skip to main content

Title: The impact of boldness on demographic rates and life‐history outcomes in the wandering albatross

Differences among individuals within a population are ubiquitous. Those differences are known to affect the entire life cycle with important consequences for all demographic rates and outcomes. One source of among‐individual phenotypic variation that has received little attention from a demographic perspective is animal personality, which is defined as consistent and heritable behavioural differences between individuals. While many studies have shown that individual variation in individual personality can generate individual differences in survival and reproductive rates, the impact of personality on all demographic rates and outcomes remains to be assessed empirically.

Here, we used a unique, long‐term, dataset coupling demography and personality of wandering albatross (Diomedea exulans) in the Crozet Archipelago and a comprehensive analysis based on a suite of approaches (capture‐mark‐recapture statistical models, Markov chains models and structured matrix population models). We assessed the effect of boldness on annual demographic rates (survival, breeding probability, breeding success), life‐history outcomes (life expectancy, lifetime reproductive outcome, occupancy times), and an integrative demographic outcome (population growth rate).

We found that boldness had little impact on female demographic rates, but was very likely associated with lower breeding probabilities in males. By integrating the effects of boldness over the entire life cycle, we found that bolder males had slightly lower lifetime reproductive success compared to shyer males. Indeed, bolder males spent a greater proportion of their lifetime as non‐breeders, which suggests longer inter‐breeding intervals due to higher reproductive allocation.

Our results reveal that the link between boldness and demography is more complex than anticipated by the pace‐of‐life literature and highlight the importance of considering the entire life cycle with a comprehensive approach when assessing the role of personality on individual performance and demography.

more » « less
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Date Published:
Journal Name:
Journal of Animal Ecology
Medium: X Size: p. 676-690
p. 676-690
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Events during one stage of the annual cycle can reversibly affect an individual's condition and performance not only within that stage, but also in subsequent stages (i.e. reversible state effects). Despite strong conceptual links, however, few studies have been able to empirically link individual‐level reversible state effects with larger‐scale demographic processes.

    We studied both survival and potential reversible state effects in a long‐distance migratory shorebird, the Hudsonian GodwitLimosa haemastica. Specifically, we estimated period‐specific survival probabilities across the annual cycle and examined the extent to which an individual's body condition, foraging success and habitat quality during the nonbreeding season affected its subsequent survival and reproductive performance.

    Godwit survival rates were high throughout the annual cycle, but lowest during the breeding season, only slightly higher during southbound migration and highest during the stationary nonbreeding season. Our results indicate that overwintering godwits foraging in high‐quality habitats had comparably better nutritional status and pre‐migratory body condition, which in turn improved their return rates and the likelihood that their nests and chicks survived during the subsequent breeding season.

    Reversible state effects thus appeared to link events between nonbreeding and breeding seasons via an individual's condition, in turn affecting their survival and subsequent reproductive performance. Our study thus provides one of the few empirical demonstrations of theoretical predictions that reversible state effects have the potential to influence population dynamics.

    more » « less
  2. Abstract

    Under life‐history theories of ageing, increased senescence should follow relatively high reproductive effort. This expectation has rarely been tested against senescence varying between and within the two sexes, although such an approach may clarify the origins of sex‐specific ageing in the context of a given mating system.

    Nazca boobies (Sula granti; a seabird) practise serial monogamy and biparental care. A male‐biased population sex ratio results in earlier and more frequent breeding by females. Based on sex‐specific reproductive schedules, females were expected to show faster age‐related decline for survival and reproduction. Within each sex, high reproductive effort in early life was expected to reduce late‐life performance and accelerate senescence.

    Longitudinal data were used to (a) evaluate the sex specificity of reproductive and actuarial senescence and then (b) test for early‐/late‐life fitness trade‐offs within each sex. Within‐sex analyses inform an interpretation of sex differences in senescence based on costs of reproduction. Analyses incorporated individual heterogeneity in breeding performance and cohort‐level differences in early‐adult environments.

    Females showed marginally more intense actuarial senescence and stronger age‐related declines for fledging success. The opposite pattern (earlier and faster male senescence) was found for breeding probability. Individual reproductive effort in early life positively predicted late‐life reproductive performance in both sexes and thus did not support a causal link between early‐reproduction/late‐life fitness trade‐offs and sex differences in ageing. A high‐quality diet in early adulthood reduced late‐life survival (females) and accelerated senescence for fledging success (males).

    This study documents clear variation in ageing patterns—by sex, early‐adult environment and early‐adult reproductive effort—with implications for the role mating systems and early‐life environments play in determining ageing patterns. Absent evidence for a disposable soma mechanism, patterns of sex differences in senescence may result from age‐ and condition‐dependent mate choice interacting with this population's male‐biased sex ratio and mate rotation.

    more » « less
  3. Abstract

    Extreme climatic events may influence individual‐level variability in phenotypes, survival and reproduction, and thereby drive the pace of evolution. Climate models predict increases in the frequency of intense hurricanes, but no study has measured their impact on individual life courses within animal populations.

