Studies focusing syntopic species help to understand how they partition resources and coexist. The objective of this work was to describe the social system, habitat use and diet of the hoary fox (Pseudalopex vetulus) and the crab-eating fox (Cerdocyon thous), in an area of cattle farms in Central Brazil. It is also reported a confrontation between the two species, observed during a study on the behavioral repertory of the hoary fox. Social system and habitat use were studied by direct observation of foxes in the field and diet, through scat analysis. Crab-eating foxes were found in pairs in 34 (59%) of 58 encounters and hoary foxes were solitary in 58 (84.0%) of 69 encounters, with no seasonal variation in the group size of both species. During one encounter of a crab-eating fox couple, the male vocalized to call the female that had remained behind. Hoary foxes were sighted in grazed pasture in a higher proportion (84%) than crab-eating foxes (67%) and they were never found in forest neither in swamp. Besides, both species were rarely seen together, and the only encounter registered ended in a conflict, with the crab-eating fox driving the hoary fox out. Twenty-seven taxa were identified in the diet of the two canids, with the crab-eating fox (n = 32 scats) consumed fruits, insects (mainly Orthoptera and Coleoptera) and vertebrates (most Cricetidae and Squamata) and the hoary fox (n = 23 scats) ate primarily termites (Isoptera). Results indicate that crab-eating fox couples keep more tight bonds than hoary fox couples. The coexistence of both species may be related to the detected differences in habitat use and diet. / Estudos enfocando espécies sintópicas ajudam a entender como elas partilham os recursos e coexistem. O objetivo deste trabalho foi descrever o sistema social, o uso do habitat e a dieta da raposa-do-campo (Pseudalopex vetulus) e do cachorro-do-mato (Cerdocyon thous), em uma área de fazendas de gado no Brasil Central. Também é relatado um confronto entre as duas espécies observado durante um estudo sobre o repertório comportamental da raposa-do-campo. O sistema social e o uso de habitat foram estudados a partir da observação direta dos animais no campo e a dieta, através da análise de fezes. Os cachorros-do-mato foram encontrados em duplas em 34 (59%) de 58 encontros e as raposas-do-campo estavam solitárias em 58 (84%) de 69 encontros, não havendo variação sazonal no tamanho de grupo das duas espécies. Durante um dos encontros de uma dupla de cachorro-do-mato, o macho vocalizou para chamar a fêmea que havia ficado para trás. As raposas-do-campo foram avistadas em pastagens em uma proporção maior (84%) que os cachorros-do-mato (67%) e nunca foram encontradas em florestas ou brejos. Além disso, as duas espécies raramente foram vistas juntas, sendo que o único encontro registrado terminou em conflito, com o cachorro-do-mato expulsando a raposa-do-campo. Vinte e sete táxons foram identificados na dieta dos dois canídeos. O cachorro-do-mato (n = 32 fezes) consumiu frutos, insetos (principalmente Orthoptera e Coleoptera) e vertebrados (a maioria Cricetidae e Squamata) e a raposa-do-campo (n = 23 fezes) se alimentou principalmente de cupins (Isoptera). Os resultados indicam que casais de cachorros-do-mato mantêm laços mais estreitos que casais de raposa-do-campo. A coexistência de ambas as espécies pode estar relacionada às diferenças detectadas no uso do habitat e na dieta. / Mestre em Ecologia e Conservação de Recursos Naturais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The natural regeneration in disturbed areas might become a slow process due to harsh conditions and constraints imposed by the environment. The positive interactions in these locations are important for the establishment of woody plant community. In abandoned pastures the isolated remnant trees facilitate regeneration by easing the environmental conditions, reducing competition below their canopies and attracting animal dispersers that might increase the local seed rain. Thus, this study aimed to understand the role of isolated trees in the regeneration process and evaluate which factors might affect this process. For this purpose, we selected an abandoned pasture in Deciduous Seasonal Forest conditions (DSF), located within the borders of Parque Estadual do Pau Furado (Pau Furado State Park), Uberlândia MG. In a 10 - hectare area we selected twenty isolated trees and set four 4m² - plots in each one, two below the canopy and two outside the canopy (open area). All the regenerating woody individuals found in the plots were measured and identified. Some characteristics of the trees were also measured: tree height, canopy coverage and area, and distance from the nearest DSF fragment. The environmental data of temperature and relative humidity were gathered in both environments (below and outside the canopy) in two distinct seasons (dry and rainy). The natural regeneration was represented