Alfaro et al. 2009 : Fostering Other Sorts of Diversity

Alfaro et al. point out that the PJ innovations could have been a 'key innovation' that allowed them to successfully colonize new environments or develop more functional/trophic diversity. I find these statements to be intriguing merely for suggesting that different diversity currencies (stealing a term from DJ) could be increased by key innovation, independent from each other. What could this mean for the Simpsonian ecological explanation of key innovations? Why would a key innovation increase speciation rate in some cases and not in others? (Never mind how to explain cases where key innovation affect extinction rates (as in insects...)

Really not quite certain why "establishing 'ecological' footholds" is less testable than allowing for a wider diversity of other trophic characters, as Alfaro et al. argue.