The concept of regulation in ecosystems has been given considerable attention in the ecological literature, but no formal treatment has been offered. This study proposes a rigorous definition of regulation which is derived from the mathematics of information and communication theory. A theoretical, mathematical equivalent of the definition is also offered which implies serious limitations as to the value of most traditional laboratory population studies and deterministic population models in understanding regulation in ecosystems. The empirical validity of this theoretical equivalence is tested through use of a competition model of two diatoms. Other observations concerning the relationship between environmental variability and regulation are also reported.

<p>Biodiversity in forests depends on long canopy continuity and existence of different elements which function as substrates for varying organisms. Bryophytes often occupy specific substrates with a patchy distribution. The aim of this thesis was to increase the ecological knowledge about two threatened moss species; <i>Buxbaumia viridis</i>, inhabiting decaying wood, and <i>Neckera pennata</i>, inhabiting bark of base-rich deciduous trees. </p><p>Establishment from spores was investigated in <i>Buxbaumia viridis</i> and <i>Neckera pennata</i> and models were created to predict germination of spores as a function of pH and water potential. The effects of pH, phosphorus and nitrogen concentration were studied in <i>Buxbaumia viridis</i>, both on spore germination and on sporophyte occurrences in the field. Colony growth in relation to precipitation and microhabitat variables was studied in <i>Neckera pennata</i>, and a model was used to predict growth of colonies over time. Metapopulation dynamics of <i>Buxbaumia viridis</i> were analyzed as an effect of precipitation, habitat quality and patch quantity. A spatial explicit patch occupancy model was constructed to simulate metapopulation sizes and extinction risk over 100 years.</p><p>The quality of the substrate was very important for spore establishment. Germination success increased with increasing pH in both species. <i>Buxbaumia viridis</i> was less sensitive to low pH than <i>Neckera pennata</i> when water was freely available. However, there was a strong interaction between pH and water potential in prediction of the final cumulative germination: the spores reacted positively to one factor only when the other factor was in a favourable range.</p><p>Precipitation, moisture holding capacity and interference competition were the main factors affecting colony growth of <i>Neckera pennata</i>. <i>Buxbaumia viridis</i> showed large fluctuations in number of occupied patches among years. Both colonizations and extinctions were highly related to precipitation. Spore germination and sporophyte occurrences in the field were positively related to phosphorus concentration and pH of the substrate.</p>

Biodiversity in forests depends on long canopy continuity and existence of different elements which function as substrates for varying organisms. Bryophytes often occupy specific substrates with a patchy distribution. The aim of this thesis was to increase the ecological knowledge about two threatened moss species; Buxbaumia viridis, inhabiting decaying wood, and Neckera pennata, inhabiting bark of base-rich deciduous trees. Establishment from spores was investigated in Buxbaumia viridis and Neckera pennata and models were created to predict germination of spores as a function of pH and water potential. The effects of pH, phosphorus and nitrogen concentration were studied in Buxbaumia viridis, both on spore germination and on sporophyte occurrences in the field. Colony growth in relation to precipitation and microhabitat variables was studied in Neckera pennata, and a model was used to predict growth of colonies over time. Metapopulation dynamics of Buxbaumia viridis were analyzed as an effect of precipitation, habitat quality and patch quantity. A spatial explicit patch occupancy model was constructed to simulate metapopulation sizes and extinction risk over 100 years. The quality of the substrate was very important for spore establishment. Germination success increased with increasing pH in both species. Buxbaumia viridis was less sensitive to low pH than Neckera pennata when water was freely available. However, there was a strong interaction between pH and water potential in prediction of the final cumulative germination: the spores reacted positively to one factor only when the other factor was in a favourable range. Precipitation, moisture holding capacity and interference competition were the main factors affecting colony growth of Neckera pennata. Buxbaumia viridis showed large fluctuations in number of occupied patches among years. Both colonizations and extinctions were highly related to precipitation. Spore germination and sporophyte occurrences in the field were positively related to phosphorus concentration and pH of the substrate.

