We are not at the top of the food chain. Armed with a powerful and accurate firearm, we can take down any animal on the planet, but only if we see them first. If a mountain lion, bear, or orca sees you (on an ice floe) before you notice it, chances are it will get you before you have a chance to cover your ass.
We are at the top of the chain when we maximize our potential. If we put our mind to it, we could mercilessly eradicate nearly anything (except probably cockroaches and rats)
When we allow ourselves to end up floating on the ocean or stumbling around unprepared in the arctic tundra, we are going to end up as worm food. Without our brain and the advantage it gives us, we are pretty much fleshy pulps.