L'augmentation de populations de cerfs pose d'importants problèmes écologiques et socio-économiques à l'échelle locale et mondiale. Des signes de densité-dépendance sont souvent observés, mais les cerfs restent abondants malgré l'importante dégradation du milieu qu'ils provoquent. Ceci soulève la question de l'ajustement des cerfs aux changements de milieu qu'ils créent ? Nous avons abordé cette question en recherchant comment les cerfs gèrent leur ressource alimentaire en fonction du risque de prédation. La prédation, en plus de son effet consommateur (élimination de proie), peut moduler le comportement et la physiologie des proies (effet non consommateur) qui doivent balancer le fait de se nourrir et le risque de prédation. Cette étude contribue à mieux comprendre comment les cerfs maintiennent d'abondantes populations dans des milieux qu'ils ont eux-mêmes appauvris.Notre projet s'est intéressé au cerf-à-queue-noire Sitka (Odocoileus hemionus sitkensis) sur trois îles de l'archipel d'Haïda Gwaii (B.C., Canada). Ces îles sont dépourvues des principaux prédateurs naturels du cerf (loup et puma) et ont été colonisées par les cerfs il y a plus de 60 ans. Lors de notre étude, ces îles présentaient des niveaux contrastés de nourriture et de risque de prédation : sur deux îles, les cerfs vivaient sans prédateur mais avaient fortement appauvri leur milieu (îles sans risque/pauvre). Sur la troisième île, les cerfs étaient chassés et bénéficiaient d'un sous-bois forestier partiellement restauré comme nourriture (île risquée/riche).Dans ce cadre, nous avons étudié : 1) sur quelles ressources les cerfs pouvaient maintenir de denses populations dans des milieux très abroutis ?; 2) comment le stress alimentaire ou le risque de prédation influençaient la réponse physiologique au stress des cerfs?; 3) les cerfs naïfs à la prédation ont-ils maintenu des niveaux de vigilance dans des milieux très abroutis et comment répondaient-ils à des stimuli olfactifs de prédateurs ?; et 4) comment, dans des milieux très abroutis, les cerfs naïfs à la prédation répondaient-ils à une chasse expérimentale pour faire peur et comment cela affectait la végétation ?Notre étude a montré que : 1) les chutes de feuilles de la canopée et la pousse annuelle de plantes rhizomateuses offraient une grande quantité d'énergie pour les cerfs et contribuaient au maintien de denses populations de cerfs dans des milieux appauvris ; 2) La présence de stress alimentaire ou de risque de prédation n'affectaient pas la réponse physiologique au stress des cerfs, suggérant l'existence d' ajustements comportementaux et/ou physiologiques permettant de réduire l'exposition des cerfs à ces deux stresseurs ; 3) sur les îles sans risque/pauvre, les cerfs ont maintenu la vigilance malgré 60 ans d'isolation à la prédation. En outre, les cerfs naïfs à la prédation évitaient de manger en présence d'urine de loup (dangereux) mais pas en présence d'urine d'ours (moins dangereux), suggérant que les cerfs présentaient une stratégie innée de nourrissage sensible au risque. Les cerfs restaient aussi moins longtemps aux stations d'appâtage en présence d'urine de loup mais n'augmentaient pas leur niveau de vigilance, suggérant qu'ils géraient le risque spatialement plutôt que par la vigilance ; 4) En réponse à une chasse expérimentale pour faire peur réalisée sur une des îles sans risque/pauvre, seuls les cerfs les moins tolérant à la perturbation humaines évitaient la zone chassée. Ceci souligna l'importance de la sélection des traits comportementaux induis par l'homme dans la gestion de la faune et de la flore. Nous avons aussi suivi la croissance de quatre espèces de plantes côtières à croissance rapide et avons montré que notre chasse expérimentale favorisait la croissance de la moitié d'entre elles, soulignant l'interaction complexe entre le comportement de nourrissage et les caractéristiques des plantes, ainsi que l'importance des objectifs dans le choix des outils de gestion.