by 245 woody individuals (224 in the plots below the canopy and 21 in the plots outside the canopy), distributed in 51 species, 42 genera, and 22 botany families. The most important families were Fabaceae, Myrtaceae, Rubiaceae, Malvaceae and Bignoniaceae. The plots below the canopy showed higher density of individuals and species richness when compared to the plots outside the canopy. When it comes to dispersion syndrome, the zoochore species were predominant (46.9%), indicating that isolated trees attract dispersers that deposit the seeds on site. As a direct effect of canopy shading we recorded lower temperature and higher values of relative humidity below the canopy in both seasons. The shading also affected the grass coverage that was reduced below the canopy. This reduction is important for seedlings establishment and growing, since alien grasses set limits to natural regeneration due to competition. From the analyzed environmental and biophysical factors by using Canonical Correspondence Analysis (CCA), the height, the canopy area and RH showed a relation to distribution of woody species. The relation species/environment was significant in the dry season (p<0.05), according to Monte Carlo test even though it only explained 23.7 of data variation. In stressful environments, as abandoned pastures, a successful regeneration will probably rely on the existence of isolated trees that act as facilitators easing, thus, the environmental conditions below their canopies. / A regeneração natural em áreas degradadas pode se tornar um processo lento, devido às condições adversas e das barreiras impostas pelo ambiente. Nesses locais, as interações positivas podem ser muito importantes para o estabelecimento da comunidade lenhosa. Em pastagens abandonadas, as árvores remanescentes isoladas facilitam a regeneração por amenizar as condições ambientais e reduzir a competição abaixo de sua copa, e atrair animais dispersores que podem incrementar a chuva de sementes no local. Assim, o presente estudo teve como objetivo compreender o papel de árvores isoladas no processo de regeneração e avaliar quais fatores podem estar atuando nesse processo. Para essa finalidade, selecionou-se uma pastagem abandonada (sem uso) em condições de Floresta Estacional Decidual (FED), situada dentro dos limites do Parque Estadual do Pau Furado, Uberlândia, MG. Em uma área de 10 hectares, foram escolhidas vinte árvores isoladas, e em cada uma foram instaladas quatro parcelas de 4m², duas sob a copa e duas fora da copa (área aberta). Todos os indivíduos lenhosos regenerantes encontrados nas parcelas foram medidos e identificados. Algumas características da árvore também foram mensuradas: altura da árvore, área e cobertura da copa e distância do fragmento de FED mais próximo. Os dados ambientais de temperatura e umidade relativa do ar e cobertura do solo foram medidos nos dois ambientes (dentro e fora da copa) em duas estações distintas (seca e chuvosa). A regeneração natural foi representada por 245 indivíduos do componente lenhoso (224 nas parcelas sob a copa e 21 nas parcelas fora), distribuídos em 51 espécies, 42 gêneros e 22 famílias botânicas. As famílias que mais se destacaram foram Fabaceae, Myrtaceae, Rubiaceae, Malvaceae e Bignoniaceae. As parcelas sob a copa das árvores apresentaram maior densidade de indivíduos e riqueza de espécies que as parcelas abaixo da copa. Quanto às síndromes de dispersão, nas parcelas sob a copa houve uma predominância de espécies zoocóricas (46,9%), um indicativo de que as árvores isoladas atraem dispersores que depositam sementes no local. Como efeito direto do sombreamento pela copa, observamos temperaturas mais baixas e valores mais altos de umidade relativa nas parcelas abaixo da copa, nas duas estações do ano. O sombreamento também afetou a cobertura de gramíneas, que foi reduzida abaixo da copa das árvores. Essa redução é importante para o estabelecimento e crescimento das plântulas, pois as gramíneas exóticas limitam a regeneração por serem fortes competidoras. Dentre os fatores ambientais e biofísicos avaliados, usando Análise de Correspondência Canônica (ACC), a altura, área de copa e UR apresentaram relação com a distribuição das espécies lenhosas. A relação espécie/ambiente foi significativa na estação seca (p<0,05) pelo teste de Monte Carlo, mesmo explicando somente 23,7% da variação dos dados. Em ambientes estressantes, como pastagens abandonadas, o sucesso da regeneração pode, muitas vezes, depender da existência de árvores isoladas que atuam como facilitadoras amenizando, desta forma, as condições ambientais abaixo da copa das árvores. / Mestre em Ecologia e Conservação de Recursos Naturais

