Evidence for an age‐dependent influence of environmental variations on a long‐lived seabird's life‐history traits

Abstract

Theoretical and empirical studies have highlighted the effects of age on several life-history traits in wild populations. There is also increasing evidence for environmental effects on their demographic traits. However, quantifying how individuals differentially respond to environmental variations according to their age remains a challenge in ecology. In a population of Black-browed Albatrosses monitored during 43 years, we analyzed how life-history traits varied according to age, and whether individuals of different ages responded in different ways to environmental conditions. To do so, we: (1) examined how age affected seven life-history traits, (2) investigated differences in temporal variance of demographic traits between age classes, and (3) tested for age-dependent effects of climate and fisheries covariates on demographic traits. Overall, there was a tendency for traits to improve during the first years of life (5-10 years), to peak and remain stable at middle age (10-30 years), and decline at old ages. At young ages, survival and reproductive parameters increased, except offspring body condition at fledging, suggesting that younger parents had already acquired good foraging capacities. However, they suffered from inexperience in breeding as suggested by their higher breeding failures during incubation. There was evidence for reproductive and actuarial senescence. In particular, breeding success and offspring body condition declined abruptly, suggesting altered foraging capacities of old individuals. Middle-aged individuals had the lowest temporal variance of demographic traits. Although this is predicted by the theory of environmental canalization, it could also results from a higher susceptibility of young and old birds due to their respective inexperience and senescence. The highest temporal variances were found in old individuals. Survival was significantly influenced by sea surface temperatures in the foraging zone of this albatross population during breeding. During warm events survival of young and old individuals improved, whereas a decrease was observed for middle-aged individuals. Presumably, during cold years with poor environmental conditions, young and old breeding birds may suffer more from intraspecific competition for resources than middle-aged individuals. This study showed that age, known as a major factor structuring demography in long-lived species, can also potentially influence the response of populations to global change.

Forecasting ocean warming impacts on seabird demography: a case study on the European storm petrel

“…This suggests that senescence starts at this age and thus that the population can be divided into 3 age classes: juveniles, adults and senescing individuals, as in other long-lived seabird species (Pardo et al 2013). Senescing individuals have higher mortality compared to younger adults and could also be influenced by reproductive senescence as a consequence of altered foraging capacities of older individuals, in accordance with similar findings for black-browed albatross (Pardo et al 2013). We found similar λ in Scenarios A and B (respectively accounting or not for senescence); this may be explained by the fact that there were very few females alive after Year 16.…”

“…Some demographic traits of the storm petrel were described in previous studies (Sanz-Aguilar et al 2008, Soldatini et al 2014, but information on senescence and age effects on the species' demography is still lacking. In particular, the differential re sponses of age classes to environmental constraints shape survival and reproductive traits at a population level and probably in fluence the response of populations to global climate change (Pardo et al 2013). As a consequence, in order to understand the influence of future climate on this and other seabird species, an assessment on how climate is currently related to population metrics is needed (McClure et al 2013).…”

Senescence or selective disappearance? Age trajectories of body mass in wild and captive populations of a small-bodied primate

“…[16,19,20]). In the wild, studies of FS have largely focused on long-lived, large-bodied animals that face relatively low levels of environmental hazard (ungulates [10,21], sea-birds [22], seals [23] and primates [6,24]). Because FS is more detectable when EM is low, this taxonomic bias may lead to an overestimation of the prevalence of FS compared with the influences of selective disappearance in natural populations across species.…”

The influence of environmental conditions on the age pattern in breeding performance in a transequatorial migratory seabird

“…Age-specific differences in breeding performance have been observed in several seabirds (Nevoux et al, 2007;Vieyra et al, 2009;Pardo et al, 2013). In most cases young individuals perform less well than older individuals (Martin, 1995), thereby indicating improvement in performance with age leading to a peak and then decline (i.e., senescence) (Clutton-Brock, 1988).…”

“…Despite this, few studies have ever examined at the same time how environmental conditions affect age patterns in breeding performance (Bunce et al, 2005;Pardo et al, 2013;Oro et al, 2014). Depending on environmental conditions, different age patterns can exist (see Oro et al, 2014): in most studies, either (a) differences among age classes in breeding performance were found to decrease under better environmental conditions (Sydeman et al, 1991;Laaksonen et al, 2002;Barbraud and Weimerskirch, 2005;Bunce et al, 2005) or (b) environmental conditions had no clear influence on breeding performance (Nevoux et al, 2007;Vieyra et al, 2009;Lee, 2011;Pardo et al, 2013); just one study found that differences between age-classes were greater under favorable environmental conditions (Oro et al, 2014).…”