Effects of herbivory, fire, and tree harvesting on Acacia drepanolobium were studied using plant population dynamics as the philosophical basis of research. Specifically, growth rates, chrono-sequence of re-growth, biomass and charcoal yield, herbivory, flowering, seed production, germination, mortality and the ants of Acacia drepanolobium were studied in the black cotton ecosystem of Mpala Research Centre, Laikipia, Kenya, between September 1995 and December 2000. Acacia drepanolobium was the most abundant tree or shrub with densities ranging from 80% to 98% of all the overstorey species, but it was the least browsed of all the trees and shrubs in the black cotton ecosystem, ranging from a mean of 7.2% to 9% of the individuals browsed. The tree is inhabited by four Acacia ant species, Crematogaster mimosae, Crematogaster sjoestedti, Crematogaster nigriceps, and Tetraponera penzigi, which are believed to be obligate, and which probably play a role in the low browsing rates observed. Six herbivore treatments replicated three times (no herbivores - O; only cattle - C, all herbivores allowed - MWC {control}, mega-herbivores {elephants and giraffe} and wildlife {W} – MW only, wildlife – W - only {all wildlife except mega-herbivores} and wildlife and cattle only - WC) was the main experimental design used in understanding the dynamics of the tree species under influence of different herbivores. Mean annual height growth of A. drepanolobium trees was 24.9 cm yr-1, while the mean Relative Growth Rates ranged from 14.6 x 10 –3 cm cm-1 yr-1 to 18.7 x 10 –3 cm cm-1 yr-1. Growth rates were different among the herbivore treatments and between seasons. Shoots of the tree grew by a mean range of 6.8 cm to 9.1 cm, were similar among the treatments but differed among the seasons. Canopy volume increased over time although it fluctuated with seasons, suggesting an increase in bushiness of A. drepanolobium in the ecosystem. Trees occupied by different ant species showed differences in shoot density (number of new shoots per twig), being greater in Crematogaster nigriceps occupied trees compared with the other ant species. Swollen thorn (gall) density per unit of twig length was greatest in treatments with megaherbivores; these galls were significantly larger on trees occupied by the ant Crematogaster nigriceps. Treatments with herbivores were more spinescent than the total exclusion treatment. Spine lengths ranged from 0.8 to 2.4 cm, and recorded a progressive reduction of up to 36.36.7% in treatments without browsers suggesting a relaxation of induced defence in A. drepanolobium. Flowering in A. drepanolobium was low and staggered over the study period ranging from 0.8% to 2.0% of the trees with no differences among the treatments suggesting that the level of herbivory was not sufficient to influence reproduction of the tree in the experimental site. Consequently, seedling recruitment was very low within the experimental site. However, a nearby site recorded flowering of between 22.7% and 93.5%. Mean pod production, mean number of seeds per tree and mean weight of pods and seeds had a positive linear relationship with tree density (R2=0.77, 0.81 and 0.81 respectively). Trees occupied by Crematogaster mimosae were the most likely to flower (68%) compared with C. nigriceps (5.8%), again suggesting that ants had an effect on the tree’s reproduction. Mortality of A. drepanolobium trees averaged 0.9% to 4.2% over the study period, being significantly greater in treatments with mega-herbivores. Seedling survival ranged from 42% to 75%, being greatest in the cattle only treatment. Between 30% and 100% (mean 67.2%), of A. drepanolobium seeds were attacked by a bruchid beetle (Bruchus sp.). Seeds attacked by bruchid beetles had significantly lower germination rates. Similarly, seeds passed through a fire also recoded significantly low germination rates compared with normal seeds. Fire (3.4%) and bruchid beetles (20.7%) germination compared with (control) undamaged seeds (84%) play an important role in the population dynamics of A. drepanolobium. Fewer A. drepanolobium seeds (33%) were recovered from the surface compared with buried (72%) seeds after a fire, indicating seed loss from the effect of fire and predation. In the burn experiment, fire top-killed 16% of A. drepanolobium trees but no tree or seedling was killed. On the other hand, fire significantly reduced the density of non-A. drepanolobium trees by between 50% and 100%, with none of them showing signs of coppicing after the fire unlike top-killed A. drepanolobium trees. Woody biomass from A. drepanolobium was strongly related to stem diameter (Y = 3.77x + 1.17, R2 = 0.96, P < 0.001). Mean charcoal production from earthen kilns was 2.83 Mg ha- 1. Height and stem diameter in coppicing stands increased at a mean rate of 28.6 cm yr-1 and 0.7 cm yr-1 respectively. Biomass in coppicing stands accumulated at a mean rate of 1.3 Mg ha-1 yr-1 in a 14-year period, yielding dry biomass of 18.26 Mg ha-1 useable wood that can produce a minimum of 3.0 Mg ha-1 of charcoal. This study shows that Acacia drepanolobium populations are affected by several factors including herbivory, fire and ants. The population dynamics of this tree shows that it can be harvested for sustainable charcoal yield over a 14-year cycle. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

