I don't want to see a misunderstanding of care so let me state that a plant and insect only diet without calcium supplementation for bearded dragons, whether through vertebrate or calcium powder sources, results in conditions like metabolic bone disease. Do a quick search on bearded dragon diets in the wild, especially from Australian museums and zoos, and you'll see most believe occasional rodent and small lizards make up a small part of bearded dragon's diets in the wild. There's some good books that go more in depth. They are quite capable of catching smaller lizards or coming upon a rodent nest. Calcium is present in comparatively very small amounts in most invertebrates and ,in captivity, I would not recommend using the specialty "calcium rich" invertebrates like phoenix worms as the primary food source.
It is possible to raise healthy bearded dragons without any vertebrate supplementation in captivity using calcium powder. However, it is also beneficial, though not necessary if using calcium powder, to occasionally supplement with small rodents.