Terminology

I love this site....thanks for contributing!

QUESTION:  I'm looking for an elegant term or word to describe a species that is a keystone? capstone?  species ..... the best corrollary to offer is the term "the canary in the coalmine" ... from which  critical conclusions can be drawn by examining their predicament/health. An example might be the certain tree frog that told us the entire Amazon was in huge trouble. (I forget the frog type.)

     It would be a biological term to indicate that if this one species is in any way compromised, all other balance/future/survival for all other species  -- perhaps in an ecosystem, tho I'd like a term for the whole web of life -- is severely at risk.

      I know we have the apex predator and can look to the health of, say, eagles in an ecosystem and if they're in trouble we know the entire foodchain beneath them is already at risk.

     I want a term that is known in biology or ecology or even poetry ;) (please include definition in your reply) to describe just this!  I hope one exists because I need it as a metaphor for a profound discussion I'll be launching. I always appreciate any recommendation of secondary sources to read as well.

      You didn't mention this in your explication above, so I must specifically request that you respond to this via my email and don't make me come back to this site and search and search and hope it's been answered. I will look forward to hearing from you.

    Thanks heaps!