Although seldom reported, necrophagy is a relatively common phenomenon in nature. Among necrophagous vertebrates, scavengers are the only ones who have a diet composed almost exclusively by carrion. There are five species of scavengers recorded in Brazil and in some Brazilian regions these species can live in sympatry, interacting with each other and with species of Falconiformes. The aims of this study were: 1. to investigate the use of perches and food resources by necrophagous birds in different areas of Uberlândia city (MG), and 2. to establish the types of interactions (intra- and inter-specific) between the studied populations. The research was performed between December 2006 and December 2007, though field observations were concentrated in the dry period (June to September 2007). Three types of habitats were selected for the field work (urban environment, urban-rural environment and rural environment). The observations followed focal animal ad libitum analises, and were carried out from 9 am to 6 pm. All areas were sampled monthly, performing 90 hours of observation (30 hours in each area). Two species of necrophagous birds were recorded: Coragyps atratus (Black Vulture) and Caracara plancus (Crested Caracara). The rural-urban environment showed higher frequency of records of scavengers and Crested caracara using perches (5646). Moreover, the urban environment served as a deposit of waste and carcass of animals stemming both from urban environments as well as rural environments. Interactions for food were often marked by agonistic interactions, although there were displays which prevent disputes, such as warning postures and sounds production (including vocalization ). Interspecific allopreening was recorded at a higher frequency than expected and probably occurs as a way of rapprochement between Crested caracara and Black vultures when grouping in mixed flock. These mixed flocks seemed to be favored by the surveillance ability of the Crested caracara and because of its vocalization ability and thus producing scream of warning, useful for the flock. / A necrofagia é freqüente na natureza, embora seja um fenômeno pouco reportado para os vertebrados. Entre estes, urubus são os únicos que possuem uma dieta composta quase que exclusivamente de carcaças. No Brasil, são registradas cinco espécies de urubus e em algumas regiões brasileiras essas espécies podem viver em simpatria, interagindo entre si e com espécies de falconiformes. Os objetivos do presente estudo foram: 1. avaliar a utilização de poleiros e de recursos alimentares por aves necrófagas em diferentes áreas do município de Uberlândia (MG); e 2. estabelecer os tipos de interações (intra-específicas e interespecíficas) existentes entre as populações estudadas. A pesquisa foi desenvolvida entre dezembro de 2006 e dezembro de 2007, sendo que as observações de campo se concentraram no período de seca (junho a setembro de 2007). Foram selecionadas três áreas para realização do trabalho (ambiente urbano, ambiente rural-urbano e ambiente rural). As observações seguiram o modelo animal focal e ad libitum no objeto focal, tendo sido realizadas das 9 h às 18h. Em cada mês todas as áreas foram amostradas, totalizando 90 horas de observação (30h em cada área). Duas espécies de aves necrófagas foram registradas: Coragyps atratus (urubu-de-cabeça-preta) e Caracara plancus (carcará). A interface rural-urbana apresentou maior freqüência de registros de urubus e caracarás, quanto à utilização de poleiros (5.646). Adicionalmente, a franja urbana serve como depósito de lixo e carcaça de animais advindas tanto do ambiente urbanos quanto do ambiente rural. Interações alimentares são freqüentemente marcadas por interações agonísticas, embora haja indícios de displays que evitam disputas físicas tais como posturas de advertência e produção de sons, parecido com vocalização. Comportamento social interespecífico, Interspecific Allopreening , foi registrado em uma freqüência superior ao esperado e provavelmente ocorre como modo de aproximação entre caracarás e urubus na formação de um bando misto, que parece ser favorecido pela vigilância dos caracarás devido à sua capacidade de vocalização e, conseqüentemente, produção de grito de alerta. / Mestre em Ciências Veterinárias

Os ecossistemas aquáticos são afetados por processos que ocorrem em escalas finas (locais) e amplas (regionais). Os processos locais incluem, por exemplo, filtros ambientais e interações interespecíficas, enquanto que os regionais abrangem principalmente questões relacionadas à dispersão de indivíduos. O entendimento de como esses processos atuam sobre comunidades, populações e interações em peixes de riachos é fundamental para a conservação dos ecossistemas aquáticos, pois permite predizer as consequências de alterações antrópicas e fornece subsídios para ações de manejo e políticas de conservação. Na presente tese, eu desenvolvi cinco estudos em distintas escalas espaciais. Cada um é apresentado em capítulos distintos. Nos capítulos 1 e 2, eu abordei questões relacionadas à compreensão de como alterações antrópicas feitas em distintas escalas espaciais influenciam as diversidades alfa e beta de comunidades de peixes