After going over my notes from Mei-Yin's camp, I've concluded that the animals on this island are not only used to humans, but used to captivity. Even with their accelerated growth rates, their behavior indicates that they have been regularly domesticated for decades at least. Otherwise, they'd never obey the whims of mankind so easily.
With that in mind, I believe that my theory about this island being curated is back in play. In fact, it's possible that not only are animal populations being controlled, but that the animals themselves are genetically modified. However, before I bring this to Rockwell, there's one more rumor that I want to confirm.