They do eat each other, that's for sure.
We drained and cleaned out a tiny pond on a friends place on time.
It was down to maybe 30x20 a few feet deep.
All that was in it was bull frogs and tadpoles.

As the water went down the bull frogs feasted on all the tadpoles.
It was funny to watch the last bull frogs too stuffed to move.
Literally burping up tadpoles before being able to slowly hop away.