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.城市化及其引发的生态干扰，正成为野生动物面临的日益严峻的挑战。非洲啮齿类的行为模式及其对夜间人工光（artificial light at night, ALAN）等环境扰动的响应机制，相关研究仍较为匮乏。我们以城市生境中的安戈尼水鼠（Otomys angoniensis）为研究对象，通过探究其运动活动，旨在明确其时间生态位特征及对夜间人工光的响应能力。鉴于现有文献对该物种种群的时间生态位描述存在不一致，我们分别在标准实验室条件、夜间人工光实验室条件以及自然环境中开展实验，以明晰其在不同光照条件下的活动节律模式。安戈尼水鼠在实验室与自然环境中均表现出夜行活动特征，但自然环境下其活动振幅、节律中值（MESOR）及活动稳健性均较实验室处理组高出近三倍。与严格夜行性动物不同，安戈尼水鼠的活动并未被光照所掩盖，且在实验室2勒克斯夜间人工光条件下，其活动强度并未出现下降。在自然生境中，安戈尼水鼠栖息于茂密的草本植被中，因此其在人工饲养条件下表现出的主要夜行活动特征，可归因于实验过程中缺乏足够的遮蔽物。自然环境下其活动水平更高，可能源于日间光照强度更强以及存在自然的温度周期变化。我们据此推测，尽管安戈尼水鼠在实验室中表现出夜行活动特征，但其在自然生境中的活动模式可能更偏向昼行性。伴随城市化进程产生的夜间人工光，可能会通过栖息地退化、破碎化及破坏导致植被覆盖减少，从而间接影响安戈尼水鼠的生存。