An ongoing study of bats on the small volcanic Island of Montserrat suggests that the common method to determine the ecological situation of a region, is possibly flawed.
According to
Nature, when an agency wants to determine the ecological situation of a region, they usually ask researchers to perform a quick survey of the region, this is called a rapid biodiversity assessment. Researchers don't complain, because these can easily be done in the 3 to 5 years it takes to get a PhD, and it is not too hard to make a report and get it published. An ongoing study of bats on the Montserrat is now resulting in data that indicate that this may not always be accurate.
Montserrat was hit by Hurricane Hugo in September 1989, and this had resulted in the near total disappearance of all leaves (defoliation). Ecologist Scott Pedersen at South Dakota State University in Brookings and his colleagues caught bats in mist nets before and after the hurricane and found that around 90% of the bats had disappeared. They also noticed that there were less small fruit-eating species and more omnivorous and large fruit-eating species.
Pedersen has used the same method to analyze the bat population for more than 30 years and he has seen that this population is not stable. He has seen as few as four species on the island and as much as ten. He says that this shows that short-term surveys can be misleading.
"Several species seem to come and go and I ask myself, is this migration? No. Is this extinction? No. What is actually happening is that as populations fluctuate over time, they simply become rare enough to become 'temporarily invisible' to our human biases and technology," he says. "If this is the case in the pocket-sized system we are studying, then I really don't know what to make of all the rapid biodiversity surveys taking place in larger habitats like Amazonia."
Robert Ewers, an ecologist at the University of Cambridge, UK says that he and his colleagues have the same problem. He did a project in the Atlantic forests of Brazil that quite clearly illustrated the sampling problem. He says that his project was limited to two years, and that he thinks he needed four years in order to get the full picture.
Penelope Firth, deputy director of the US National Science Foundation (NSF) Division of Environmental Biology, disagrees. According to her, the agency does not put a limit on how long a biodiversity survey can take. "Many are five-year projects, quite a few are three years," she says. She adds that the NSF gives researchers the possibility to ask for a renewal and that, thanks to that, surveys of six years or longer are not rare.
She also says that "Ecologists and statisticians have invested considerable effort into understanding the consequences and implications of employing a finite sampling effort."
Pedersen remains unconvinced. He says that "Almost everybody in the bat world that I know seems cynical regarding the efficacy and accuracy of rapid surveys, but we are all quite happy to take the cash and do what we can."
Jeff Foster, an ecologist at Northern Arizona University in Flagstaff travels a middle-road. "Unquestionably, long-term research studies are lacking in nearly every ecosystem," he says "But the real question here is, what is the best bang for the buck?".
According to Foster, rapid assessments are not appropriate for studies of food relationships or population dynamics. However, in order to estimate how many species there probably are in the region, a rapid assessment will be the best method, because it doesn't really matter if you miss a few species.
He adds that "we do not know how much spending is going into rapid assessment programmes and whether long-term studies are being underfunded because of this allocation".
