So, the process that began the evolution of sapience in humans was ultimately triggered by a changing climate forcing chimpanzees into a drastically new habitat; I am trying to write about a race of sapient arboreal aliens who are adapted for forest dwelling much better than humans are physically anatomically adapted for plains-dwelling.
It occurs to me that, for this to work, they will have to evolve sapience without their basic habitat changing, so I came up with this explanation: Their presapient ancestors lived on one of two continents that had been separated for tens of millions of years, and eventually these two continents remerged with one another; As a result of this, there was essentially two species for every ecological niche on the same landmass, which caused a drastic increase in interspecies competition; Sapience then evolved as a result of needing to rapidly develop a drastic advantage in order to avoid being outcompeted by a species brilliantly adapted to the exact same ecological niche.
My question, then, is this: Is this actually enough evolutionary pressure to cause sapience? Is the need to outcompete a equally (if not more so) well adapted rival enough justification for sapience, or does the scenario I've worked out not work in reality? If not, how else can sapience emerge without a change to basic habitiat?