Jaguar's and Climate Change

What if there was a nuclear apocalypse? Let's say that this nuclear apocalypse affects life on Earth from all over. But there's a lot of places on Earth, so let's just focus on one spot: the rainforests. But that's also a broad spectrum, so let's narrow it down to just one animal: a jaguar. To fit this new wasteland, the jaguars pelt color would be altered not only by radiation but also by evolution to fit a new environment. It's pelt would turn to shades of brown to match the sullen landscape it now resides in of dirt and shrapnel. Secondly it would most likely shrink in size to make up for it's now miniscule diet, since prey has been dwindling by a lot. Instead of six feet, it would more likely be around four feet in length. That's how our jaguars would change.