Individual heterogeneity in reproductive rates and cost of reproduction in a long‐lived vertebrate

Abstract

Individual variation in reproductive success is a key feature of evolution, but also has important implications for predicting population responses to variable environments. Although such individual variation in reproductive outcomes has been reported in numerous studies, most analyses to date have not considered whether these realized differences were due to latent individual heterogeneity in reproduction or merely random chance causing different outcomes among like individuals. Furthermore, latent heterogeneity in fitness components might be expressed differently in contrasted environmental conditions, an issue that has only rarely been investigated. Here, we assessed (i) the potential existence of latent individual heterogeneity and (ii) the nature of its expression (fixed vs. variable) in a population of female Weddell seals (Leptonychotes weddellii), using a hierarchical modeling approach on a 30-year mark-recapture data set consisting of 954 individual encounter histories. We found strong support for the existence of latent individual heterogeneity in the population, with "robust" individuals expected to produce twice as many pups as "frail" individuals. Moreover, the expression of individual heterogeneity appeared consistent, with only mild evidence that it might be amplified when environmental conditions are severe. Finally, the explicit modeling of individual heterogeneity allowed us to detect a substantial cost of reproduction that was not evidenced when the heterogeneity was ignored.

Extreme climate events and individual heterogeneity shape life‐history traits and population dynamics

“…4). Hence, they were more likely to remain in the successful category; a pattern that has been documented for a number of seabirds and mammals (Cam et al 2002, Lescroe¨l et al 2009, Chambert et al 2013. Interestingly, statistical uncertainties indicate that survival does not differ among stages (Appendix B: Table B5), suggesting that all individuals adopt a bethedging strategy regardless of their phenotype: spreading the risk of reproduction instead of compromising their survival.…”

Use of posterior predictive checks as an inferential tool for investigating individual heterogeneity in animal population vital rates

“…2013), which can be considered as enough evidence to conclude that individual heterogeneity exists in this population. However, this does not convey how this level of variability manifests in realized quantities of interest, such as those identified in the previous paragraph.…”

“…Another interesting biological implication of including individual heterogeneity in the model was also revealed by the detection of a reproductive cost on future reproduction that was not detected in the homogeneity model (Chambert et al. 2013). Furthermore, the more complicated model M3 does not provide better predictions of quantities T ( y ) than model M2 .…”

“…2013) that was motivated by two ecological questions: (i) the magnitude and (ii) the temporal stability of underlying individual heterogeneity in reproductive rates of female Weddell seals ( Leptonychotes weddellii Lesson). Chambert et al.…”

Successful by Chance? The Power of Mixed Models and Neutral Simulations for the Detection of Individual Fixed Heterogeneity in Fitness Components

“…In contrast to studies relying on NS, studies employing linear mixed models (hereafter, MM) commonly report evidence for fixed heterogeneity (e.g., Cam and Monnat 2000;Royle 2008;Chambert et al 2013Chambert et al , 2014Guillemain et al 2013). Interestingly, Cam et al (2013) have provided evidence for fixed heterogeneity in a data set for which the existence of fixed heterogeneity had been dismissed based on NS (Steiner et al 2010).…”