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Our earth is currently undergoing unprecedented human induced climate change, which is expected to drive widespread changes in species distributions and abundances that will affect natural pest suppression. Recent studies have suggested that climate change may cause changes to predator and herbivore assemblages in ways that alter multi-trophic food webs and affect the stability of ecosystems. Moreover, higher temperatures and increased climatic variability are expected to induce differential responses from predators and their prey that will undoubtedly disrupt species interactions. This thesis aims to test how climate change will impact the ability of natural enemies to continue to control pests in agroecosystems, and how they will continue to survive and function. In a field experiment using 13 farm sites across a natural temperature gradient, I found that temperature had direct positive effects on the abundances of the dominant parasitoid (an aphid specialist) and hyperparasitoid species, highlighting the importance of specific species responses in shaping larger communities. I also found that overall community composition was affected by temperature, with composition in warmer sites changing more throughout the season than cooler sites. In a future of inevitable climatic changes this result tells us we can expect arthropod community structure to change, which will have questionable impacts on overall population dynamics. To build on the field experiments, I used laboratory experiments to test differential responses of species to both drought and temperature and found that natural enemies responded to drought and temperature in a non-additive way, suggesting that the interaction between various climate change drivers is more important than their singular effect. Also, different species of natural enemies responded differently to abiotic factors, highlighting the importance of conserving natural enemies that can maintain important functional attributes in the face of climate change. Although biodiversity can be important for ensuring ecosystem functioning, response diversity, rather than species richness, may better promote ecosystem resilience, especially in the face of changing climate. The mechanisms underlying biodiversity effects are often difficult to disentangle, however, by manipulating the diversity of climate responses exhibited by ecosystem service providers, I tested how the rates and stability of prey suppression by predators are affected by climate warming and drought. I found that predator combinations with different individual responses to climate change maintained greater and less variable (i.e. more stable) prey suppression, compared with single predator species or combinations of predators with similar climate responses. This response complementarity became strongest through time and under drought or high temperature treatments. I suggest that response complementarity provides ‘insurance’ effects, which may be more important than previously envisaged for maintaining ecosystem functions such as biological control under global environmental change. Overall, the non-additive effects of different climate drivers, combined with differing responses across trophic levels, suggests that predicting future pest outbreaks will be more challenging than previously imagined.

In host-parasitoid systems, there is a continuous coevolutionary arms race where each species imposes a strong selection pressure on the other. The host needs to develop defence strategies in order to escape parasitism and the parasitoid must evolve counter-defence strategies in order to overcome the host’s immune defence and successfully reproduce. This makes host-parasitoid systems excellent model systems for understanding evolutionary processes underlying host race formation and speciation. In order to gain a better understanding of the complexity of host-parasitoid interactions several aspects must be considered, such as search behaviour and host selection in the parasitoid, the development of immune responses in the host and counter-defence strategies in the parasitoid. In this thesis, I investigate interactions and coevolution in a natural host-parasitoid system, consisting of five species of Galerucella leaf beetles and three species of Asecodes parasitoids, by combining behavioural ecology with chemical ecology and immunology. In the studies performed, I found that pheromone production and responses in the beetles are connected to the phylogenetic relatedness between the Galerucella species (Paper I). I found no evidence that Asecodes exploits the adult pheromone to locate host larvae, but observed an ability in the parasitoids to distinguish a better host from a less suitable one based on larval odors (Paper II). The studies also revealed large differences in immune competence between the Galerucella species, which were linked to differences in hemocyte composition in the beetle larvae (Paper III, IV). Further, the results suggest that parasitism success in polyphagous Asecodes is strongly affected by former host species of the parasitoid (Paper IV). In conclusion, the results of this thesis suggest an on-going evolution in both parasitoid virulence and host immune responses in the Asecodes-Galerucella system. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.</p>

Migratory behaviour of the Ya Ha Tinda (YHT) elk population is diminishing while the number of residents remaining on the YHT winter range year-round is increasing. Previous research addressing the fitness consequences of each migratory strategy assumed there was no advantage to either segment when they shared the YHT winter range. In testing this assumption, I found no spatial segregation of migrant and resident home-ranges during winter. Both groups were exposed to similar forage resources and residents were exposed to higher night-time, but not day-time predation risk. Residents were better than migrants at reducing the foraging costs of vigilance and increased vigilance in areas of high wolf predation risk, but not near human activity because of habituation. Migrants were not habituated to humans and exhibited more constant vigilance regardless of spatial variations in risk. My results do not support the previous assumption. Instead, I found residents may be at an advantage on the winter range while forage is abundant and no snow is present. / Ecology

