Effects of natural and artificial environmental light on the temporal activity and ecological dynamics in an urban African rodent

Urbanisation and its associated ecological disruptions are of growing concern to wildlife. The behaviour of African rodents and their responses to environmental perturbations, such as artificial light at night (ALAN), is poorly studied. We investigated the locomotor activity of the urban Angoni vlei rat (Otomys angoniensis) to ascertain its temporal niche and response capacity to ALAN. Due to inconsistencies in the literature regarding the temporal niche of this species, we conducted investigations under both standard and artificial light at night (ALAN) laboratory conditions, and under natural environmental settings, to better understand its activity patterns under various light regimes. Otomys angoniensis exhibited nocturnal activity under both laboratory and natural ambient conditions, but the amplitude, MESOR and robustness were almost three times higher under natural conditions compared to during the laboratory treatment. Unlike strictly nocturnal animals, the activity of O. angoniensis was not masked by light, and its activity was not reduced under 2 Lux ALAN in the laboratory. In nature, O. angoniensis occupies dense grass habitats, and therefore its predominantly nocturnal activity in captivity could be ascribed to the lack of adequate cover during experiments. The greater activity under natural conditions could be a consequence of brighter daytime light and natural temperature cycles. We suggest that although O. angoniensis displays nocturnal activity in the laboratory, it may be more diurnal in its natural habitat. ALAN associated with urbanisation will likely affect O. angoniensis indirectly because of a reduction of vegetation cover as a result of habitat degradation, fragmentation and destruction.