2.3.2. Maintenance
The mobilized energy \(E_M\) fuels all metabolic processes starting in priority with the costs of maintenance of existing tissues \(E_m\), which is often referred to as the standard metabolic rate in ecophysiology literature. Here, we include in maintenance costs also routine activities of individuals including foraging and digestion, so that they might be compared to routine metabolic rate in the ecophysiology literature. The maintenance costs are explicitly modeled to describe the share of mobilized energy between maintenance and the production of new tissues [Charnov et al., 2001, Holt and Jørgensen, 2014, Mollet et al., 2010], with precedence of the former over the latter, as well as to link mechanistically starvation mortality to energetic starvation when neither mobilized energy nor gonad energy reserves can cover the costs of maintenance (see next section New tissue production for more details).
The maintenance energy rate \(E_m\) scales with individual’s somatic mass \(w(i,t)\) with the same exponent as maximum ingestion rate. Thus, for a given temperature, the production of new tissues, and notably somatic growth, is not limited by disproportionately increasing maintenance costs relative to ingestion rate as somatic mass increases [Lefevre et al., 2017, Lefevre et al., 2018]. In addition, the maintenance rate also increases with the temperature \(T(i,t)\) experienced by individuals [Gillooly et al., 2002] and can be described as
with \(C_m\) the mass-specific maintenance rate and \(varphi_m\) the Arrhenius function describing the effect of temperature on \(E_m\), defined as:
with \(\varepsilon{}_m\) the activation energy for maintenance rate increase with temperature.