On the whole Susanna I agree with your comments, surely though it is every-ones duty to protect and preserve animals and the environment for our offspring.
As a Christian (an aging one of no fixed church movement) I remember the old stance Christians had with animals, believing that they had no souls and humans could do with them whatever they felt necessary,,, I always had a problem with the animal thing was one of the two hundred or so reasons that I could not settle into a fixed religious group, I had thoughts (Biblically based) that did not fit with traditional Christian thinking. They read something into Genesis and Psalms that I couldn't see?
Modern Christian thinking however, is largely sympathetic to animals and less willing to accept that there is an unbridgeable gap between animals and human beings.
Although most theologians don't accept that animals have rights, they do acknowledge that some animals display sufficient consciousness and self-awareness to deserve moral consideration. The growth of the environmental movement has also radically changed Christian ideas about the role human beings play in relation to nature.
Few Christians nowadays think that nature exists to serve humanity, and there is a general acceptance that human dominion over nature should be seen as stewardship and partnership rather than domination and exploitation. I personally do believe that humankind was charged with the duty to protect the environment, even if one doesn't believe that, humankind has a duty to the planet that is home and unlike you, I don't believe that other animals will continue to pop up as a replacement to those lost, no matter how humankind treats the planet...