My story takes place thousands of years in the Earth's future after a climate apocalypse. It centers around Alaska and western Canada, but the climate in that region has transformed to more closely resemble modern day Central America.
There is a lot of focus on the natural world. Specific descriptions of plants and animals are crucial to my story, so I'm having trouble pinning down what kinds of plants and animals can feasibly exist in this setting. I'd love to be able to include some big cats and primates and other plants and animals from Central or South America, but I feel like even with a gradual warming of the climate, the huge desert region in between the jungles of southern Mexico and the forests of Northern California would be an unpassable boundary for most species.
The time frame isn't set in stone, but we're talking at least 2,000 years after a major climate related mass extinction, probably no more than 5,000 years. So what can I get away with? Are there certain plants or animals that are more conceivably capable of making that kind of migration without human intervention?