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Posted on 12/14/2008 11:45:59 PM PST by neverdem
Bat study raises doubts over our understanding of Earth's ecosystems.
One of the most common techniques for diagnosing the ecological health of a region may be painting an inaccurate picture of biodiversity, a study of the bats on the tiny volcanic island of Montserrat suggests.
To understand an area's ecology, researchers are often asked by funding agencies to conduct a short survey, known as a rapid biodiversity assessment.
Such surveys are convenient: they fit easily into the typical 3-5-year timescale of a PhD, match the length of time within which grant-giving agencies expect to see results, and are relatively quick to write up and publish.
Yet an ongoing study on Montserrat is yielding data that suggest these short-term surveys may not always paint an accurate picture.
Montserrat was devastated by Hurricane Hugo in September 1989, causing near total defoliation of the island. Ecologist Scott Pedersen at South Dakota State University in Brookings and his colleagues captured some of the island's bats in mist nets before and after the hurricane and found a 10-fold decrease in the population1. They further noted that the composition of the bat community shifted from small fruit-eating species to more omnivorous and larger fruit-eating species.
Over 30 years of using the same mist-netting method to capture and analyse bat populations, Pedersen has seen as few as four species and as many as ten on the island at any one time. The findings, he says, show that short-term surveys could be misleading ecologists.
"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."
"We've found similar problems in our own work," says Robert Ewers, an ecologist at the University of Cambridge, UK. Data on birds in the Atlantic forests of Brazil have shown Ewers and his colleagues very clearly that snapshots do not give a good representation of diversity. Different ecological pictures have appeared for Ewers depending on whether he sampled in the wet or the dry season and whether he sampled for two years instead of one. Even sampling for two years, which was all Ewers could manage, wasn't enough. He believes he probably needed to double the survey time to get the full picture.
"Ecologists are aware of the sampling problem, it's just that it is so difficult to avoid because granting agencies restrict sampling to a maximum of two years," Ewers adds.
Penelope Firth, deputy director of the US National Science Foundation (NSF) Division of Environmental Biology, says the agency does not limit the duration of biodiversity surveys. "Many are five-year projects, quite a few are three years," she says. The NSF even allows investigators to submit proposals for renewing their awards, and thus six-year and longer surveys are not uncommon, according to Firth.
"Ecologists and statisticians have invested considerable effort into understanding the consequences and implications of employing a finite sampling effort," she adds.
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But Pedersen is sceptical. "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," he says.
"Unquestionably, long-term research studies are lacking in nearly every ecosystem," says Jeff Foster, an ecologist at Northern Arizona University in Flagstaff. "But the real question here is, what is the best bang for the buck?". For trophic interactions or population dynamics, a rapid assessment is not suitable. But for determining how many species are likely to be present, a rapid assessment will be far more appropriate even if you happen to miss a few species, Foster explains.
The problem, he adds, is 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".
I’m looking at a large, prehistoric bug on my desk. It is called a “Weta”, and it is the coolest bug in the world. Only found in New Zealand, and he (for it is a he, this time) is very much alive.
They look dangerous, but aside from a nasty wee nip, they’re quite harmless. We tend to treat them like exotic animals rather than bugs in NZ: most people wouldn’t dream of stepping on one.
He can jump, much like a grass-hopper. Huge long antennae that he uses as feelers. Unchanged in over a million years.
> They don’t know what they don’t know. It’s not something new.
Scientists still know very little about the Weta. They really don’t even know what questions to ask.
As for me and my Weta mate, we’re going to do the FRee Republic thing for another half hour, then watch “The Guns of Navarone” together — assuming this Weta doesn’t get bored.
Wetas are cool. What kind do you have?
I think fireflies are pretty cool, too... Would be kinda neat to cross a Weta with a firefly and get a weta that lights up in the dark. Now that would be something out of an old B movie! :-)
> Wetas are cool. What kind do you have?
We’ve got the “small” ones: the Giant Wetas are really only found on the rat-free islands offshore. Still, we are still talking about a fairly sizable bug...
> I think fireflies are pretty cool, too... Would be kinda neat to cross a Weta with a firefly and get a weta that lights up in the dark. Now that would be something out of an old B movie! :-)
(grin!) Strangely enough, glow-worms and wetas are often found in the same habitat: moist caves and tunnels in the dark.
Not far from where I live there is a tourist attraction, well worth the effort and money. It is run by the water company (”WaterCare”), and it is a narrow-gauge train that follows the tracks thru the bush and up to one of our dams, thru the original tunnels that were carved out of the hills when the dam was being built.
In the tunnels, glow-worms have set up — thousands and thousands of them. And quite often, you see wetas as well.
Well worth the price, just to see ‘em.
Bama's educated voters no doubt.
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So the obvious question is ... are there ever multiple short-duration surveys that can be put together to create a dataset covering a longer time-span?
Since short (3-4 year) studies are not sufficient, it would make sense for specific institutions/universities to set up long term studies whereby grad students would conduct a study for one period and then another would take up the study for the next period. They would each write their thesis, and these studies could be conducted for decades so long as the organization kept the flow of PhD candidates following the long term studies.
My question was ... have there been multiple short studies for the same locations? If so, have they ever been combined? And if such studies exist and they have not been combined, why not?
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