My stances as bridge crew, Spaceship Earth are as follows:
* Species always move in response to environmental shifts. These natural movements should be respected and supported. It's not as much of a crunch as people might think because in most areas, some species will move out as others are moving in. Yes, there will be some calamities, but that's supposed to happen.
* However, you are at liberty to slay noxious lifeforms that are attempting to invade your territory. I don't hesitate to stomp velvet ants which are not historic to my area, because I do not wish them to establish.
* Exotic species are those transported by humans into a new location. If they become a nuisance due to overpropagation, they are then invasive species. These should be removed if at all possible. Never underestimate humanity's ability to destroy things.
* It is critical to protect escape routes if we wish species to survive. The easiest ways to do this are connecting national parks or other refuges and establishing riparian corridors along the north-south axis, along with mountain access in areas where that's the closest source of colder temperatures.
A much thornier question is whether humans should assist species in making survival moves they could not make on their own. Historically humanity's record of good choices in moving species is nearly nonexistent and its tendency to create disasters is high. But without some help, you can forget about most of the flora and fauna in Europe because their mountain ranges run east-west, blocking the retreat. They hemorrhage species with every major shift, and that's going to be a great deal worse now that humans have wrecked the ecosystem. I have not yet formed a firm stance on this issue as there are compelling arguments on both sides. It may need to be decided on a case-by-case basis.
I am more sympathetic to species that will fall off the cliff and die without assistance. This applies to many alpine species due to the layered habitat zones. Those at higher elevations have nowhere to go. Additionally, every move upward necessarily shrinks the available territory. This makes mountains another high priority for protection.