My main point was simply that moral positions that are not human-centric can and do exist. It strikes me that the difficulty with accepting the possibility of

My main point was simply that moral positions that are not human-centric can and do exist. It strikes me that the difficulty with accepting the possibility of human responsibility for non-human parts of reality may simply be a consequence of the moral position that is currently quite widespread - something like the one you describe. That position requires a line to be drawn (as OP noted), or perhaps rather values to be assigned, to the human and non-human, but that valuation is impossible in practice, and so really it just allows us to accommodate our own interests whenever the need takes us, and ignore our hypothetical responsibilities. As to the specifics of your point, I think the answer has to be no: if your position is explicitly to not elevate humans over other living beings then surely it is a contradiction to err on one side or the other?