A careful study in fossil fish is attempting to show the effect of environment alterations on species changes.

"Evolutionary biologists have used these living species to propose at least two models of how adaptive radiations work. One model proposes a single "burst" of divergence followed by a long period of relative stability. Another, sometimes known as the "general vertebrate model," introduced the idea of staged divergences, with habitat-driven changes in body type preceding diversification of head types."

http://www.physorg.com/news/2011-12-fish-fossil-head-first-diversity-vertebrate.html