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What if hydrology is more important for predicting biodiversity than
biology? New research challenges current thinking about biodiversity
and opens up new avenues for predicting how climate change or human
activity may affect biodiversity patterns.
Researchers have invented a method for turning simple data about
rainfall and river networks into accurate assessments of fish
biodiversity, allowing better prediction of the effects of climate
change and the ecological impact of man-made structures like dams.
The mathematics behind the new method also can be used to model and
predict a wide range of other questions, from the transmission of
waterborne illnesses to vegetation patterns on land adjacent to rivers.
In the article in Nature, an international group of researchers
demonstrates that the biodiversity of fish species in a river system
can be accurately predicted with a simple method that uses only the
geomorphology of the river network and rainfall measurements for the
The 3,225,000 km2 Mississippi-Missouri river basin covers
all or part of 31 US states, spanning diverse habitat types and
encompassing very different environmental conditions. The one thing
linking all these habitats is the river network. Using geomorphological
data from the US Geological Survey, the researchers -- hydrologists
from Princeton University and the EPFL in Lausanne, Switzerland, and
biologists from the University of Maryland -- identified 824 sub-basins
in the network. In these, the simple presence (or not) of 433 species
of fish was established from a database of US freshwater fish
populations. Data on the average runoff production --the amount of
rainfall that ends up in the river system and not evaporated back into
the air -- was then used to calculate the habitat capacity of each
With just four parameters, it's "an almost ridiculously simple
model," explains EPFL professor Andrea Rinaldo. The model results were
compared to extensive data on actual fish species distributions.
Various different measures of biodiversity were analyzed, and the
researchers were surprised to find that the model captured these
complex patterns quite accurately. The model is all the more remarkable
for what it does not contain -- any reference, anywhere, to the
biological properties of individual fish species.
It is a formulation that could be applied to any river system, or in
fact, any network at all. All that's needed are the geomorphology of
the landscape and an estimate of average dispersal behavior and habitat
capacity. This model is general enough that it could be used to explore
population migrations or epidemics of water-borne diseases in addition
to biodiversity patterns. The researchers plan to extend their work to
explore the extent to which simple hydrology can act as the determining
factor in a wide range of biodiversity patterns.
"These results are a powerful reminder of the overarching importance
of water, and the water-defined landscape, in determining patterns of
life," notes Princeton professor Ignacio Rodriguez-Iturbe. It provides
a framework that could be used to connect large scale environmental
changes to biodiversity. Changes in precipitation patterns, perhaps due
to global climate change, could be mapped to changes in habitat
capacities in the model, ultimately providing a way to estimate how
climate change would alter large-scale patterns of biodiversity. It
could also be used for an assessment of the impact of specific, local
human activities, such as flow re-routing or damming, on the
biodiversity patterns in a river network.
Ecole Polytechnique Fédérale de Lausanne. May 2008.
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