Les changements climatiques altèrent la phénologie des organismes, c’est-à-dire la succession dans le temps des éléments de leur cycle de vie. L’expression de la diapause chez les insectes, soit l’arrêt de développement permettant de survivre aux dégradations saisonnières de l’environnement biotique et abiotique, est en particulier affectée. Cette thèse aborde différents facteurs environnementaux agissant sur les stratégies saisonnières des parasitoïdes de pucerons du genre Aphidius. Dans les agro-systèmes céréaliers de l’ouest de la France, les communautés d’hôtes et de parasitoïdes ont changé rapidement au cours de la dernière décennie. Ainsi, plusieurs espèces de parasitoïdes n’entrent plus qu’en faible proportion en diapause, dû à l’augmentation des températures, à la baisse du nombre de jours de gel et à la présence accrue de leurs hôtes pendant l’hiver ; ces pressions de sélection agissent sur les seuils d’entrée diapause. Les parasitoïdes présentent des ajustements plastiques de leur réponse aux stimuli environnementaux qui induisent la diapause. Ils y entrent en plus forte proportion s’ils se développent dans des morphes de pucerons sexués (annonciateurs de ressources limitées) que dans des hôtes asexués, ce qui souligne la co-évolution de leurs cycles de vie. Cette plasticité s’avère également transgénérationnelle puisque la compétition entre femelles induit la diapause estivale chez leurs descendants. De plus, l’incidence de la diapause hivernale augmente après plusieurs générations de parasitoïdes soumises aux mêmes conditions. Les adaptations locales des parasitoïdes aux nouvelles conditions environnementales mènent à la perte d’expression de la stratégie de diapause – qui comporte des coûts écologiques et physiologiques – au profit de stratégies hivernales d’activité à l’état adulte. La modification de l’activité-densité des espèces au sein des communautés de pucerons-(hyper)parasitoïdes, due aux changements de stratégie d’hivernation, pourrait bouleverser l’équilibre des réseaux trophiques et altérer positivement ou négativement l’efficacité du service écosystémique de lutte biologique. / Climate changes alter the phenology of organisms, i.e. the succession over time of the elements of their life-cycle. Diapause expression in insects – that is, the developmental arrest allowing survival to seasonal degradations in the biotic and abiotic environment – is particularly affected. This thesis addresses the existence of different environmental factors acting on the seasonal strategies of Aphidius aphid parasitoids. In cereal agro-systems of western France, host and parasitoid communities have changed rapidly over the past decade. Hence, some parasitoid species enter diapause at low levels due to temperature increase, decrease in frost events and the presence of their hosts during winter, which impose selection on diapause induction thresholds. Parasitoids show plastic adjustments of their response to environmental stimuli inducing diapause. They enter diapause at higher proportion if they develop in sexual morphs of aphids (which inform for upcoming limited resources) than in asexual hosts, which underlines the co-evolution of their life-cycles. Transgenerational plasticity is also involved in these responses since maternal competition induces summer diapause in their offspring. Moreover, winter diapause incidence increases after some parasitoid generations experience the same environmental conditions. Local adaptations of parasitoids to new environmental conditions lead to a loss of diapause expression – which involves ecological and physiological costs – to the benefit of adult overwintering strategies. Modifications in species activity-density within aphids-(hyper)parasitoids communities, due to changes in overwintering strategies, could affect food-webs’ stability and alter positively or negatively the efficiency of biological pest control.

Species-species and species-habitat interactions have been demonstrated to be important in influencing diversity across a variety of ecosystems. Despite generalities in the importance of these interactions, appropriate mechanisms to explain them are absent in many systems. In sandhill systems of the southeast U.S., gopher tortoises have been hypothesized to be a crucial species in the maintenance of diversity and function. However, the mechanisms and magnitude in which they influence their communities and habitats have rarely been empirically quantified. I examined how habitat structure influences tortoise abandonment of burrows and how tortoise densities influence nonvolant vertebrate community diversity. Tortoise burrow abandonment is directly influenced by canopy closure, with each percent increase in canopy cover relating to a ~2% increase in the probability of burrow abandonment. In addition, tortoise burrow density was positively correlated with diversity and evenness, but not species richness. This influence was directly proportional to burrow density, supporting a dominance role for this species and rejecting the commonly asserted keystone species mechanism. I also quantified the influence of tortoises in influencing diversity relative to other environmental and habitat variables. Through this research, I have demonstrated that disturbance and habitat structure are important, but diversity responds most to density of burrows in the habitat. These findings demonstrate the intricate relationships interacting to maintaining diversity in sandhill systems. In particular, habitat change leading to declines of gopher tortoises may have drastic negative impacts on vertebrate species diversity.

