Do birds and bees dance to the same tune?

[Roger Bagula]

http://www.iol.co.za/index.php?set_id=1&click_id=143&art_id=nw20071025010512263C270156
Do birds and bees dance to the same tune?

Paris - A clutch of scientific studies showing that the foraging
patterns of albatrosses, bumblebees and deer conform to a single
mathematical axiom all got it wrong, researchers said on Wednesday.

The new work overturns a cornerstone study from 1996 claiming that the
airborne seabirds trace an elegant pattern known as Levy flights, named
after the French mathematician who first described them.

It also upends or casts a long shadow over a slew of follow-on studies
by biologists seeking to extend the albatross findings to other animals,
including bees, reindeer, grey seals, spider monkeys and microscopic
zoo-plankton.

One study even found evidence of Levy flights in the peregrinations of
Peruvian fishing boats chasing down anchovies off the coast of South
America.

If all this published research turns out to be baseless - as now seems
likely - it raises the intriguing and troubling question of how so many
scientists working independently could have gone so badly astray.

Lead author Andrew Edward, a research scientist at the Canadian
government's fisheries and oceans department, uncovered two problems
with the study on albatrosses, only one of which affected subsequent
research.

The first was simply an error in the raw data collected from tracking
devices attached to the birds, which were mistakenly thought to be in
the air when they were, for much of the time, soaking up the sun while
sitting on rocks.

The more important error, however, was in methodology, which is what
started the chain-reaction of mistakes.

Edwards has proposed another calculation based on more sophisticated
statistical methods for testing whether Levy flights really apply, even
if he is sceptical that the initial results will hold.

His critique, published in the British journal Nature, in no way
suggests that the studies called into question were fraudulent, only
that they recovered a statistical method of calculation that turned out
to be wrong.

The system of peer-reviewed publication - whereby prestigious scientific
journals ask experts to vet article submissions - is intended to prevent
dubious or dodgy scholarship from getting into print.

Edwards is reluctant to draw hasty conclusions but did suggest in a
phone interview one possible explanation for the cavalcade of scientific
error.

"If you are a biologist going out collecting data for four months on
some animal it is hard to spend the time reading all the theoretical
literature, so you use a method that others have already used," he said.

Another possible explanation is the well-documented human urge to find
order and patterns - and occasionally to impose them - on observed
phenomenon.

"Mathematics is the closest that we humans get to true magic," the
famous British mathematician Ian Stewart once said. "How else to
describe the patters in our head that - by some mysterious agency -
capture patterns of the universe around us?"

A celebrated case of science bent out of shape by wishful thinking
occurred in the United States in the late 1980s.

When two respected scientists claimed to have achieved cold fusion - the
spontaneous creation of thermonuclear energy - an era of unlimited
energy seemed to be at hand.

Despite widely expressed scepticism, at least two other established
research labs in the US successfully reproduced the cold fusion results
before it was clearly proven that the whole thing was an illusion.

Levy flights display the properties of fractals, geometric shapes that
can can be subdivided in parts that are themselves a reduced-scale copy
of the whole.

The fractal-like patterns found in nature - fern leaves, snow flakes,
crystals and even the body's blood vessels - continue to exert a
bewitching fascination.

AFP

Published on the Web by IOL on 2007-10-25 01:05:12
© Independent Online 2005. All rights reserved. IOL publishes this
article in good faith but is not liable for any loss or damage caused by
reliance on the information it contains.
http://www.iol.co.za/index.php?set_id=1&click_id=143&art_id=nw20071025010512263C270156

[ Back to EurekAlert! ] Public release date: 24-Oct-2007
[ | E-mail Article ]

Contact: Athena Dinar
***@bas.ac.uk
44-012-232-21414
British Antarctic Survey
Animal behavior study overturned

An international team of scientists has overturned an ecological study
on how some animals search for food. Previously it was believed that
wandering albatrosses and other species forage using a Lévy flight
strategy - a cluster of short moves connected by infrequent longer ones.
Published this week in the journal Nature, the team discovered that
further analyses and new data tell a different story for the albatrosses
and possibly for other species too.

