Tropical rainforests contain exceptionally high biodiversity and account for >30% of the world's carbon fixed by photosynthesis. Consequently, there are compelling reasons to deepen our understanding of the mechanisms that maintain these highly diverse forests and of the potential long-term threats to their preservation. An important process shaping tropical plant communities is negative density dependence (NDD). NDD occurs when plant performance is negatively impacted by increased neighbourhood density. Reduced performance at high neighbourhood density is thought to arise through ecological interactions between plants and their natural enemies. Thus in a healthy ecosystem, trophic interactions play vital roles as mechanisms driving NDD and are important as dispersers facilitating escape from NDD mortality. However, interruption to ecological processes caused by human activities, such as hunting, can perturb NDD interactions and cause cascading effects throughout an ecosystem. In my thesis I investigate the role of dispersal and mortality in NDD dynamics of tropical tree communities, as well as investigating local and global impacts of removing ecological interactions in tropical rainforests. In my thesis, I begin by addressing the presence and variation in strength of NDD among tree species and ontogenetic stages, the mechanisms driving NDD, and the role of trophic interactions in this process. The Janzen-Connell hypothesis predicts that host-specific natural enemies drive NDD by selectively reducing conspecific density, and increase diversity by suppressing competitive exclusion, thus allowing heterospecifics to persist. In chapters 2 and 3 of this thesis, I show that mortality driven by conspecific NDD is prevalent at the early life stages, and this effect is considerably stronger during the year after germination. Furthermore, this process is driven exclusively by host-specific fungal pathogens, which cause mortality selectively among conspecifics and drive diversity. As seedlings age beyond their first year, NDD interactions become less impacted by conspecifics but are impacted by closely related neighbours or by general neighbourhood density, representing changes in the mechanism driving NDD as seedlings age, and a decline in host-specificity of natural enemies. Equally, relative growth rates (RGR) are reduced under high neighbourhood density irrespective of species identity. Results suggest insect herbivores are the strongest driver of reduced RGR but not mortality under increased neighbourhood density. As a consequence of stronger inter than intra-specific NDD effects on RGR, insects had no impact on seedling diversity in the short term. This study supports assertions that regionally rare species experience stronger NDD than common species, accounting for the high variability in species relative abundance in the tropics. In the second part of my thesis, I address the role of large vertebrate dispersers in shaping tropical tree communities and the consequences of defaunation for tree assemblage and carbon storage. Dispersal allows seeds to escape NDD and persist to reproductive maturity and is therefore vital for the maintenance of diversity. Vertebrates disperse the seeds of more than 70% of neo-tropical tree species. However, many large vertebrates are becoming scarce due to widespread hunting. The decline of large vertebrates and their role as dispersers is predicted to alter tree community composition. Additionally, large vertebrates are responsible for the dispersal of large-seeded species, which are linked to species with high wood density. With wood density positively associated with carbon storage, there is a potential cascading influence of defaunation on global carbon storage. We investigate the consequences of declining large vertebrate mortality agents in chapter 3, and the consequences of declining large vertebrate dispersers in chapters 4 and 5. Although community composition is altered in a defaunated forest, species dispersed by extirpated fauna do not appear to drive this. In fact we find that many species thought to be heavily reliant on extirpated fauna manage to persist. Although it is thought that the simultaneous loss of seed predation from large terrestrial vertebrates may create compensatory effects, we found little support for this, with an absence of large terrestrial vertebrates driving only temporary changes to species diversity. Neither a loss of large frugivores or large-seeded species lead to declines in species with high wood density, but we detect a worrying decline in large stemmed species, which has negative implications for carbon storage. Overall, my thesis highlights the importance of NDD and trophic interactions, particularly fungal pathogens, at the early life stages in shaping tropical tree communities and in maintaining diversity. I provide evidence that the removal of trophic interactions among larger natural enemies and dispersers does not impact community assemblage in the directional manner found in previous studies. I provide evidence for the variability in response to trophic interactions among species and ontogenetic stages. I show disproportionate relative importance among natural enemies and dispersers in the maintenance of tropical tree assemblage, with implications for conservation and for assessing the consequences for tree diversity under the influence of degradation.

