Behavioural aspects of enzootic geophagy amongst large mammal herbivores
Doctoral Thesis
| dc.contributor.author | Hendrikus Johannes Beukes Butler | en_ZA |
| dc.date.accessioned | 2026-09-09T12:19:55Z | |
| dc.date.issued | 2022 | en_ZA |
| dc.description | Geophagy - the deliberate ingestion of soils by animals - is an unlikely yet widespread occurrence. Soil has low nutritional value, wears teeth, impedes digestion by impaction within the digestive tract, and, from an ecological view, congregation of animals at ‘lick' sites may increase interspecific competition intensity and frequency of encounters with predators. In addition, it increases the risk of disease transmission. The widespread occurrence of geophagy in both herbivorous and carnivorous mammals, as well as insectivores, rodents, primates (including humans), and even birds and reptiles are thus a conundrum that must surely reflect that the benefits of soil consumption outweigh the many costs thereof. But the benefits are, for the most part, unresolved for large mammalian herbivores, thus current knowledge is insufficient to facilitate a detailed understanding of the trade-off. Suggested reasons for animals to practice geophagy are mainly divided into two concepts, either that soil consumption contributes mineral supplementation to the diet, or that clay in the digestive tract has detoxification properties, for example aiding in the precipitation of potentially harmful plant secondary compounds and/or intestinal parasites. Thus far, geophagy in natural settings has been limited largely to studies on single species, often single populations of those species, leading to varied interpretations. An objective source of data that encompasses variations in geophagy that occur across species and habitats is lacking. In this study, geophagy amongst large mammal herbivore assemblages was approached across four habitat types in southern African savannas. These habitats are, in descending order of aridity, the Kalahari, Nama Karoo, Grassveld, and Bushveld habitats. A study of the physico-chemical, mineralogical, and geochemical properties of ‘lick' sites frequently visited by herbivores, including laboratory analyses of elemental composition using XRD and XRF analyses, revealed few commonalities across habitats. Physical properties varied even within habitats, such that factors like soil colour - which has been suggested as a stimulus for geophagy, and cation exchange capacity (CEC), which did not differ between iii ingested and non-ingested soils, appeared to be unimportant to herbivores. A high Ca content was observed in geophagic soils in arid habitats, implying possible supplementation of this mineral, but varying quantities of essential elements like Fe, Mg, K, Mn, P, Cr, Co, Zn, and Mo likely also play a role because they better explain the variance in frequency of soil consumption across habitats than Ca alone. In the Bushveld habitat, however, occurrence of kaolinite, a mineral commonly found in antacid medication, indicates that here soil consumption served more to relieve gastric disorders than to act as a mineral supplement. In a second study, these geochemical properties of soil were compared with similar assays applied to argillaceous dung pellets sampled in the vicinity of lick sites. These results showed lower-than-expected concentrations of some essential elements like Ca, Cr, Mg, Mo and Na, in dung pellets, but higher-than-expected levels of Co, Cu and K, suggesting that while herbivores are able to absorb some minerals from soil, others are precipitated. A negative relationship between parasite faecal egg load and soil concentration further supported the protection hypothesis of geophagic soil. Relative frequency of geophagy across mammalian herbivore species, habitats, and seasons was evaluated based on recordings of site visits using camera traps. These data were based on 27 261 images representing 27 970 trap hours (1 222 trap days) across the sites and seasons, and included information for 24 herbivore species. In general, relative frequencies were higher in habitats dominated by grasses than in the Bushveld, a mixed tree/grass savanna, and the Nama Karoo, comprising a complex mixture of grass and dwarf karroid shrubs. However, this pattern varied across seasons depending on the habits of the dominant species in each. Browsers utilised geophagy sites more frequently in summer months, whereas grazers were more commonly encountered during autumn and winter. Interestingly, in the Bushveld, browsers practiced geophagy more often during autumn, and grazers more often during the spring. This “switch” suggests that phenological patterns in the vegetation - which are vastly different for woody plants that dominate the Bushveld compared with grasses that dominate elsewhere - play a role as a stimulus for soil consumption, with iv animals turning to this resource when the nutritional value of their staple foods (browse or grass) declines. These observations support the supplementation hypothesis of geophagy. All species, irrespective of habitat and season, visited geophagy sites almost exclusively during daylight hours, minimizing the risk of predation by nocturnal apex predators like lion (Panthera leo). But activity times at different sites varied across species: generally low levels of temporal niche overlap between species suggest that competition for foraging at lick sites is mitigated by temporal niche partitioning. Overall, this study presents quantitative data for geophagy and related aspects over a wider array of mammalian herbivores and habitats than most other investigations on geophagy. The results emphasized that geophagy is a regular, non-trivial dietary behaviour amongst large mammalian herbivores. They also highlight that soil consumption serves as both nutritional supplementation and protection, but that the relative intensities of these two mechanisms vary across habitats (and across seasons), as well as serving differently-adapted species (such as browsers and grazers) differently. Further studies tracking simultaneous changes in availability and nutritional quality of plant foods with the frequency of geophagy will give more context-dependent predictive insights into this behaviour. Similarly, in vitro and in vivo experimentation is still needed to fully understand the physiological implications of soil consumption. Since these are not feasible for most wildlife species, proxy-based approaches using dung pellet analyses, as presented in this study, hold some promise for investigation of benefits and banes of geophagy. v | |
| dc.identifier.uri | http://hdl.handle.net/11660/13394 | |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.title | Behavioural aspects of enzootic geophagy amongst large mammal herbivores | en_ZA |
| dc.type | Thesis |
Files
Original bundle
1 - 1 of 1
Loading...
- Name:
- Butler 22 PhDThesis.pdf
- Size:
- 13.76 MB
- Format:
- Adobe Portable Document Format