Complexity science has come into the limelight in recent years as the scientific community begins to grapple with higher-order natural phenomena that cannot be fully explained via the behaviour of components at lower levels of organization. Network modeling and analysis, being a powerful tool that can capture the interconnections that embody complex behaviour, has therefore been at the forefront of complexity science. In ecology, the network paradigm is relatively young and there remain limitations in many ecological network studies, such as modeling only one type of species interaction at a time, lack of realistic network structure, or non-inclusion of community dynamics and environmental stochasticity. I introduce bioenergetic network models that bring together for the first time many of the fundamental structures and mechanisms of species interactions present in real ecological communities. I then use these models to address some outstanding questions that are relevant to understanding ecological networks at the systems level rather than at the level of subsets of interactions. Firstly, I find that realistic red-shifted environmental noise, and synchrony of species responses to noise, are associated with increased variability in ecosystem properties, with implications for predictive ecological modeling which usually assumes white noise. Next, I look at simultaneous species extinction and invasion, finding that as their individual impacts increase, their combined impact becomes decreasingly additive. In addition, the greater the impact of extinction or invasion, the lesser their reversibility via reintroduction or eradication of the species in question. For modifications of pairwise species interactions by third-party species, a phenomenon that has so far been studied one interaction at a time, I find that the many interaction modifications that occur concurrently in a community can collectively have systematic effects on total biomass and species evenness. Finally, examining a higher level of organization in the form of compartmentalized networks, I find that the relationship between intercompartment connectivity and the impacts of species decline depends considerably on network topology and whether the consumer-resource functional response is prey- or ratio-dependent. Overall, the results vary considerably across model communities with different parameterizations, underscoring the contingency and context dependence of nature that scientists and policy makers alike should no longer ignore. This work hopes to contribute to a growing multidisciplinary understanding, appreciation and management of complex systems that is fundamentally transforming the modern world and giving us insights on how to live more harmoniously within our environment.

Examiner les liens existant entre la variabilité environnementale, les traits d'histoire de vie, la dispersion et les décisions d'accouplement est un enjeu central en Ecologie et en Evolution. J'ai exploré ces questions chez un amphibien, le sonneur à ventre jaune (Bombina variegata). Dans le premier volet de ma thèse, je me suis intéressé à l'influence des variations spatiotemporelles de l'environnement sur les patrons de covariation entre les traits d'histoire de vie, la dispersion et les types comportementaux à l'échelle inter-populationnelle. J'ai examiné comment le degré de stochasticité interannuel de l'habitat de reproduction régule le positionnement des populations le long du slow-fast continuum et génère des syndromes de dispersion parmi les populations. J'ai ensuite analysé les conséquences de ces syndromes sur les patrons de différenciation génétique au sein des populations. Dans le second volet de ma thèse, je me suis intéressé au rôle de la canalisation environnementale dans la stratégie d'histoire de vie de B. variegata et j'ai évalué comment diverses formes de variations météorologiques pouvaient affecter la dynamique de différentes populations. Dans chacune d'elles, j'ai mesuré l'impact de facteurs météorologiques sur des paramètres démographiques tels que la survie, le recrutement et les probabilités de reproduction. Dans le troisième et dernier volet de ma thèse, je me suis intéressé au choix d'accouplement des femelles, en examinant successivement les hypothèses de bons gènes et de gènes compatibles puis en me focalisant sur le rôle de la qualité et de la disponibilité des sites de reproduction sur les décisions d'accouplement des femelles / Investigating the links between environmental variability and life history traits, dispersal and breeding decisions is critical challenge for ecologists. I have examined this issue in anuran, the yellow-bellied toad (Bombina variegata). In the first part of my thesis, I have examined the influence of spatio-temporal variation of the environment on the covariation patterns between life history traits, dispersal and behavioral types at inter-population scale. I have investigated how the level of breeding habitat stochasticity may regulate the position of B. variegata populations along the slow-fast continuum and may promote dispersal syndromes among populations. Then I have analyzed the consequence of such dispersal syndromes on population genetic differentiation. In the second part of my thesis, I have focused on the role of the environmental canalization in the life history strategy of B. variegata and I have evaluated how various forms of weather variation (mean and extreme events) could affect the dynamics of different populations. In each studied populations, I have quantified the impacts of weather variation on various demographic parameters as survival, recruitment and breeding probabilities. In the third part of my thesis, I have investigated female mate choice in B. variegata by successively examining good genes and compatible gene hypotheses, and then by evaluating the role of breeding habitat quality and availability on mating decisions