Weimerskirch
Henri
Weimerskirch
Henri
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PreprintEffect of extreme sea surface temperature events on the demography of an age-structured albatross population( 2017-02) Pardo, Deborah ; Jenouvrier, Stephanie ; Weimerskirch, Henri ; Barbraud, ChristopheClimate changes include concurrent changes in environmental mean, variance and extremes, and it is challenging to understand their respective impact on wild populations, especially when contrasted age-dependent responses to climate occur. We assessed how changes in mean and standard deviation of sea surface temperature (SST), frequency and magnitude of warm SST extreme climatic events (ECE) influenced the stochastic population growth rate log(λs) and age structure of a black-browed albatross population. For changes in SST around historical levels observed since 1982, changes in standard deviation had a larger (threefold) and negative impact on log(λs) compared to changes in mean. By contrast, the mean had a positive impact on log(λs). The historical SST mean was lower than the optimal SST value for which log(λs) was maximized. Thus, a larger environmental mean increased the occurrence of SST close to this optimum that buffered the negative effect of ECE. This ‘climate safety margin’ (i.e. difference between optimal and historical climatic conditions) and the specific shape of the population growth rate response to climate for a species determine how ECE affect the population. For a wider range in SST, both the mean and standard deviation had negative impact on log(λs), with changes in the mean having a greater effect than the standard deviation. Furthermore, around SST historical levels increases in either mean or standard deviation of the SST distribution led to a younger population, with potentially important conservation implications for black-browed albatrosses.
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PreprintInteracting effects of unobserved heterogeneity and individual stochasticity in the life-history of the Southern fulmar( 2017-09-19) Jenouvrier, Stephanie ; Aubry, Lise M. ; Barbraud, Christophe ; Weimerskirch, Henri ; Caswell, HalIndividuals are heterogeneous in many ways. Some of these differences are incorporated as individual states (e.g., age, size, breeding status) in population models. However, substantial amounts of heterogeneity may remain unaccounted for, due to genetic, maternal, or environmental factors. Such unobserved heterogeneity (UH) affects the behavior of heterogeneous cohorts via intra-cohort selection and contributes to inter-individual variance in demographic outcomes such as longevity and lifetime reproduction. Variance is also produced by individual stochasticity, due to random events in the life cycle of wild organisms, yet no study thus far has attempted to decompose the variance in demographic outcomes into contributions from unobserved heterogeneity and individual stochasticity for an animal population in the wild. We developed a stage-classified matrix population model for the Southern fulmar breeding on Ile des Pétrels, Antarctica. We applied multi-event, multi-state markrecapture methods to estimate a finite mixture model accounting for UH in all vital rates and Markov chain methods to calculate demographic outcomes. Finally, we partitioned the variance in demographic outcomes into contributions from unobserved heterogeneity and individual stochasticity. We identify three UH groups, differing substantially in longevity, lifetime reproductive output, age at first reproduction, and in the proportion of the life spent in each reproductive state. 14% of individuals at fledging have a delayed but high probability of recruitment and extended reproductive lifespan. 67% of individuals are less likely to reach adulthood, recruit late and skip breeding often but have the highest adult survival rate. 19% of individuals recruit early and attempt to breed often. They are likely to raise their offspring successfully, but experience a relatively short lifespan. Unobserved heterogeneity only explains a small fraction of the variances in longevity (5.9%), age at first reproduction (3.7%) and lifetime reproduction (22%). UH can affect the entire life cycle, including survival, development, and reproductive rates, with consequences over the lifetime of individuals and impacts on cohort dynamics. The respective role of unobserved heterogeneity versus individual stochasticity varies greatly among demographic outcomes. We discuss the implication of our finding for the gradient of life-history strategies observed among species and argue that individual differences should always be accounted for in demographic studies of wild populations.