Knowledge of offspring production (recruitment) is fundamental to understanding and forecasting the dynamics of a population. In this thesis, I focus on two demographic characteristics of fish stocks that are important to recruitment: population density and age structure. First, populations produce more recruits at low density, but quantifying this response has proven difficult. Using data from hundreds of populations of walleye (Sander vitreus), an economically important freshwater fish, I demonstrate that the growing-degree-day metric (a temperature index) is better than age at explaining variation in density-dependent growth and maturity both within and among populations. I then incorporate multi-lake measures of density-dependent life history change into a temperature-based biphasic model of growth and reproduction to predict sustainable rates of mortality for walleye throughout most of their range. Second, the age (or size) structure of a population may also affect recruitment because of positive effects of maternal age on offspring production and survival; however, evidence for these ‘maternal influences’ on recruitment is limited. Using both an analytical model and a meta-analysis of stock-recruitment data from 25 species of exploited marine fish, I show that (i) maximum reproductive rate increased with the mean age of adults in a population, and (ii) the importance of age structure increased with a species’ longevity. I then demonstrate a similar effect of maternal influences on reproductive rate in a detailed study of Lake Erie walleye. By highlighting the importance of fisheries-induced demographic change to recruitment, this thesis provides insight into past and present failures. However, it also demonstrates clearly the benefits of proactive management strategies that (i) identify and respect the limits of exploitation, (ii) protect from exploitation reproductively valuable individuals—principles that apply generally to any freshwater, marine, or terrestrial species that is of recreational, commercial, or conservation value.

Many mammals are social. The most basic social behaviour is when the actions of one conspecific are directed toward another, what we call the dyadic interaction. Both intrinsic and extrinsic factors may affect an individuals propensity to interact with other members of a population. I used a social cervid, elk (Cervus elaphus), as a model species to test the importance of intrinsic and extrinsic factors of sociality on dyadic interactions. Dyadic interactions not only form the basis for social structure and information transfer within a population, but are also routes of pathogen transmission. My objective in this thesis was thus twofold: to improve our understanding of sociobiology, but also to gain insight into how sociality may underlie the transmission of communicable wildlife disease. I used a hierarchical, autecological approach from DNA, through individual, dyad, group, subpopulation, and ultimately population to explore the effects of intrinsic factors (e.g., sex and pairwise genetic relatedness) and extrinsic factors (e.g., season, conspecific density, habitat, and elk group size) on sociality. Elk in Riding Mountain National Park (RMNP), Manitoba, Canada, are exposed to the causal agent of bovine tuberculosis (Mycobacterium bovis; TB); however, spatial variation in apparent disease prevalence suggests that TB can only persist in one subpopulation within the Park. Using the natural RMNP system and a captive elk herd that I manipulated, I explored factors that influence interaction rates and durations (as a proxy for pathogen transmission) among elk. Sexual segregation in elk results in seasonal and sex-based differences in interaction rate and duration; with interactions peaking in autumn-winter for both sexes. Female-female dyads interact more frequently than male-male dyads. However, male-male dyads interact for longer durations than do female-female dyads. Interaction rate and duration did not covary with pairwise relatedness. Conspecific density also had sex-specific results for interaction rate and duration. Whereas male-male dyadic interaction rates increase with density, female-female dyads increase until they reach a threshold and subsequently reduce their interaction rates at high density. I observed density dependence in interaction rates in experimental trials and from field data. Furthermore, social networks revealed that social familiarity (i.e., heterogeneity of interactions) can be both frequency- and- density dependent depending on the strength of the relationship (i.e., number of repeat interactions). Density also affected the likelihood that an interaction would occur; however, this was modified by vegetation association used by elk. My results reveal several ecological and evolutionary implications for information transfer and pathogen transmission. In particular, I show that seasonal inter-sex routes of transfer may exist and that transfer is likely to be density-dependent. Finally, I conclude that such transfer is modified by available resources.

