Answer:Because of the lack of owls, the mice population would explode, similar to how wolves were exterminated in Yellowstone and how that allowed deer population to increase steeply and cause damage to the environment, because the mouse population was eliminated of a big predator, the mice population would have no sort of boundary to restrict it from becoming an invasive species. That could cause damage to the environment and could cause the food chain to crumble. For the types of mice, I'm not sure because it depends on the area and species, could you specify further?