Conservationists concerned about the extinction of plants and animals are overlooking the danger to thousands of other species that depend on the threatened ones and could themselves go extinct, researchers reported in the new issue of the journal Science.
Using a base of 12,200 plants and animals considered threatened or endangered, the researchers calculated what's been lost so far and what could be lost in the future.
"We estimate that at least 200 affiliate species have become extinct historically from the extinction of their hosts in these groups," the team wrote, "and another 6,300 affiliate species are currently 'co-endangered' — likely to go extinct if their currently endangered hosts in these groups become extinct."
Study co-author Heather Proctor, of Canada’s University of Alberta, said in a statement that "what we found is that with the extinction of a bird, or a mammal or a plant, you aren’t just necessarily wiping out just one, single species. We’re also allowing all these unsung dependent species to be wiped out as well.”
The team used a mathematical model to look at what's termed "coextinction," adding the study marked the first time the phenomenon had been quantitatively estimated.
Not just mites, lice
In many cases, species facing coextinction tend to be things like mites and lice. But some others are more likely to be missed by humans, such as a type of butterfly from Singapore that disappeared after the vines that had provided food for its larvae became extinct.
Overall, the researchers said, the loss of one species when a different one becomes extinct shows how interconnected the world is.
“What we wanted to learn was, if the host goes extinct, how many other species will go with it,” Proctor said.
“It would be easy if there were always a one-to-one relationship with a host and its affiliate; however, not all parasites, for example, are restricted to a single host species,” Proctor said. “The trick was in trying to determine how many other species could act as hosts and factoring that degree of dependence into the study.”
Beetles, butterflies at risk, too
Using their model the group calculated that extinction of the 6,279 plants listed as threatened or endangered by the International Union for Conservation of Nature would also result in the loss of 4,672 species of beetles and 136 types of butterfly.
Loss of the 1,194 threatened birds could also mean disappearance of 342 species of lice and 193 types of mites.
If the 114 endangered primates were to go extinct, they said, there could also be the loss of 20 types of nematodes, 12 lice and nine fungi to depend on the primates.
"While coextinction may not be the most important cause of species extinctions, " the researchers concluded, "it is certainly an insidious one."