Many mammals are social. The most basic social behaviour is when the actions of one conspecific are directed toward another, what we call the dyadic interaction. Both intrinsic and extrinsic factors may affect an individuals propensity to interact with other members of a population. I used a social cervid, elk (Cervus elaphus), as a model species to test the importance of intrinsic and extrinsic factors of sociality on dyadic interactions. Dyadic interactions not only form the basis for social structure and information transfer within a population, but are also routes of pathogen transmission. My objective in this thesis was thus twofold: to improve our understanding of sociobiology, but also to gain insight into how sociality may underlie the transmission of communicable wildlife disease. I used a hierarchical, autecological approach from DNA, through individual, dyad, group, subpopulation, and ultimately population to explore the effects of intrinsic factors (e.g., sex and pairwise genetic relatedness) and extrinsic factors (e.g., season, conspecific density, habitat, and elk group size) on sociality. Elk in Riding Mountain National Park (RMNP), Manitoba, Canada, are exposed to the causal agent of bovine tuberculosis (Mycobacterium bovis; TB); however, spatial variation in apparent disease prevalence suggests that TB can only persist in one subpopulation within the Park. Using the natural RMNP system and a captive elk herd that I manipulated, I explored factors that influence interaction rates and durations (as a proxy for pathogen transmission) among elk. Sexual segregation in elk results in seasonal and sex-based differences in interaction rate and duration; with interactions peaking in autumn-winter for both sexes. Female-female dyads interact more frequently than male-male dyads. However, male-male dyads interact for longer durations than do female-female dyads. Interaction rate and duration did not covary with pairwise relatedness. Conspecific density also had sex-specific results for interaction rate and duration. Whereas male-male dyadic interaction rates increase with density, female-female dyads increase until they reach a threshold and subsequently reduce their interaction rates at high density. I observed density dependence in interaction rates in experimental trials and from field data. Furthermore, social networks revealed that social familiarity (i.e., heterogeneity of interactions) can be both frequency- and- density dependent depending on the strength of the relationship (i.e., number of repeat interactions). Density also affected the likelihood that an interaction would occur; however, this was modified by vegetation association used by elk. My results reveal several ecological and evolutionary implications for information transfer and pathogen transmission. In particular, I show that seasonal inter-sex routes of transfer may exist and that transfer is likely to be density-dependent. Finally, I conclude that such transfer is modified by available resources.

Knowledge of offspring production (recruitment) is fundamental to understanding and forecasting the dynamics of a population. In this thesis, I focus on two demographic characteristics of fish stocks that are important to recruitment: population density and age structure. First, populations produce more recruits at low density, but quantifying this response has proven difficult. Using data from hundreds of populations of walleye (Sander vitreus), an economically important freshwater fish, I demonstrate that the growing-degree-day metric (a temperature index) is better than age at explaining variation in density-dependent growth and maturity both within and among populations. I then incorporate multi-lake measures of density-dependent life history change into a temperature-based biphasic model of growth and reproduction to predict sustainable rates of mortality for walleye throughout most of their range. Second, the age (or size) structure of a population may also affect recruitment because of positive effects of maternal age on offspring production and survival; however, evidence for these ‘maternal influences’ on recruitment is limited. Using both an analytical model and a meta-analysis of stock-recruitment data from 25 species of exploited marine fish, I show that (i) maximum reproductive rate increased with the mean age of adults in a population, and (ii) the importance of age structure increased with a species’ longevity. I then demonstrate a similar effect of maternal influences on reproductive rate in a detailed study of Lake Erie walleye. By highlighting the importance of fisheries-induced demographic change to recruitment, this thesis provides insight into past and present failures. However, it also demonstrates clearly the benefits of proactive management strategies that (i) identify and respect the limits of exploitation, (ii) protect from exploitation reproductively valuable individuals—principles that apply generally to any freshwater, marine, or terrestrial species that is of recreational, commercial, or conservation value.

