As for ecology: could it be that not every part of the cake is stable? As in, at some places the surface has little or no crust to seperate it from the hot inner layers, leaving a utterly inhospitable chunk of land of lifeless land?
Perhapes creatures have developted to adapt to the structure: Great serpents lay ther very durable eggs at the Rim only to have them be scattered vie the Bores, creating seasons where foot-long meaty tubes can be scooped up by the hundreds. This could be a time in which primitive cultures can partake in a salmon-like collecting season, which might be interesting. Over time, these small "Bore Worms" make there way down to the ends of the cake, in which they breed like there forfathers did while packing on the pounds. Hence, the young and tasty Bore Worms become the mighty Rim Wyrms, able to hunt both whale, men, and younger Rim Wyrms.