Gene Veith has a balanced article here on the environmentalism, Christians, and conservatives.
Though I'm not sure his argument works to the effect that because God created each species, therefore their existence is his will.
His point is well taken that Darwinists should care less about extinction. But from a theological viewpoint, perpetual existence is obvious not God's sovereign will [whereby everything comes to past.] And it doesn't seem to be his revealed will [which we are commanded to obey.] Since "is" doesn't automatically entail "ought," I'm not convinced. For example, can we really say "It was God's will that dinosaurs not be extinct?"
If you have an informed opinion on the issue, I'd be interested in hearing your thoughts on this.
Update: As Jeff and Josh have pointed out in the comments section below, Mike Bullmore (former TEDS professor and now pastor at Crossway Church in Kenosha, Wisconsin) has an article that may be relevant to this discussion about Christians and environmentalism: The Four Most Important Passages for a Christian Environmentalist (TrinJ).
Just to clarify my provisional position: it seems right to have a general disposition to preserve the species God has created. I want to be careful, however, to avoid our common impulse to create new rules or to go beyond what God has commanded. E.g., if one thinks it is an absolute requirement, then one could conceivably destroy an entire human community in order to preserve one spotted owl.