The reasons behind endangerment of one species cannot easily be applied to another, UC Davis conservation biologists warn in a new study.

In the December issue of the journal Conservation Biology, professors Tim Caro, John Eadie and Andrew Sih examine the common research practice of using surrogate animals to predict or identify what is endangering another species. Such "umbrella" or "flagship" substitutes are chosen because they are biologically similar to the troubled species or can be used to develop a predictive model to which the original species can be related.

But the UC Davis authors say population disturbances affect common and rare species in different ways. "After all, target species are the ones that are doing poorly, whereas [others] continue to persist or even thrive despite human disturbance," they write.

The authors list three criteria that must be met in order to use substitute species with confidence -- and then conclude that meeting all the criteria is virtually impossible. Therefore, they say, "Where at all possible, we advocate making every possible effort to examine the target species directly before resorting to substitute species."