Introducing a dominant civilization to a planet would more likely cause a sort of regression towards the mean in ecosystem diversity, at least over the short- to medium-term. In a highly complex and delicately-balanced ecosystem (i.e. Earth) it tends to reduce diversity as species and ecosystems are pushed aside, whereas in a non-existent ecosystem (i.e. Mars) it would cause something to exist in the first place, even if the system isn&#x27;t as complex as what evolved on Earth over billions of years.<p>There would certainly be more life on Mars after it was colonized, not less - even if that at first only consists of a few dozen species used to support humans.