Τα τελευταία χρόνια, αν και η Περιββαλοντική Εκπαίδευση στην προσχολική ηλικία εντάσσεται στην ευέλικτη ζώνη, αποτελεί αναπόσπαστο κομμάτι της εκπαιδευτικής θεματολογίας. Στην παρούσα διπλωματική εργασία σκοπός είναι να διερευνηθεί το κατά πόσο τα παιδιά προσχολικής ηλικίας καταννοούν τις τροφικές σχέσεις που αναπτύσσονται σε ένα οικοσύστημα και συγκεκριμένα στο δέντρο. Ταυτόχρονα, εστιάζουμε στις στάσεις που αναπτύσσουν τα παιδιά ως προς τις ανθρώπινες παρεμβάσεις στο οικοσύστημα. Τέλος, μέσω της διδακτικής παρέμβασης που αποτελείται από 10 δραστηριότητες,επιδιώκουμε να αναπτύξουμε ή και να βελτιώσουμε τις γνώσεις και τις στάσεις που έχουν τα παιδιά σχετικά με τα παραπάνω θέματα. / In recent years, although Environmental Education in early childhood is part of the flexible zone is an integral part of education topics. In this thesis, the goal is to investigate whether preschool children understand food chains that are developed in a specific ecosystem and especially the tree. Simultaneously, we focus on attitudes that children develop towards the human intervention in the ecosystem. Finally, through an instructional intervention that consists of 10 activities, we try to develop or improve their knowledge and attitudes that have children on these issues.

Made available in DSpace on 2015-03-26T13:30:17Z (GMT). No. of bitstreams: 1 texto completo.pdf: 436016 bytes, checksum: 72156ad33ca23312aa5140289d5a3713 (MD5) Previous issue date: 2006-04-28 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The organic coffee production system needs techniques for handling herbivore populations and that cause low negative effects on the natural enemies. The use of alternative bioprotectors like enriched biofertilizer and phytoprotectors mixtures to replace pesticides in an herbivore management program has been frequent in organic system of coffee production. The aim of this study was to investigate the effects of three alternative bioprotectors, the biofertilizer Supermagro, lime sulphur and Viçosa mixture (Viça Café Plus®) on the southern red mite Oligonychus ilicis (McGregor) (Acari: Tetranychidae) and on its predatory mite Iphiseiodes zuluagai (Denmark & Muma) (Acari: Phytoseiidae). It was studied the toxicity and the sublethal effects of the bioprotectors on the instantaneous growth rate (ri) of these mites. The bioprotectors showed larger acute toxicity to O. ilicis than to I. zuluagai. Only lime sulphur had estimated lethal concentration (CL95) with possibility to use in the field to control O. ilicis. The three alternative bioprotectors decreased ri for both species, but I. zuluagai was more affected than O. ilicis. The effectiveness of the alternative bioprotectors was verified for control of O. ilicis in a greenhouse experiment with two concentrations of each product. Lime sulphur treatment (0.104% of calcium polysulfide) and Viça Café Plus® (2%) had higher and lower effectiveness, respectively, while the other treatments had intermediate effectiveness. Therefore, lime sulphur would be suitable to control the southern red mite O. ilicis. The biofertilizer Supermagro and Viçosa mixture (Viça Café Plus®) could be used to supply mineral nutrition of plants. The use of lime sulphur to control O. ilicis must be in a criteriously manner because higher concentrations would be harmful to the predatory mite I. zuluagai. Environmental and biological factors could influence the behavior of herbivores and natural enemies under the use of alternative bioprotectors and could also affect their effectiveness to keep biological control on organic coffee agroecosystem. So, supplementary trials should be done aiming to confirm these results in field conditions. / O sistema de produção orgânica de café requer técnicas para o manejo da população de herbívoros que tenham menor impacto sobre os inimigos naturais. A utilização de biofertilizantes enriquecidos e de caldas fitoprotetoras, como alternativa ao manejo convencional de herbívoros, tem sido freqüente em condições de cultivo orgânico do cafeeiro. Seu uso se deve à