A giant panda is a carnivore's digestive tract (short gut, no cellulose-fermenting foregut) pointed at a diet of almost pure cellulose. That mismatch is modeled directly: only the dry-matter fraction of intake carries calories, and only a small share of that gross energy is actually absorbed (apparent digestibility) — the rest passes straight through:
assimilated = intake_kg/h × 0.30 (dry-matter fraction)
× caloric_density(part) × digestibility(part)
net_kcal/h = feeding ? assimilated − BMR×mult×1.15
: 0 − BMR×mult×0.85
reserve(t+dt) = reserve(t) + net_kcal/h × dt
Young shoots digest far better than woody culm (roughly 27% vs 13% apparent dry-matter digestibility here, leaves in between) — which is exactly why wild pandas migrate to track emerging shoots. Baseline BMR is set low, reflecting measured giant-panda resting metabolic rate running about 38% below the value predicted for a placental mammal of the same body mass — one of the adaptations that makes a bamboo diet survivable at all, alongside the near-continuous feeding time budget the slider controls.
- Feeding time budget — wild pandas spend roughly 55–60% of each day foraging; push it below ~35% here and the reserve trends into deficit even on shoots.
- Fat reserve chart — the only real store of surplus energy; it saturates near a healthy ceiling and empties toward starvation if net rate stays negative for days.
- Net-rate gauge — flips between the assimilation gain of a feeding bout and the metabolic drain of a resting bout in real time.