One of the concepts conservationists often try to use to indicate the limitations of economic approaches to valuation is to distinguish between things that have intrinsic value and those that have instrumental value.
Happiness might be an example of an intrinsic value, because being happy is good just because it's good to be happy, not because being happy leads to anything else. If happiness seems too trivial, ``human well being'' might be a better example.
Having a net worth of a million dollars is an instrumental value. Having those assets is good only to the extent that you can use them to get something else--like happiness or personal well-being.
Perhaps if we all agreed about the source of intrinsic value in nature, arguing that biodiveristy is intrinsically valuable would be compelling.4 Things that are intrinsically valuable seem to be of virtually infinite value, so it is worth almost any price to save them. Unfortunately, I doubt that we'll ever agree on a source of intrinsic value in nature. To see why, let's take a brief tour through some different ethical theories.