Knowledge of scale-dependent factors that affect the distribution of ungulate herds, such as cattle, is essential for the development of more accurate predictive models of animal movement and the management of sustainable agriculture. Our objectives were to evaluate the seasonal and diurnal patterns of herd spread, explore grouping dynamics, and the influence of dominance ranks, seasonal changes in forage biomass, use of shade, water and supplemental feed areas on cattle distribution. Positional and activity information of eleven free-ranging Bonsmara, Bos taurus, cows were obtained at five minute intervals using Global Positioning System collars. We conducted a total of 12 trials each of three weeks from August 2007 to August 2009 in a 457ha shrub-dominated savanna in South Texas. Spread was obtained by calculating the average Euclidean distance of individuals to the center of the herd. The association software package, ASSOC1, was used to analyze spatio-temporal interactions. Normalized Difference Vegetation Index, an indicator of available forage biomass, was calculated using satellite imagery. Number of GPS fixes was used as an indicator of animal use of shade patches and water and supplemental feeding areas. In this semi-arid environment, herd spread was greatest and subgroup division occurred during summer when forage biomass was high. Herd spread was the least and shade patches were used more during winter when forage biomass was low. Throughout the year spread was smallest and use of shade patches highest during the midday period compared to other periods of the day. Location of individuals in the center of the herd was not associated with their dominance ranking. There was no significant overall pattern of seasonal changes in cattle use of water and supplemental feeding areas. Seasonal forage availability and shade patches seem to have a greater influence on herd dispersion patterns and grouping dynamics than any effect of social dominance. Herd distribution is likely related to changes in forage biomass and temperature fluctuations which drive compensatory night-time feeding and thermoregulatory actions. Accurate ethological studies of herds depend on our ability to understand herd dynamics at multiple scales that affect and are relevant to animal's response to the landscape.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The dispersal of herbivorous insects in large plantations must be modelled by taking into account many behavioral aspects of the individual movement. The insect ability to search for (and find) better plant quality are of fundamental importance to the development of a mathematical model. Also, many insects present an aggregation tendency which seems to be a population strategy to optimize harvesting and survival. In the present work, in order to analyze the spatio-temporal dynamics of an insect population, both kinds of behaviour are microscopically described by a Coupled Map Lattice model which includes a short range taxis for plant quality to a long range taxis with respect to their own population density. We observed, in the macroscopic scale, stable and dynamical heterogeneous spatial pattern formation when the difference between the scales is significant. / A dispersão de insetos herbívoros em uma plantação deve ser descrita levando em conta o complexo movimento individual do inseto na procura do alimento. Este movimento é influenciado pela textura da plantação e, fundamentalmente, pela qualidade da vegetação definida pela atratividade que as plantas exercem sobre o inseto. Além disso, muitos herbívoros apresentam um comportamento de agregação como uma estratégia para melhorar sua eficiência na alimentação ou simplesmente porque o agrupamento favorece a sobrevivência da espécie. Neste trabalho, desenvolvemos um modelo do tipo Rede de Mapas Acoplados para analisar a dinâmica espaço-temporal de uma população de insetos (crescimento e dispersão) em grandes plantações texturizadas sob a hipótese de movimento orientado dos herbívoros com relação à qualidade do seu alimento e um comportamento de agregação não local em relação aos co-específicos. Observamos, na escala macroscópica, a formação de padrões espaciais heterogêneos estáveis e dinâmicos quando a diferença entre as escalas de movimentação é significativa.

Anthropogenic disturbances are ubiquitous in coastal marine ecosystems. As such, more intensive monitoring efforts are necessary to conserve these valuable habitats. Bioindicators, organisms that predictably respond to changes in environmental variables, may be utilized in monitoring efforts to assess ecosystem functioning. To incorporate organisms into monitoring programs as bioindicators managers need to first understand the difference between the natural phenology of the focal organisms and their responses to different forms of anthropogenic disturbance. To determine if gammaridean amphipods could be used as indicators of changes in environmental quality in sub-tropical seagrass ecosystems, I conducted spatial and temporal surveys of amphipod communities in south Florida. Amphipod community structure varied significantly across sites and seasons. Variation in community structure was largely driven by macrophyte biomass, food availability, seasonally variable factors (epiphyte abundance, dissolved oxygen, salinity, and temperature), water-column nitrogen concentration, and factors related to freshwater input, including low Thalassia testudinum and high Halodule wrightii densities, and salinity. Amphipods are also susceptible to mechanical damage in seagrass habitats and could be used as indicators of ecological functioning of a region. A major source of mechanical damage in seagrass ecosystems is caused by boat propellers. I simulated propeller scars in continuous seagrass beds to investigate the effects of scarring on seagrass ecosystem functioning. Seagrasses located adjacent to propeller scars experienced a shift in the limiting resource from light to phosphorus. Amphipod community structure, however, was not impacted by scarring, but amphipod density was reduced in fragmented patches. To determine if plant-herbivore interactions were impacted by propeller scarring, we removed amphipods from half of the experimental plots and measured epiphyte biomass and community composition. Top-down control on epiphyte biomass or community composition by amphipods was not affected by fragmentation, despite reduced amphipod densities. My dissertation research demonstrates that amphipods could be incorporated into existing management programs in sub-tropical seagrass ecosystems as environmental indicators. Reduced amphipod densities in fragmented seagrass beds suggests that amphipods could also be used as ecological indicators, but more research is needed to determine the extent of the impacts of fragmentation on higher trophic levels.

