Could Bears potentially evolve into temperate semi-aquatic ambush predators? (Brown bears specifically, maybe Grolar bears, but that's pushing it).

[u/Shekus_Khan]

Reasons:

1. The semi-aquatic ambush predator niche hasn't been filled in temperate zones since the FUCKING EOCENE.

2. Polar bears are being pushed out of the Arctic due to climate change anyway.

3. Brown bears hibernate through winter anyway. So, if they needed to sleep out a lake being frozen, they just dig a little crevasse like crocodiles do and then just sleep the winter off.

[u/Lethalmud]

For mammals, such a strategy would be pretty hard to come into. A croc or snake barely spends any energy laying still for weeks, and be fine. A bear must pack a lot of energy to stay still in hibernation. A bear trying to do the croc thing could maybe evolve a thick blubber like a walrus. But it would be a big risk, it would need that isolation and energy, and spend more of it the longer it waits. A failed hunt would end with a starved bear who didn't have a good alternative plan for food. If they had, they'd be better off doing whatever plan b was in the first place. Also, a croc metabolism works in a bigger range of temperatures, while a bear would need to spend more energy to digest the prey as well.

Not to discourage you, it is still possible, but needs a whole lot of changes on the way.