Avec l'apparition massive des borderline products, les frontières traditionnelles entre la denrée alimentaire et les autres catégories de produits que l'on ingère ne cessent de se brouiller. Certes des éléments de définition de cette denrée se trouvent dans divers textes juridiques, notamment communautaires à l'image du règlement Food Law, mais toujours est-il que malgré tout demeure en partie le mystère identitaire qui entoure cette notion. Aussi, afin de pouvoir appliquer aux produits litigieux un statut adéquat et déterminer par la même le régime juridique qui doit être le leur, des références précises de l'aliment doivent être mises en évidence au travers de son analyse d'ensemble, l'étude tant de sa fonction que de sa présentation s'avérant indispensable pour résoudre cette problématique non dépourvue d'importance pratique.

Most climate change predictions focus on the response of individual species to changing local conditions and ignore species interactions, largely due to the lack of a sound theoretical foundation for how interactions are expected to change with climate and how to incorporate them into climate change models. Much of the variability in species interaction strengths may be governed by fundamental constraints on physiological rates, possibly providing a framework for including species interactions into climate change models. Metabolic rates, ingestion rates and many other physiological rates are relatively predictable from body size and body temperature due to constraints imposed by the physical and chemical laws that govern fluid dynamics and the kinetics of biochemical reaction times. My dissertation assesses the usefulness of this framework by exploring the community-level consequences of physiological constraints. In Chapter 2, I incorporated temperature and body size scaling into the biological rate parameters of a series of realistically structured trophic network models. The relative magnitude of the temperature scaling parameters affecting consumer energetic costs (metabolic rates) and energetic gains (ingestion rates) determined how consumer energetic efficiency changed with temperature. I systematically changed consumer energetic efficiency and examined the sensitivity of network stability and species persistence to various temperatures. I found that a species' probability of extinction depended primarily on the effects of organismal physiology (body size and energetic efficiency with respect to temperature) and secondarily on the effects of local food web structure (trophic level and consumer generality). This suggests that physiology is highly influential on the structure and dynamics of ecological communities. If consumer energetic efficiency declined as temperature increased, that is, species did best at lower temperatures, then the simulated networks had greater stability at lower temperatures. The opposite scenario resulted in greater stability at higher temperatures. Thus, much of the community-level response depends on what species energetic efficiencies at the organismal-level really are, which formed the research question for Chapter 3: How does consumer energetic efficiency change with temperature? Existing evidence is scarce but suggestive of decreasing consumer energetic efficiency with increasing temperature. I tested this hypothesis on seven rocky intertidal invertebrate species by measuring the relative temperature scaling of their metabolic and ingestion rates as well as consumer interaction strength under lab conditions. Energetic efficiencies of these rocky intertidal invertebrates declined and species interaction strengths tended to increase with temperature. Thus, in the rocky intertidal, the mechanistic effect of temperature would be to lower community stability at higher temperatures. Chapter 4 tests if the mechanistic effects of temperature on ingestion rates and species interaction strengths seen in the lab are apparent under field conditions. Bruce Menge and I related bio-mimetic estimates of body temperatures to estimates of per capita mussel ingestion rates and species interaction strengths by the ochre sea star Pisaster ochraceus, a keystone predator of the rocky intertidal. We found a strong, positive effect of body temperature on both per capita ingestion rates and interaction strengths. However, the effects of season and the unique way in which P. ochraceus regulates body temperatures were also apparent, leaving room for adaptation and acclimation to partially compensate for the mechanistic constraint of body temperature. Community structure of the rocky intertidal is associated with environmental forcing due to upwelling, which delivers cold, nutrient rich water to the nearshore environment. As upwelling is driven by large-scale atmospheric pressure gradients, climate change has the potential to affect a wide range of significant ecological processes through changes in water temperature. In Chapter 5, my coauthors and I identified long-term trends in the phenology of upwelling events that are consistent with climate change predictions: upwelling events are becoming stronger and longer. As expected, longer upwelling events were related to lower average water temperatures in the rocky intertidal. Furthermore, recruitment rates of barnacles and mussels were associated with the phenology of upwelling events. Thus climate change is altering the mode and the tempo of environmental forcing in nearshore ecosystems, with ramifications for community structure and function. Ongoing, long-term changes in environmental forcing in rocky intertidal ecosystems provide an opportunity to understand how temperature shapes community structure and the ramifications of climate change. My dissertation research demonstrates that the effect of temperature on organismal performance is an important force structuring ecological communities and has potential as a tractable framework for predicting the community level effects of climate change. / Graduation date: 2013 / Access restricted to the OSU Community, at author's request, from Nov. 20, 2012 - Nov. 20, 2014

