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Biology
A method for ecological
analysis adapted to US needs
The CPMV method (for Coordonnées principales
de matrice de voisinage), developed by Québec researchers,
recently proved its effectiveness in analyzing a major American
study in lacustrine ecology. It may seem surprising that local
researchers could help American researchers, with their powerful
research facilities. But this is what happened when Pierre
Legendre and Daniel Borcard, of the Inter-university Research
Group in Limnology and Aquatic Environment (GRIL), helped their
American colleagues analyze their own data.
Respectively a professor and a lecturer in the Department
of Biology at University of Montréal, Pierre Legendre
and Daniel Borcard are specialists in digital ecology, a
field that deals with computer analysis of ecological data.
From 1984 to 1991, American researchers accumulated thousands
of data sets, gathered in 154 samplings, at Little Rock Lake,
Wisconsin. Their research looked into the effects of acidification
of a lake on species of zooplankton—a herbivorous,
carnivorous or detritivorous organism that lives in bodies
of water. Their data covered 73 species of zooplancton and
13 environmental variables (conductivity, acidity, nitrogen
level, etc). However, they had no global method for analyzing
the data they had collected. In July 2003, they contacted
Pierre Legendre, whose method of “multivariable” analysis
is known worldwide. Mr. Legendre is also the author of Digital
Ecology, the first book to combine ecology and data
analysis methods. The book, which is read worldwide, is now
in its fourth edition.
To conduct their study, the American researchers chose
a lake with a narrows that they could separate into two ponds
with a temporary physical barrier. One part of the lake was
gradually acidified with sulfuric acid (the chemical compound
responsible for acid rain) in order raise the pH, and the
other was left in its natural state. Little Rock Lake thus
became an open-air laboratory, one of whose objectives was
to compare the time evolution of zooplancton in the two neighbouring
environments, with their different chemical compositions.
In the first phase, the Legendre-Borcard team had to check
whether the communities of zooplancton reacted differently
in the acidified basin. Their method enabled them to determine
that the two communities had kept a common functioning and
dynamics. The global functioning had not been disrupted.
However, the community in the acidified pool adjusted to
the changes. Thus, the two researchers were able to confirm
the effectiveness of their method in a time context. A big
step forward for ecology.
Mr. Legendre’s laboratory regularly welcomes postdoctoral
researchers. They bring a fresh point of view to research
problems, and all members of the laboratory benefit from
this unique experience. Two young researchers (Pedro Peres-Neto,
trained in digital ecology, and Stéphane Dray, trained
in biostatistics) are currently working to refine the method.
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