Optimizing lifetime reproductive output: Intermittent breeding as a tactic for females in a long‐lived, multiparous mammal

Abstract

In iteroparous species, intermittent breeding is an important life-history tactic that can greatly affect animal population growth and viability. Despite its importance, few studies have quantified the consequences of breeding pauses on lifetime reproductive output, principally because calculating lifetime reproductive output requires knowledge of each individual's entire reproductive history. This information is extremely difficult to obtain in wild populations. We applied novel statistical approaches that account for uncertainty in state assessment and individual heterogeneity to an 18-year capture-recapture dataset of 6,631 female southern elephant seals from Macquarie Island. We estimated survival and breeding probabilities, and investigated the consequences of intermittent breeding on lifetime reproductive output. We found consistent differences in females' demographic performance between two heterogeneity classes. In particular, breeding imbued a high cost on survival in the females from the heterogeneity class 2, assumed to be females of lower quality. Individual quality also appeared to play a major role in a female's decision to skip reproduction with females of poorer quality more likely to skip breeding events than females of higher quality. Skipping some breeding events allowed females from both heterogeneity classes to increase lifetime reproductive output over females that bred annually. However, females of lower quality produced less offspring over their lifetime. Intermittent breeding seems to be used by female southern elephant seals as a tactic to offset reproductive costs on survival and enhance lifetime reproductive output but remains unavoidable and driven by individual-specific constraints in some other females.

Environment‐sensitive mass changes influence breeding frequency in a capital breeding marine top predator

“…Capital breeding species in fluctuating environments are likely to be particularly prone to skipping breeding episodes when survival takes precedence over reproduction (Stearns, ). Skipped breeding episodes among experienced breeders are known in capital breeding phocid seals, but mechanistic explanations of the process have often relied anecdotally on Boyd’s () finding that body mass accounted for more variation in pregnancy rates in capital breeding than income breeding species (Chambert, Rotella, Higgs, & Garrott, ; Desprez et al, ). Desprez et al () used resighting records at Macquarie Island to investigate intermittent breeding of southern elephant seals Mirounga leonina.…”

“…Skipped breeding episodes among experienced breeders are known in capital breeding phocid seals, but mechanistic explanations of the process have often relied anecdotally on Boyd’s () finding that body mass accounted for more variation in pregnancy rates in capital breeding than income breeding species (Chambert, Rotella, Higgs, & Garrott, ; Desprez et al, ). Desprez et al () used resighting records at Macquarie Island to investigate intermittent breeding of southern elephant seals Mirounga leonina. Using a multievent model incorporating uncertain reproductive status and categorizing adult females into breeding heterogeneity classes, they found that there was a survival cost to breeding for females in the infrequently breeding class.…”

“…Using a multievent model incorporating uncertain reproductive status and categorizing adult females into breeding heterogeneity classes, they found that there was a survival cost to breeding for females in the infrequently breeding class. This latter class they suggested comprised females of lower quality in some phenotypic property positively related to fitness, and while variability in individuals’ ability to forage and gain resources were hypothesized to be likely explanatory factors, no phenotypic or other measures of animals were provided to support this (Desprez et al, ). Similarly, Chambert, Rotella, and Garrott, () proposed that female Weddell seals ( Leptonychotes weddellii ) that skipped breeding in Erebus Bay, Antarctica were in poorer condition than regular breeders.…”

“…Determining how often animals breed can be challenging, requiring information additional to that needed to estimate survival (Desprez, Gimenez, McMahon, Hindell, & Harcourt, ). Ideally, breeding events can be compiled from direct observations on known, representative individuals, occurring over the duration of the animals’ lifespan, with individuals equally detectable and breeding state known without error.…”

“…The latter is problematic even for long‐term studies – if an animal is not observed in a given year but is resighted later, is this a failure to detect a breeding episode or a non‐breeding year for that animal? In practice, determining animals’ breeding status when they are not observed at the main study site is difficult and this has prompted development of statistical methods to account for uncertain state and individual heterogeneity (Desprez et al, ; King & McCrea, ; Rouan, Gaillard, Guédon, & Pradel, ).…”