Biologists and physicists identified ‘Lévy flights’, named after the
French mathematician Paul Lévy, as an efficient way for animals to
search for sparse food. They have been attributed to a wide range of
organisms, including zooplankton, grey seals, spider monkeys and even
Peruvian fisherman.

The first attempt to demonstrate their existence in a natural biological
system suggested that wandering albatrosses perform Lévy flights when
searching for prey on the ocean surface - a finding followed by similar
inferences about the search strategies of deer and bumblebees. However,
this research shows this is not the case. Based on new high-resolution
data collected from loggers attached to the legs of wandering
albatrosses on the sub-Antarctic island of South Georgia, the team show
that the previous claims about the Lévy flight behaviour were unfounded.
They also re-analysed the existing data sets for deer and bumblebees
using new statistical methods, again finding that none exhibits evidence
of Lévy flights.

“It now seems the albatrosses come across food at simpler random
intervals”, says lead author Dr Andrew Edwards from British Antarctic
Survey (now at Fisheries and Oceans Canada). “Our work also questions
whether other animals thought to exhibit Lévy flights really do all
forage in the same way.”

This research improves scientists’ understanding of the foraging
behaviour of the wandering albatross – an endangered species. It may
also help develop a new theory for how animals forage – an essential
piece in the wider ecological jigsaw puzzle.

###

Issued by the British Antarctic Survey Press Office.

Athena Dinar – tel: ++44 1223 221414, mob:[phone], email:
***@bas.ac.uk
Linda Capper – tel: ++44 1223 221448, mob: [phone], email:
***@bas.ac.uk

Author contact:

Dr Andrew Edwards, Pacific Biological Station, Fisheries and Oceans
Canada, Nanaimo, BC, Canada. (Formerly at British Antarctic Survey).
Tel: [phone] (work), [phone] (home). From 21– 28
October: tel: [phone] (a hotel in Victoria, BC). Email:
***@pac.dfo-mpo.gc.ca
Dr Mervyn Freeman, British Antarctic Survey, tel. ++44 (0) 1223 221543,
Mobile: [phone], email: ***@bas.ac.uk
Dr Nick Watkins, British Antarctic Survey, tel. ++44 (0) 1223 221545,
mobile: [phone], email: ***@bas.ac.uk
Dr Gandhi Viswanathan, Universidade Federal de Alagoas, tel. ++ (82)
32141427, email: ***@pq.cnpq.br

Notes for Editors

Still images and video (DV-cam) are available of albatrosses at British
Antarctic Survey’s Bird Island Research Station. Please contact the BAS
press office as above.

Revisiting Lévy flight search patterns of wandering albatrosses,
bumblebees and deer by Andrew M. Edwards, Richard A. Phillips, Nicholas
W. Watkins, Mervyn P. Freeman, Eugene J. Murphy, Vsevolod Afanasyev,
Sergey V. Buldyrev, M.G.E da Luz, E. P. Raposo, H. Eugene Stanley,
Gandhi M. Viswanathan is published in the journal Nature on Thursday 25
October 2007.

Organisations involved in this research: British Antarctic Survey,
Boston University (US), Yeshiva University (US), Universidade Federal do
Parana (Brazil), Universidade Federal de Pernambuco (Brazil),
Universidade Federal de Alagoas (Brazil).

A Lévy flight is named after the French mathematician Paul Pierre Lévy
and is a type of random walk in which increments are distributed
according to a probability distribution with a heavy power law tail.

The work at BAS forms part of the COMPLEXITY and DISCOVERY 2010 science
programmes at BAS. NATURAL COMPLEXITY provides a new perspective on, and
understanding of, complicated natural phenomena including biological
food webs, animal foraging and iceberg calving. DISCOVERY 2010 is
investigating and describing the response of an ocean ecosystem to
climate variability, climate change and commercial exploitation.

