Effects of early life mass mortality events on fish populations

Mass mortality events are ubiquitous in nature and can be caused by, for example, diseases, extreme weather and human perturbations such as contamination. Despite being prevalent and rising globally, how mass mortality in early life causes population-level effects such as reduced total population biomass, is not fully explored. In particular for fish, mass mortality affecting early life may be dampened by compensatory density-dependent processes. However, due to large variations in year-class strength, potentially caused by density-independent variability in survival, the impact at the population level may be high in certain years. We quantify population-level impacts at two levels of mass mortality (50% and 99% additional mortality) during early life across 40 fish species using age-structured population dynamics models. The findings from these species-specific models are further supported by an analysis of detailed stock-specific models for three of the species. We find that population impacts are highly variable between years and species. Short-lived species that exhibit a low degree of compensatory density dependence and high interannual variation in survival experience the strongest impacts at the population level. These quantitative and general relationships allow predicting the range of potential impacts of mass mortality events on species based on their life history. This is critical considering that the frequency and severity of mass mortality events are increasing worldwide.publishedVersio

Effects of early life mass mortality events on fish populations

Mass mortality events are ubiquitous in nature and can be caused by, for example, diseases, extreme weather and human perturbations such as contamination. Despite being prevalent and rising globally, how mass mortality in early life causes population-level effects such as reduced total population biomass, is not fully explored. In particular for fish, mass mortality affecting early life may be dampened by compensatory density-dependent processes. However, due to large variations in year-class strength, potentially caused by density-independent variability in survival, the impact at the population level may be high in certain years. We quantify population-level impacts at two levels of mass mortality (50% and 99% additional mortality) during early life across 40 fish species using age-structured population dynamics models. The findings from these species-specific models are further supported by an analysis of detailed stock-specific models for three of the species. We find that population impacts are highly variable between years and species. Short-lived species that exhibit a low degree of compensatory density dependence and high interannual variation in survival experience the strongest impacts at the population level. These quantitative and general relationships allow predicting the range of potential impacts of mass mortality events on species based on their life history. This is critical considering that the frequency and severity of mass mortality events are increasing worldwide.publishedVersio

Jeu spatial et interactions comportementales dans la relation prédateur-proie

Predators and prey engage into a space race where predators seek to select areas with high prey availability while prey try to avoid areas with a high probability of encountering a predator. Predators and prey continuously make choices that can alter the outcome of this space race. For example, by using different locations in the landscape, they can alter the probability of an encounter, the probabilities of detection or the probability of success of an attack. Many empirical studies show the importance of habitat in these choices. On the other hand, little is known about avoidance by prey or predator search strategies that would be unrelated to habitat. The space race, however, does not fully summarize the interaction between predators and prey, which also depends on many non-spatial behaviors. The vigilance and grouping behaviour of prey are relatively common defenses, and there are many examples where prey become active at another time of day to escape their predator. However, it is still unclear how those behaviors interact with the spatial dimension of the prey-predator game. In this thesis, I will try to fill these gaps. In the first chapter, I propose a theoretical model showing the importance of accounting for spatial behaviors when studying the classical interaction between vigilance and group size in prey. In the second chapter, I present a mechanism of predator avoidance by prey, relying on the spatial and temporal anchors of predators and independent on the habitat. Finally, in the last chapter, I develop a patch selection model to predict how past information should be used to determine movement. This model emphasize the importance of movement unpredictability in the predator-prey game. These different works are part of a behavioral ecology of the landscape and aim to integrate behavioral mechanisms in the study of ecological dynamics at the landscape scale.Prédateurs et proies sont entraînés dans une course spatiale où les prédateurs cherchent à sélectionner les zones du paysage avec une forte disponibilité en proies alors que les proies tentent d’éviter les zones du paysage avec une forte probabilité de rencontrer un prédateur. Ils procèdent incessamment à de nombreux choix susceptibles de modifier l’issue de cette course. Ainsi, en sélectionnant des endroits différents, ils peuvent tenter d'altérer les probabilités de détection, de rencontre ou encore la probabilité de réussite d’une attaque. De nombreuses études empiriques montrent l’importance de l’habitat dans ces choix. On connaît par contre peu les mécanismes de recherche (par les prédateurs) ou d’évitement (par les proies) qui ne seraient pas relatifs à l’habitat. La course spatiale ne résume cependant pas entièrement l’interaction entre prédateurs et proies, laquelle dépend de nombreux comportements non-spatiaux. La vigilance et la socialité des proies constituent des défenses relativement répandues. On a aussi fréquemment observé de nombreux exemples où les proies deviennent actives à un autre moment de la journée pour échapper à leur prédateur. Cependant, on connaît relativement peu les interactions de ces comportements avec la dimension spatiale du jeu proie-prédateur. Dans cette thèse, j'ai pour objectif de combler ces différents manques. Dans le premier chapitre, je propose un modèle théorique montrant l’importance de la prise en compte des comportements spatiaux dans l’interaction classique entre vigilance et taille de groupe chez les proies. Dans le second chapitre, je présente un mécanisme d’évitement des prédateurs par les proies, s'appuyant sur les ancres spatiales et temporelles des prédateurs et ne dépendant pas de l’habitat. Enfin, dans le dernier chapitre, je développe un modèle de choix de parcelles permettant de prévoir comment les connaissances passées sont susceptibles d'être utilisées pour orienter les déplacements. Ce modèle rappelle notamment l’importance de l’imprévisibilité du déplacement dans le jeu prédateur-proie. Ces différents travaux se placent dans le cadre d’une écologie comportementale du paysage et visent à intégrer des mécanismes comportementaux dans l’étude des dynamiques écologiques à l’échelle du paysage