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ArticleExtreme climate events and individual heterogeneity shape life-history traits and population dynamics(Ecological Society of America, 2015-11) Jenouvrier, Stephanie ; Peron, Clara ; Weimerskirch, HenriExtreme climatic conditions and their ecological impacts are currently emerging as critical features of climate change. We studied extreme sea ice condition (ESIC) and found it impacts both life-history traits and population dynamics of an Antarctic seabird well beyond ordinary variability. The Southern Fulmar (Fulmarus glacialoides) is an ice-dependent seabird, and individuals forage near the ice edge. During an extreme unfavorable year (when sea ice area is reduced and distance between ice edge and colony is high), observed foraging trips were greater in distance and duration. As a result, adults brought less food to their chicks, which fledged in the poorest body condition. During such unfavorable years, breeding success was extremely low and population growth rate (λ) was greatly reduced. The opposite pattern occurred during extreme favorable years. Previous breeding status had a strong influence on life-history traits and population dynamics, and their responses to extreme conditions. Successful breeders had a higher chance of breeding and raising their chick successfully during the following breeding season as compared to other breeding stages, regardless of environmental conditions. Consequently, they coped better with unfavorable ESIC. The effect of change in successful breeder vital rates on λ was greater than for other stages' vital rates, except for pre-breeder recruitment probabilities, which most affected λ. For environments characterized by ordinary sea ice conditions, interindividual differences were more likely to persist over the life of individuals and randomness in individual pathways was low, suggesting individual heterogeneity in vital rates arising from innate or acquired phenotypic traits. Additionally, unfavorable ESIC tended to exacerbate individual differences in intrinsic quality, expressed through differences in reproductive status. We discuss the strong effects of ESIC on Southern Fulmar life-history traits in an evolutionary context. ESICs strongly affect fitness components and act as potentially important agents of natural selection of life histories related to intrinsic quality and intermittent breeding. In addition, recruitment is a highly plastic trait that, if heritable, could have a critical role in evolution of life histories. Finally, we find that changes in the frequency of extreme events may strongly impact persistence of Southern Fulmar populations.
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ArticleEffects of climate change and fisheries bycatch on Southern Ocean seabirds : a review(Inter-Research, 2012-05-21) Barbraud, Christophe ; Rolland, Virginie ; Jenouvrier, Stephanie ; Nevoux, Marie ; Delord, Karine ; Weimerskirch, HenriOver the last century, major climate changes and intense human exploitation of natural living resources have occurred in the Southern Ocean, potentially affecting its ecosystems up to top marine predators. Fisheries may also directly affect seabirds through bycatch and additional food resources provided by discards. The past 20 yr of research has seen an increasing number of studies investigating the effects of climate change and fisheries activities on Southern Ocean seabirds. Here, we review these studies in order to identify patterns in changes in distribution, phenology, demography and population dynamics in response to changes in climate and fisheries bycatch. Shifts in distribution and breeding phenology were documented in parallel to increases in sea-surface temperatures and changes in sea-ice cover. Above all warm sea-surface temperatures negatively affected demographic parameters, although exceptions were found. Relationships suggest non-linear effects of sea-ice cover on demographic parameters and population dynamics, with optimum sea-ice cover conditions appearing to be the rule. Fishing efforts were mainly negatively related to survival rates, and only for a few species positively related to breeding success. A handful of studies found that chronic mortality of immature birds due to fisheries negatively affected populations. Climate factors and fisheries bycatch may simultaneously affect demographic parameters in a complex way, which can be integrated in population models to project population trajectories under future climate or fisheries scenarios. Needed are studies that integrate other environmental factors, trophic levels, foraging behaviour, climate−fisheries interactions, and the mechanisms underlying phenotypic plasticity, such as some pioneering studies conducted elsewhere.
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ArticleFathers matter : male body mass affects life-history traits in a size-dimorphic seabird(The Royal Society, 2017-05-03) Cornioley, Tina ; Jenouvrier, Stephanie ; Borger, Luca ; Weimerskirch, Henri ; Ozgul, ArpatOne of the predicted consequences of climate change is a shift in body mass distributions within animal populations. Yet body mass, an important component of the physiological state of an organism, can affect key life-history traits and consequently population dynamics. Over the past decades, the wandering albatross—a pelagic seabird providing bi-parental care with marked sexual size dimorphism—has exhibited an increase in average body mass and breeding success in parallel with experiencing increasing wind speeds. To assess the impact of these changes, we examined how body mass affects five key life-history traits at the individual level: adult survival, breeding probability, breeding success, chick mass and juvenile survival. We found that male mass impacted all traits examined except breeding probability, whereas female mass affected none. Adult male survival increased with increasing mass. Increasing adult male mass increased breeding success and mass of sons but not of daughters. Juvenile male survival increased with their chick mass. These results suggest that a higher investment in sons by fathers can increase their inclusive fitness, which is not the case for daughters. Our study highlights sex-specific differences in the effect of body mass on the life history of a monogamous species with bi-parental care.
