DeusKyogre1286 t1_ism2veo wrote
As a person who did their Honours thesis on a related question, I can only put most of my thoughts on the first question and its relation to North American fish ecology, though I can imagine that given how long evolution/speciation takes, that barring the specific case of African cichlids, most lakes have not really existed for very long. In North America, especially Canada, most of our lakes were formed from glaciation a mere 10 000 years ago - a great glacier quite literally scraped away holes in the land, and these became filled by meltwater, forming lakes and rivers, many of which were once far more interconnected than they are now so there was once an opportunity to disperse where none now seemingly are.
Given this scenario, we can then think about how fish get into these lakes, and eventually begin to speciate, but the fact is that, there just hasn't been a great deal of time geologically speaking for fish to even start diverging, because although these lakes may have formed 10 000+ years ago, the fish probably didn't get there 10 000+ years ago. Some of the fish are of highly conserved lineages, and spread out from refugia in the southwest and southern parts of North America, but many more, especially the most important varieties are actually the product of human activity - people literally dumping lakes with fish to stock them in the 19th century. Think about that - even if these lakes are quite isolated, there hasn't been all that much time for speciation (200+ years), and most of these lakes aren't actually fit for habitation and only have fish as they are cyclically restocked, usually on an annual basis.
Lastly, as u/GreenStrong has provided, there has recently been some suggestion that ducks are acting as zoochoric agents, and spreading out fish eggs, but although this is a plausible practical vector of dispersal under lab conditions, it's still unclear (as far as I've heard!) if this actually could have happened enough times for it to have been a meaningful mechanism of dispersal.
TinKicker t1_isnxad5 wrote
Just to add a related anecdote to your post….
My family has owned property on Manitoulin Island (world’s largest freshwater island, in Lake Huron) for over a century. The island is home to more than one hundred individual lakes…all formed at roughly the same time and in the manner described above.
However, each lake had its own individual speciation. Brown trout were only found in this lake. Whitefish were only in that lake. Walleye in these two lakes over there…. Smallmouth bass and yellow perch, for some reason, could be found in pretty much any of the lakes, although the perch from the largest lake had begun to diverge in their appearance from normal yellow perch; they were darker in color, had a pronounced dorsal hump, and would reach sizes way beyond normal perch. Locals just called them giant perch.
Unfortunately, cormorants, careless people and government-run stocking programs have caused major changes to fish stocks in the last twenty years.
Frammingatthejimjam t1_iso8uef wrote
Somewhat off topic but doesn't Manitoulin have the world's largest island on a lake on an island on a lake?
TinKicker t1_iso96k3 wrote
Yep! Lake Kagawong on Manitoulin is home to Kakawaie Island, which has a small unnamed body of water in its interior.
weirdclownfishguy t1_ismrnwh wrote
African Cichlids are a really cool example of evolution producing more or less that same result multiple times. Lakes Malawi and Tanganyika have so many species that look so similar to each other
Viewing a single comment thread. View all comments