manutenção de condições nutricionais adequadas às plantas e ao suposto baixo impacto sobre inimigos naturais de herbívoros. O objetivo deste estudo foi investigar os efeitos de três bioprotetores alternativos, o biofertilizante Supermagro, a calda sulfocálcica e calda Viçosa comercial (Viça Café Plus®), sobre o ácaro herbívoro Oligonychus ilicis (McGregor) (Acari: Tetranychidae) e o ácaro predador Iphiseiodes zuluagai (Denmark & Muma) (Acari: Phytoseiidae). Testes de toxicidade aguda e latente foram realizados para verificar os efeitos letais e subletais dos bioprotetores alternativos sobre essas duas espécies de ácaros. Os bioprotetores apresentaram toxicidade aguda maior para O. ilicis, e somente a concentração letal (CL95) estimada para a calda sulfocálcica apresentou viabilidade de ser utilizada no campo. Os três bioprotetores, utilizados em concentrações subletais, afetaram a taxa instantânea de crescimento populacional (ri) de ambas as espécies, sendo que I. zuluagai teve a ri menor que O. ilicis. A eficiência dos três bioprotetores para o controle de O. ilicis em casa de vegetação foi também verificada, sendo testadas duas concentrações de cada produto. O tratamento com maior eficiência foi a calda sulfocálcica na concentração de 0,104% de polissulfetos de cálcio, enquanto a Viça Café Plus® a 2% foi o de menor eficiência. Os demais tratamentos apresentaram eficiência de controle intermediária. Portanto, dentre os três bioprotetores alternativos, a calda sulfocálcica seria o mais indicado para a finalidade de controlar o ácaro- vermelho do cafeeiro O. ilicis. O biofertilizante Supermagro e a calda Viçosa comercial, ao serem utilizados para o fornecimento de nutrientes às plantas, poderão ter função complementar e auxiliar no controle do ácaro. No entanto, o uso da calda sulfocálcica para o controle populacional de O. ilicis deverá ser de forma criteriosa, de maneira a ter menor impacto sobre o ácaro predador I. zuluagai. Como fatores ambientais e biológicos poderão influenciar a resposta dos herbívoros e dos seus inimigos naturais à aplicação dos bioprotetores alternativos e a sua eficiência, a condução de experimentos em condições de campo poderão ser complementares aos resultados obtidos.

Etant donné le rôle clé des grands herbivores sur la diversité végétale spécifique et fonctionnelle, notre objectif était de mieux comprendre la relation entre l'herbivorie et les communautés végétales principalement à une échelle spatiale fine, afin de concilier des objectifs de gestions des populations et de conservation de la flore. Pour cela, nous avons abordé cette problématique en intégrant des approches taxonomiques et fonctionnelles, et en étudiant les interactions aux niveaux inter- et intra-spécifiques. Nous avons combiné les informations de trois bases de données : (1) des données de régime alimentaire issus d'analyses d'ADN metabarcoding réalisées sur des faeces de chamois (Rupicapra rupicapra), chevreuil (Capreolus capreolus) et mouflons (Ovis gmelini musimon) du Massif des Bauges, (2) des données sur les caractéristiques des communautés végétales (composition floristique, biomasse, phénologie), (3) des données de traits fonctionnels des plantes. L'analyse de variabilité intra-spécifique des trois grands herbivores nous a permis de valider l'hypothèse de variation de niche (NVH) de Van Valen au niveau intra-spécifique mais aussi au niveau inter-spécifique, soit une relation positive entre la largeur de niche de l'espèce et sa variabilité intra-spécifique. Ensuite, grâce à deux populations de chamois d'alpage, l'une vivant en sympatrie avec le mouflon et l'autre vivant en allopatrie, nous avons pu mettre en évidence l'absence d'effets négatifs de la population introduite de mouflon sur le régime alimentaire de la population native de chamois, autant au niveau de la niche alimentaire taxonomique que fonctionnelle. L'analyse des critères de sélection alimentaire nous a finalement permis de mettre en avant des différences de critères de choix entre les deux espèces à certaines saisons, expliquant ainsi partiellement le partitionnement des niches taxonomiques et fonctionnelles entre les deux espèces. Par ailleurs, les scénarios proposés d'évolution de la sélection alimentaire au cours de l'année pour les deux espèces concordaient avec les caractéristiques morphologiques spécifiques à l'espèce d'ongulé. Finalement, contrairement à la littérature où aucune étude n'était capable de discriminer les effets directs et indirects des traits fonctionnels à cause de corrélations, nous avons pu, grâce à des analyses de pistes, démontrer que, dans la plupart des cas, les traits biomécaniques avaient un effet direct sur le choix alimentaire alors que les