Big-brained mammals tend to be less abundant than their smaller-brained peers By In Gibraltar, the Barbary macaque, Macaca sylvanus, is quite abundant. Photo by Manuela Gonzalez-Suarez/University of Reading Dec. 23 (UPI) -- Across a given landscape or ecosystem, mammals with big brains are less abundant than those with smaller brains, new analysis suggests. As a result, populations of bigger-brained mammals tend to be sparser. The findings, published this week in the Journal of Animal Ecology, may explain why the densities of mammal populations, including populations of mice, monkeys, kangaroos and foxes, vary so widely across different landscapes. Advertisement For the study, scientists used sophisticated statistical methods to parse the influence of various physiological factors, including brain size, body mass and diet, on population density for 656 non-flying terrestrial mammal species.