Biodiversity is being lost around the world and anthropogenic activities, like non-native species introductions and urbanization, are among the leading causes of decline. Broadening our understanding of human-driven impacts on biodiversity can lead to more effective solutions and contribute towards stemming biodiversity losses. In this thesis, I explored the impacts of non-native species introductions and urbanization on butterfly-plant communities. I evaluated potential factors influencing the range expansion of a newly introduced species (Chapter 1), examined the role of urbanization in structuring biological communities (Chapter 2), and identified important ecological interactions between native and non-native species (Chapter 3). In my first chapter, I found that the newly introduced European Common Blue butterfly (Polyommatus icarus) was more abundant in urban and disturbed habitat that was unmown and where their preferred larval host plant (Lotus corniculatus), a non-native species, was present. I also found that P. icarus was not a strong flier relative to other butterfly species, suggesting that adult dispersal may not be a driving factor in range expansion. Instead, this species could expand its range in the future by colonizing habitats in developed regions across Canada given the association I found between P. icarus and disturbed habitat. In my second chapter, I found that urbanization led to the biotic homogenization of butterfly communities around Montréal, QC, favouring a few, highly abundant, non-native species. Homogenization was detected at both the taxonomic and functional levels and was driven by increases in P. icarus abundance in the more urban sites. In my third chapter, I found that non-native plants were well integrated into native butterfly nectar diets in an at-risk oak savanna ecosystem on Vancouver Island, BC and that usage of non-native plants increased when they were more available during the season. I also found that native butterflies visited non-native plants more often than flower availability predicted on its own, suggesting that butterflies may even prefer non-native nectar. Findings from my thesis research broaden our understanding of the ways in which butterfly communities can be influenced by human activities like urbanization and the introduction of non-native species, informing conservation efforts and directing future research needs.

No description available.

The aim of this thesis was to increase knowledge about metapopulation and metacommunity processes in patchy, dynamic landscapes, using epiphytic bryophytes as a model system. Host trees and deciduous forest stands in the coniferous landscape are patchy, temporal and undergo changes in habitat quality during succession. Epiphytes must track this dynamic habitat network for their long-term survival. Community patterns at different spatial scales were explored and linked to regional metapopulation processes and local population dynamics. Spatial structuring in species richness both at a local and regional scale indicated stronger dispersal limitation but lower sensitivity to habitat quality in species with large asexual than in species with small sexual diaspores. In sexually dispersed species, a strong rescue effect was indicated by a bimodal frequency distribution of the species and by increasing local abundance with increasing patch connectivity. Present connectivity to other deciduous forest patches had positive effects on richness of asexually dispersed species, whereas richness of sexually dispersed species was instead related to the landscape connectivity 30 years ago. A study of local growth and reproduction suggested that this is caused by delayed sexual, but not asexual, reproduction. Habitat conditions affected the production of sporophytes, but not of asexual diaspores. No differences in either growth rates or competitive abilities among species with different dispersal and life-history strategies were found. In vitro experiments showed that establishment is higher from large asexual diaspores than from small sexual. Establishment of all diaspore types was limited by pH. There were indications of trade-offs between high germination and protonemal growth rates, desiccation tolerance and a rapid development of shoots from protonema. The results indicated that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance (diaspore size) versus age at first reproduction, and dispersal distance versus sensitivity to habitat quality. Trade-offs in species traits may have evolved as a consequence of conflicting selection pressures imposed by habitat turnover, connectivity and irregular water supply rather than by species interactions. Syndromes of interrelated species traits imply that fairly small changes in habitat conditions can lead to distinct changes in metacommunity diversity: the results indicate that increasing distances among patches cause most harm to asexually dispersed species, whereas cuttings of forests of high age and quality as well as increasing patch dynamics are most harmful to sexually dispersed species. / Senarelagd disputation från: 2009-09-26, Lindahlsalen, EBC, Villavägen 9, 75236 Uppsala, Uppsala, 10:00

No description available.

