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Depuis le début du 20ième siècle, les changements d'usage des terres, la disparition des prédateurs et les régulations de la chasse ont provoqué une augmentation des populations de cervidés dans les forêts tempérés et boréales. Ce phénomène, qui est un grand succès de la conservation de ces espèces, a toutefois conduit à des surabondances qui ont entrainé des effets négatifs en cascades sur la végétation et les communautés animales qui en dépendent.J'ai utilisé l'expérience naturelle qu'est l'introduction du cerf à queue noire sur l'archipel d'Haïda Gwaii pour étudier les conséquences de sa surabondance sur un écosystème tempéré peu perturbé par les activités anthropiques. J'ai ainsi pu mettre en évidence les contrôles descendants directs et indirects qu'exerce l'herbivore sur les Bryophytes (positifs), les plantes vasculaires (négatifs) et sur l'avifaune (négatifs) quand il n'est pas limité par les prédateurs ou la chasse.J'ai complété ces résultats par une analyse régionale sur 20 ans pour montrer que la perte de biodiversité enclenchée par la surabondance de ces cerfs était un phénomène d'érosion continu se prolongeant bien au-delà de l'impact initial. A l'échelle de l'Amérique du Nord, j'ai ensuite pu montrer, conformément aux prédictions faite à partir des études locales, qu'il existait une relation entre surabondance des populations d'ongulés et déclin de l'avifaune du sous-bois du continent. Enfin, j'ai analysé les suivis d'une expérience de réduction des densités de cerfs entamée sur deux îles il y a 13 ans. La végétation et l'avifaune se sont partiellement reconstituées démontrant qu'il est possible (1) de restaurer les réseaux trophiques fortement modifiés et (2) qu'une telle restauration si elle est possible prendra du temps et ne convergera pas (rapidement) vers un état initial. Afin de limiter les conséquences dommageables provoquées par la surabondance des cervidés, la conservation des prédateurs et l'augmentation de la chasse doivent être favorisés. / Since the past century land use changes, elimination of predators and hunting regulations triggered an increase of deer populations in temperate and boreal forests. This remarkable conservation success, lead to deer overabundance and to a cascade of negative effects on vegetation and on animal communities depending on it. I used the natural experiment provided by the introduction of black-tailed deer to Haida Gwaii to analyze the consequences of overabundant herbivore populations on temperate ecosystem only slightly modified by human activities. This unique situation allowed me to demonstrate the direct and indirect top-down effects that herbivores uncontrolled by predation or hunting exert on Bryophytes (positive) and Vascular plants (negative) as well as on songbirds (negative).I used an analysis of regional trends spanning over 20 years to show that biodiversity erosion caused by overabundant deer extends far beyond the initial impact. At the North-American scale I was able to establish a relationship between expanding deer populations and continent wide declines in understory birds. Finally I analyzed the results of an experimental reduction in deer populations initiated 13 years ago on two islands. The understory plants and songbirds responded positively and we show that (1) it is possible to restore trophic networks even after their dramatically modification, (2) that such a restoration while possible takes time and does not (rapidly) converge towards an identified initial state. From a practical standpoint I recommend that to mitigate negative effects of overabundant deer, predator conservation and hunting have to be promoted.

Archaeological and paleontological datasets are used in conservation to add time-depth to ecology. In central Texas several top carnivores including prehistoric Native American hunters have been extirpated or have had their historic ranges restricted, which has resulted in pest-level white-tailed deer (Odocoileus virginianus texana) populations in some areas. Predator extermination has dramatically reduced the average body size of members of the extant predator guild, and large carnivores most capable of hunting white-tailed deer are extirpated. Character release in the remaining “large” predatorsmesocarnivoresis a predicted outcome related to the adaptive vacuum at the top of the trophic hierarchy. Differences in body size of deer between prehistory and modernity are expected given that a lack of predation likely has increased intraspecific competition for forage among deer resulting in smaller body size today. In fact modern deer from settings without harvest pressure are significantly smaller than those from harvested areas and from prehistoric deer. From a natural history perspective, this research highlights potential evolutionary causes and effects of top-predator removal on deer populations and related components of biological communities in central Texas.

