This Exstinks

Number of Threatened Species May Be Drastically Underestimated

The number of species in danger of extinction may be some 50 percent higher than currently estimated, according to a new study in the journal Science. The International Conservation Union's Red List cites 12,200 species teetering on the brink, but researchers say at least 6,300 may be "co-endangered," meaning their survival depends on threatened host species. These parasitic species are often overlooked because they are less charismatic than their hosts (to say the least). For example, while seabirds are celebrated, the mites and lice that live on them don't get a lot of press. However, if the seabird disappears, the mites and lice go along with it. There's not always a one-to-one correspondence between host and parasite, so the "trick was in trying to determine how many other species could act as hosts and factoring that degree of dependence into the study," said researcher Heather Proctor. "While coextinction may not be the most important cause of species extinctions," the study concludes, "it is certainly an insidious one."