Elevational trends in life histories: revising the pace‐of‐life framework

Abstract

Life-history traits in birds, such as lifespan, age at maturity, and rate of reproduction, vary across environments and in combinations imposed by trade-offs and limitations of physiological mechanisms. A plethora of studies have described the diversity of traits and hypothesized selection pressures shaping components of the survival-reproduction trade-off. Life-history variation appears to fall along a slow-fast continuum, with slow pace characterized by higher investment in survival over reproduction and fast pace characterized by higher investment in reproduction over survival. The Pace-of-Life Syndrome (POLS) is a framework to describe the slow-fast axis of variation in life-history traits and physiological traits. The POLS corresponds to latitudinal gradients, with tropical birds exhibiting a slow pace of life. We examined four possible ways that the traits of high-elevation birds might correspond to the POLS continuum: (i) rapid pace, (ii) tropical slow pace, (iii) novel elevational pace, or (iv) constrained pace. Recent studies reveal that birds breeding at high elevations in temperate zones exhibit a combination of traits creating a unique elevational pace of life with a central trade-off similar to a slow pace but physiological trade-offs more similar to a fast pace. A paucity of studies prevents consideration of the possibility of a constrained pace of life. We propose extending the POLS framework to include trait variation of elevational clines to help to investigate complexity in global geographic patterns.

Life-History Responses to the Altitudinal Gradient

“…reduced clutch size or reproductive attempts per year, with elevation. As an opposite pattern, the duration of the incubation and nesting phases increase with elevation (Krementz and Handford1984;Badyaev 1997a;Badyaev and Ghalambor 2001;Boyle et al 2015;Hille and Cooper 2015;Laiolo et al 2015b). Ruling out the effect of body size, low predation pressures and poor food availability likely contribute to prolonged parental care, as a result of bird parents spending increasingly longer periods outside the nest (Boersma 1982).…”

Urbanization Is Associated with Divergence in Pace-of-Life in Great Tits

“…In short, the pace-of-life continuum differentiates between, on the one hand slow individuals with slow life-histories (e.g., high survival, delayed reproduction), reactive behaviors (e.g., shyness, low aggressiveness, and low activity) and low metabolism, and on the other hand fast individuals with fast life-histories, proactive behaviors and high metabolism (Réale et al, 2010). Although the POLS concept has attracted paramount attention in behavior ecology and eco-physiology, empirical support for the POLS hypothesis is currently mixed (Hille and Cooper, 2015), perhaps because POLS theory still lacks a conceptual framework to predict which ecological conditions will favor which syndromes. Most notably, many studies in the last decade have tested adaptive explanations for the evolution of repeatable individual differences in behavior (aka personality) (Wolf et al, 2007) and a number of theoretical studies have attempted to predict the conditions favoring the evolution of personalities (Dingemanse and Wolf, 2010).…”

The intensity of male-male interactions declines in highland songbird populations

“…In fact, extra-pair paternity in the species, affecting on average ≈ 12% of nests, drops in conditions of breeding synchrony . In parallel, the value of male parental effort should increase, triggered by the low likelihood of cuckoldry and by substantial gains in offspring survival due to male care in the restrictive environmental conditions (Moller and Birkhead 1994;Badyaev and Ghalambor 2001;Hille and Cooper 2015). Since the attack of song stimuli is considered an unambiguous assay of aggression (Hof and Podos 2013), the longer distances of approach displayed by high elevation water pipits may be interpreted as the result of reduced aggressive motivation and, more broadly, weaker strength of intrasexual selection (i.e., fewer fitness benefits of male-male competition).…”

“…The decline in temperature, solar energy, productivity and the increase in seasonality of resources, are the most striking constraints faced by mountain-dwelling organisms, which have evolved a series of characteristics that permit breeding and persistence in these conditions (Lomolino 2001;Hille and Cooper 2015). Besides direct anatomical or physiological adaptations to cold temperatures, life-history differentiation is the most commonly documented output of shifting selection pressures along elevation.…”