Cette thèse s'intéresse à l'étude des stratégies d'introduction de populations dans l'environnement. Les deux principaux contextes présentés sont la lutte biologique et la réintroduction d'espèces. Si ces deux types d'introduction diffèrent, des processus biotiques et abiotiques les influencent de manière similaire. En particulier les populations introduites, souvent de petite taille, peuvent être sensibles à diverses formes de stochasticité, voire subir une baisse de leur taux de croissance à faible effectif, ce qu'on appelle « effet Allee ». Ces processus peuvent interagir avec les stratégies d'introduction des organismes et moduler leur efficacité. Dans un premier temps, nous modélisons le processus d'introduction à l'aide de systèmes dynamiques impulsionnels : la dynamique de la population est décrite par des équations différentielles ordinaires qui, à des instants donnés, sont perturbées par des augmentations soudaines de la taille de la population. Cette approche se concentre sur l'influence des effets Allee sur les populations isolées (réintroduction) ou dans un cadre proie-prédateur (lutte biologique). Dans un second temps, en nous concentrant sur l'aspect réintroduction, nous étendons ce cadre de modélisation pour prendre en compte des aspects stochastiques liés à l'environnement ou aux introductions elles-mêmes. Finalement, nous considérons un modèle individu centré pour étudier l'effet de la stochasticité démographique inhérente aux petites populations. Ces différentes approches permettent d'analyser l'influence de la distribution temporelle des introductions et ainsi déterminer les stratégies qui maximisent les chances de succès des introductions. / This thesis investigates introduction strategies of populations in the environment. Two main situations are considered: biological control and species reintroduction. Although these two kinds of introductions are different, many biotic and abiotic processes influence them in a similar way. Introduced populations are often small and may be sensitive to various stochastic factors. Further, small populations may suffer from a decrease of their growth rate when the population is small, a feature called "Allee effect". These processes may interact with introduction strategies and modulate their efficiency. First, we represent the introduction process using impulsive dynamical systems: population dynamics are described by ordinary differential equations that are disrupted at some instants by instantaneous increases of the population size. This approach focuses on the influence of Allee effects on single-species (reintroduction) or predator-prey interactions (biological control). Then, we concentrate on the reintroduction approach and extend the previous deterministic framework to take into consideration stochastic factors arising from the environment or from introductions themselves. Finally, we consider an individual-based model to study the effects of demographic stochasticity which is inherent to small populations. These different approaches allow to investigate the temporal distribution of introductions and determine which introduction strategies maximize the probability of success of introductions.

Large carnivores are among the most challenging species to conserve in our modern and crowded world. Having large spatial requirements and living in low density, they generally require wide and relatively undisturbed areas. In Europe, one of the most anthropized areas of the planet, these needs must be fulfilled in a complex human-dominated landscape. The reintroduced brown bear population living in the Central Alps represents one of the most emblematic examples of a constrained carnivore: despite a steady population increase in the first few years after reintroduction, the population did not substantially expand its range, nor has the Alpine-Dinaric metapopulation been reestablished as envisioned. Although humans have lived in the Alps for centuries, little is known about their impact on the bear population. In other environments humans are known to function as a “super-predator” by changing habitats, competing for space, consuming resources, and harvesting, which alters the ecological niche of animals, especially large carnivores. This dissertation aims to evaluate this phenomenon by assessing the effects of human disturbance on brown bears in the Alps. Anthropogenic disturbance is generally assessed by structural proxies, such as infrastructure and land use, which overlook the impact of human presence. In the first Chapter, we developed the Cumulative Outdoor activity Index (COI) to derive anthropogenic disturbance using crowdsourced data by Strava and validated it with ground truth observations derived from a local camera trapping survey. The intensity of COI provided an effective measure of functional anthropogenic disturbance, and it outperformed all commonly-used proxies of structural disturbance in predicting bear habitat use. When displacement is not an option because of habitat limitations and social mechanisms, bear mobility may clash with human activity. During the moments of lowest mobility, such as resting periods, animals have decreased ability to cope with risky situations, and therefore the selection of suitable resting areas is crucial for the long-term survival of individuals. In the second Chapter, we measured multi-scale response to risk perception (i.e., COI) and resource proximity using bedding sites by GPS radio-collared adult brown bears in the Alps. To map resources across the study area, we developed a GIS-database combining spatial and non-spatial ecological information to map fruit availability. We observed that bears apply a security-food trade-off strategy, avoiding functional anthropogenic disturbance while in proximity to resources. In the third Chapter, we explicitly tested the effect of an abrupt interruption of human mobility during COVID-19 lockdown on bears’ use of ecological corridors. Using bear occurrences reported to local authorities during the recent COVID-19 outbreak, we observed that bears used human-dominated areas more frequently, approached more intensively hot spots for road crossing network, and used areas further from the population core areas more often than previous years, suggesting that connectivity increased with reduced human mobility. In a comparatively human-free system, for the fourth Chapter we used longitudinal morphometric data to analyze drivers of changes in body mass as part of an international collaboration with biologists studying the grizzly bear in the Greater Yellowstone Ecosystem. Specifically, we analyzed changes in lean body mass and fat percentage during years of major ecosystem perturbations. We observed that individual lean body mass during the last two decades was primarily associated with population density, but not body fat percentage, showing density-dependent factors. Our combined findings (Chapters 1-3) showed that brown bears have to adapt their space use, movement, and resource proximity as a result of functional anthropogenic disturbance. In Chapter 4 we explored one effect of unconstrained bear space use on individuals, as manifested through density-dependent effects on body size. In the Alps, however, we found multiple instances of the human-super predator outcompeting bears so as to make density-dependent effects likely less significant as compared to human-caused mortality. These effects could occur in a variety of socio-ecological contexts across Europe, jeopardizing the long-term establishment of both newly reintroduced bear populations, as well as spatially limiting those naturally present in the environment. In response to disturbance, bears have had to reduce their ecological niche in human-dominated landscapes. Allowing humans and bears to coexist in the same landscape is a challenging task, but it is essential for the long-term survival of this newly reintroduced population that are otherwise at risk of extinction.

