Earthchild

This story is set in the far-ish future of Earth, where humans have colonized space, and foreign life forms have done more than just colonized Earth... they've taken over so completely, that there are no Earth-native species left. This setting summary sounds a great deal like a fast-forward past the Chtorr series, however in this case we see the alien species competing for resources instead of working cooperatively; the system here is still in flux, finding its points of stability, if there are to be any. The narrative is told from the point of view of one last human surviving within it. Here's the blurb from the back cover: "She called herself Reee and she was the last human being on Earth. This was the one thing she was sure of. Because Earth was not a dead planet, not by a long way. There were all manner of strange plants and bizarre animals, and there were the blue boys who insisted they were human -- but she always set fire to them. There was however Indigo, the all-devouring protoplasmic ocean that was literally gobbling up everything in the world. And there was the enigmatic Emeroo to whom she owed her continued existence. There were also the so-called Martians -- humans who had fled to Mars and only came back to Earth to scout for survivors and vent their futile furies on the inhospitable homeworld. And that is as much as we are going to tell about Earthchild, one of the strangest and most fascinating science fiction novels DAW Books (or anyone else) ever published." .