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ArticleMating behavior, population growth, and the operational sex ratio : a periodic two‐sex model approach(University of Chicago Press, 2010-04-21) Jenouvrier, Stephanie ; Caswell, Hal ; Barbraud, Christophe ; Weimerskirch, HenriWe present a new approach to modeling two‐sex populations, using periodic, nonlinear two‐sex matrix models. The models project the population growth rate, the population structure, and any ratio of interest (e.g., operational sex ratio). The periodic formulation permits inclusion of highly seasonal behavioral events. A periodic product of the seasonal matrices describes annual population dynamics. The model is nonlinear because mating probability depends on the structure of the population. To study how the vital rates influence population growth rate, population structure, and operational sex ratio, we used sensitivity analysis of frequency‐dependent nonlinear models. In nonlinear two‐sex models the vital rates affect growth rate directly and also indirectly through effects on the population structure. The indirect effects can sometimes overwhelm the direct effects and are revealed only by nonlinear analysis. We find that the sensitivity of the population growth rate to female survival is negative for the emperor penguin, a species with highly seasonal breeding behavior. This result could not occur in linear models because changes in population structure have no effect on per capita reproduction. Our approach is applicable to ecological and evolutionary studies of any species in which males and females interact in a seasonal environment.
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ArticleWhen the going gets tough, the tough get going: effect of extreme climate on an Antarctic seabird’s life history(Wiley, 2022-08-18) Jenouvrier, Stephanie ; Aubry, Lise M. ; van Daalen, Silke F. ; Barbraud, Christophe ; Weimerskirch, Henri ; Caswell, HalIndividuals differ in many ways. Most produce few offspring; a handful produce many. Some die early; others live to old age. It is tempting to attribute these differences in outcomes to differences in individual traits, and thus in the demographic rates experienced. However, there is more to individual variation than meets the eye of the biologist. Even among individuals sharing identical traits, life history outcomes (life expectancy and lifetime reproduction) will vary due to individual stochasticity, that is to chance. Quantifying the contributions of heterogeneity and chance is essential to understand natural variability. Interindividual differences vary across environmental conditions, hence heterogeneity and stochasticity depend on environmental conditions. We show that favourable conditions increase the contributions of individual stochasticity, and reduce the contributions of heterogeneity, to variance in demographic outcomes in a seabird population. The opposite is true under poor conditions. This result has important consequence for understanding the ecology and evolution of life history strategies.
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ArticleCauses and consequences of pair‐bond disruption in a sex‐skewed population of a long‐lived monogamous seabird(Ecological Society of America, 2022-04-01) Sun, Ruijiao ; Barbraud, Christophe ; Weimerskirch, Henri ; Delord, Karine ; Patrick, Samantha C. ; Caswell, Hal ; Jenouvrier, StephanieMany animals form long-term monogamous pair bonds, and the disruption of a pair bond (through either divorce or widowhood) can have significant consequences for individual vital rates (survival, breeding, and breeding success probabilities) and life-history outcomes (lifetime reproductive success [LRS], life expectancy). Here, we investigated the causes and consequences of pair-bond disruption in wandering albatross (Diomedea exulans). State-of-the-art statistical and mathematical approaches were developed to estimate divorce and widowhood rates and their impacts on vital rates and life-history outcomes. In this population, females incur a higher mortality rate due to incidental fishery bycatch, so the population is male-skewed. Therefore, we first posited that males would show higher widowhood rates negatively correlated with fishing effort and females would have higher divorce rates because they have more mating opportunities. Furthermore, we expected that divorce could be an adaptive strategy, whereby individuals improved breeding success by breeding with a new partner of better quality. Finally, we posited that pair-bond disruptions could reduce survival and breeding probabilities owing to the cost of remating processes, with important consequences for life-history outcomes. As expected, we showed that males had higher widowhood rates than females and females had higher divorce rates in this male-skewed population. However, no correlation was found between fishing effort and male widowhood. Secondly, contrary to our expectation, we found that divorce was likely nonadaptive in this population. We propose that divorce in this population is caused by an intruder who outcompetes the original partner in line with the so-called forced divorce hypothesis. Furthermore, we found a 16.7% and 18.0% reduction in LRS only for divorced and widowed males, respectively, owing to missing breeding seasons after a pair-bond disruption. Finally, we found that divorced individuals were more likely to divorce again, but whether this is related to specific individual characteristics remains an important area of investigation.
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ArticleAlbatrosses respond adaptively to climate variability by changing variance in a foraging trait(Wiley, 2021-06-05) Patrick, Samantha C. ; Martin, Julien G.A. ; Ummenhofer, Caroline C. ; Corbeau, Alexandre ; Weimerskirch, HenriThe ability of individuals and populations to adapt to a changing climate is a key determinant of population dynamics. While changes in mean behaviour are well studied, changes in trait variance have been largely ignored, despite being assumed to be crucial for adapting to a changing environment. As the ability to acquire resources is essential to both reproduction and survival, changes in behaviours that maximize resource acquisition should be under selection. Here, using foraging trip duration data collected over 7 years on black-browed albatrosses (Thalassarche melanophris) on the Kerguelen Islands in the southern Indian Ocean, we examined the importance of changes in the mean and variance in foraging behaviour, and the associated effects on fitness, in response to the El Niño Southern Oscillation (ENSO). Using double hierarchical models, we found no evidence that individuals change their mean foraging trip duration in response to a changing environment, but found strong evidence of changes in variance. Younger birds showed greater variability in foraging trip duration in poor conditions as did birds with higher fitness. However, during brooding, birds showed greater variability in foraging behaviour under good conditions, suggesting that optimal conditions allow the alteration between chick provisioning and self-maintenance trips. We found weak correlations between sea surface temperature and the ENSO, but stronger links with sea-level pressure. We suggest that variability in behavioural traits affecting resource acquisition is under selection and offers a mechanism by which individuals can adapt to a changing climate. Studies which look only at effects on mean behaviour may underestimate the effects of climate change and fail to consider variance in traits as a key evolutionary force.
