Credit: Manuela Gonzalez-Suarez/University of Reading Mammals with big brains tend to be less abundant in local areas than those with smaller brains, new research has shown. The University of Reading led an international team of scientists in considering the effect of brain size for the first time in studying why populations densities of land mammals like mice, monkeys, kangaroos and foxes vary so widely in local areas, even among similar creatures. Using statistical models to test different scenarios for hundreds of species, they found an overall trend of mammals with larger brains occurring at lower densities. Where different species had similar diets and body masses, brain size was found to be the deciding factor.