Crowding in the Serengeti: how group size, nomads and seasons shape lion life
For social species such as lions, crowding can mean many things: a bigger pride, a larger coalition of males, or more nomadic males roaming nearby. In our new paper in the Journal of Animal Ecology we show that these kinds of crowding affect Serengeti lions in different ways, and often differently in the wet and dry seasons.
The paper comes from Eva Conquet’s PhD in our group. We analysed 30 years (1984–2014) of data from the Serengeti Lion Project, led by Craig Packer: 1,347 individually known lions in 65 prides and 242 male coalitions (stable groups of males). For each season, we asked how survival, growing up, breeding and the raising of cubs changed with the number of females in a pride, the size of male coalitions, and the number of nomadic coalitions (males without a territory of their own) roaming through a pride’s area.
Larger coalitions helped resident males survive, especially in the dry season: from 89% a year for a coalition of two to 95% for three. In the dry season, larger nomadic coalitions were also more likely to take over a pride. The number of adult females in a pride lowered the survival of subadults (young lions not yet adult) in the wet season but raised it in the dry season.
Nomadic males did not change the survival of adult females, which depended only on age and habitat. But they mattered for reproduction: in the wet season, a pride whose home range held five nomadic coalitions raised 0.33 cubs per female to their first birthday, against 0.54 with two coalitions.
So density, the number of animals crowding an area, has to be measured with the animals’ social life in mind, and its effects can change with the seasons. The work is part of our project on populations under environmental change.