Differential effects of food availability on minimum and maximum rates of metabolism

Abstract

Metabolic rates reflect the energetic cost of living but exhibit remarkable variation among conspecifics, partly as a result of the constraints imposed by environmental conditions. Metabolic rates are sensitive to changes in temperature and oxygen availability, but effects of food availability, particularly on maximum metabolic rates, are not well understood. Here, we show in brown trout (Salmo trutta) that maximum metabolic rates are immutable but minimum metabolic rates increase as a positive function of food availability. As a result, aerobic scope (i.e. the capacity to elevate metabolism above baseline requirements) declines as food availability increases. These differential changes in metabolic rates likely have important consequences for how organisms partition available metabolic power to different functions under the constraints imposed by food availability.

Keywords: Salmo trutta; energy metabolism; metabolic power; plasticity; standard metabolic rate.

Figure 1.

Change in maximum metabolic rate (MMR), standard metabolic rate (SMR), and aerobic scope (AS) of juvenile brown trout as a function of changing food availability. SMR and MMR were first measured after fish had been on an intermediate ration for 28 days and then again after they had been switched to either a lower, intermediate (i.e. the same as previously), or higher ad libitum ration for an additional 28 days. AS is defined as the difference between SMR and MMR for each fish. Plotted are back-transformed metabolic rate values (± 95% CI) standardized for a 10 g fish; positive/negative values indicate an increase/decrease in metabolic rate relative to initial values. Change in maximum metabolic rate (MMR), standard metabolic rate (SMR), and aerobic scope (AS) of juvenile brown trout as a function of changing food availability. SMR and MMR were first measured after fish had been on an intermediate ration for 28 days and then again after they had been switched to either a lower, intermediate (i.e. the same as previously), or higher ad libitum ration for an additional 28 days. AS was defined as the difference between SMR and MMR for each fish. Plotted are back-transformed metabolic rate values (± 95% CI) standardized for a 10 g fish; positive/negative values indicate an increase/decrease in metabolic rate relative to initial values.