Food regulates the Serengeti wildebeest: a 40‐year record

The conservation of migratory wildlife species in the savannah habitat can be a challenge because of frequent and prolonged drought and their requirements for a large area. We investigated the performance of the wildebeest (Connochaetes taurinus) population in the 25,624 km2 Kilimanjaro landscape of Kenya and Tanzania, which comprises Amboseli-West Kilimanjaro-Magadi-Natron after 2009 drought. We used total aerial counts to determine the spatial distribution and numbers of wildebeests during wet and dry season in 2010 and 2013. Global Positioning System and digital voice recorders were used to count wildebeests along established transects within blocks. There was an increase in the wildebeest population by 103% during the wet season and 14% during the dry season between 2010 and 2013. The seasonal variation in density occurred between the four counting blocks with Natron and Magadi areas recording the highest densities. Generally, the increase in population could be attributed to the recovery of the population after the 2009 drought. The current cross border collaboration between Kenya and Tanzania in aerial surveys is an important step in the conservation of this migratory species in the landscape. This study demonstrates that detailed knowledge of density and spatial distribution of migratory species is required to plan effective conservation action.

AimThe study tests the hypothesis that land‐use changes in Narok District have had an impact on the wildebeest population [Connochaetes taurinus mearnsi (Burchell)] in the northern part of the Serengeti–Mara ecosystem.LocationThe Serengeti–Mara ecosystem is a vast area of rangelands, straddling the Tanzanian–Kenyan border in East Africa. The area is home to some 1.3 million wildebeest, of which some 30,000 animals currently reside in the Kenyan part of the ecosystem.MethodsWe analysed the temporal changes in the wildebeest population in the Kenyan part of the Serengeti–Mara ecosystem and their relationship with possible driving forces of change, such as rainfall, normalized difference vegetation index (NDVI), livestock numbers and land‐cover changes. Changes in the spatial distribution of wildebeest for three periods were compared with spatial changes in livestock distribution and land cover. The analyses were repeated for the Tanzanian part of the ecosystem and results compared. We thus tested the relative importance of land‐use changes among the different potential driving forces of change in the wildebeest populations.ResultsThe wildebeest population in the Kenyan part of the Serengeti–Mara ecosystem declined drastically over the past 20 years and is currently fluctuating around an estimated population of 31,300 animals, which is about 25% of the population size at the end of the 1970s. The wildebeest population in the Kenyan part of the Serengeti–Mara ecosystem has, over the last decades, been controlled by food supply during the dry and the wet seasons. Expansion of large‐scale mechanized wheat farming in the Loita Plains since the early 1980s has drastically reduced the wildebeest wet season range, forcing the wildebeest population to use the dryer rangelands in the south‐eastern part of the Loita eco‐unit, or to move to the Mara eco‐unit, where competition with cattle is higher. The expansion of the farming area has not influenced the size of the total cattle population in the Kenyan part of the study area, nor its spatial distribution. The much larger migratory wildebeest population of the Serengeti, in Tanzania, has not been affected by a downward trend from the late 1970s and is regulated by food supply in the dry season (Mduma et al., 1999). Around the Serengeti, in Tanzania, land‐use changes are much less widespread, occur at a lower rate and affect a much smaller area compared with the Kenyan part of the ecosystem. Moreover, land‐use changes around the Serengeti have taken place away from the main migration routes of wildebeest.ConclusionsOver the last decades, the decline in the Kenyan wildebeest population did not seem to affect the much larger Serengeti wildebeest population. However, if more land were to be converted to large scale farming closer to the Masai Mara National Reserve, the dry season range for both the Kenyan and the Serengeti population would be reduced. This might have serious consequences for both populations and therefore for the entire Serengeti–Mara ecosystem.

The Serengeti wildebeest migration is a rare and spectacular example of a once-common biological phenomenon. A proposed road project threatens to bisect the Serengeti ecosystem and its integrity. The precautionary principle dictates that we consider the possible consequences of a road completely disrupting the migration. We used an existing spatially-explicit simulation model of wildebeest movement and population dynamics to explore how placing a barrier to migration across the proposed route (thus creating two disjoint but mobile subpopulations) might affect the long-term size of the wildebeest population. Our simulation results suggest that a barrier to migration—even without causing habitat loss—could cause the wildebeest population to decline by about a third. The driver of this decline is the effect of habitat fragmentation (even without habitat loss) on the ability of wildebeest to effectively track temporal shifts in high-quality forage resources across the landscape. Given the important role of the wildebeest migration for a number of key ecological processes, these findings have potentially important ramifications for ecosystem biodiversity, structure, and function in the Serengeti.