Predators exert strong direct and indirect effects on ecological communities by intimidating their prey. Non-consumptive effects (NCEs) of predators are important features of many ecosystems and have changed the way we understand predator-prey interactions, but are not well understood in some systems. For my dissertation research I combined a variety of approaches to examine the effect of predation risk on herbivore foraging and reproductive behaviors in a coral reef ecosystem. In the first part of my dissertation, I investigated how diet and territoriality of herbivorous fish varied across multiple reefs with different levels of predator biomass in the Florida Keys National Marine Sanctuary. I show that both predator and damselfish abundance impacted diet diversity within populations for two herbivores in different ways. Additionally, reef protection and the associated recovery of large predators appeared to shape the trade-off reef herbivores made between territory size and quality. In the second part of my dissertation, I investigated context-dependent causal linkages between predation risk, herbivore foraging behavior and resource consumption in multiple field experiments. I found that reef complexity, predator hunting mode, light availability and prey hunger influenced prey perception of threat and their willingness to feed. This research argues for more emphasis on the role of predation risk in affecting individual herbivore foraging behavior in order to understand the implications of human-mediated predator removal and recovery in coral reef ecosystems.

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第18359号 / 人博第672号 / 新制||人||162(附属図書館) / 25||人博||672(吉田南総合図書館) / 31217 / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 市岡 孝朗, 教授 加藤 眞, 教授 松井 正文 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DGAM

L’écologie nutritionnelle des populations de cervidés revêt une grande importance en contexte de population surabondante. L’intense pression d’herbivorie de certaines populations de cervidés nuît à la régénération de la flore endémique et entraîne une baisse de la biodiversité. On explique encore mal la sélection alimentaire chez ces herbivores, ce qui nuit d’une part à notre capacité de prédire d’éventuels changements dans les trajectoires floristiques, et d’autre part à notre capacité d’anticiper la réponse démographique de ces herbivores. Or, notre capacité à acquérir des connaissances sur l’écologie nutritionnelle des herbivores peut être limitée par les contraintes logistiques et méthodologiques nécessaires à l’évaluation de la qualité nutritionnelle dans un contexte d’étude écologique, de même que par un manque d’objectivité dans la définition de devises alimentaires appropriées pour l’animal d’étude. Les principaux objectifs de mon projet de doctorat sont donc de développer de nouvelles méthodologies dans l’étude des interactions entre un grand cervidé, le cerf de Virginie (Odocoileus virginianus) et son habitat, et d’implémenter ces nouveux outils dans le cadre d’études écologiques. J’ai effectué mes recherches à l’île d’Anticosti, qui est un laboratoire naturel bien adapté à l’étude des populations abondantes de cervidés. Le cerf de Virginie y a été introduit en l’absence de prédateurs naturels il y a plus de 100 ans, et cette population de cervidés est l’une des les plus denses au monde. La forte pression d’herbivorie a profondément changé la composition floristique sur l’île. Puisque l’industrie forestière et le tourisme issu de la chasse au cerf y sont les deux activités économique les plus importantes, l’étude des interactions cerf-forêt y est cruciale, tant sur le plan scientifique que pour le développement régional. Cette thèse se décline en 4 chapîtres centraux (i.e. chapitres 1,2, 3 et 4) écrits sous formes d’articles. Les deux premiers articles sont consacrés à l’élaboration de nouvelles méthodes facilitant le monitoring de la nutrition du cerf de Virginie à l’île d’Anticosti. Dans un premier temps (chapitre 1), j’utilise des modèles prédictifs utilisant la spectroscopie dans le proche infrarouge ainsi que certaines propriétés chimiques des fèces de cerf afin de prédire son régime alimentaire. Je compare ensuite (chapitre 2) différentes méthodes afin de prédire des variables alimentaires obtenues par des digestions In vitro de différents fourrages qui utilisent la liqueur ruminale de cerf. Les deux chapitres suivants sont intégrateurs et propose des implémentations de nouvelles méthodes dans le cadre d’études écologiques à l’échelle du paysage. Je propose dans le chapitre 3 un nouvel indice de qualité alimentaire qui utilise la spectroscopie dans le proche infra-rouge, les géostatistiques ainsi que des données d’inventaires floristiques afin d’estimer les patrons de qualité alimentaire à l’échelle du paysage. Finalement, dans le chapitre 4, je cherche à expliquer les patrons de régénération en sapin beaumier dans certains secteurs de l’île d’Anticosti en dépit des densités élevées de cerf de Virginie. Pour ce faire, je teste une hypothèse qui stipule que les conditions édaphiques des parcelles en régénération affectent négativement la qualité alimentaire des tissus foliaires.