What do the difficulty levels mean?

[HolyHotFries]

A walk in the park
Challenge accepted
Ultra-hardcore
Pure insanity
Your worst nightmare

Does anyone know the difference between these difficulty levels? Is it just more enemies? Less days between waves? Is health or damage effected? Is the economy effected? Less resources on the map?

[eizenhorn91]

Resource sources on map, their count and spawns, resources on map (carts), waves, days between them, count, enemy types, initial enemies on map count and types and spawns. Health or damage not affected.

[HolyHotFries]

Thanks!