Calf mortality and parasitism in periurban livestock production in Mali

Migratory ungulates may be particularly vulnerable to the challenges imposed by growing human populations and climate change. These species depend on vast areas to sustain their migratory behavior, and in many cases come into frequent contact with human populations outside protected areas. They may also act as spatial coupling agents allowing feedbacks between ecological systems and local economies, particularly in the agropastoral subsistence economies found in the African savanna biome. We used HUMENTS, a spatially realistic socioecological model of the Greater Serengeti Ecosystem in East Africa, to explore the potential impacts of changing climate and poaching on the migratory wildebeest (Connochaetes taurinus) population, the fire regime, and habitat structure in the ecosystem, as well as changes in the size and economic activities of the human population outside the protected area. Unlike earlier models, the HUMENTS model predicted only moderate declines in the wildebeest population associated with an increasing human population over the next century, with a gradual expansion of agriculture, more poaching, and increases in fire frequency and reduced tree density. Changes in rainfall were predicted to have strong asymmetric effects on the size and economic activity of the human population and on livestock, and more moderate effects on wildlife and other ecological indicators. Conversely, antipoaching had a stronger effect on the ecological portion of the system because of its effect on wildebeest (and therefore on fire and habitat structure), and a weaker effect on the socioeconomic component, except in areas directly adjacent to the protected-area boundary, which were affected by crop-raiding and the availability of wildlife as a source of income. The results highlight the strong direct and indirect effects of rainfall on the various components of socioecological systems in semiarid environments, and the key role of mobile wildlife populations as agents of spatial coupling between the human-dominated and natural portions of ecosystems. They also underscore the fundamental importance of considering the spatial configuration of hunting refuges across the landscape in relation to human populations.

Salt Poisoning as a Cause of Morbidity and Mortality in Neonatal Dairy Calves

Introgressive hybridization poses a threat to the genetic integrity of black wildebeest (Connochaetes gnou) and blue wildebeest (Connochaetes taurinus) populations in South Africa. Black wildebeest is endemic to South Africa and was driven to near extinction in the early 1900s due to habitat destruction, hunting pressure and disease outbreaks. Blue wildebeest on the other hand are widely distributed in southern and east Africa. In South Africa the natural distribution ranges of both species overlap, however, extensive translocation of black wildebeest outside of its normal distribution range in South Africa have led to potential hybridization between the two species. The molecular identification of pure and admixed populations is necessary to design viable and sustainable conservation strategies, since phenotypic evidence of hybridization is inconclusive after successive generations of backcrossing. The aim of this study was to assess levels of hybridization in wildebeest using both species-specific and cross-species microsatellite markers. Black wildebeest (157) and blue wildebeest (122) from provincial and national parks and private localities were included as reference material, with 180 putative hybrid animals also screened. A molecular marker panel consisting of 13 cross-species and 11 species-specific microsatellite markers was developed. We used a Bayesian clustering model to confirm the uniqueness of blue- and black wildebeest reference groups, assign individuals to each of the two clusters, and determine levels of admixture. Results indicated a clear partition between black wildebeest and blue wildebeest (the average proportions of membership to black wildebeest and blue wildebeest clusters were QI = 0.994 and QI = 0.955 respectively). From the putative hybrid samples, only five hybrid individuals were confirmed. However, high levels of linkage disequilibrium were observed in the putative hybrid populations which may indicate historical hybridization. Measures of genetic diversity in the black wildebeest populations were found to be lower than that of the blue wildebeest. The observed lower level of genetic diversity was expected due to the demographic history of the specie. This study will make a significant contribution to inform a national conservation strategy to conserve the genetic integrity of both species.

Associations of serum haptoglobin in newborn dairy calves with health, growth, and mortality up to 4 months of age

Wildlife translocations have historically assisted in re-establishing species in areas of extinction and are currently employed in over 50 countries. Ironically, they may also be responsible for the extinction of pure genetic lineages via hybridization, thereby negatively impacting endangered, indigenous, and rare species. Due to recent evolutionary divergence, black wildebeest (Connochaetes gnou) and blue wildebeest (Connochaetes taurinus) can mate and produce fertile offspring when sympatric. A total of 6929 translocated black and blue wildebeest from 273 private ranches and 3 provincial protected areas protected (PPAs) were documented over 5 years, across 5 South African provinces. We analyzed dispersal patterns and wildlife ranching economics to identify conservation implications and to infer if translocations are likely to persist in their current form. Findings indicate (1) 58.45% of sampled private ranches manage for both wildebeest populations, (2) blue wildebeest males are primarily translocated, (3) wildebeest are introduced across provincial lines, (4) wildebeest are introduced to within and amongst the private and commercial industry from multiple sources, and (5) wildebeest revenue accounted for 20.8% of revenue generated from all wildlife translocations. Unwanted conservation implications concern ecological integrity, genetic swamping, and regulatory efficiency. We caution against risks posed by the game industry upon the PPA's ability to function as nature conservation units and act as stocking sources and the plausibility that black wildebeest populations incorporate varying degrees of introgressive hybrids. Moreover, wildebeest account for 1/5 of revenue generated from all game translocations. This is indicative of its likelihood to persist in their current form, thereby inducing hybridization and facilitating outbreeding depression. We caution that concerns are likely to worsen if no intervention is taken. Lastly, we coin the concept of Ecological Sustainable Network (ESN); we designed a framework for standardizing procedures to advance effective wildlife translocation practices worldwide.