traits chimiques n'avaient qu'un effet indirect. Enfin, d'un point de vue méthodologique, nous conseillons l'utilisation d'indices d'azote fécaux uniquement dans l'étude de la variation à long terme de la qualité des régimes de manière spécifique à chaque espèce et chaque site, et non pas pour comparer des qualités de régime entre espèces ni pour étudier les variations fines à l'échelle intra-saisonnière. La complémentarité des approches nous a permis de mieux appréhender la structuration des communautés d'herbivores, et devrait nous aider à mieux évaluer l'état actuel et l'évolution des relations entre individus, entre espèces et avec leur environnement.Mots-clés : ongulés, interactions intra- et inter-spécifiques, approche taxonomique et fonctionnelle, ADN metabarcoding, NIRS, massif des Bauges, sélection alimentaire / Given the key role of large herbivores on species and functional plant diversity, we aimed at better understanding the relationship between herbivory and plant communities mainly at a fine-scale, in order to reconcile objectives of population management and plant conservation. For this purpose, we used both taxonomic and functional approaches, and studied interactions at the inter- and intra-specific levels. We combined information coming from three databases: (1) diet data from DNA-metabarcoding applied on chamois (Rupicapra rupicapra), roe deer (Capreolus capreolus) and mouflon (Ovis gmelini musimon) faeces from the Bauges Massif, (2) characteristics of plant communities (plant composition, biomass, phenology), (3) plant functional traits. Analyses of intra-specific variability of the three large herbivores allowed us to upscale the niche variation hypothesis (NVH) of Van Valen from the intra- to the inter-specific level, i.e. we observed a positive relationship between the species niche breadth and among-individual variation. Then, based on two chamois subpopulations living in pastures, one living in sympatry with the mouflon and the other living in allopatry, we revealed the absence of negative effects of the introduced mouflon population on native chamois population diet, both for the taxonomic and functional dietary niche. Analyses of diet selection criteria allowed us to highlight differences in choice criteria between chamois and mouflon in some seasons, which helped to explain the taxonomic and functional niche partitioning of the two species. Furthermore, the proposed scenario of the evolution of diet selection over the year for both species were consistent with ungulate-specific morpho-physiological features. Finally, contrary to the literature where no studies could discriminate the direct and indirect effects of functional traits on diet selection because of correlations, we used path analyses, which allowed us to show that in most cases, biomechanical traits had a direct effect on diet choices, whereas chemical traits had an indirect effect. Furthermore, from a methodological point of view, we advised to use nitrogen fecal indices only to study the evolution of species-specific and location-specific population long-term diet quality, but not to compare diet quality between species, nor to study slight fluctuations at the intra-seasonal level. The complementarity of the approaches allowed us to better account for the structuration of herbivore communities, which should help to better assess the actual state and the evolution of relationships among individuals, species and their environment.Key-words: ungulates, intra- and inter-specific interactions, taxonomic and functional approach, DNA metabarcoding, NIRS, Bauges Massif, diet selection

Herbivory is a key process that mediates the abundance of primary producers and community composition in both terrestrial and aquatic ecosystems. On tropical coral reefs, changes in herbivory are often related to phase shifts between coral-dominance and dominance by seaweeds, or foliose macroalgae. Resilience or capacity to resist and reverse such phase shifts is, therefore, viewed as a critical function on coral reefs. This thesis used grazer exclusion and assay experiments at six sites within three different fisheries management regimes in Kenya to identify the impacts of herbivores (sea urchins and fishes) on algal dynamics in the context of coral reef resilience. First, I examined the grazing rates necessary to prevent phase shifts by quantifying consumption and algal production. Here, I found that, over a 390-day experiment, at least 50 percent of algal production must be consumed to avoid accumulation of algal biomass. Using video observations, I also showed that scraping parrotfishes remove more algae (per unit of fish biomass) than previously assumed, and that sea