de riachos. No capítulo 3, eu procurei entender como processos previstos na teoria de metacomunidades influenciam mudanças temporais na composição e abundâncias de espécies em comunidades locais. No capítulo 4, eu estudei como os impactos antrópicos levam a alterações no papel trófico e no intestino de populações de uma espécie generalista e persistente. Por fim, no capítulo 5, eu usei uma abordagem de aninhamento, desenvolvida inicialmente na Ecologia de Comunidades, para avaliar a ocupação de larvas de uma espécie de quironomídeo (Diptera) sobre o corpo de seu hospedeiro (uma espécie de peixe da família Loricaridae). / Aquatic ecosystems are influenced by processes that occur at fine (local) and broad (regional) scales. Local processes include, for example, environmental filters and interspecific interactions, whereas regional processes encompass mainly questions regarding individual dispersion. Knowledge on how these processes affect communities, populations and interactions in stream fish is essential for conservation of aquatic ecosystems, as it allows predicting consequences of human-alterations and provides subsidy for management actions and conservation policies. In this dissertation, I developed five studies using distinct spatial scales. I presented each one in a separate chapter. In the 1st and 2nd chapters, I addressed questions concerned with the understanding of how human alterations at different spatial scales influence alpha and beta diversity of stream fish communities. In the 3rd chapter I looked for understanding how processes predicted in metacommunity theory influence mid- to long-term changes in composition and species abundances of local communities. In the 4th chapter, I studied how anthropic impact drives modification in the trophic role and intestine of a generalist and persistent fish species. Lastly, in the 5th chapter, I employed nestedness approach previously developed for Community Ecology to evaluate occupation of chironomid species larvae (Diptera) on the body of its host (an armored catfish species of the family Loricariidae).

La connaissance des facteurs qui influent sur les populations de tiques et en particulier sur leurs distributions est un préalable indispensable à l’étude des maladies qu’elles transmettent. Parmi eux, l’importance des facteurs biotiques et en particulier celle de la compétition interspécifique est peu connue et souvent négligée. L’objectif de ce travail était d’évaluer le rôle de la compétition interspécifique sur la distribution de deux espèces de tiques d’importance vétérinaire, Amblyomma variegatum et A. hebraeum. Alors que seule A. variegatum favorise la transmission de la dermatophilose, une maladie de peau débilitante pour les ruminants, les deux espèces sont vectrices de la cowdriose, maladie due à une bactérie Ehrlichia ruminantium qui représente une contrainte économique majeure pour l’élevage. L’impact de l’espèce vectrice dans l’épidémiologie de la cowdriose (différences de souches circulantes, sévérité des cas,…) est inconnu bien qu’ayant potentiellement des conséquences en termes de surveillance (risque épidémiologique à l’introduction d’animaux) et de contrôle (développement de vaccin régional adapté aux souches circulantes) de la maladie. Ces deux espèces ont une distribution contiguë en Afrique australe avec peu de chevauchement (distribution parapatrique) suggérant une préférence environnementale différentielle ou une compétition exclusive entre elles. Une revue des données de la littérature a permis de mettre en évidence un chevauchement de leur niche trophique, climatique, et temporelle, et une interférence comportementale via la production de leurs phéromones. Les deux espèces pourraient donc rentrer en compétition directement par interférence communicative ou reproductive (hybridation stérile), ou indirectement via le partage de ressources, prédateurs ou pathogènes communs. Le rôle des facteurs biotiques et abiotiques sur le maintien de la parapatrie de ces deux espèces a été analysée (i) d’une part par la comparaison de leur niche environnementale réalisée en Afrique australe, et aux deux zones de contact au Zimbabwe et Mozambique, par des méthodes d’ordination et de modèles de niche (Maxent) ; (ii) et d’autre part par l’étude de leurs distributions et de leurs interactions (distribution sur les hôtes, croisements hétérospécifiques) dans la zone de contact au Mozambique. Globalement les résultats montrent qu’en Afrique Sud-Est et au Zimbabwe les deux espèces occupent des niches environnementales distinctes, celle d’A. hebraeum incluant des zones plus chaudes et plus sèches que celle d’A. variegatum. Au contraire au Mozambique les deux niches se chevauchent considérablement. L’enquête de terrain dans cette zone montre que les deux espèces y sont moins souvent trouvées en sympatrie que les données prédites, suggérant une distribution en partie déterminée par des interactions biotiques. Dans