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Avec l’apparition massive des borderline products, les frontières traditionnelles entre la denrée alimentaire et les autres catégories de produits que l’on ingère ne cessent de se brouiller. Certes des éléments de définition de cette denrée se trouvent dans divers textes juridiques, notamment communautaires à l’image du règlement Food Law, mais toujours est-il que malgré tout demeure en partie le mystère identitaire qui entoure cette notion. Aussi, afin de pouvoir appliquer aux produits litigieux un statut adéquat et déterminer par la même le régime juridique qui doit être le leur, des références précises de l’aliment doivent être mises en évidence au travers de son analyse d’ensemble, l’étude tant de sa fonction que de sa présentation s’avérant indispensable pour résoudre cette problématique non dépourvue d’importance pratique / With the widespread appearance of borderline products, the traditional boundaries between the food and other categories of products that we ingest are constantly blurred. Then of course the defining elements of this commodity are in various legal texts, including the Community Food Law Regulation image, but the fact that still remains part of the mystery surrounding the identity concept. Also, in order to apply the products at issue and determine an appropriate status by the same legal regime that should be theirs, precise references to the food must be demonstrated through its comprehensive analysis, the study as its function as their presentation proving indispensable to solve this problem is not without practical importance

Les insectes endophytophages, tels que les insectes foreurs de tiges, les galligènes et les mineurs de feuilles, vivent et se nourrissent à l’intérieur des végétaux. L'hypothèse de l'alimentation sélective stipule que ces organismes endophytes possèdent un avantage adaptatif par rapport aux ectophages en accédant aux tissus les plus nutritifs tout en évitant les principaux composés défensifs de la plante. Ce comportement d’alimentation sélective peut être également renforcé par une manipulation de la physiologie de la plante comme cela a été démontré chez les insectes galligènes mais également suggéré chez certains insectes mineurs. Ces derniers sont en effet capables d’induire un phénotype « îles vertes » qui se manifestent par la persistance de la photosynthèse au niveau de la zone minée à l'automne alors que le reste de la feuille entre en sénescence et jaunit. L’objectif de notre étude a été d’étudier, en conditions de terrain, les capacités de manipulation du végétal dans le système Malus domestica / Phyllonorycter blancardella. Cet insecte hautement spécialisé complète l’ensemble de son développement dans une zone restreinte d’une seule feuille. / Endophytophagous insects, such as stem-boring, gall-forming and leaf-mining insects, live within plant tissues and feed internally. The selective feeding hypothesis states that this life-style presumably provides adaptive advantages for the insect over other external-feeding modes by allowing access to most nutritional tissues while avoiding main plant defensive compounds. This selective feeding behavior can be reinforced by manipulating the plant physiology which has been clearly demonstrated in gallers but also suggested in leaf-miner insects due to the autumnal formation of “green islands” around mining caterpillars in yellow leaves. This study aimed to investigate, under field conditions, the ability of insects to manipulate their host-plant in the Malus domestica / Phyllonorycter blancardella biological system. This insect is highly specialized and entirely develops within a restricted area of a single leaf. We first characterized the plant-insect interface by describing larval mouthparts and leaf anatomy alterations resulting from the insect feeding activity.