Bank voles, grey-sided voles, and field voles had synchronous 3-4 year density cycles with variable amplitudes which averaged about 200-fold in each species. Cycles of vole predators (red fox and Tengmalm's owl), and their (foxes') alternative prey (mountain hare and forest grouse) lagged behind the vole cycles. The nomadic Tengmalm's owl responded with a very rapid and strong numerical increase to the initial cyclic summer increase of voles (the owl’s staple food). Owl breeding densities in the springs were highly correlated with vole supply in the previous autumns. This suggested that the number of breeding owls was largely determined in the autumn at the time of the owl's nomadic migrations, and that immigration was crucial for the rapid rise in owl numbers. The owl's numerical response was reinforced by the laying of earlier and larger clutches when food was plentiful. In addition, the owl has an early maturation at one year of age. The transition between subsequent vole cycles was characterized by a distinct shift in rate of change in numbers from low to high or markedly higher values in both summer and winter. Regulation increased progressively throughout the cycle since the rate of change decreased continuously in the summers. Moreover, there was a similar decrease of the rate of change in winter. Rate of change was delayed density-dependent. The delayed density-dependence had an 8 month time-lag in the summers and a 4 month time-lag in the winters relative to the density in previous autumns and springs, respectively. These findings suggest that vole cycles are likely to be generated by a time-lag mechanism. On theoretical grounds, it has been found that a delayed density- dependence of population growth rate with a 9 month time-lag caused stable limit cycles with a period between 3 and 4 years. Some mechanisms for the delayed density-dependence are suggested and discussed. The mechanisms are assumed to be related to remaining effects of vole populations past interactions with predators, food supplies, and/or diseases. Unlike the other voles, the bank vole had regular and distinct seasonal declines in density over winter. These declines are proposed to be due to predation, mainly by Tengmalm's owl. Supranivean foraging for epiphytic tree lichens and conifer seeds most likely explains why this species was frequently taken by the owl under snow-rich conditions. The alternative prey hypothesis predicts that a reduction of predator numbers should increase the number of alternative prey. Alternative prey should be less effectively synchronized to the vole cycle by predation at declining and low vole (main prey) densities; they may also lose their 3-4 year cyclicity. The appearance of sarcoptic mange among foxes in northern Sweden in the mid 1970s provided an opportunity to "test" these ideas, and these were found to be supported. In areas with highest mange infection rates, foxes declined markedly from the late 1970s to mid 1980s, whereas hare numbers rose rapidly and appeared non-cyclic. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1991, härtill 7 uppsatser</p> / digitalisering@umu

Une question fondamentale en écologie des populations est l’identification des facteurs influençant la dynamique d’une population. L’objectif principal de cette thèse est de déterminer quelles sont les réponses démographiques et populationnelles de prédateurs marins supérieurs face aux fluctuations d’abondance de leurs proies, aux variations climatiques, à la densité-dépendance tout en tenant compte de l’hétérogénéité inter et intra-individuelle (âge, expérience, sexe, qualité ou stratégie). Pour ce faire, nous nous baserons sur l’analyse de suivis à long-terme individuels et populationnels d’oiseaux marins longévifs et prédateurs apicaux phylogénétiquement très proches dans deux biomes contrastés : le labbe de McCormick Catharacta maccormicki sur l’archipel de Pointe Géologie en Antarctique et le labbe subantarctique Catharacta lonnbergi sur l’archipel des Kerguelen en milieu subantarctique. Nous tirerons parti d’estimations d’abondances de leurs proies respectives : le manchot Adélie Pygoscelis adeliae et le manchot empereur Aptenodytes forsteri en Antarctique, et le pétrel