les rares sites avec présence des deux espèces, A. variegatum et A. hebraeum partagent les mêmes sites de fixation sur les animaux et forment un pourcentage relativement élevé de couples hétérospécifiques. Ce pourcentage, bien que similaire entre les femelles A. variegatum et A. hebraeum, semble impliquer des processus de discrimination spécifique propres aux deux espèces intervenant au niveau de l’agrégation, de la fixation et du contact des individus. Nos résultats suggèrent l’existence d’une compétition exclusive entre les deux espèces, due à une compétition sexuelle probablement associée à une compétition indirecte. La frontière parapatrique semble occuper une position stable le long d’un gradient environnemental au Zimbabwe mais pas au Mozambique. Les conditions entrainant la coexistence ou l’exclusion des deux espèces avec formation d’une frontière parapatrique sont discutés à l’aide de modèles théoriques de compétition. / Studying the factors that influence tick populations and their distributions is an essential pre-requisite to understanding the dynamics of the diseases they transmit. The relative importance of biotic factors such as interspecific competition is not well known and often neglected. The objective of this study was to assess the influence of interspecific competition on the distribution of two tick species of veterinary importance, Amblyomma variegatum and A. hebraeum. Whereas only A. variegatum is known to favor dermatophilosis, a debilitating skin disease of ruminants, both species are good vectors of Ehrlichia ruminantium, the bacteria causing heartwater, a fatal disease of ruminants that presents a major constraint for livestock development in Africa. The impact of vector species in heartwater epidemiology (differences of circulating strains, severity of clinical cases…) is poorly known but may have important implications for surveillance (epidemiological risk of imported animals) and control (adapting regional vaccine programs to circulating strains) of the disease. These two ticks have abutting and marginally overlapping (i.e. parapatric) distributions in southern Africa, suggesting either differential environmental preferences or exclusive competition between the two species. A review of published data highlighted an important overlap of their trophic, climatic and seasonal niche, and existence of chemical behavior interference through pheromone production. Therefore, the two species might compete either directly by communicative or reproductive interference (sterile hybridization), or indirectly by sharing the same resources, predators or pathogens. The role of biotic and abiotic factors in determining parapatry of these species was assessed by (i) comparing their realized environmental niche in southern Africa, and at contact zones in Zimbabwe and Mozambique, using ordination techniques and environmental niche modeling (Maxent); (ii) studying their distributions and their interactions (distribution on co-infested host, heterospecific mating) at the contact zone in Mozambique. Globally, the results indicated the two species occupied distinctly different environmental niches in southern Africa and at the contact zone in Zimbabwe, with the niche of A. hebraeum including both hotter and drier areas than that of A. variegatum. However, in Mozambique their niches overlapped considerably. Field studies within this zone showed that sympatry was observed less frequently than predicted by niche models, suggesting an importance of biotic interactions. At the rare sites where both species were present, A. variegatum and A. hebraeum were observed to share the same preference sites on hosts and formed a high percentage of heterospecific pairs. Though this cross-mating rate was not significantly different between A. variegatum and A. hebraeum females, our observations suggest different mechanism of species discrimination involved for the two species acting at the aggregation, fixation and partner contact level. Our results strongly suggest exclusive competition between these species may arise from sexual competition probably interacting with other indirect forms of competition. The parapatric boundary apparently occupies a stable location along an environmental gradient at the contact zone in Zimbabwe but not in Mozambique. Conditions inducing coexistence or exclusion of both species with the formation of parapatric distributions are discussed in relation to theoretical models of competition. When sexual competition is introduced in these models, the relative frequency of two species is determined by their endogenous fitness (a function of environmental conditions), density dependent effects of competitive interactions, historical distributions and dispersal rates: survival of the first prevails when the immigration rate of a fitter invading species remains lower than an invasion threshold.

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...

