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In Atlantic salmon, space use of potential breeders stabilises population dynamics and shapes sexual selection. / L’utilisation de l’espace par les potentiels reproducteurs stabilise la dynamique de la population et façonne la sélection sexuelle chez le saumon Atlantique.Bouchard, Colin 14 December 2018 (has links)
La fragmentation des habitats ainsi que la réduction de leur disponibilité sont des menaces importantes pour les écosystèmes, notamment aquatiques. La disponibilité et la qualité des sites de fraie du saumon Atlantique peut donc être limitante dans certaines rivières. Après la migration en rivière, les femelles saumon vont chercher à s'établir dans un des sites de fraie disponibles. La distribution spatiale des femelles va alors influer sur la distribution spatiale des mâles reproducteurs qui vont chercher soit à monopoliser plusieurs femelles (pour les mâles dominants), soit à les approcher en adoptant un comportement "furtif" (pour les mâles satellites). L'accès des mâles aux femelles va donc dépendre de la distribution spatiale des femelles et des déplacements des mâles dans la rivière. La distribution des femelles va également jouer sur la distribution spatiale des juvéniles, les concentrant à certains endroits. Cette concentration peut augmenter la mortalité densité-dépendante qui modifie la dynamique de la population. Cette thèse avait pour but d'évaluer comment l'utilisation de l'espace des potentiels reproducteurs, c'est à dire les individus matures, influence la dynamique de la population et la sélection sexuelle.Des séries temporelles de stock (oeufs déposés) et de recrutement (juvéniles) pour la population de saumon de la Nivelle ont été associées à des mesures de l'agrégation spatiale des nids creusés par les femelles. L'effet des déplacements et de la distribution des reproducteurs sur leur participation à la reproduction a notamment été testé via la reconstruction du réseau d'interactions sexuelles dans la Nivelle.J'ai ainsi démontré que l'agrégation spatiale des nids influa sur la variabilité du recrutement mais pas sur le recrutement moyen. Cette agrégation qui résulte de l'agrégation des femelles a également été liée au nombre de reproducteurs ayant engendrés des juvéniles. Le réseau d'interactions sexuelles a permis de mettre en évidence une structure sociale locale au sein de la population. Cette structure et les compétiteurs présents pouvaient par exemple diminuer le succès reproducteur des mâles. Notamment, les tacons matures qui participent à la reproduction avant de migrer en mer renforçaient la compétition sexuelle dont les mâles dominants faisaient l'objet. Enfin, ces mêmes tacons matures adoptèrent des comportements spatiaux du fait de leur statut de maturité avec des individus bougeant peu et des individus se déplaçant vers l'amont. Ces comportements spatiaux influaient leur participation à la reproduction, l'étendue des domaines de vie et les déplacements vers l'amont augmentaient la probabilité de rencontrer une femelle.Mes résultats m'ont permis de mettre en évidence l'effet de l'utilisation de l'espace des potentiels reproducteurs sur la dynamique de la population et sur la sélection sexuelle. Ainsi, en combinant différentes échelles spatiales et temporelles il a été montré que l'agrégation des femelles pouvait être bénéfique pour la dynamique de la population. Il semble que les femelles tendent à s'agréger d'abord sur les meilleurs sites de fraie avec une plus forte stabilité environnementale. Cette distribution des femelles affecta la capacité des mâles à monopoliser plusieurs femelles, une agrégation modérée permettant une monopolisation. La participation des mâles furtifs anadromes ou tacons matures était également dépendante de l'agrégation des femelles. Il apparait que la disponibilité d'habitats adéquats pour la reproduction semble limitante dans la Nivelle et notamment du fait de la présence de barrages. Ce manque semble affecter le système d'appariement de la population et la sélection sexuelle y opérant. Des mesures visant à améliorer la qualité des sites de fraie déjà disponibles ainsi que leur accessibilité pourraient être envisagées. / Habitat fragmentation and reduction in the availability of suitable habitats are significant threats to ecosystems in particularly for freshwater ones. For instance, accessibility, availability, and quality of breeding sites of Atlantic salmon, \textit{Salmo salar}, can be restricting in some rivers due to human activities and dams. Such threats may affect distribution of potential breeders because after their up-river migration, salmon females distribute within available breeding sites. Spatial distribution of females determines the spatial distribution of breeder males. Dominant males try to monopolise several females, whereas subordinate males adopt a sneaky behaviour. Access to females by males depends on the spatial distribution of females and on males' displacements within a river. The spatial distribution of females generates the spatial distribution of juveniles, aggregating them at some breeding sites. The latter aggregation of juveniles may raise the density-dependent mortality with potential consequences on population dynamics. The thesis aims to assess how space use of potential breeders, namely mature individuals able to spawn or fertilise eggs, influence population dynamics and sexual selection.I combined different approaches and different temporal and spatial scales to potential effects of space use of potential breeders. Time series of stock (deposited eggs) and of recruitment (juveniles) for the salmon population of the Nivelle River were combined with measures of spatial aggregation of nests. The effects of displacements and spatial distribution of potential breeders on their participation in reproduction were tested through inferring the sexual network of the population.I found that spatial aggregation of nests improved the recruitment variability but did not affect the average recruitment. The spatial aggregation of nests resulting from female aggregation was also linked to the number of effective breeders through a U-shaped curve. Such relationships suggested mate monopolization dependent on the spatial aggregation of females. The negative effect of the spatial isolation of females on their number of mates also suggest such mate monopolization. Then, the inferred sexual network enabled me to highlight a local social structure within the population. The latter structure and social competitors impacted the reproductive success of anadromous males. The participation of mature parr was one of the factors diminishing the sexual competition faced by anadromous males. Finally, mature parr were more mobile and moved more upstream than immature parr. Spatial behaviours of mature parr were linked to their participation in reproduction, individuals exhibiting wider home ranges had a higher probability to encounter females.Altogether my results show that space use of potential breeders affect both population dynamics and sexual selection. Then, spatial aggregation of females and of their nests can be beneficial for population dynamics as shown by combining different temporal and spatial scales. Females seemed to aggregate within the best breeding sites with a better environmental stability. The spatial distribution of females affected the ability of males to monopolise several females and participation of sneaky males. The availability of suitable good breeding habitats seemed restricting in the Nivelle, potentially due to the presence of impassable upstream dams. The lack of suitable breeding sites seemed impacting the mating system of the population and the sexual selection operating in. Some management actions to improve the quality of breeding sites and their availability could be planned.
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Life History, Maternal Quality and the Dynamics of Harvested Fish StocksVenturelli, Paul Anthony 03 March 2010 (has links)
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.
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Life History, Maternal Quality and the Dynamics of Harvested Fish StocksVenturelli, Paul Anthony 03 March 2010 (has links)
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.
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