Are We the “Custodians” of the Planet?

What are the fundamental roles of human beings in the larger picture? Are we the “custodians of the planet”? In terms of being the most “intelligent” and “evolved” species on the planet as many claim we are, does that mean we are owed the privilege of taking advantage of “lesser” animals in whatever way suits our cause? Or do we also have responsibilites to protect and defend the innocent lives of those helpless to defend themselves against us?