A standardized approach to estimate life history tradeoffs in evolutionary ecology

Abstract

As tradeoff s limit the maximum Darwinian fi tness individuals can reach, measuring reliably the strength of tradeoff s using appropriate metrics is of prime importance to understand the evolution of traits under constraints. Tradeoff s involving phenotypic traits and fi tness components, however, are diffi cult to quantify in free-ranging populations because of confounding eff ects due to environmental variation and individual heterogeneity. Furthermore, although some methods have been used previously to quantify tradeoff s, these methods cannot be applied with respect to binary traits, which are common to describe life histories (e.g. probability of reproduction, nesting success, off spring survival). Here, we demonstrate how to measure reliably the strength of tradeoff s involving binary traits using (auto)correlation estimates obtained from generalized linear (mixed) models. We fi rst propose a standardized approach that accounts for the variation in the nature of the tradeoff s being compared (e.g. continuous/binary traits, repeated/non-repeated measures), and then apply this method to longitudinal data from two contrasting species of large herbivores. Empirical estimates of tradeoff s varied among traits, and between-species comparisons suggested that reproductive tradeoff s between successive breeding attempts might only occur in capital breeders. Th e empirical results we obtained clearly demonstrate that the method we provide allows measuring reliably the strength of tradeoff s under most circumstances, including tradeoff s on binary traits. Our original approach therefore off ers an important fi rst step for comparing the strength and, hence, the relative importance of diff erent tradeoff s, and opens the door to a better understanding of the evolution of life history traits in free-ranging populations.A major goal of life history studies is to understand how natural selection shapes individual fi tness-related traits, such as growth, reproduction, and survival (Roff 1992, Stearns 1992. Without any resource limitation, a ' Darwinian demon ' , would evolve (Law 1979). Nevertheless, resources are usually limited so that individuals have to allocate resources to a given function at the cost of other functions (Williams 1966). According to this principle of energy allocation, the maximum fi tness individuals can reach is limited by tradeoff s that occur among fi tness components during a lifetime (Williams 1966). Although tradeoff s among life history traits have shaped the diversity of life history strategies we currently observe, tradeoff s involving phenotypic traits and fi tness components are diffi cult to measure in freeranging populations for two main reasons. First, tradeoff measures are subject to confounding eff ects of environmental variation in resource availability (van Noordwijk and de Jong 1986). Second, tradeoff s are usually assessed from traits measured on diff erent individuals within a population, leading to between-individual variation, and the data generally consist of repeated measure...

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

“…; Wheatley et al . ; Hamel, Craine & Towne ; Hassrick, Crocker & Costa ; Hamel, Yoccoz & Gaillard ). This uncertainty in the latter species appears primarily because these latter species either do feed (bison, goats, sheep, deer), or at times do (Weddell seals) during lactation, which weakens the obligate relationship between maternal expenditure and stored reserves during lactation given the additional nutrition animals accumulated from feeding during nursing and that cannot be accounted for (Proffitt, Garrott & Rotella ).…”

Individual heterogeneity and capture–recapture models: what, why and how?

“…When measurable variables are missing, or insufficient to account satisfactorily for heterogeneity (Hougaard 1991), investigators can assume a discrete or continuous distribution of demographic parameters (Royle 2008, Péron et al 2010. In agreement with the concept of frailty, investigators assume that there are differences in demographic parameters between individuals that cannot be associated with measurable covariates and use latent variables to quantify them (Hougaard 1995, Yashin et al 2008, Cam et al 2013, Hamel et al 2014. 2) However, not all individual heterogeneity is fixed.…”

Life-history plasticity in female threespine stickleback

“…The level of effort put toward reproduction can affect the probability of survival (Gunderson, 1997;Moore and Attisano, 2011), future reproduction via reduced growth (Roff, 2000;Tsiklris et al, 2007) or both (Koivula et al, 2003), depending upon environmental conditions (Shine, 1980;Hamel et al, 2014). Plasticity in level of reproductive effort has been documented in a variety of ectotherms, including insects (review in Nylin and Gotthard, 1998), fish (Pampoulie et al, 2000;Kolm, 2001), snakes (Brown and Shine, 2007) and marine iguanas (Vitousek et al, 2010).…”

“…Individual life-history traits are integrated within a complex network of positive and negative (tradeoff) relationships not just among themselves (Stearns, 1989;Roff, 1992), but also with many other aspects of the phenotype (Forsman, 2014). This complexity places limits on the extent to which individual traits can shift plastically and still cumulatively produce the maximum reproductive fitness (Brown and Shine, 2007;Hamel et al, 2014). This complexity is particularly important for female animals because of the large per-offspring investment that females make.…”