Abstract My main objectives in this thesis were to explore general patterns and mechanisms driving salmonid invasions globally and, more specifically, to examine the invasion dynamics and impacts of the North American brook trout in North European stream systems. Non-native salmonids have often spread extensively and caused many harmful impacts on their native counterparts. Among the three globally introduced salmonids, the European brown trout appeared as the 'worst' alien species (strongest impact on native fish), followed by the North American rainbow trout and brook trout. Brook trout, which is widely established in European streams, was found to be a non-aggressive species. Moreover, the growth of brown trout was unaffected by brook trout, indicating negligible interspecific interactions between the two species. Habitat niche segregation between brook trout and brown trout was evident, with brook trout occupying mainly low-velocity pool habitats, whereas brown trout resided in fast-flowing riffles. At the river-wide scale, brook trout occurred mainly in small, slightly acid headwater streams, whereas brown trout was found primarily in larger downstream river sections. Evidently, North European streams with a very low number of native fish species offer underutilized niche space for tolerant headwater specialists such as brook trout. However, the habitat niche filled by brook trout was not completely vacant, as brown trout co-occurred with brook trout in numerous small and mid-sized (3–16 m wide) streams. In these streams, brown trout reproduction was negligible presumably related to the presence of brook trout. Brook trout had also increased in density relative to brown trout during the 10-yr study period (1994 vs. 2004). Moreover, the growth rate and population densities of brook trout were high and the species had spread extensively towards the upmost headwater streams during the 10-yr study period. Thus, harmful effects on the native brown trout by brook trout are likely to occur in the core habitat of the invader, i.e. headwater streams, leaving populations of the native species unaffected elsewhere. Due to the high conservation value of the potentially impacted populations of brown trout, I strongly caution against further stocking of brook trout in European watersheds.

Étant au somment de la chaîne alimentaire, les grands prédateurs ont la capacité d'influencer le fonctionnement des écosystèmes, y compris au sein de leur guilde. En Afrique, les lions (Panthera leo) et les hyènes tachetées (Crocuta crocuta, hyènes ci-après) sont les plus gros et les plus nombreux prédateurs, et les hyènes sont souvent considérées comme subordonnées aux lions. Néanmoins, notre compréhension de leurs interactions est très limitée, d'autant plus dans les milieux boisés. Ce travail vise à identifier les mécanismes permettant la coexistence des hyènes et des lions. L'hypothèse principale est que les hyènes évitent les lions à la fois dans l'espace et dans le temps. Une revue de la littérature montre que malgré leur fort potentiel pour la compétition d'exploitation (régimes alimentaires similaires) et d'interférence (kleptoparasitisme et prédation), les lions partagent la quasi-totalité de leur distribution avec les hyènes et leurs densités sont positivement corrélées. J'ai collecté des données sur l'écologie des hyènes et des lions durant 2.5 ans à partir d'observations directes et de colliers GPS dans le Parc National de Hwange (PNH), au Zimbabwe. PNH est caractéristique d'une savane dystrophique arborée semi-aride dominée par l'éléphant (Loxodonta africana). L'écologie de la hyène y est largement influencée par la localisation des points d'eau artificiels, des carcasses d'éléphants et des lions. Les hyènes sélectionnent les habitats riches en proies et près des points d'eau, tout comme le font les lions qu'elles n'évitent que dans des conditions extrêmes de vulnérabilité et de risques. Les carcasses d'éléphants représentent une ressource alimentaire majeure pour les hyènes qui en ont augmenté leur utilisation en réponse à une augmentation de la compétition avec les lions. La disponibilité de ces carcasses facilite probablement la coexistence entre les deux carnivores. Les rencontres avec les lions autour de carcasses sont communes et les deux espèces peuvent rester à proximité pendant plusieurs nuits consécutives. En revanche, les rencontres non liées aux carcasses sont de très courte durée et les deux prédateurs s'éloignent rapidement l'un de l'autre. Contrairement à l'hypothèse classique, les hyènes n'évitent pas les lions de manière systématique. Les interactions entre les deux espèces sont complexes et les hyènes répondent aux lions de manière dynamique et réactive plutôt que prédictive. Bien que les lions soient leur plus grand compétiteur, les hyènes restent à proximité dans certaines circonstances, car ils représentent une source alimentaire grâce au charognage et au kleptoparasitisme. Ces résultats apportent de nouvelles connaissances sur les mécanismes de coexistence et d'interactions entre grands carnivores ainsi que sur l'impact potentiel des décisions de gestion sur