Spatial race and behavioural interactions in the predator-prey game

Prédateurs et proies sont entraînés dans une course spatiale où les prédateurs cherchent à sélectionner les zones du paysage avec une forte disponibilité en proies alors que les proies tentent d’éviter les zones du paysage avec une forte probabilité de rencontrer un prédateur. Ils procèdent incessamment à de nombreux choix susceptibles de modifier l’issue de cette course. Ainsi, en sélectionnant des endroits différents, ils peuvent tenter d'altérer les probabilités de détection, de rencontre ou encore la probabilité de réussite d’une attaque. De nombreuses études empiriques montrent l’importance de l’habitat dans ces choix. On connaît par contre peu les mécanismes de recherche (par les prédateurs) ou d’évitement (par les proies) qui ne seraient pas relatifs à l’habitat. La course spatiale ne résume cependant pas entièrement l’interaction entre prédateurs et proies, laquelle dépend de nombreux comportements non-spatiaux. La vigilance et la socialité des proies constituent des défenses relativement répandues. On a aussi fréquemment observé de nombreux exemples où les proies deviennent actives à un autre moment de la journée pour échapper à leur prédateur. Cependant, on connaît relativement peu les interactions de ces comportements avec la dimension spatiale du jeu proie-prédateur. Dans cette thèse, j'ai pour objectif de combler ces différents manques. Dans le premier chapitre, je propose un modèle théorique montrant l’importance de la prise en compte des comportements spatiaux dans l’interaction classique entre vigilance et taille de groupe chez les proies. Dans le second chapitre, je présente un mécanisme d’évitement des prédateurs par les proies, s'appuyant sur les ancres spatiales et temporelles des prédateurs et ne dépendant pas de l’habitat. Enfin, dans le dernier chapitre, je développe un modèle de choix de parcelles permettant de prévoir comment les connaissances passées sont susceptibles d'être utilisées pour orienter les déplacements. Ce modèle rappelle notamment l’importance de l’imprévisibilité du déplacement dans le jeu prédateur-proie. Ces différents travaux se placent dans le cadre d’une écologie comportementale du paysage et visent à intégrer des mécanismes comportementaux dans l’étude des dynamiques écologiques à l’échelle du paysage.Predators and prey engage into a space race where predators seek to select areas with high prey availability while prey try to avoid areas with a high probability of encountering a predator. Predators and prey continuously make choices that can alter the outcome of this space race. For example, by using different locations in the landscape, they can alter the probability of an encounter, the probabilities of detection or the probability of success of an attack. Many empirical studies show the importance of habitat in these choices. On the other hand, little is known about avoidance by prey or predator search strategies that would be unrelated to habitat. The space race, however, does not fully summarize the interaction between predators and prey, which also depends on many non-spatial behaviors. The vigilance and grouping behaviour of prey are relatively common defenses, and there are many examples where prey become active at another time of day to escape their predator. However, it is still unclear how those behaviors interact with the spatial dimension of the prey-predator game. In this thesis, I will try to fill these gaps. In the first chapter, I propose a theoretical model showing the importance of accounting for spatial behaviors when studying the classical interaction between vigilance and group size in prey. In the second chapter, I present a mechanism of predator avoidance by prey, relying on the spatial and temporal anchors of predators and independent on the habitat. Finally, in the last chapter, I develop a patch selection model to predict how past information should be used to determine movement. This model emphasize the importance of movement unpredictability in the predator-prey game. These different works are part of a behavioral ecology of the landscape and aim to integrate behavioral mechanisms in the study of ecological dynamics at the landscape scale