Les cultures intermédiaires délivrent des services écosystémiques de réduction de la lixiviation de nitrate et de production de l’effet engrais vert pour la culture principale suivante. L’objectif de ce travail était de caractériser un grand nombre d’espèces et d’analyser les performances de mélanges bispécifiques de type légumineuse/non-légumineuse pour produire simultanément ces services écosystémiques de gestion de l’azote. Les traits fonctionnels foliaires mesurés sur 36 espèces sont robustes mais sont peu précis pour différencier les stratégies des espèces. Les températures cardinales de germination mesurées au laboratoire indiquent que la majorité des espèces est adaptée à des conditions de semis d’été. Une modèle conceptuel implémenté en GLM permet de prédire le comportement des deux espèces en mélange. Les mesures réalisées en expérimentations au champ couplées avec des simulations avec le modèle STICS ont permis d’évaluer les performances de certains mélanges bispécifiques pour produire simultanément les services écosystémiques. L’efficacité dépend du choix des espèces associées, qui doit être adapté en fonction des conditions pédoclimatiques et de la date de destruction des couverts. / Cover crops produce ecosystem services for nitrogen management during fallow period such as decreasing nitrate leaching and producing green N manure effect for the next cash crop. The aim of this work was to characterize a large number of species using a functional analysis and to analyze the performances of bispecific legume/non-legume mixtures to simultaneously produce both ecosystem services. Leaf functional traits measured on 36 cover crops were found robust but lacked of precision in differentiating species strategies. The cardinal temperatures for germination measured in laboratory have shown that the majority of species is adapted to summer sowing conditions. A conceptual model was designed and implemented in GLM to predict the behavior of species in mixtures. The measurements carried out in field experiments coupled with STICS model simulations confirmed the potential efficiency of some bispecific mixtures to simultaneously produce ecosystem services of nitrogen management. This efficiency depends on the choice of the two species to associate which must be adapted according to the pedoclimatic conditions as well as the date of cover crop destruction.

In this thesis I assessed the causes of long-term changes in two large, commercially important decapod crustacean populations, American lobster (Homarus americanus) and snow crab (Chionoecetes opilio), in the northwest (NW) Atlantic Ocean. By combining available time-series data, including commercial landings, research surveys, and local ecological knowledge (LEK), I explored the causes of an observed ecosystem shift in the NW Atlantic (~1950–2009) which entailed a region-wide decline of groundfish and an increase in benthic invertebrates, including these decapods. Three hypotheses were examined to explain the increase in decapod abundance: (1) the predation hypothesis, whereby a decrease in predatory groundfish led to an increase in their decapod prey (top-down effects); (2) the climate hypothesis, whereby changes in temperature or other climatic variables helped to increase decapod numbers (bottom-up effects); and (3) the anthropogenic hypothesis, whereby changes in fishing pressure drove decapod population dynamics. I explored these hypotheses separately for lobster and snow crab, which may experience different ecological and commercial pressures. First, I investigated the interactions between predatory groundfish and lobster in the inshore region of southwest Nova Scotia. Long-term fisheries-independent abundance indices for lobsters and their predators are available for Gulf of Maine (GOM) waters in the USA, but not in Canada. To address research gaps I designed and executed a survey to collect the LEK of lobster fishermen fishing in the Canadian GOM. Forty-two fishermen were interviewed. Corresponding survey results from the USA were compared to the LEK results. Both sources provided evidence for a top-down effect (predation release), contributing to observed increases in GOM lobster abundance and landings. Second, I explored relationships between lobster abundance and landings in the NW Atlantic as they may relate to temporal changes in predators, temperature, climate (North Atlantic Oscillation Index, NAOI), and fishing. Available landings data and fisheries-independent abundance estimates were collated to investigate trends in lobster abundance and catch. Links between lobster, groundfish, temperature and climate indices were explored using mixed effects models. Results offered partial support for the predation hypothesis, namely in the waters off Newfoundland, Nova Scotia, and southern New England as well as broad support for a climate effect on early life stages. This effect appeared related to a region-wide climate signal, the NAOI, but was independent of changes in water temperature. Fishing effort appeared to be following lobster abundance, rather than regulating abundance in a consistent way. Third, variation in snow crab abundance was examined through meta-analysis of time-series data of cod and crab abundance and temperature. Temperature had opposing effects on the two species: snow crab abundance was negatively correlated with temperature whereas cod and temperature were positively related. Controlling for the effect of temperature, the analysis revealed significant negative interactions between snow crab and cod abundance, with cod leading snow crab up to a five-year lag. Results indicate that snow crab is largely influenced by temperature during early post-settlement years and becomes increasingly regulated by top-down mechanisms as they approach fishery recruitment. Overall, I conclude that both climate and predation can act as population controls on large decapod populations, but these variables affect decapods at different life stages.

