Long-term historical and projected herbivore population dynamics in Ngorongoro crater, Tanzania

Abstract

The Ngorongoro Crater is an intact caldera with an area of approximately 310 km 2 located within the Ngorongoro Conservation Area (NCA) in northern Tanzania. It is known for the abundance and diversity of its wildlife and is a UNESCO World Heritage Site and an International Biosphere Reserve. Long term records (1963-2012) on herbivore populations, vegetation and rainfall made it possible to analyze historic and project future herbivore population dynamics. NCA was established as a multiple use area in 1959. In 1974 there was a perturbation in that resident Maasai and their livestock were removed from the Ngorongoro Crater. Thus, their pasture management that was a combination of livestock grazing and fire was also removed and 'burning' stopped being a regular occurrence until it was resumed in 2001 by NCA management. The Maasai pasture management would have selected for shorter grasses and more palatable species. Vegetation mapping in 1966-1967 recorded predominately short grasslands. Subsequent vegetation mapping in the crater in 1995 determined that the grassland structure had changed such that mid and tall grasses were dominant. After removal of the Maasai pastoralists from the Ngorongoro Crater in 1974, there were significant changes in population trends for some herbivore species. Buffalo, elephant and ostrich numbers increased significantly during 1974-2012. The zebra population was stable from 1963 to 2012 whereas population numbers of five species declined substantially between 1974 and 2012 relative to their peak numbers during 1974-1976. Grant's and Thomson's gazelles, eland, kongoni, and waterbuck (wet season only) declined significantly in the Crater in both seasons after 1974. In addition, some herbivore species were consistently more abundant inside the Crater during the wet than the dry season. This pattern was most evident for the large herbivore species requiring bulk forage, i.e., buffalo, eland, and elephant. Even with a change in grassland structure, total herbivore biomass remained relatively stable from 1963 to 2012, implying that the crater has a stable carrying capacity. Analyses of rainfall indicated that there was a persistent cycle of 4.83 years for the annual component. Herbivore population size was correlated with rainfall in both the wet and dry

Diurnal pastoralism does not reduce juvenile recruitment nor elevate allostatic load in spotted hyenas

“…The NCA is inhabited by the Maasai tribe, a semi-nomadic, pastoralist ethnic group traditionally ranging from central Kenya to southern Tanzania (Fratkin, 2001). The Maasai and their livestock resided in the Crater until 1974, when they were evicted and required to live in other parts of the NCA (Moehlman et al, 2020). They were still allowed to enter the Crater to conduct diurnal pastoralism until it was banned at the end of 2016 (Melubo & Lovelock, 2019).…”

Spatial and seasonal group size variation of wild mammalian herbivores in multiple use landscapes of the Ngorongoro Conservation Area, Tanzania

“…Various studies on herbivores analyzed the long-term population trends and assessed the seasonal stability of wild herbivore communities in the Ngorongoro Conservation Area (NCA) [ 30 ]. In addition, some studies found that the exclusion of resident pastoralists and their livestock from the Ngorongoro crater resulted into both increasing and decreasing trends of some ungulate species whereas overall, wildlife biomass remained unchanged [ 31 , 32 ]. However, as humans continue to impact natural habitats and livestock populations still grow within NCA, there is an increasing need to understand how this affects distributions and group sizes of wild herbivores in this Man and Biosphere reserve [ 33 , 34 ].…”

A learning network approach to resolve conservation challenges in the Ngorongoro Conservation Area

“…Concomitant with these changes, there is mounting evidence to show that populations of some wildlife species (i.e. gazelle species, wildebeest, kongoni ( Alcelaphus buselaphus cokii ), waterbuck ( Kobus ellipsiprymnus ) and eland ( Taurotragus oryx ) have declined in the Ngorongoro caldera (Estes et al., 2006, Moehlman et al, 2020). These species preferred the short grasslands as maintained through prescribed burning.…”

“…These species preferred the short grasslands as maintained through prescribed burning. Since the practice of burning was banned from 1975, grasslands supported taller grass stands benefitting Cape buffalo ( Syncerus caffer , Fyumagwa et al., 2007) and elephant populations, while plains zebras have remained stable (Moehlman et al, 2020).…”

“…While some aspects of ecology in and around the caldera have been well studied (e.g. Sinclair et al, 2015), fundamental aspects of NCA biology outside of the caldera are less well understood, especially relating to climate change (but see Moehlman et al, 2020 for the caldera), the impact of tourism, and the interaction between humans, cattle and wildlife. The conflict of interest here is between the effects that residents and visitors have on the environment versus the economic value of increased tourism.…”