By Alister Doyle, Environment Correspondent
OSLO, May 7 (Reuters) - Simple rules about river flows decide how many type of fish thrive in any one spot, a finding that could help site dams to minimise disruptions to wildlife, researchers said on Wednesday.
A study of the vast Mississippi-Missouri river system in the United States found that areas with most fish species were those where multiple streams were close to one another and where there was a lot of rainwater running into the rivers.
"This will help identify which parts of a river basin are 'hot spots', meaning they have more species than others and therefore should receive special care," said Ignacio Rodriguez-Iturbe of Princeton University, who led the research.
In the basin, covering half the country from Montana to New York, the scientists examined 824 tributary areas with a total of 433 freshwater fish species ranging from carp to catfish.
Pickwick Lake, at the borders of the states of Alabama, Mississippi and Tennessee, had the most species with 156, according to the report in the Journal Nature. Species diversity was lower towards the Rocky Mountains, a drier region, and in areas far from tributaries.
"We made the assumption that if you have a lot of water you have a lot of resources, so you can support more fish and then it allows for more species," lead author Rachata Muneepeerakul of Princeton told Reuters.
He said that the team of scientists, including experts based in Switzerland and Italy, also assumed that all fish species behaved in the same way. "This seemingly oversimplified assumption matched the empirical patterns quite well," he said.
The model could help in positioning dams to curb disruptions to river life, or help predict areas of river basins that could be affected by changes in rainfall patterns because of global warming.
"If you have a change in connectivity of rivers due to human activity -- for example, the building of a dam -- our model can also measure how that will affect the numbers and distribution of species," Rodriguez-Iturbe said in a statement.
Worries about loss of biological diversity can have big economic implications. In the 1970s, the discovery of the rare snail darter fish in the Little Tennessee River held up construction of a dam.
Muneepeerakul also said that other simple principles might underpin other habitats -- mountains, jungles, deserts -- and could also be a guide to slowing biodiversity loss.
The scientists also said that the river water model might help understand dispersal in rivers of seeds or even of diseases, for instance the bacteria that cause cholera.
-- For Reuters latest environment blogs click on: blogs.reuters.com/environment/ (Editing by Giles Elgood)