The original study was published in Nature in 1996 based on albatross
data collected from Bird Island Research Station in 1992. Another Nature
paper in 1999 developed this idea further using data from bumblebees and
deer and using computer simulation.

The wandering albatrosses inhabit Bird Island, a 5km-long rocky island
off South Georgia in the South Atlantic Ocean. With no food to be found
on the island, the birds undertake long foraging trips, flying close to
the ocean surface to spot and feed on squid. Loggers attached to the
birds’ legs tell ecologists how often the birds land on the water to feed.

Estimates suggest that 300,000 seabirds are killed annually in the
world’s long-line fisheries, many of which are albatrosses. Since 2001,
by-catch rates in well-regulated fisheries have decreased substantially,
remained stable in less well-regulated ones and probably increased in
pirate fisheries, for which no real data exist. 19 of the 21 species of
albatross are threatened with extinction.

British Antarctic Survey is a world leader in research into global
issues in an Antarctic context. It is the UK’s national operator and is
a component of the Natural Environment Research Council
(www.nerc.ac.uk). It has an annual budget of around £40 million, runs
nine research programmes and operates five research stations, two Royal
Research Ships and five aircraft in and around Antarctica. More
information about the work of the Survey can be found at:
www.antarctica.ac.uk

Fisheries and Oceans Canada

Fisheries and Oceans Canada is the lead federal government department
responsible for developing and implementing policies and programs in
support of Canada's economic, ecological and scientific interests in
oceans and inland waters.


[ Back to EurekAlert! ] [ | E-mail Article ]

[Roger Bagula]

http://www.sciencenews.org/articles/20071215/mathtrek.asp

Science News Online

Week of Dec. 15, 2007; Vol. 172, No. 24
Flying without Fractals
A new study raises doubts about fractal patterns in animal behavior

Julie J. Rehmeyer

Scientific fashions can rise and fall, like the hems of each year's
skirts. Unlike haute couture, however, scientific fads can shed light on
the world.

Fractals have been in fashion for a couple of decades or so, and
researchers have been finding fractal-based patterns in the ways that
many animals search for food. Albatrosses, deer, and bumblebees are
among the growing array of animals with fractal-based search patterns.
But a new study has found flaws in the methodology used in all such
animal studies, raising questions about whether fractal search patterns
really do occur in animal behavior.

f9116_1130.jpg

Albatrosses don't use fractal search patterns after all, a new study shows.
iStockphoto

Wandering albatrosses were the first animal studied that seemed to use
fractal search techniques. In 1996, Gandhimohan M. Viswanathan of Boston
University and his colleagues clipped recording devices to the legs of
albatrosses to track when the birds were in the water and when they were
not. The researchers figured that the birds were resting or feeding when
wet and flying when dry.

Most of the time, the albatrosses flew short distances, as the
researchers had expected. But sometimes, they flew very far indeed. On
rare occasions, the data showed, the birds would fly for as long as 96
hours. The pattern formed by frequent short journeys, less frequent
longer journeys and rare very long journeys is known as a "Lévy flight."

These very long journeys are the critical element that distinguishes
Lévy flights from other, more common statistical patterns. By contrast,
a speck of dust would never leap to the other side of a room in its
random jostlings, so its motion wouldn't form a Lévy flight.

Lévy flights are the statistical fingerprint of a fractal. If the
albatross's travels form a Lévy flight, a graph of it would show
connected clumps, and these clumps would be made up of smaller clumps,
which in turn would be made up of still smaller clumps. If it were a
perfect fractal, this pattern would continue forever like an infinite
set of Russian dolls. In nature, it can only continue for a few steps.

f9116_244.jpg

The drawing on the left shows the path of a dot traversing a Lévy
flight. Most steps are small, but occasionally, the dot jumps a long
way. This forms a pattern of clumps made up of smaller clumps made up of
smaller clumps. The drawing on the right, by contrast, shows Brownian
motion. The random motions of a speck of dust are Brownian. The dust can
travel significant distances, but only by a series of steps. It doesn't
make huge jumps.
Wikipedia

