Investigating black rhinoceros ("Diceros bicornis") ecology towards improved conservation and management practices
Authors:   , Duthé Vanessa 
Published: November 2023

Savanna systems are facing growing pressures exerted by climate change, ecosystem degradation and the ongoing decline in biodiversity. Particularly, the decline of endangered charismatic megafauna such as large herbivores, has several consequences for such ecosystems. These include impacts such as weakened community stability, modification of food-web dynamics and alteration of nutrient cycles. Often considered as keystone species, large herbivores, exercise considerable influence on whole communities through habitat modification, resource partitioning, and competition. Despite their significant ecological importance and their threatened status, large herbivores have been relatively under-researched due to the inherent challenges associated with studying them, and are now mostly restricted to protected areas. Black rhinoceros (Diceros bicornis L.) are among the most endangered large herbivore species on Earth and have received limited scientific attention. The strategy for the recovery of black rhino involves restocking historical ranges with surplus animals from protected areas, as populations reach carrying capacity. This implies promoting population growth in current ranges, and selecting suitable habitats for translocations. Challenges lie not only in identifying factors linked to habitat suitability and maximised growth rate but also in integrating changing conditions, such as shifts in vegetation composition due to climate change and the influence of sympatric herbivores. Population growth is intricately connected not only to environmental abiotic and biotic conditions but also to management actions. Hence research on the species is critical in furthering our ecological knowledge and to ascertain whether management actions are having their desired effect in terms of reaching conservation targets. This thesis aims at increasing unambiguous knowledge of black rhino ecology, practical to its management and that of its environment, through a contemporary approach with the integration of monitoring techniques and modern methodologies, and three important scopes: space use, foraging and interactions. This work is based on several black rhino populations situated in reserves across KwaZulu-Natal, South Africa, in particular that of Ithala Game Reserve. In Chapter I, I investigate black rhino forage and habitat selection across multiple spatial scales. Knowing that forage selection is an important component linked to herbivore spatial distribution, I describe forage selection by the means of direct-observation transects on feeding paths and subsequent habitat selection based on monitoring data and ecosystem productivity (NDVI). I compare the nutritional and chemical composition of preferred and avoided plant species through metabolomics (LC-MS) and elemental analysis (CHN). I show that black rhinos’ spatial distribution was negatively associated with ecosystem productivity, but positively associated with specific vegetation types that contain highly preferred, chemically distinct, plant species. Black rhinos thus occupy their habitat across space and time through selective foraging on preferred plants. In Chapter II, because understanding interspecific herbivore dynamics within protected areas is crucial for their effective management, using DNA metabarcoding, I investigate resource partitioning between black rhino and three abundant sympatric herbivores, elephant, kudu and impala. While broad categories of foraging strategies can be used to explain coexistence, fine-grained information on seasonal foraging is needed to precisely assess resource partitioning. I describe seasonal diet composition and overlap; and compare foraging strategies between the four herbivores. I quantify the potential encroachment on black rhino dietary niche in Ithala Game Reserve. I found that diet composition and overlap shifted seasonally, where resource scarcity during the dry season generated a more even composition and reduced overlap of diets. Mesoherbivores encroached more on black rhinos than elephants did. In an environment more suited to browsers, the mixed feeders, elephant and impala, maintained nearly solely browsing through the year. This chapter shows that long-standing broad categories of foraging strategies and body size are limited in their use in protected areas and that seasonal strategies are central to managing increasingly threatened populations. In Chapter III, I investigate potential variables driving black rhino forage selection. Foraging behaviour is governed by decisions at various scales and shaped by the perception of morphological and physiological properties of plants. Pre-ingestive cues allow differentiating and choosing between food items. I thus compare the traits and volatile organic compounds (VOCs, through GC-MS) of preferred and avoided plant species determined by feeding-path transects, and examine their relative importance in determining preference or avoidance. This chapter suggests that both morphological and olfactory cues are important for black rhino forage selection. Discriminant volatiles such as Caryophyllene and Hexenol acetate were found to be important across seasons but volatiles alone were not as robust in explaining choice of forage, particularly in the growing season. This chapter provides the first steps to disentangling factors driving black rhino choice and potential applications to conservation management. Considering the ability to utilise plant odour and morphological cues will aid models pertaining to both the foraging behaviour of black rhino and the ecosystem consequences resulting from their foraging activities. In Chapter IV, I measure the impact of dehorning on black rhino home ranges and the efficacy of dehorning as a poaching deterrent. Because poaching for horns is the biggest threat to black rhino, by proactively dehorning entire rhinoceros populations, conservationists aim to deter poaching and prevent species loss. However, such conservation interventions may have hidden and underestimated effects on animals’ behaviour and ecology. Here, I use long-term monitoring data to estimate home ranges before and after dehorning, and trends in dehorning and mortalities. I estimate the effect of such a tool on social interactions based on home-range overlap. While preventative dehorning at these reserves coincided with a nationwide decrease in black rhino mortality from poaching and did not infer increased natural mortality, dehorned black rhinos decreased their home range area and were less likely to engage in social encounters. Dehorning black rhinos as an anti-poaching measure alters their behavioural ecology, although the potential population-level effects of these changes remain to be determined. In conclusion, this thesis suggests that the black rhino is an intricate species that demonstrates behavioural plasticity to changing ecosystem conditions and management interventions. The ongoing evaluation and adaption of management strategies and consistent monitoring are crucial for ensuring effective conservation efforts. Behavioural ecology, such as space and resource utilisation, can serve as early indicators of concealed consequences and facilitate adaptive management for large herbivores. This thesis furthers our understanding of a critically endangered large herbivore and highlights the need for continued research.