urchins, if released from predation, have similar impacts to fishes. Then I focused on algal succession, and found that sea urchins and fishes have different effects that are mediated by their abundances and species composition. Where sea urchins were less abundant and parrotfishes absent (e.g. young fisheries closures), progression of algae from turfs to early and then late successional macroalgae occurred rapidly and within 100 days. I then turned my focus to the removal of already established macroalgae (grown for > 1 yr in the absence of herbivores) and showed that sea urchins and browsing fishes were able to remove significant amounts of macroalgae where either herbivore was abundant. However, using multiple-choice selectivity assays and in situ video recordings, I found that browsing fishes fed very selectively with low overlap in diet among species, leading to low functional redundancy within a high diversity system. Finally, using long-term survey data (from 28 sites) to build a 43-year chronosequence, I showed that it is possible that the effects of herbivory will not be constant across transitions from open fishing to fishery closures through non-linear grazing intensity. Therefore, increases in herbivory within fisheries closures may not be immediate and may allow a window of opportunity for algae to go from turf to unpalatable macroalgae until scraping and browsing fishes fully recover from fishing (~ 20 years). The findings in this thesis are novel and raise concern over the potential implications of the slow recovery of parrotfishes or, given lower than expected functional redundancy in grazing effects, the absence of even one browsing fish species in fisheries closures. Overall, this thesis highlights the importance of herbivore community dynamics in mediating interactions among algae, and provides new insights for conservation and management actions that attempt to bolster the resilience of coral reefs.

Les poissons herbivores jouent un rôle écologique majeur face au phénomène de « coral-algal phase-shift », qui sévit depuis le début des années 80 dans les récifs coralliens de la Caraïbe. Dans cette étude, les habitudes alimentaires des principales espèces de poissons herbivores ont été étudiées afin de comprendre comment ces espèces utilisent et se partagent les ressources trophiques en milieu récifal et dans les herbiers. Les niches trophiques de ces espèces ont été décrites par deux méthodes complémentaires: les analyses des contenus des tractus digestifs et les analyses des isotopes stables du carbone C3C/ 12C) et de l'azoteCSN/ '4N). La qualité nutritionnelle des sources alimentaires a été évaluée par leurs concentrations de macronutriments (protéines, lipides, glucides solubles et insolubles) afin d'expliquer en partie le choix des ressources par les herbivores. Parmi les 14 espèces de poissons étudiées, appartenant aux familles des Pomacentridae, des Acanthuridae et des Scaridae, huit types de niches trophiques ont été décrits, indiquant une diversité fonctionnelle de ces espèces. Les niches trophiques décrites sont occupées par une ou plusieurs espèces, indépendamment de leur morphologie et de leurs affinités taxinomiques. Les résultats de cette étude suggèrent une complémentarité entre ces espèces, en terme d'utilisation des ressources, et soulèvent la question de leur conservation afin de préserver leur rôle écologique dans les écosystèmes côtiers de la Caraïbe. / Herbivorous fishes play a major ecological role against the « coral-algal phase-shift » phenomenon in the coral reefs of the Caribbean. In this study, the feeding patterns of the most important species of herbivorous fishes have been studied to understand how these species use and share the trophic resources on reefs and seagrass beds . Trophic niches of these species have been described by two complementary methods: the analyses oftheir digestive contents and the analyses of stable isotopes of carbon C3C/ J2C) and nitrogen (lsN/14N). The nutritional quality of the sources has been evaluated by their concentrations of macronutrients (proteins, lipids, soluble and insoluble carbohydrates) to explain partially the choice of resources by herbivorous fishes . Among the 14 studied species of herbivorous fishes (Pomacentridae, Acanthuridae and Scaridae), eight types of trophic niches have been described, indicating a functional diversity of these species . The trophic niches are occupied by one or several species, independently oftheir morphology or their taxonomie affinities. The results of this study suggest a complementarity among these species and raise the question of their conservation to preserve their ecological role on marine ecosystems of the Caribbean.