Using a state-space population model to detect age-dependent species interactions.

Models that incorporate species interactions and their effects on the dynamics of commercially important fish stocks are needed to better understand the importance of ecological interactions and to facilitate sustainable fisheries. We developed a dynamic age-structured population model for the North-East Arctic stock of Atlantic haddock (Melanogrammus aeglefinus) based on scientific survey and commercial landings data. Our goal was to investigate climate effects and ecological interactions within the haddock food-web. A Bayesian state-space framework was used to separate information from ecological noise and observation error. Our results indicate significant impacts of species interactions on haddock dynamics. Haddock survival was associated with indices of cod (negative effect), and capelin biomass (positive effect). The latter may reflect lower predation by predators such as marine mammals at high capelin biomass. We further detect weak density dependence in the survival of young haddock, and a convex relationship between haddock abundance and the scientific survey indices. Our findings highlight the importance of considering natural resources as part of an ecosystem with its diverse interactions both within and between species. This study shows that it is possible to detect ecological interactions with a population model based on noisy data.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A theory of the use of information by enemies in the predator-prey space race

We currently lack a comprehensive theory about how behaviourally responsive predators and prey use the information they acquire about the environment and each other’s presence while engaged in the ‘space race’. This limits our understanding of the role of behaviour in trophic relationships and our ability to predict predators and prey distributions. Here we combined a simulation model with a genetic algorithm to discover how predators and prey behaving optimally should use information in environments with different levels of heterogeneity in prey forage distribution and prey vulnerability. Our results demonstrate the key role of movement unpredictability in successful strategies for both predators and prey, supporting the ‘shell-game’ hypothesis. We however reveal striking differences between predators and prey in the magnitude of this unpredictability, and in how it varies with the environment. Our work offers a robust theoretical framework to better understand predator-prey space use and interpret empirical studies

Space Use and Leadership Modify Dilution Effects on Optimal Vigilance under Food-Safety Trade-Offs

International audienceDilution of predation risk within groups allows individuals to be less vigilant and forage more while still facing lower risk than if they were alone. How group size influences vigilance when individuals can also adjust their space use and whether this relationship differs among individuals contributing differently to space use decisions remain unknown. We present a model-based study of how dilution affects the optimal antipredator behavior of group members in groups where all individuals determine their vigilance level while group leaders also determine space use. We showed that optimal vigilance did not always decrease with group size, as it was sometimes favorable for individuals in larger groups to use riskier patches while remaining vigilant. Followers were also generally less vigilant than leaders. Indeed, followers needed to acquire more resources than leaders, as only the latter could decide when to go to richer patches. Followers still benefit from dilution of predation risk compared with solitary individuals. For leaders, keeping their leadership status can be more important than incorporating new group members to increase dilution. We demonstrate that risk dilution impacts both optimal vigilance and space use, with fitness reward being tied to a member's ability to influence group space use

data_lion_IPP_Wet_Day

Lion data used to assess the RSF during the wet season and day period. id = individual id ; response = the variable response used in the IPP, weight = the variable used as weight in the regression ; veget_type = type of vegetation ; dist2water = distance to waterhole in km ; dist2water_log = log(1+ distance to waterhole in km

Despotic leadership in space use can control dilution effects on optimal vigilance under food/safety trade-offs - Model files

These files contains model code for a manuscript in preparation "Despotic leadership in space use can control dilution effects on optimal vigilance under food/safety trade-offs".<br

Zebra diel migrations reduce encounter risk with lions at night

International audienc