8 May 2008
Biodiversity: It's In The Water
by Kate Melville
Hydrology may be more important for predicting biodiversity than biology, say an international group of scientists whose study in the latest issue of Nature challenges current thinking about biodiversity and opens up new avenues for predicting how climate change or human activity may affect biodiversity patterns. Their new method for predicting biodiversity, described by them as "ridiculously simple," uses only the geomorphology of a river network and rainfall measurements to accurately predict the biodiversity of fish species in a river system.
Top layer: runoff distribution; Middle: sub-basin locations; Bottom: fish species distribution
For their study, the researchers examined the Mississippi-Missouri river basin, which covers all or part of 31 US states, spanning diverse habitat types and encompassing very different environmental conditions. Using geomorphological data from the US Geological Survey, the researchers 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 sub-basin.
With just four parameters, it's "an almost ridiculously simple model," explains researcher 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. The 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," said co-researcher 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."
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Source: Ecole Polytechnique Fédérale de Lausanne
Graphic courtesy Nature