How many mammal species live in the forest? It sounds like a simple question, but the actual distributions of shy, small or rare mammals are often murky, confounding conservationists seeking to protect them.
Yet a paper to be published in the journal Molecular Ecology proposes a new way to track biodiversity: by capturing flies that feed on carcasses. The flies? stomachs offer DNA diaries of their recent meals, giving scientists clues to which animals live and die in the forest.
?The animals are there, but you just don?t see them,? said Fabian Leendertz, a wildlife epidemiologist at the Robert Koch Institute in Berlin and an author of the paper. ?Those flies will find them and will tell us what is there.?
Dr. Leendertz?s team captured 115 carrion flies in forests in Ivory Coast and Madagascar by baiting traps with meat. After mashing up the flies and extracting DNA, they were able to identify 20 mammalian species that the flies had fed on, including the endangered Jentink?s duiker, of which only an estimated 2,000 or so remain.
Because carrion flies are notoriously indiscriminate eaters, they yield DNA from a broad sample of species. The flies are also widely distributed ? one of their more commonly recognized representatives is the bluebottle fly ? so the method could be used throughout much of the world.
?It?s a way to measure biodiversity in areas that are not easily monitored in traditional ways,? said Ida Schnell, a doctoral researcher at the Center for GeoGenetics at the Natural History Museum of Denmark.
Traditional methods of measuring biodiversity include counting animals directly or looking for traces of them like droppings, tracks or nests. More recently, scientists have embraced technological solutions like setting up camera traps that detect motion and photograph wildlife passing by. Such cameras often miss rare or small animals, however.
Scientists also gather feces and other biological samples and extract DNA to study mammalian populations. But these types of samples tend to be most useful for zeroing in on a species already known to be present.
Invertebrates that feed on flesh and blood have the potential to help with the first step of the research process: finding out whether a species is present at all.
Ms. Schnell was a co-author of a paper last spring for which researchers used land-dwelling leeches? blood meals to assess biodiversity.
After testing only 25 leeches captured in a Vietnamese rain forest, her team managed to identify DNA from several rare species, including the Annamite striped rabbit.
Biologists had been using camera traps in the hope of spotting the rabbit but had had no success and wondered if it had gone extinct.
Dr. Leendertz said that carrion flies could also help scientists monitor wildlife disease epidemics, alerting them to unexpected die-offs. His team is collecting flies regularly in the Ta? National Park in Ivory Coast and is looking for signs of anthrax, which has a history of killing primates in the area.
Students are trapping flies at 25 rain forest locations throughout Africa as part of a larger biodiversity monitoring program. Dr. Leendertz?s group has even set up flytraps near Berlin to see what the local forest has to offer.
Ms. Schnell said:?You can just get so, so, so many huge data sets with this method. I really think that?s a big improvement in conservation biology.?
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