Can a Fish Save an Ecosystem?

All ecosystems have a linchpin or series of linchpins around which various life forms depend. In the far north that linchpin is the salmon. “Wild Salmon Center President Guido Rahr states it better and more eloquently than I ever could in the TEDx Talk below (thanks to Field & Stream for the find). I won't tread that ground again.
  But what about other ecosystems? What are their linchpins that hold the environment together and that others depend? Can we identify them and what are we doing to preserve them?

The American Bison used serve a similar purpose as the salmon through the interior of North America. Their regular migrations across plains had a dramatic affect on the ecosystems and balance.

North American Bison range map by year. Source:
http://en.wikipedia.org/wiki/American_bison

Now, perhaps in place of the bison, whitetail deer that used to be found more often in woodland landscapes have moved west. They might occupy an open niche, but they don't have the same impact as the massive herds of buffalo that once roamed the plains. Animals and organisms that relied on the impact of the bison – prairie chickens, prairie dogs just to name a few – are lost.

Similarly, the Passenger Pigeon used to migrate throughout the east and midwest in numbers that by an estimate where huge. Undoubtedly they played a similar role in that ecosystem at that time. What we lost at that time is difficult to say.

Passenger Pigeon former distribution in orange,
breeding grounds in red. Source:
 http://en.wikipedia.org/wiki/Passenger_pigeon

Years ago, Jimmy Buffet wrote an article (that I can't find a link to) but it was a long the lines of "everything wants to eat a quail - including me." We know quail are natural prey for many predators and in trouble across most of their native range. As are ruffed grouse in many areas. Monarch butterflies the same. These are just the obvious examples.

We need to look and understand the critical issues and populations, and identify strongholds now so that we can move forward intelligently.