At the time, the researchers weren't sure why the birds would fly in
that particular pattern. They thought perhaps food was distributed on
the ocean in similar clumps. But a few years later, Viswanathan and his
colleagues showed that Lévy flights provide the best strategy in
searching for objects at random locations. This suggested that the
bird's behavior has adaptive value. "If I lost my child in the woods,
the best way to find my child would be to do a search with Lévy flight
motion," says H. Eugene Stanley of Boston University, a co-author on all
of the studies. "A simple random walk retraces its same sites over and
over and over again."

Soon, Viswanathan's team and other researchers found similar behavior in
reindeer, spider monkeys, bumblebees, zooplankton, and jackals. The
research on jackals was especially important because jackals can spread
rabies. If they travel in Lévy flights, that would mean they could
spread rabies quickly over long distances.

In the decade since the original albatross study, animal tracking
methods and statistical methods have both improved. So Andrew M. Edwards
of the British Antarctic Survey collaborated with Viswanathan and his
colleagues to revisit the albatross study and see if it still stands up.
They found that it doesn't.

The researchers started by analyzing recent data from tracking
albatrosses, which includes GPS data. From the new data, they found that
the albatrosses weren't taking the very long flights at all. So they
reexamined the old data to work out the discrepancy and discovered that
the albatrosses weren't necessarily flying whenever they weren't in the
water. They also spent time sitting on their nests. So, the animals'
longest dry periods don't correspond to very long journeys after all.

Next, the researchers turned to their studies of other animals. The data
on deer foraging had a problem similar to the issue with the albatross
data, and the bumblebee data didn't stand up to stricter statistical
scrutiny.

Stanley says the original study was valuable even though it turned out
to be wrong. "Niels Bohr got a Nobel Prize for the Bohr atom," he says,
"but his theory is absolute rubbish. The truth is much more complicated
and less poetic. But Bohr's atom theory was very important nonetheless,"
because it was a step that led to the more sophisticated theories. The
development of the theory of Lévy flights in animal behavior is
following a similar trajectory, he says.

Frederic Bartumeus of Princeton University says he's not surprised to
find out that some of the old studies were flawed. "They're showing that
we have to be careful how we analyze data to say that we definitely have
these Lévy flight patterns, and that's good," he says. "But that doesn't
mean there are no Lévy flights in nature."

Indeed, many researchers are continuing to study a variety of animals,
from honeybees to humans. Bartumeus and others are optimistic that some
of these animals will be rigorously shown to exhibit Lévy flight
behavior. Viswanathan himself shares the optimism, but "the jury is
still out," he says.

If you would like to comment on this article, please see the blog version.

References:

Edwards, A.M. . . . H.E. Stanley, and G.M. Viswanathan. 2007. Revisiting
Lévy flight search patterns of wandering albatrosses, bumblebees and
deer. Nature 449(Oct. 25):1044-1048. Abstract available at
http://dx.doi.org/10.1038/nature06199.

Peterson, I. 1997. Fractal past, fractal future. Science News Online
(March 1). Available at
www.sciencenews.org/pages/sn_arc97/75th/ip_essay.htm.

Peterson, I. 1996. Trails of the wandering albatross. Science News
150(Aug. 17):104. Available at www.sciencenews.org/pages/pdfs/
data/1996/150-07/15007-11.pdf.

Viswanathan, G. M. . . . and H.E. Stanley. 1999. Optimizing the success
of random searches. Nature 401(Oct. 28):911–914. Abstract available at
http://dx.doi.org/10.1038/44831.

Viswanathan, G. M. . . . and H.E. Stanley. 1996. Lévy flight search
patterns of wandering albatrosses. Nature 381(May 30):413–415. Abstract
available at http://dx.doi.org/10.1038/381413a0.

For a tremendous amount of information about fractals, visit
http://classes.yale.edu/fractals.



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