The rocky ground/caves/falling dirt system partly exists to give the map some 'shape', as I found some early colonies looked really dull and lifeless when fully built out. BUT critically it also reduces the potential population of each map, as you can't turn all those caves into food supply, which is a bit of a hacky way to 'optimise' the game.
I am currently planning on making a game mode where you start with crabs, though, and the map shape is inverted with a cave in the centre. (This is part of the reason I want crabs to be as fleshed out as possible)