When I was little I unwittingly made an ecology experiment in the local pond. It had been long ago stocked with white, orange and copper colored goldfish, people would walk around the pond and say, "ooh, look at the goldfish", dogs would jump in the pond and get covered with muck, bullfrogs would croak in the evening, deer would come drink in the mornings, periodically someone would dredge the pond, and it had been that same way for over 50 years. I liked fishing at other local ponds and came home one day with a bucket of little bluegills and a couple catfish. They stayed in an aquarium for some time but then I thought to "just let them go", and put them in the goldfish pond. The next spring I was surprised to see little bluegill fry around the edge of the pond. Within 2 years I couldn't see any gold fish. There were a couple brown-fish (copper colored goldfish), but nothing bright, and there were many bluegills and a few little catfish. A few years after that the community filled the pond and returned it to meadow. So a non-native fish was out competed by natives, but not native to that pond, and the "return to the wild" meant the pond and all the associated habitat and enjoyment was lost.
I hear and read of this general opinion, supported by state laws on habitat restoration and hunting, that native is good and non-native is bad. But I have to wonder sometimes. Does a barred owl really look all that different from a spotted owl to their rodent prey, and wouldn't either be better than no owl? Is a collared Eurasian dove all that different from a mourning dove? Is the "invasive" trout species outcompeting the endangered trout because the streams are getting a little warmer and only the fittest are surviving? What is bad and what good, or are both but anthropomorphic delusions? Would those iguanas in Florda still be pests if there were no canals to dig, garden trees to eat or patios to defecate on? Or would they just be more gater food?
Would there be some other bird species plaguing American farms if the house sparrows, starlings and rock pigeons were not introduced centuries ago? American crows, blackbirds and chickadees, maybe? After all, it's not just the birds, it's the food for the birds that breeds more birds. Some other native bird can always sieze the opportunity (like crows did); the introduced pest birds had already evolved to take advantage of human activity, they arrived pre-adapted for that habitat, ironically habitats made by modern humans, who were themselves invasive. Whoa!
Do non-native, invasive, pest, mean different things in different places at different times?