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. / In many temperate environments deer populations have been increasing, raising serious ecological and socio-economic concerns both locally and globally. Signs of density dependence are often observed in such populations, but deer abundance often remains high with regard to the dramatic degradation of the environment they have induced. This raises the question: How do deer do to adjust to the environmental changes they created? The present study addressed aspects of this question focusing on how deer manage their food resource in relation to predation risk. In addition to its consumptive effect (prey removal), predation is increasingly recognized for its non-consumptive effect on prey behavior and physiology, the importance of which is linked to the strength of the trade-off between foraging and predation risk. A better understanding on how deer manage food resource and predation risk in heavily browsed environment may thus help to better understand how deer maintain abundant populations in self-induced depleted environment.We tackled this question by studying Sitka black tailed deer (Odocoileus hemionus sitkensis) on three islands of the Haida Gwaii archipelago (B.C., Canada). These islands are devoid of the main natural predators of deer (wolves and cougars) and were colonized by deer over 60 years ago. At the time of the study, these islands presented contrasted levels of food and predation risk: on two islands, deer were predator-free but had strongly depleted their environment (safe/poor islands). On the third island, deer were culled by means of regular hunts and had access to a partially recovered forest understory in terms of food supply (risky/rich island).We considered four questions: 1) on what resources do abundant deer populations rely in heavily browsed environment?; 2) how do deer physiological stress response vary with either food stress or predation risk?; 3) do predator-naïve deer maintain anti-predator behaviors, like vigilance, in heavily browsed environments and how do they respond to predator olfactory cues?; and 4) how do predator-naïve deer respond to an experimental hunting for fear in a heavily browsed environment and how does it affect the vegetation? We showed that: 1) the subsidies from canopy litterfall and the annual growth from rhizomatous plants offered a large energy supply for deer and contributed to maintain abundant deer population in forests with depleted understory; 2) deer did not mount a physiological stress response in presence of either starvation or predation risks, and we suggested that behavioral and/or physiological adjustments allowed deer to mitigate their exposure to either stressor; 3) on safe/poor islands, deer maintained vigilance despite 60 years of isolation from predation. Predator-naïve deer avoided eating bait in presence of urine of wolf (dangerous) but not of bear (less dangerous). This suggested an innate threat-sensitive foraging strategy in deer. Deer also remained less time at the bait stations in presence of wolf urine but did not increase their vigilance levels. This suggested that deer were likely to manage risk more by space use than by vigilance; 4) In response to an experimental hunting for fear conducted on one of the safe/poor island, we showed that the deer less-tolerant to humans avoided the hunting area; The deer more-tolerant to human disturbance did not. This stressed the importance to consider the human-induced selection of behavioral traits during wildlife management. We also monitored the growth of four fast-growing coastal plant species and showed that the hunting for fear promoted the growth of half of them. This highlighted the intricate interaction among deer foraging behavior and plant characteristics and emphasized the importance of management targets in the choice of management tools. We discussed the long-terms effect of hunting as management tool for deer.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Agriculture expansion and intensification reassemble bird communities, including the loss of species, reduced diversity and the population increase of some species able to use the novel resources available. In some circumstances these species may be perceived as overabundant and conflict with human activities. This dissertation examines 1) the influence of the land use in agricultural landscapes in the abundance of eared dove and 2) the recognition of eared dove's populations as overabundant in the Southwestern of Brazil. The study was conducted in grain-producing regions comprising the part of the States of Rio Grande do Sul, Santa Catarina, Paraná and São Paulo. We counted birds along 50 routes, each comprising 12 counting stations, placed on secondary roads and relate occurrence and abundance with land uses. We applied questionnaires to farmers record their perception about damages by eared doves in agriculture. Our data demonstrated that the eared dove was the most abundant species, representing 48% of total individuals counted and also one of the most common, being found in 93% of samples. At the landscape scale, the abundance of eared doves was associated positively with routes crossing landscapes dominated by plantations in winter and negatively associated with routes with large tracts of forests and mixed farming in summer. At the local scale the abundance of doves in winter was greater in routes with higher frequency of maize plantations and in summer in routes with higher frequency of