Bunnies
Bunnies are way too good at reproducing. The females can already breed when they're just 5 to 6 months old. Their gestation period (pregnancy) only lasts a month and they can even give birth to duodecaplets (12 babies at once). After giving birth, they just need a few days before they can be impregnated again.
That basically explains why carnivores don't run out of food.