leur écologie qui peuvent être utiles pour leur conservation / Being at the top of the food chain, apex predators have the potential to influence the whole community structure through food webs, even within their own guild. In Africa, lions (Panthera leo) and spotted hyaenas (Crocuta crocuta, hyaenas hereafter) are the largest and most numerous predators, with hyaenas often thought to be subordinate to the larger lion Never the less, our understanding of their interactions is limited, even more in wooded ecosystems. This work focuses on identifying the mechanisms allowing for hyaenas and lions to coexist, such as resource and habitat partitioning. The main hypothesis is that hyaenas should avoid lions both spatially and temporally. A literature review shows that despite the high potential for exploitative and interference competition (high range and diet overlaps), hyaenas are present at nearly all sites occupied by lions and their densities are positively correlated. I collected data on hyaena and lion ecology, through direct observations and GPS collars, during 2.5 years of fieldwork in Hwange National Park (HNP), Zimbabwe. HNP is characteristic of a semi-arid dystrophic wooded savanna dominated by elephants (Loxodonta africana). In HNP, hyaena ecology is largely influenced by the location of artificial waterholes, elephant carcasses and lions. Hyaenas select for habitats where prey are abundant and locations close to artificial waterholes, as do lions. Hyaenas only spatially avoid lions in extreme conditions of vulnerability and risk. Elephant carcasses are a major source of food for hyaenas and their used increased during a period of increased intraguild competition with lions, which lead to switch in hyaena foraging strategy from active hunting to scavenging. The presence of large carcasses is probably promoting coexistence between the two large carnivores. Encounters with lions at carcasses are common and can occur during several consecutives nights with the two predators staying in the vicinity of each other. However, when not related to food, encounters are very short with both predators often moving away after being in contact. In stark contrast with the classical hypothesis, hyaenas in HNP do not show a general pattern of lion avoidance. Interactions between these two species are complex and hyaenas appear to respond to lion presence is reactive rather than predictive and very dynamic. Even though lions are their main competitors, in some circumstances hyaenas stay in their vicinity, as they can also be a source of food through scavenging and kleptoparatism. These results bring some light on the mechanisms of interaction and coexistence between large carnivores as well as the impact on management decisions on their ecology that could prove useful for planning their conservation

Le principal objectif de ce travail était de déterminer l’efficience d’utilisation de l’eau (WUE) de diverses espèces d’acacias d’origine Australienne et Sahélienne par la discrimination isotopique au niveau de la feuille (Δ13Cf) et par différentes techniques de mesure. Les acacias ont montré une forte variabilité interspécifique de Δ13Cf. Cette variabilité a été confirmée par les mesures directes d’échanges gazeux au niveau des feuilles (efficience intrinsèque d’utilisation de l’eau, Wi) et par des mesures effectuées au niveau de la plante entière (efficience de transpiration, TE). Une forte variabilité interspécifique des traits foliaires(densité stomatique DS, proportion d’azote dans les feuilles %N, surface massique SLA, assimilation nette du CO2 à la saturation Asat, conductance stomatique en vapeur d’eau à la saturation gssat) et de la croissance (ratio biomasse racinaire sur biomasse aérienne R/S) a également été constatée entre les espèces. WUE était pratiquement contrôlée par gssat.L’hypothèse selon laquelle les espèces se développant dans les zones arides présenteraient une WUE plus élevée n’a pas été vérifiée. Au contraire, les espèces des zones semi-humides ont présenté une WUE plus élevée que celles de zones semi-arides et arides. / The main objective of this work was to compare water use efficiency (WUE) among various Australian and Sahelian acacia species using isotope discrimination at leaf level (Δ13Cf) and various methods of measurement. Acacia species exhibited a large inter-specific variability of Δ13Cf. This variability was confirmed by direct leaf gas exchange measurements (intrinsic water use efficiency, Wi) and by measurement at the whole plant level (transpiration efficiency, TE). A large interspecific variability of leaf traits (stomatal density DS, leaf nitrogen concentration %N, specific leaf area SLA, net CO2 assimilation of the saturation Asat, stomatal conductance for water vapor of the saturation gssat) and growth characteristics (root shoot biomass ratio R/S) has also been reported. WUE was controlled for gssat. The hypothesis that the species from arid areas exhibit higher WUE was not confirmed. In contrast, the species from semi-wet area exhibited a higher WUE than those from semi-arid and arid zones

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