I've always been fascinated by the ice age and theories about how the ice age affected the spread of species over the continents. I'm sure some of you have heard about the theory/hypothesis about Dall Sheep and their current locations today correlating with the past locations of the ice sheets over Alaska. Interestingly, I have also been reading about lake trout distribution and how their current range almost perfectly matches the maximum extent of the ice sheets over North America during the ice age.
My question is to anyone with expert knowledge on the subject is; why do the ranges overlap so well? What is the significance of the two overlapping ranges? I am assuming that the ice sheets had something to do with the creation of the large oligotrophic lakes that the lake trout thrive in, but what or how did the lake trout survive on top of, underneath, or in the middle of gigantic ice sheets? That part just doesn't make sense to me. It makes sense that after the ice sheets started melting, that the meltwater produced lakes that the lake trout took refuge in, but how did they get in or on the ice to begin with? Did they live in the outwash plains at the terminal ends of glaciers? Did they live in ice-dammed lakes like Glacial Lake Missoula and Glacial Lake Ahtna? If so, wouldn't they all die when the dammed lakes burst open, causing massive floods? I realize nobody was there to witness these events, or at least there are no historical records of these events taking place so any explanation would be purely speculative, but I just thought that maybe somebody with expert knowledge on the local geology might know of some plausible explanations that have been proposed. If so, I would love to hear a good explanation. Thanks.