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ArticleClimate change and functional traits affect population dynamics of a long‐lived seabird(John Wiley & Sons, 2018-06-17) Jenouvrier, Stephanie ; Desprez, Marine ; Fay, Remi ; Barbraud, Christophe ; Weimerskirch, Henri ; Delord, Karine ; Caswell, HalRecent studies unravelled the effect of climate changes on populations through their impact on functional traits and demographic rates in terrestrial and freshwater ecosystems, but such understanding in marine ecosystems remains incomplete. Here, we evaluate the impact of the combined effects of climate and functional traits on population dynamics of a long‐lived migratory seabird breeding in the southern ocean: the black‐browed albatross (Thalassarche melanophris, BBA). We address the following prospective question: “Of all the changes in the climate and functional traits, which would produce the biggest impact on the BBA population growth rate?” We develop a structured matrix population model that includes the effect of climate and functional traits on the complete BBA life cycle. A detailed sensitivity analysis is conducted to understand the main pathway by which climate and functional trait changes affect the population growth rate. The population growth rate of BBA is driven by the combined effects of climate over various seasons and multiple functional traits with carry‐over effects across seasons on demographic processes. Changes in sea surface temperature (SST) during late winter cause the biggest changes in the population growth rate, through their effect on juvenile survival. Adults appeared to respond to changes in winter climate conditions by adapting their migratory schedule rather than by modifying their at‐sea foraging activity. However, the sensitivity of the population growth rate to SST affecting BBA migratory schedule is small. BBA foraging activity during the pre‐breeding period has the biggest impact on population growth rate among functional traits. Finally, changes in SST during the breeding season have little effect on the population growth rate. These results highlight the importance of early life histories and carry‐over effects of climate and functional traits on demographic rates across multiple seasons in population response to climate change. Robust conclusions about the roles of various phases of the life cycle and functional traits in population response to climate change rely on an understanding of the relationships of traits to demographic rates across the complete life cycle.
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PreprintEffects of climate change on an emperor penguin population : analysis of coupled demographic and climate models( 2012-06-21) Jenouvrier, Stephanie ; Holland, Marika M. ; Stroeve, Julienne ; Barbraud, Christophe ; Weimerskirch, Henri ; Serreze, Mark ; Caswell, HalSea ice conditions in the Antarctic affect the life cycle of the emperor penguin (Aptenodytes forsteri). We present a population projection for the emperor penguin population of Terre Adelie, Antarctica, by linking demographic models (stage-structured, seasonal, nonlinear, two-sex matrix population models) to sea ice forecasts from an ensemble of IPCC climate models. Based on maximum likelihood capture-mark-recapture analysis, we find that seasonal sea ice concentration anomalies (SICa) affect adult survival and breeding success. Demographic models show that both deterministic and stochastic population growth rates are maximized at intermediate values of annual SICa, because neither the complete absence of sea ice, nor heavy and persistent sea ice, would provide satisfactory conditions for the emperor penguin. We show that under some conditions the stochastic growth rate is positively affected by the variance in SICa. We identify an ensemble of 5 general circulation climate models whose output closely matches the historical record of sea ice concentration in Terre Adelie. The output of this ensemble is used to produce stochastic forecasts of SICa, which in turn drive the population model. Uncertainty is included by incorporating multiple climate models and by a parametric bootstrap procedure that includes parameter uncertainty due to both model selection and estimation error. The median of these simulations predicts a decline of the Terre Adelie emperor penguin population of 81% by the year 2100. We find a 43% chance of an even greater decline, of 90% or more. The uncertainty in population projections reflects large differences among climate models in their forecasts of future sea ice conditions. One such model predicts population increases over much of the century, but overall, the ensemble of models predicts that population declines are far more likely than population increases. We conclude that climate change is a significant risk for the emperor penguin. Our analytical approach, in which demographic models are linked to IPCC climate models, is powerful and generally applicable to other species and systems.