Decomposing the variance in southern elephant seal weaning mass: partitioning environmental signals and maternal effects

Oosthuizen, W. Chris; Bester, Marthán N; Altwegg, Res; McIntyre, Trevor; Bruyn, P. J. Nico de

doi:10.1890/es14-00508.1

Cited by 30 publications

(39 citation statements)

References 88 publications

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“…While it is often difficult to identify temporal changes in the quality or quantity of prey of wide-ranging and migratory marine predators, the size of southern elephant seals at weaning can be used as a broad-scale index representing relative changes in the foraging conditions encountered by breeding females during their pre-partum foraging migrations [11]. Since southern elephant seals are capital breeders fasting for the duration of the nursing period and raising their pup exclusively off stored energetic reserves [12], the foraging success of females over the pre-partum period (a function of foraging conditions over the winter months) strongly influences the energy expended on their pups over the lactation period and consequently the size of pups at weaning [13].…”

Section: Introductionmentioning

confidence: 99%

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

2017

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The population of Southern elephant seals (Mirounga leonina) at Macquarie Island has declined since the 1960s, and is thought to be due to changing oceanic conditions leading to reductions in the foraging success of Macquarie Island breeding females. To test this hypothesis, we used a 55-year-old data set on weaning size of southern elephant seals to quantify a decrease in weaning size from a period of population stability in 1950s to its present state of on-going decline. Being capital breeders, the size of elephant seal pups at weaning is a direct consequence of maternal foraging success in the preceding year. During the 1940-1950s, the mean of female pups at weaning was similar between the Heard and Macquarie Island populations, while the snout-tail-length length of male weaners from Heard Island were longer than their conspecifics at Macquarie Island. Additionally, the snout-tail-length of pups at weaning decreased by 3cm between the 1950s and 1990s in the Macquarie Island population, concurrent with the observed population decline. Given the importance of weaning size in determining first-year survival and recruitment rates, the decline in the size at weaning suggests that the decline in the Macquarie Island population has, to some extent, been driven by reduced maternal foraging success, consequent declines in the size of pups at weaning, leading to reduced first-year survival rates and recruitment of breeding females into the population 3 to 4 years later.

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Section: Introductionmentioning

confidence: 99%

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

2017

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“…While we do not relate pup growth directly to environment, given the consistency of these relationships we are confident that pup growth is related to SAM (also see Oosthuizen et al . ).…”

Section: Discussionmentioning

confidence: 97%

“…; Postma, Bester & de Bruyn ; Postma, Bester & De Bruyn ; Oosthuizen et al . ) that have been able to establish how environmental states affect a mother seals’ condition and then show how this relates to pup condition and subsequent survival (McMahon, Burton & Bester , ; Postma, Bester & de Bruyn ). When environmental conditions are good, otherwise small and medium females become effectively, medium and large females respectively.…”

Section: Discussionmentioning

confidence: 99%

Seal mothers expend more on offspring under favourable conditions and less when resources are limited

McMahon

Harcourt

Burton

et al. 2017

Journal of Animal Ecology

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In mammals, maternal expenditure on offspring is a complex mix of several factors including the species' mating system, offspring sex and the condition and age of the mother. While theory suggests that in polygynous species mothers should wean larger male offspring than females when resources and maternal conditions allow, the evidence for this remains equivocal. Southern elephant seals are highly dimorphic, polygynous capital breeders existing in an environment with highly variable resources and should therefore provide clear evidence to support the theoretical expectations of differential maternal expenditure in male and female pups. We quantified maternal size (mass and length) and pup size at birth and weaning for 342 elephant seal mothers at Macquarie Island. The study was conducted over 11 years of contrasting sea-ice and Southern Annular Mode values, both indices of maternal prey resources. Overall, large females weaned male pups that weighed 17 kg (15·5%) more than female pups. Maternal condition varied by as much as 59 kg among years, and was positively related to Southern Annular Mode, and negatively to maximum sea-ice extent. Smaller mothers weaned relatively larger male pups under favourable conditions, this effect was less apparent for larger mothers. We developed a simple model linking environmental variation to maternal masses post-partum, followed by maternal masses post-partum to weaning masses and then weaning masses to pup survival and demonstrated that environmental conditions affected predicted survival so that the pups of small mothers had an estimated 7% increase in first year survival in 'good' vs. 'bad' years compared to 1% for female pups of large mothers. Co-occurrence of environmental quality and conservative reproductive tactics suggests that mothers retain substantial plasticity in maternal care, enhancing their lifetime reproductive success by adjusting reproductive expenditure relative to both prevailing environmental conditions and their own capabilities.

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“…, Oosthuizen et al. ), but is useful to further assess the validity of hypotheses and model results (Grosbois et al. ).…”

Section: Discussionmentioning

confidence: 99%

Twenty‐nine years of population dynamics in a small‐bodied montane amphibian

et al. 2018

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Identifying population declines before they reach crisis proportions is imperative given the current global decline in vertebrate fauna and associated challenges and expense of recovery. Understanding life histories and how the environment influences demography are critical aspects of this challenge, as is determining the biological relevance of covariates that are best supported by the data. We used 29 yr of data on chorus frogs at two sites to estimate demographic parameters, examine life history, assess weather‐related covariates, and determine the magnitude of process variation in target parameters. Average estimates of survival probabilities were 0.51 (Standard Error [SE] = 0.04) and 0.43 (SE = 0.04), and average estimates of recruitment probabilities were 0.64 (SE = 0.07) and 0.44 (SE = 0.04). Process variation accounted for ≥76% of the total temporal variation in both parameters at one pond and in survival probability alone at the other, suggesting that the covariates in our top models were explaining predominantly process rather than sampling variation. Estimates of population growth rates indicated a declining population at one pond (i.e., negative population growth rates in 15 of 18 yr), and comparisons with historical estimates suggested declines in survival probability at the other. The amount of deviance explained was low, providing little support for the influence of covariates on target parameters, despite model selection support. Synthesis and applications: This analysis illustrates the value of disentangling components of variance when assessing demographic drivers and highlights the need for adequate demographic information in assigning conservation labels.

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Decomposing the variance in southern elephant seal weaning mass: partitioning environmental signals and maternal effects

Cited by 30 publications

References 88 publications

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

Five decades on: Use of historical weaning size data reveals that a decrease in maternal foraging success underpins the long-term decline in population of southern elephant seals (Mirounga leonina)

Seal mothers expend more on offspring under favourable conditions and less when resources are limited

Twenty‐nine years of population dynamics in a small‐bodied montane amphibian

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