Species that occupy the same area and use the same resources must either compete with each other or find ways to minimize competition. For rodents, 1 important resource is nesting sites. Here we show that striped mice and bush Karoo rats compete actively for access to preferred
nesting sites. The larger bush Karoo rats agressively chase striped mice away from the large stick lodges they build, a valuable resource. But if bush Karoo rats die, these lodges are soon taken over by striped mice.
Female bush Karoo rats are solitary but don't move far away from their lodges. Males don't seem to have defined home ranges but roam over large areas, searching for females. Males grow much faster than females and get 10-20% bigger than females. All of this comes at a cost: they don't live that long but disappear much sooner from the population than females.
use of mini Gps
GPS collars have been used on many large mammals, but Lindelani Makuya is the first to use them on small mammals of only 100g body mass. Using these collars, she measures daily range sizes. By putting mini-GPS on several bush Karoo rats the same day, she studies how daily ranges overlap in space and time. A first paper validating the method has been published in 2023.
The bush Karoo rat (Otomys unisulcatus) is a diurnal rodent from southern Africa with an adult body mass of 70-180g. Living in an open habitat and being easily habituated to observers, it can be easily observed directly in the field.
It is famous for its huge stick lodges it builds for protection against predators, heat and cold. These stick lodges can be 1.5m high and 2-3m broad, and decades old. A stick lodge can be used by at least 20 generations of bush Karoo rats, maybe more than one hundred.
The bush Karoo rat is a solitary central place forager. Being a strict herbivore, it forages from its lodge collecting food plants, always returning to its lodge. Though the home range of one bush Karoo rat can contain several lodges, connected by runways.
It’s an annual species: every year, a new generation of bush Karoo rats is born in spring (August-November), which has to survive the coming dry and food restricted summer and cold wet winter, before breeding the next spring. Food availability during the dry season differs dramatically for different generations.
The vast majority of bush Karoo rats lives solitarily, but small groups are also observed, most often two siblings sharing a nest, or 2-4 closely related females, i.e. a mother and her adult daughters from different litters. It is not aggressive at all, and territorial disputes between bush Karoo rats are rarely observed. In contrast, we often observe bush Karoo rats chasing away the smaller but more abundant striped mice from their lodges. Striped mice love to nest in abandoned bush Karoo rat lodges!