Abstract
Links between metabolism and components of fitness such as growth, reproduction and survival can depend on food availability. A high standard metabolic rate (SMR; baseline energy expenditure) or aerobic scope (AS; the difference between an individual's maximum and SMR) is often beneficial when food is abundant or easily accessible but can be less important or even disadvantageous when food levels decline. While the mechanisms underlying these context-dependent associations are not well understood, they suggest that individuals with a higher SMR or AS are better able to take advantage of high food abundance. Here we show that juvenile brown trout (Salmo trutta) with a higher AS were able to consume more food per day relative to individuals with a lower AS. These results help explain why a high aerobic capacity can improve performance measures such as growth rate at high but not low levels of food availability.
Highlights
Metabolic rate reflects the energetic cost of fuelling all processes and functions needed to support life [1]
Standard metabolic rate (SMR), organisms must grow, reproduce and evade predators but within the bounds set by the upper limits of their maximum metabolic rate (MMR); the difference between MMR and standard metabolic rate (SMR) is referred to as aerobic scope (AS)
Larger fish were able to consume more food, but after controlling for size, individual differences were explained by their metabolic traits but to varying degrees: average daily consumption was greater in individuals with a higher AS (F1,26.0 1⁄4 8.77, p 1⁄4 0.006; body mass: F1,26.0 1⁄4 127.5, p, 0.001) but was not a function of SMR (F1,26.1 1⁄4 0.53, p 1⁄4 0.47; body mass: F1,26.1 1⁄4 97.2, p 0.001) when the effect of each metabolic trait was considered separately
Summary
Metabolic rate reflects the energetic cost of fuelling all processes and functions needed to support life [1]. An organism must expend energy on basic functions that maintain homeostasis. Consistent individual differences in metabolism are associated with components of fitness such as growth, reproduction and survival [3]. These relationships can vary depending on environmental conditions, most notably with food availability, whereby a high SMR or AS is often beneficial when food is abundant or accessible but less important or even disadvantageous when food availability declines [3,4]. We know very little about the importance of these metabolic traits for non-behavioural aspects of foraging such as feeding capacity that directly influence energy intake
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