Stake is a part of bounty you get.

Say the bounty is 1,000,000 tokens and there are total 1,000 stakes in total for all participants, that means that 1 stake is 1,000,000/1,000 = 1,000 tokens

It is made this way to make sure that there is enough bounties for everyone taking part, and there is no unneeded allocated funds left in the end.