Abstract:
The presence of artificial light at night (ALAN) is one of many contributing factors to global change today. The spectral range of ALAN can also alter the potential effects of light pollution in certain contexts which creates an exceptionally complex cascade of impacts. The purpose of this thesis was to examine the interactions of various environmental factors including ALAN on biological variables, locomotor activity and corticosterone concentration, of two species of rodent. This was accomplished by manipulating the environmental factors; environmental enrichment, temperature and lighting in captivity. A pilot field study was also conducted in order to test the future feasibility of incorporating information garnered from the laboratory study into larger scale real world experiments. The two species were collected from the field and was subsequently subjected to various light cycles, during which locomotor activity was monitored and urinary corticosterone stress hormone was assessed. Results showed that Micaelamys namaquensis, a nocturnal species, reacted favourably to the addition of enrichment by increasing activity levels whereas Rhabdomys dilectus, a diurnal species decreased activity levels while improving the strength of entrainment. Both M. namaquensis and R. dilectus decreased activity during a light cycle which simulated natural dawn and dusk patterns of light. The two species reacted differently when a 24hr
ambient temperature cycle was introduced, with M. namaquensis increasing its locomotor activity and R. dilectus decreasing overall activity. M. namaquensis decreased its average activity in response to ALAN and did not show any difference in reaction towards different types of light at night. R. dilectus on the other hand increased its activity under ALAN but also showed no preference between different spectra of light at night. While corticosterone concentrations were monitored during all the environmental factor experiments, fluctuations in hormone concentrations were noted, however found to be statistically non-significant. Thus, only speculations could be made regarding the impacts of the various environmental factors on the stress physiology of M. namaquensis and R. dilectus. These results highlight the importance of considering species specific outcomes even under virtually identical circumstances. Understanding the impacts of environmental factors is crucial in order to extrapolate laboratory-based findings into real world experiments. This work can be used to further understand the impacts of different environmental factors on the circadian systems of nocturnal and diurnal rodent species as well as the potential implication of ALAN under various environmental conditions. In future, this can be combined into a large-scale field experiment in order to monitor the impacts of light pollution using the methodology elucidated during the pilot study. The results of this study show that the impacts of ALAN can be incredibly diverse and specific to the species in which they are examined.
