Unlike every other species of cat, lions are social animals that live in groups. They gather in prides that consist of 1 to 21 females and their offspring and 1 to 9 males. But why they do so has been a mystery. One popular hypothesis has been that the female lions come together to hunt cooperatively. However, a new study, published in the journal Animal Behaviour, says that prides form to protect their territory, and themselves, from other lion groups.
Anna Mosser and Craig Packer, ecologists at the University of Minnesota, St. Paul, analyzed 38 years' worth of behavioral data from 46 lion prides in Tanzania’s Serengeti National Park. They looked at territory size and quality, pride composition, fitness of individuals, reproductive success and how these factors changed in relation to neighboring prides.
Larger prides gained access to better territory, often the regions closest to river confluences where there was good hunting. And they were also better able to hold on to disputed territories and gain new territory of better quality. Females within these larger groups produced more cubs and were less likely to be hurt or killed.
“The most important way to think about this is that lion prides are like street gangs,” Packer told BBC News. “They compete for turf. The bigger the gang, the more successful it is at controlling the best areas.”
In addition, the ecologists were surprised to discover that males sometimes killed females of neighboring prides. In doing so, males may be able to reduce their neighbors' numbers and alter the power balance between the prides.