WASHINGTON, July 25 (UPI) -- U.S. scientists say how common any animal species is in any ecosystem is determined by a simple rule regarding body weight and place in the food chain.
"You can predict how common something might be just by knowing its body weight -- how big an individual is -- and how high up the food chain it is," says biologist Ryan Hechinger of the University of California at Santa Barbara, lead author of the study.
The two factors work together: body size determines how much food an animal needs; how many calories it burns, Hechinger says.
Bigger animals need more food because they burn more calories, so there aren't as many big animals as small animals, he says.
And the higher up the food chain, the less food there is and the less common an animal species is, whether it's big or small.
The research was funded by the joint National Science Foundation-National Institutes of Health Ecology of Infectious Diseases program.
"This comprehensive study has revealed a very simple rule that underlies a complex system," program officer Sam Scheiner said in a foundation release Monday.
"Extracting such simplicity from complexity will allow scientists to better understand and manage all natural systems from forests, to lakes, to ocean fisheries," Scheiner says.