Table 1.
Major groups of common mechanistic growth models under ad libitum conditions, with specification of contribution and consumption processes (Eq (2)) and applied values of the allometric exponents b and d.
Fig 1.
Energy balance and resulting growth equation of the Maintenance-Growth Model (MGM).
Arrows represent fluxes of energy through a growing (non-reproducing) animal. Some of the energy ingested as food (S) disappears as losses through egestion or excretion. The assimilated energy (eS) is distributed between feeding costs (RF), maintenance costs (RM), growth overhead costs (RG) and energy becoming bounded in reproductive and somatic biomass (G). Maintenance costs are divided between basal (RMB) and negotiable (RMN) maintenance costs.
Fig 2.
Components of MGM for house crickets under ad libitum growth.
a) Ingestion rate (S) as a function of body mass (W), initially a power function that breaks at maturity (W = Wmat). b) Feeding costs (RF) as a function of ingestion rate (S), shaped as a ‘hockey-stick’. c-d) Maintenance costs (RM) as a function of body mass (W) for (c) males and (d) females, including basal maintenance costs (RMB) and negotiable maintenance costs (RMN). In males, basal maintenance costs increase linearly with total body mass. In females, basal maintenance costs increase linearly with somatic body mass until maturity (W = Wmat) and then increase linearly with reproductive body mass. Negotiable maintenance costs increase superlinearly with body mass in both sexes.
Fig 3.
Observed and predicted ingestion rate, growth rate and body mass as functions of age.
Data points represent individual empirical data for house crickets reared under ad libitum conditions at 28.6°C. Dashed curves are age-wise average values of individual empirical data. Model predictions (red curves) were obtained from numerical solutions to the growth equation (Eq (4)) with insertion of estimated fixed parameter values (SI9 Table in S1 File).
Fig 4.
Observed and predicted ingestion and growth rate as functions of growth rate and body mass.
Data points represent individual empirical data for house crickets reared under ad libitum conditions at 28.6°C. Dashed curves are age-wise average values of individual empirical data. Model predictions were obtained from numerical solutions to the growth equation (Eq (4)) with insertion of estimated fixed parameter values (SI9 Table in S1 File).
Fig 5.
Observed and predicted metabolic rates.
a-b) Total metabolic rate Rtot versus body mass (logarithmic scales) for male (a) and female (b) house crickets reared under ad libitum conditions at 28.6°C, predicted by MGM (Eq (SI5) in S1 File, solid curve) and calculated based on empirical data and literature estimates (Eq (SI37) in S1 File, dashed curve). Points represent calculated values for individuals. Dashed curves are average values of individual empirical data. Vertical dashed lines indicate mass at break point for feeding costs (S = S1). Vertical dash-dotted lines indicate mass at maturity. Predictions were obtained by inserting the numerical solution to the MGM growth equation (Eq (4) with estimated fixed parameter values from SI9 Table in S1 File) into model specifications of contributing metabolic components and summing (Rtot = RF + RG + RM). c-d) Predicted components of total metabolic rate versus body mass (linear scales) for males (c) and females (d). RF: Feeding costs (Eq (SI14) in S1 File). RG: Growth overhead costs (Eq (SI6) in S1 File). RM: Maintenance costs (Eqs (SI25) & (SI27) in S1 File). RMB: Basal maintenance costs (Eq (SI24) in S1 File). RMN: Negotiable maintenance costs (Eq (SI15) in S1 File). Filled circles (•) indicate break point for feeding costs (S = S1). Unfilled circles (o) indicate maturity.