sugar cane and soybean plantations. Thus, the type of land use influenced the abundance of doves. Of the farmers interviewed, 41% claimed some kind of damage to their crops. Among these, 70% reported damages of less than 10% of the planted area. The highest percentage of positive responses about damages occurred in Paraná, with 54% of complaints. Sixty seven percent of the reported damages were located up to 100 km from nesting colonies. The probability of reporting damages decreases 1% every 10 km away from a colony. We consider that eared doves can be classified as overabundant in parts of the States of Paraná and São Paulo, where the agricultural landscape favor high abundance of this species all over the year and risk of conflicts with agriculture is higher. / A expansão da agricultura e a intensificação dos processos agrícolas levam a um rearranjo nas comunidades de aves, incluindo a perda de diversidade e o aumento populacional de espécies capazes de aproveitar os novos recursos disponíveis. Em algumas circunstâncias espécies podem apresentar um marcado aumento populacional passando a ser percebidas como superabundantes e conflitantes para atividades humanas. Esta dissertação analisa 1) a influência do uso do solo na abundância da pomba-de-bando e 2) a aplicação de conceitos de superabundância para esta espécie no Sudoeste do Brasil. A área de estudo abrangeu regiões produtoras de grãos dos Estados do Rio Grande do Sul, Santa Catarina, Paraná e São Paulo. Contamos aves em 50 rotas, cada uma com 12 estações de contagem, alocadas em estradas vicinais em meio a matrizes agrícolas e relacionamos ocorrência e abundância com a paisagem. Aplicamos questionários aos agricultores com a intenção de obter dados da percepção dos mesmos frente a danos causados pela pomba na agricultura. A pomba-de-bando foi a espécie mais abundante, representando 48% do total de indivíduos contados, e também uma das mais frequentes, sendo encontrada em 93% das amostras. Na escala da paisagem, mais ampla, a abundância esteve positivamente associada às áreas destinadas à agricultura e agropecuária no inverno e negativamente associada às áreas com grandes extensões de agropecuária e remanescente florestais no verão. Na escala local, mais fina, a abundância de pombas no inverno foi maior em rotas de contagem em que houve maior frequência de plantações de milho. Já no verão a abundância foi positivamente relacionada com a maior frequência de plantações de cana-de-açúcar e soja. Assim, o tipo de uso do solo na paisagem agrícola influenciou a abundância de pombas nas duas escalas. Dos respondentes aos questionários, 41% alegaram dano às suas plantações, sendo que 70% relataram danos inferiores a 10% da área plantada. O maior percentual de respostas positivas se deu no Paraná, com 54% de reclamações. Sessenta e sete por cento responderam sim a ocorrência de danos quando o local de aplicação do questionário estava a menos de 100 km de uma colônia de pombas. A probabilidade de reclamações decaiu 1% a cada 10 km de afastamento da colônia mais próxima. Consideramos que a pomba-de-bando pode ser classificada como superabundante somente em partes do Paraná e de São Paulo, onde a paisagem agrícola favorece uma alta abundância de pombas durante todo o ano e o risco de conflitos com a agricultura é maior.

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A study was conducted to determine what impact high white-tailed deer (Odocoileus virginianus) densities were having on the native grasslands of a tallgrass: aspen forest tract embedded within an agro-urban setting. Due to excessive spring moisture, row-crops were unavailable the first year. Using microhistological fecal analysis to determine dietary composition, deer were assessed to be placing the site’s favoured native plant species at risk of extirpation. Measuring woody stem abundance and height along and near the prairie: forest ecotone, deer were found to restructure woody growth but not directly influence encroachment rates. Indirectly, however, deer facilitated forest encroachment and prairie degradation through seed dispersal, nitrogen deposition, gap-dynamics, and trampling. Comparing dietary composition to nutritional data, deer grazed to maximize fitness, selecting foods high in IVDMD, minimizing energy expenditure, and optimizing CP. High crop CP was offset by intensively grazing particular native plants. ADF was an effective nutritional marker, not AIA.

A study was conducted to determine what impact high white-tailed deer (Odocoileus virginianus) densities were having on the native grasslands of a tallgrass: aspen forest tract embedded within an agro-urban setting. Due to excessive spring moisture, row-crops were unavailable the first year. Using microhistological fecal analysis to determine dietary composition, deer were assessed to be placing the site’s favoured native plant species at risk of extirpation. Measuring woody stem abundance and height along and near the prairie: forest ecotone, deer were found to restructure woody growth but not directly influence encroachment rates. Indirectly, however, deer facilitated forest encroachment and prairie degradation through seed dispersal, nitrogen deposition, gap-dynamics, and trampling. Comparing dietary composition to nutritional data, deer grazed to maximize fitness, selecting foods high in IVDMD, minimizing energy expenditure, and optimizing CP. High crop CP was offset by intensively grazing particular native plants. ADF was an effective nutritional marker, not AIA.