    We used 45 years of demographic data of rhesus macaques to quantify the influence of major hurricanes on reproductive life courses using multiple metrics of dynamic heterogeneity accounting for life course variability and life‐history trait variances.

    To reduce intraspecific competition, individuals may explore new reproductive stages during years of major hurricanes, resulting in higher temporal variation in reproductive trajectories. Alternatively, individuals may opt for a single optimal life‐history strategy due to trade‐offs between survival and reproduction.

    Our results show that heterogeneity in reproductive life courses increased by 4% during years of major hurricanes, despite a 2% reduction in the asymptotic growth rate due to an average decrease in mean fertility and survival by that is, shortened life courses and reduced reproductive output. In agreement with this, the population is expected to achieve stable population dynamics faster after being perturbed by a hurricane (; 95% CI: 1.488, 1.538), relative to ordinary years .

    Our work suggests that natural disasters force individuals into new demographic roles to potentially reduce competition during unfavourable environments where mean reproduction and survival are compromised. Variance in lifetime reproductive success and longevity are differently affected by hurricanes, and such variability is mostly driven by survival.

    more » « less
  4. Abstract

    Evolutionary and behavioural ecologists have long been interested in factors shaping the variation in mating behaviour observed in nature. Although much of the research on this topic has focused on the consequences of mate choice and mate change on annual reproductive success, studies of a potential positive link between mate fidelity and adult demographic rates have been comparatively rare. This is particularly true for long‐lived birds with multi‐year, socially monogamous pair bonds.

    We used a 26‐year capture–mark–recapture dataset of 3,330 black brentBranta bernicla nigricansto test whether breeding with a familiar mate improved future breeding propensity and survival. We predicted that experienced breeders nesting with a new partner would have rates of survival similar to familiar pairs because long‐lived species avoid jeopardizing survival since their lifetime fitness is sensitive to this vital rate. In contrast, we expected that any costs of breeding with a new partner would be paid through skipping the subsequent breeding attempt.

    We found that unfamiliar pairs had lower subsequent breeding propensity than faithful partners. However, contrary to our expectations, individuals breeding with a new mate also suffered reduced survival.

    These results add to a small number of studies indicating that a positive relationship between mate retention and adult demographic rates may exist in a diverse array of avian species. Given these results, researchers should consider costs of mate change that extend beyond within‐season reproductive success to fully understand the potential adaptive basis for perennial social monogamy. We caution that if mate retention enhances survival prospects, improvements in annual reproductive success with pair‐bond length could be a secondary factor favouring perennial social monogamy, particularly in species with slower life‐history strategies. Furthermore, some cases where annual reproductive success does not improve with pair‐bond duration, yet multi‐year pair bonds are common, could be explained by benefits afforded by mate fidelity to adult vital rates.

    more » « less
  5. Abstract

    Despite numerous studies examining the fitness consequences of animal personalities, predictions concerning the relationship between personality and survival are not consistent with empirical observations. Theory predicts that individuals who are risky (i.e. bold, active and aggressive) should have higher rates of mortality; however, empirical evidence shows high levels of variation in behaviour–survival relationships in wild populations.

    We suggest that this mismatch between predictions under theory and empirical observations results from environmental contingencies that drive heterogeneity in selection. This uncertainty may constrain any universal directional relationships between personality traits and survival. Specifically, we hypothesize that spatiotemporal fluctuations in perceived risk that arise from variability in refuge abundance and competitor density alter the relationship between personality traits and survival.

    In a large‐scale manipulative experiment, we trapped four small mammal species in five subsequent years across six forest stands treated with different management practices in Maine, United States. Stands all occur within the same experimental forest but contain varying amounts of refuge and small mammal densities fluctuate over time and space. We quantified the effects of habitat structure and competitor density on the relationship between personality traits and survival to assess whether directional relationships differed depending on environmental contingencies.

    In the two most abundant species, deer mice and southern red‐backed voles, risky behaviours (i.e. higher aggression and boldness) predicted apparent monthly survival probability. Mice that were more aggressive (less docile) had higher survival. Voles that were bolder (less timid) had higher survival, but in the risky forest stands only. Additionally, traits associated with stress coping and de‐arousal increased survival probability in both species at high small mammal density but decreased survival at low density. In the two less abundant study species, there was no evidence for an effect of personality traits on survival.

    Our field experiment provides partial support for our hypothesis: that spatiotemporal fluctuations in refuge abundance and competitor density alter the relationship between personality traits and survival. Our findings also suggest that behaviours associated with stress coping and de‐arousal may be subject to density‐dependent selection and should be further assessed and incorporated into theory.

    more » « less