The concept of ecosystem services is a way of visualizing the instrumental value that nature has for human beings. Most ecosystem services can be performed by more than one species. This fact is sometimes used as an argument against the preservation of species. However, even though substitutability does detract from the instrumental value of a species, it also adds option value to it. The option value cannot make a substitutable species as instrumentally valuable as a non-substitutable species, but in many (...) cases, it can add enough value to make the species more valuable than the projects that threaten its existence. (shrink)