Biological invasions provide a unique opportunity to study the mechanisms that regulate community composition and ecosystem function. Invasive species that are also ecosystem engineers can substantially alter physical features in an environment, and this can lead to cascading effects on the biological community. Aquatic-terrestrial interface ecosystems are excellent systems to study the interactions among invasive ecosystem engineers, physical features, and biological communities, because interactions among vegetation, sediment, and fluids within biophysical feedbacks create and modify distinct physical features. Further, these systems provide important ecosystem services including coastal protection afforded by their natural features. In this dissertation, I investigate the interactions and feedbacks among sand-binding beach grass species (a native, Elymus mollis (Trin.), and two non-natives, Ammophila arenaria (L.) Link and A. breviligulata Fernald), sediment supply, and dune shape along the U.S. Pacific Northwest coast. Dunes dominated by A. arenaria tend to be taller and narrower compared to the shorter, wider dunes dominated by A. breviligulata. These patterns suggest an ecological control on dune shape, and thus, coastal vulnerability to overtopping waves. I investigate the causes and consequences of these patterns with experiments, field observations, and modeling. Specifically, I investigate the relative roles of vegetation and sediment supply in shaping coastal dunes over inter-annual and multi-decadal time scales (Chapter 2), characterize a biophysical feedback between beach grass species growth habit and sediment supply (Chapter 3), uncover the mechanisms leading to beach grass coexistence and whether A. breviligulata can invade and dominate new sections of coastline (Chapter 4), and examine the non-target effects resulting from management actions that remove Ammophila for the recovery of the threatened Western Snowy plover (Charadrius alexandrinus nivosus) (Chapter 5). I found that vegetation and sediment supply play important roles in dune shape changes across inter-annual and multi-decadal time scales (Chapter 2). I determined that a biophysical feedback between the beach grass growth habits and sediment supply results in species-specific differences in sand capture ability, and thus, is a likely explanation for differences in dune shape (Chapter 3). I found that all three beach grass species can coexist across different sediment deposition rates, and that this coexistence is largely mediated by positive direct and indirect species interactions. I further determined that A. breviligulata is capable of invading and dominating the beach grass community in regions where it is currently absent (Chapter 4). Combined, these findings indicate that A. breviligulata is an inferior dune building species as compared to A. arenaria, and suggest that in combination with sediment supply gradients, these species differences ultimately lead to differences in dune shape. Potential further invasions of A. breviligulata into southern regions of the Pacific Northwest may diminish the coastal protection ability of dunes currently dominated by A. arenaria, but this effect could be moderated by the predicted near co-dominance of A. arenaria in these lower sediment supply conditions. Finally, I found that the techniques used to remove Ammophila for plover recovery have unintended consequences for the native and endemic dune plant communities, and disrupt the natural disturbance regime of shifting sand. A whole-ecosystem restoration focus would be an improvement over the target-species approach, as it would promote the return of the natural disturbance regime, which in turn, would help recover the native biological community. The findings from this dissertation research provide a robust knowledge base that can guide further investigations of biological and physical changes to the coastal dunes, can help improve the management of dune ecosystem services and the restoration of native communities, and can help anticipate the impacts of future beach grass invasions and climate change induced changes to the coast. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Sept. 22, 2011 - March 22, 2012