bleu Halobaena caerulea et le prion de Belcher Pachyptila belcheri à Kerguelen. Ces jeux de données offrent une opportunité unique de pouvoir déterminer et quantifier simultanément les différentes sources de variabilité dans les changements de taille de populations naturelles occupant l’un des niveaux trophiques les plus élevés des réseaux alimentaires antarctiques et subantarctiques. Nous avons mis en évidence de la variation dans plusieurs traits vitaux des deux populations influencées par les performances des individus et de l’hétérogénéité individuelle latente. Nous discutons des mécanismes par lesquels la variabilité climatique, l’abondance de proie et la densité de population peuvent affecter différentiellement les différentes classes d’âges de chaque trait vital, et les conséquences potentielles de futurs changements environnementaux. / A fundamental endeavor in population ecology is to identify the drivers of population dynamics. The main objective of this thesis is to determine what are the demographic and population responses of superior marine predators to the fluctuations of their prey abundance, to climatic variations, to density-dependence while taking into account inter and intra individual heterogeneity (age, experience, sex, quality or strategy). To do this, we analysed long-term individual and population-based monitoring of long-lived seabirds and phylogenetically close apical predators in two contrasting biomes: the south polar skua Catharacta maccormicki at Pointe Géologie archipelago, Antarctica, and the brown skua Catharacta lonnbergi on the sub-Antarctic Kerguelen Archipelago. We will use direct abundance of their respective prey: Adélie penguin Pygoscelis adeliae and emperor penguin Aptenodytes forsteri in Antarctica, and the blue petrel Halobaena caerulea and the thin-billed prion Pachyptila belcheri prion in Kerguelen islands. These datasets provide a unique opportunity to simultaneously disentangle and quantify the different sources of variability driving variation in natural populations occupying one of the highest trophic levels of the Antarctic and sub-Antarctic food webs. We found variation in several vital traits of both populations influenced by individual performance and latent individual heterogeneity. We discuss the mechanisms by which climatic variability, prey abundance, and population density can differentially affect the different age classes of each age class, and the potential consequences of future environmental changes.

Made available in DSpace on 2016-03-15T19:26:44Z (GMT). No. of bitstreams: 1 Patricia Fabian Holzmann.pdf: 616808 bytes, checksum: e166252bee6ff56d9a6645cc9d778c3c (MD5) Previous issue date: 2009-03-03 / This study has analyzed the service franchising enterprises evaluating factors that influence the survival rate of this population under the Organizational Ecology theory. The dynamics of the evolution process of this population was analyzed considering the density dependence model connected to legitimation and competition. Such factors, as well as size, were tested in statistic models (panel, logit and probit) using the data base developed with the information presented in the Guias da Associação Brasileira de Franquias between 1996 and 2007, to evaluate their impact over the population survival rate. Other relevant factors raised in Evolutionary Economics and Service Market Organization were also discussed. / Este estudo analisou as franquias de serviços avaliando os fatores que influenciam na taxa de sobrevivência dessas empresas sob a ótica da Ecologia Organizacional. A dinâmica da evolução da população de franquias de serviços foi avaliada com base na densidade da população e processos de legitimação e competição. Tais fatores, assim como o tamanho, foram testados em modelos estatísticos (modelo econométrico de painel, logit e probit) utilizando base de dados desenvolvida com base nos Guias da Associação Brasileira de Franquias entre o período de 1996 e 2007, para avaliar seu impacto sobre a taxa de sobrevivência da população. Com base nas teorias de Economia Evolucionária e Organização de Mercado em Serviços outros fatores relevantes para a sobrevivência das franquias de serviço também foram discutidos.