In the YellowStone National Park example, a major forest fire burnt millions of acres and change a closed system overnight. If Darwin was there before the fire he would have seen and cataloged all types of flora and fauna, from apex predators all the way down. If he returned to Yellowstone 10 years after the fire, expecting to see another closed system like Galapagos, where all is still the same, he would have instead witnessed the entire flora and fauna distribution of Yellowstone is now different over millions of acres; WTF? Even new species, he did not catalog before, may have appeared in only 10 years. These would have migrated elsewhere but his theory says evolution caused this. He would sense this is not exactly right.
The best explanation for changing life, in a changing natural environment of this scope and sped, would not be competition between males of the same species for reproduction rights. This open system would be better explained with mobility of individuals seeking food and shelter. As the system reaches steady state and becomes closed, then the other may be more appropriate.
Where you and I differ is I am not using evolution as religious dogma meant to be a certain way. Rather I am changing the parameters of Darwin's experimental conditions, so the logic results come out differently.
England would not fit his theory either, since there were other wild cards. England was in flux with human intervention such as selective breeding of livestock, development of the land, and foreign trade connected to animal and plant collectors, so the system would be too open for that theory. If a English child received a fish from India and he lets it go in the lake, now we have a new species in the area that might mate with the local fish; mutation. Galapagos was closed enough to factor this out. I suppose Darwin needed to start with a simple foundation before he and others could build the finished model.
Birds often eat fruit and then fly off only to excrete the seeds far way, introducing a new species in the area. If we assume this was a closed system, we would call that a mutation.