Metabolic rate is negatively linked to adult survival but does not explain latitudinal differences in songbirds

Abstract

Survival rates vary dramatically among species and predictably across latitudes, but causes of this variation are unclear. The rate‐of‐living hypothesis posits that physiological damage from metabolism causes species with faster metabolic rates to exhibit lower survival rates. However, whether increased survival commonly observed in tropical and south temperate latitudes is associated with slower metabolic rate remains unclear. We compared metabolic rates and annual survival rates that we measured across 46 species, and from literature data across 147 species of birds in northern, southern and tropical latitudes. High metabolic rates were associated with lower survival but survival varied substantially among latitudinal regions independent of metabolism. The inability of metabolic rate to explain latitudinal variation in survival suggests (1) species may evolve physiological mechanisms that mitigate physiological damage from cellular metabolism and (2) extrinsic rather than intrinsic sources of mortality are the primary causes of latitudinal differences in survival.

Meta-analysis reveals that resting metabolic rate is not consistently related to fitness and performance in animals

“…Further, survival probability may simply be related to stochastic processes that acts indiscriminately on individuals with any RMR, or because stabilizing selection removes individuals with extreme high or low RMR (e.g., Artacho and Nespolo 2009). Recent studies published after our systematic search demonstrate a range of correlations that further suggest taxaand context-dependence; snails demonstrate a positive, stabilising correlation between RMR and survival probability (Bech et al 2020), many tropical birds show a negative correlation between BMR and survival (Boyce et al 2020;Scholer et al 2019), and BMR has no correlation with survival in root voles (Książek et al 2017). More pertinently, why more direct measures of 'true' fitness do not correlate with RMR remains to be tested, and these findings places the relevance of statements about traits that are 'fitness proxies' in doubt as reasonable proxies for fitness, unless they are validated within the study itself.…”

Rethinking the fast-slow continuum of individual differences

“…The main stumbling block for the metabolic theory is the fact that the fast-slow continuum remains largely intact after body size is controlled for (Section 2.1). This suggests that broad patterns of covariation between life history traits may owe more to selection than to simple metabolic constraints (for recent data in this direction, see Boyce et al, 2020;Malerba & Marshall, 2019). Moreover, body size is implicated in all sorts of trade-offs: a larger body can reduce predation risk, enhance mating success, buffer the effects of competition in high-density ecologies, and so forth (see Brown & Sibly, 2006).…”

Inferring Whole-Organism Metabolic Rate From Red Blood Cells in Birds

“…The importance of metabolic rate (the rate at which energy is produced while consuming oxygen and substrates) for ecological and evolutionary concepts is nowadays universally acknowledged (Glazier, 2015;Gangloff et al, 2020). Indeed, variation in metabolic rate has been linked to life-history traits like growth, reproductive output, and survival (Pettersen et al, 2019;Boyce et al, 2020), as well as behavioral traits (Biro and Stamps, 2010;Holtmann et al, 2017;Mathot et al, 2019) and hormonal profiles (Haase et al, 2016). Metabolic rate is also thought to be a key mediator of the fast-slow life-history continuum (Jimenez et al, 2014a;Auer et al, 2018;Chung et al, 2018) and to underlie various life-history tradeoffs (e.g., those between oxidative damage and longevity: Speakman et al, 2015;or sleep and predation: Ferretti et al, 2019).…”