Chapter 8
BioEnergetics Model – Landscapes to Populations
Mass gain Mass Gain is the final process that determines how much lean and fat mass will be accumulated in the animal’s body per day. This sub‐model uses Energy and Protein balance outputs and daily Target Energy to define the kilocalories and protein available for growth after having met maintenance demands. The minimum amount between Gain Target and energy and protein available for growth is chosen to determine mass growth. This is because the model assumes that the individual will gain the minimum amount of mass necessary to reach the Gain Target even if there is more energy and protein available for growth. The model also assumes that the animal prioritizes the lean target over that of the fat target. Lean gain is determined by the amount of available protein for gain (Protein Balance) and energy for gain available (Energy Balance). A one kilogram gain in lean mass requires 0.222 kg of protein and 1200 Kcal (Robbins 1994). Fat gain is determined by the remaining energy available after lean gain with a one kilogram gain in fat requiring 9100 Kcal. When the individual is starved (food limited), body lean and body fat are used as an energy source. The animal therefore loses body weight.
Preliminary Results And Discussion Figure 2 illustrates a set of preliminary model outputs demonstrating the effects of four different diet compositions (A. low energy & low protein, B. high energy &low protein; C. high energy &high protein; and D. low energy & high protein) on body mass dynamics over an active season (180 days; den emergence to denning). Impacts of energy and protein are not only in the mass accumulation (kilograms of lean and fat), but also in the time necessary to reach these goals. As expected, in diets with low available protein (scenarios A & B), animals do not develop their lean mass (line 1 [red]). However, they are able to accumulate fat (lines 2 [blue] & 4 [purple]) if energy is present. These model dynamics assume that the animal is an adult. In the case of immature animals, protein deficiencies would affect body size, since protein is the key element of structural growth.
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