Squirrels in Paradise - For squirrels, climbing on to Catalina must have been a bit like winning the lottery. How so? Well, back on the mainland there would have been more than 20 species of squirrels all competing for resources. That meant the food and shelter were in high demand and the competition fierce. That would also have meant limited food and shared habitat for roaming, hiding or raising young. On top of that, there are a lot more predators on the mainland, all interested in a nice squirrel dinner. Being able to hide would have been really important. You’d have to be quick, and probably a little nervous and twitchy since you could be killed at any minute by any of a variety of animals all out to get you. All of that competition and pressure to survive would really cramp a squirrel’s lifestyle.  It would also likely favor agility, a lean frame and a big energy investment in scrambling from predators.

Now imagine this squirrel arriving on Catalina to discover it is the only squirrel species here. No chipmunks, fox squirrels, gray squirrels or thirteen-lined ground squirrels – nobody else in the squirrel realm. There would have been no competition, and that would mean that all of those plants, little seeds, big seeds, water, and habitats were there for the taking. On top of that, there weren’t many predators around. Life without coyotes, for example, would have been a really pleasant surprise. Without competition and with limited predation, the squirrels would have had it made: Eat what you want, dig a burrow anywhere you like, and take it easy. And more calories would be going in with less energy expended, creating a recipe for plumping up. So there you go: big squirrels.

The important thing to understand is that packing on a few extra ounces over a couple years doesn’t make a giant – it just makes a fat squirrel. The fact is, there hasn’t been nearly enough time for evolution. But, in time, gigantism could come to pass with, day in and day out, squirrels eating all they want and lazing around. Not being confined to their old lifestyle, they could expand their horizons by hunting bigger seeds and fruits, which might mean there would be an advantage to being a little bigger. Not having to avoid predators at every turn might make large size less of a problem. After thousands and thousands of years of nature favoring a bigger squirrel…voila! – a giant emerges on the scene.

We need to add a final word about genetics. Remember how we talked about how gene flow is limited on isolated islands? Imagine that all squirrels on Catalina were the descendants of just one female squirrel who landed here and immediately gave birth? And what if she had a genetic anomaly that favored “smallness” over all things? That could put the brakes on everything we just talked about.

On the flip side, what if our founding squirrel had genes that put her at the biggest end of the squirrel spectrum. That might accelerate a move toward gigantism. We may never know exactly how all of these things came together, but given that we ended up with significantly bigger squirrels here, some combination of these things clearly came together. The name Catalina California ground squirrel incidentally, makes things official. Our California ground squirrel has become different enough to be considered its own subspecies, and one of Catalina’s endemic giants.

... While the Foxes Get Smaller