School of Animal, Plant and Environmental Sciences (ETDs)

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Subject: search.filters.subject.Small mammals

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    Effects and consequences of natural and artificial light at night on small mammals in peri-urban Johannesburg, South Africa
    (University of the Witwatersrand, Johannesburg, 2024) Oosthuizen, Tasha; Pillay, Neville; Oosthuizen, Marietjie
    Studies investigating artificial light at night (ALAN) have increased over recent years. However, research examining the influence of ALAN on southern African small mammal species are lacking and even information on their basic biology is scarce. To close this knowledge gap, I investigated the effect of ALAN on different facets of animal behaviour in African small mammals. Firstly, I evaluated the impact of the natural (lunar cycle) and ALAN on the community composition and species abundance in two populations of small mammals. I chose two field sites: one facing Johannesburg (exposed to ALAN) and one facing away. I conducted mark-recapture trapping to ascertain the occurrence and abundance of small mammals. The Light site had both a higher species composition and a higher animal abundance when compared to the composition and abundance of the Dark site. The lunar cycle had an effect; on nights with a full moon, the species composition and animal abundance of both study sites declined, while on new moon nights, the opposite occurred, with an increase in both the species composition and abundance on the Light and Dark sites. The absence of a negative ALAN effect on the Light site can potentially be ascribed to the availability of microhabitats for small mammals to escape illumination, leaving them seemingly unaffected. Next, I assessed the locomotor activity of three species of commonly occurring rodents on the study area, one crepuscular (19 single-striped grass mice, Lemniscomys rosalia), one species with reportedly variable activity (19 angoni vlei rats, Otomys angoniensis) and one nocturnal (19 southern multimammate mice, Mastomys coucha). They were captured at a different location than the mark-recapture study sites and tested in captivity under natural (exposed to natural light and temperature changes), laboratory (standard laboratory conditions; 12h light:12h dark and constant temperature) and ALAN treatments. Lemniscomys rosalia exhibited crepuscular activity under all three experimental treatments, Otomys angoniensis was mostly nocturnal with some diurnal activity. The temporal activity profiles of the two species that showed some activity during the light hours were unaffected by ALAN. Mastomys coucha displayed strictly nocturnal activity during the natural and laboratory treatments, but during ALAN treatments the temporal activity profiles of some animals shifted so that they were active during the start of the day. Lemniscomys rosalia and O. angoniensis were more active under the natural treatment, whilst M. coucha was more active in the laboratory treatment. When exposed to 2 Lux ALAN presented remotely, there was no effect on the level of activity in O. angoniensis, L. rosalia showed a reduction of about 20% in its activity, whereas M. coucha reduced its activity by more than 50%. Finally, I studied how ALAN impacted the foraging behaviour of the three species under four treatments (during the day, at night, 2 Lux ALAN and 10 Lux ALAN). Foraging behaviour differed in the three species under different light conditions. Lemniscomys rosalia was risk-averse when feeding during the diurnal and nocturnal (no light at night) treatments. Otomys angoniensis showed irregular responses in their foraging behaviour under all foraging treatments. Mastomys coucha showed no differences when feeding under any of the nocturnal treatments, but it was inactive under the diurnal treatment. Overall, my study revealed that the effect of ALAN is not similar for all small mammalian species and appear to depend on both the spatial and temporal niches that the different species occupy. Strictly nocturnal animals seem to be affected the most, whereas animals that are active during the day showed lesser responses. Given the rapid increase in urbanisation and anthropogenic disturbances, more and more species are exposed to ALAN. Species that prefer darker, more secluded habitats appear to be more vulnerable and at higher risk of local extinctions as a result of disturbances, such as ALAN and habitat transformation. My study highlights that ALAN affects both nocturnal and diurnal rodents to the extent that it can have fitness consequences, including changed active times, foraging efficiency, movement patterns and susceptibility to predation. Finally, the disruption of rodent behaviour can have cascading effects for ecosystems and my study also emphasises the importance of safeguarding our night skies to protect biodiversity.
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    The Impacts of Ungulate Foraging on Small Mammal Diversity in a Protected Site and Livestock Grazing Site
    (University of the Witwatersrand, Johannesburg, 2023-09) Dlamini, Sifiso; Linhsan, Emmanuel Do; Madikiza, Kim
    Vegetation cover and food availability are important determinants of how favourable an area is for the settlement of animals, especially small mammals such as rodents, which rely heavily on vegetation for protection against predators and access to food. This study investigated the impact that ungulate foraging activities (both domesticated and wild) have on small mammal diversity in two Short Euphorbia Thicket habitats within the Albany Thicket Biome: a natural site in the Great Fish River Nature Reserve and an adjacent livestock grazing site belonging to Kwandwe Private Game Reserve. Trapping was carried out over 7-day/7-night trapping sessions during the wet and dry seasons at each site, with grids of 10 x 10 traps with a 10 m spacing. Over a total of 5,600 trap nights/days, 272 unique individuals of six small mammal species (4 rodents, 1 shrew, and 1 sengi) were captured. Habitat (i.e., the 1 ha area studied on each site) and microhabitat differences were assessed for the two study sites using plant cover at different heights, the number of bushes, the presence of Euphorbia bothae, as well as the amount of bare ground and rocky surfaces around each trap station. Between the habitats, vegetation in all the height categories differed significantly during each season, while the number of bushes did not differ. The microhabitats also showed seasonal variation, with the dry season having less vegetation cover than the wet season. Although greater vegetation cover was recorded during the wet season, small mammal abundance was low, as were species richness and diversity. It was the dry season that had the higher small mammal abundance for both sites, with the protected site having four times the abundance (across all species) of the livestock grazing site. Small mammal diversity was, however, highest at the livestock grazing site, where the species were evenly represented, whereas the protected site had unevenly represented species with a lower diversity. It is concluded that both domesticated and wild ungulate foraging activities, as well as seasonal changes in climatic conditions, alter vegetation cover. This determines whether a habitat is conducive for small mammals, thereby driving their richness, abundance, and ultimately diversity within a habitat.