN-γ-vermittelten Reduktion der Parasitenbürde (mit Wirtszelltod für Typ I Parasiten, ohne für Typ II). Darüber hinaus bestätigen vorläufige Resultate aus Wühlmäusen und Apodemus spp. in Deutschland hohe genetische Vielfalt der IRGb2 Untereinheit zeigen, insbesondere an der vermuteten Grenzfläche zum ROP5, was auf eine Rolle dieses Proteins bei der Infektion hindeutet. Um die Funktion der IRGb2-b1 Proteine zu untersuchen, habe ich ein Zellkultur System, entwickelt, welches erlaubt wild-derived Gene stabil zu exprimieren. Dieses Setup gestattet es, die Auswirkungen von Polymorphismen in Irg Genen bei der Infektion mit T. gondii zu evaluieren. Insgesamt habe ich Werkzeuge erarbeitet, um den Ansatz der Öko-Immunologie in eine Labor-Umwelt zu bringen, wodurch die molekulare Untersuchung ökologisch relevanter Arten möglich wird. Durch Anwendung dieser Werkzeuge stütze ich die Hypothese, dass nicht-Mus Nagetiere, insbesondere M. glareolus, ein bedeutendes Reservoir für T. gondii darstellen. / Toxoplasma gondii is an ubiquitous parasite grouped in three main clonal lineages, type I-III. In Europe, felids, definitive hosts for the parasite, mostly prey on small mammals of Myodes glareolus and Microtus spp. (voles), and Apodemus spp., rather than Mus spp. Voles and Apodemus spp. also display higher T. gondii prevalence and survive infection to a larger extent than Mus spp., although tolerant Mus subspecies exist. This suggests that voles and Apodemus spp. are more relevant intermediate hosts than Mus spp.. Resistance to infection relies on the IFN-γ-induced IRGb2-b1, which inhibits the major parasite virulence factor ROP5. Thus, this work focuses on the protective role of IRGb2-b1 during T. gondii infection in voles and Apodemus spp. With this project I contribute with valuable tools for research on voles, such as the supply of the recombinant M. glareolus IFN-γ cytokine and novel cell systems. All vole systems show a phenotype to type I infection which is associated with in vivo resistance in Mus spp: IFN-γ-mediated host cell death and a decrease in parasite burden. The latter without cell death was observed for type II parasites, suggesting novel protective mechanisms. Further, preliminary results from voles and Apodemus spp. in Germany confirm the expected high diversity in the IRGb2-like subunit, especially at the putative interface with ROP5, which suggests a role of the protein during infection. To assess the role of IRGb2-b1-like in this phenotype, I developed a system which allows establishment of cell lines stably expressing wild-derived Irg-like genes. This setup allows evaluation of the effect of polymorphisms of Irg-like genes during infection. Taken together, I have provided tools to bring eco-immunology into a lab setting to perform molecular investigations of ecologically relevant species. Using these tools, I offer support for the hypothesis that non-Mus rodents, especially M. glareolus, constitutes a relevant T. gondii reservoir in Germany.

No description available.

State-space modelling is a powerful tool to study ecological systems. The direct inclusion of uncertainty, unification of models and data, and ability to model unobserved, hidden states increases our knowledge about the environment and provides new ecological insights. I extend the state-space framework to create multi-species models, showing that the ability to model ecosystem interactions is limited only by data availability. State-space models are fit using both Bayesian and Frequentist methods, making them independent of a statistical school of thought. Bayesian approaches can have the advantage in their ability to account for missing data and fit hierarchical structures and models with many parameters to limited data; often the case in ecological studies. I have taken a Bayesian model fitting approach in this thesis. The predator-prey interactions between the hen harrier (Circus cyaneus) and red grouse (Lagopus lagopus scoticus) are used to demonstrate state-space modelling’s capabilities. The harrier data are believed to be known without error, while missing data make the cyclic dynamics of the grouse harder to model. The grouse-harrier interactions are modelled in a multi-species state-space model, rather than including one species as a covariate in the other’s model. Finally, models are included for the harriers’ alternate prey. The single- and multi-species state-space models for the predator-prey interactions provide insight into the species’ management. The models investigate aspects of the species’ behaviour, from the mechanisms behind grouse cycles to what motivates harrier immigration. The inferences drawn from these models are applicable to management, suggesting actions to halt grouse cycles or mitigate the grouse-harrier conflict. Overall, the multi-species models suggest that two popular ideas for grouse-harrier management, diversionary feeding and habitat manipulation to reduce alternate prey densities, will not have the desired effect, and in the case of reducing prey densities, may even increase the harriers’ impact on grouse chicks.

No description available.