Evolution
Is filling the Fat Tissue card mandatory whenever a species could eat?
The designer said in direct replies that empty Fat Tissue is not hunger, and the trait text says a species may add food to it.
No. Filling Fat Tissue is optional. A Hungry species must eat up to its Population, but nothing requires it to keep eating to fill the card, whether it is a plant eater or a Carnivore. Starvation still removes only the Population that went unfed.