L’hypothèse selon laquelle l’accumulation des métaux lourds par les plantes a évolué comme mécanisme de défense contre les herbivores a été testée avec l’hyperaccumulatrice de zinc Thlaspi caerulescens (Brassicaceae). En utilisant l’écotype métallicole (poussant sur sols métallifères) et l’écotype non métallicole (sols normaux) de T. caerulescens, nos résultats ont conduit à rejeter l’hypothèse de défense par accumulation de métaux: les plantes ont été consommées indépendamment de leur concentration en Zn dans toutes les situations expérimentales examinées (conditions contrôlées, jardin expérimental, populations naturelles). Par contre, les herbivores ont montré une préférence systématique pour les plantes de l’écotype métallicole, quelle que soit leur concentration en Zn. Lorsque l’on mesure les concentrations en métabolites secondaires défensifs (glucosinolates) des écotypes métallicole et non métallicole de T. caerulescens, on constate que les individus d’origine métallicole produisent constitutivement moins de glucosinolates que les individus non métallicoles, tant dans les populations belges que dans les populations françaises. Par ailleurs, sur les sites métallifères où ont évolué les populations métallicoles, on constate à la fois une plus faible pression d’herbivorie sur les plantes (moins de dégâts) et une plus faible densité de gastéropodes que dans les sites normaux. La diminution des défenses chez l’écotype métallicole serait la conséquence d’un relâchement de la pression d’herbivorie sur les sites métallifères. <p>En outre, nous avons montré que la chenille spécialiste d’Issoria lathonia (Nymphalidae) est capable de se développer sur les feuilles riches en Zn de l’accumulatrice de zinc Viola calaminaria (Violaceae) en excrétant efficacement le Zn dans leurs fèces. <p> L’ensemble de nos résultats suggère donc que l’hyperaccumulation des métaux lourds n’a pas évolué en tant que mécanisme de défense contre les herbivores.<p> / Doctorat en sciences, Spécialisation biologie végétale / info:eu-repo/semantics/nonPublished

Plants and herbivores influence each other for more than million years. Most studies are focused on interspecific variability in herbivory intensity, but little i known about intraspecific variability and what controls it. Environmental conditions can determine intraspecific variation. Goal of this thesis is to examine importance of environmental conditions and interspecific variation for invertebrate herbivory preferences. Plant material that was used in experiments comes from several species from subfamily Carduoideae. Preferences of invertebrate herbivores are tested in food-choice experiments. Plastic arenas are made for these experiments, in which leaves are put in small tubes that are placed along the periphery. After herbivores are placed in to arena, arena is covered by net to ensure that herbivores can't escape. Plant material for experiments was grown in experimental garden and was also brought from field. Plants from garden differ in productivity of soil and water regime. In experiments with field material, plant leaves were collected from eight localities, four fields and four grasslands. Leaves were scanted before and after each experiment. Scans were processed and the amount of consumed leaf tissue was determined. For plant characteristics I measured plant functional traits, specific...

Senna mexicana chapmanii (Fabaceae: Caesalpinoideae), an attractive and threatened species native to pine rocklands of southern Florida, is consumed by folivorous caterpillars of Sulfur butterflies (Lepidoptera: Pieridae). Caterpillars may be deterred or eaten by predators, but also very important are parasitoids, both flies and wasps. This study investigated the effects of plant density on Sulfur caterpillar numbers and rates of parasitization. Senna mexicana chapmanii plantations were established at agricultural and urban areas; both sites are adjacent to protected pine rockland areas. Sulfur butterfly immature stages were collected and reared to glean information regarding number of herbivores and rates of parasitization. Continuing this weekly monitoring protocol over the course of a year provided data to determine that higher plant density has an effect on levels of parisitization and is correlated with the number of herbivores. Elucidating these patterns has important implications understanding the factors that regulate interactions in this plant/herbivore/parasitoid system.