Summary Predation upon ungulates is generally considered to have a stronger regulatory effect on sedentary than migratory populations, with migratory populations maintaining higher densities. The blue wildebeest Connochaetus taurinus is a migratory species that has suffered a general decline in numbers and distribution across its species range. Wildebeest suffer from a fragmented distribution together with isolation of populations in closed reserves, preventing migratory movements and potentially allowing predators to benefit from a ‘captive’ prey resource. In Pilanesberg National Park, South Africa, the declining blue wildebeest population (from 1074 in 1995 to 594 in 2001) is sedentary because the park (50 000 ha) is completely enclosed by fencing. This population was used to model the potential effects of predation and harvesting. The Pilanesberg population was then compared with other wildebeest populations in southern Africa. The model outputs demonstrated that increased levels of predation by lions Panthera leo on a ‘captive’ population of prey such as wildebeest, in combination with regular harvesting by park managers, can drive the population towards extinction. At lower levels of predation some other factor needs to act in combination with predation to drive the population into a decline. During our study the lion biomass density in Pilanesberg was almost three times greater than that predicted by regression models of the stable relationship between lion and prey biomass densities across African savannas. Furthermore, the ratio of lion numbers to prey numbers was substantially higher than in most other African reserves. Synthesis and applications. In African savannas, artificial closed systems provide advantages to large predators. If wildlife‐cropping schemes are implemented in such systems without careful monitoring and regulation of large predators, then ungulate populations can decline more rapidly than managers expect.

Bovine tuberculosis, caused by Mycobacterium bovis, is a pathogen of growing concern in free-ranging wildlife in Africa, but little is known about the disease in Tanzanian wildlife. Here, we report the infection status of Mycobacterium bovis in a range of wildlife species sampled from protected areas in northern Tanzania. M. bovis was isolated from 11.1% (2/18) migratory wildebeest (Connochaetes taurinus) and 11.1% (1/9) topi (Damaliscus lunatus) sampled systematically in 2000 during a meat cropping program in the Serengeti ecosystem, and from one wildebeest and one lesser kudu (Tragelaphus imberbis) killed by sport hunters adjacent to Tarangire National Park. A tuberculosis antibody enzyme immunoassay (EIA) was used to screen serum samples collected from 184 Serengeti lions (Panthera leo) and 19 lions from Ngorongoro Crater sampled between 1985 and 2000. Samples from 212 ungulates collected throughout the protected area network between 1998 and 2001 also were tested by EIA. Serological assays detected antibodies to M. bovis in 4% of Serengeti lions; one positive lion was sampled in 1984. Antibodies were detected in one of 17 (6%) buffalo (Syncerus caffer) in Tarangire and one of 41 (2%) wildebeest in the Serengeti. This study confirms for the first time the presence of bovine tuberculosis in wildlife of northern Tanzania, but further investigation is required to assess the impact on wildlife populations and the role of different wildlife species in maintenance and transmission.

In long‐distance migratory systems, local fluctuations in the predator–prey ratio can exhibit extreme variability within a single year depending upon the seasonal location of migratory species. Such systems offer an opportunity to empirically investigate cyclic population density effects on short‐term food web interactions by taking advantage of the large seasonal shifts in migratory prey biomass.We utilized a large‐mammal predator–prey savanna food web to evaluate support for hypotheses relating to the indirect effects of “apparent competition” and “apparent mutualism” from migratory ungulate herds on survival of resident megaherbivore calves, mediated by their shared predator. African lions (Panthera leo) are generalist predators whose primary, preferred prey are wildebeests (Connochaetes taurinus) and zebras (Equus quagga), while lion predation on secondary prey such as giraffes (Giraffa camelopardalis) may change according to the relative abundance of the primary prey species.We used demographic data from five subpopulations of giraffes in the Tarangire Ecosystem of Tanzania, East Africa, to test hypotheses relating to direct predation and indirect effects of large migratory herds on calf survival of a resident megaherbivore. We examined neonatal survival via apparent reproduction of 860 adult females, and calf survival of 449 giraffe calves, during three precipitation seasons over 3 years, seeking evidence of some effect on neonate and calf survival as a consequence of the movements of large herds of migratory ungulates.We found that local lion predation pressure (lion density divided by primary prey density) was significantly negatively correlated with giraffe neonatal and calf survival probabilities. This supports the apparent mutualism hypothesis that the presence of migratory ungulates reduces lion predation on giraffe calves.Natural predation had a significant effect on giraffe calf and neonate survival, and could significantly affect giraffe population dynamics. If wildebeest and zebra populations in this ecosystem continue to decline as a result of increasingly disrupted migrations and poaching, then giraffe calves will face increased predation pressure as the predator–prey ratio increases. Our results suggest that the widespread population declines observed in many migratory systems are likely to trigger demographic impacts in other species due to indirect effects like those shown here.

Habitat disturbance effects on the physiological stress response in resident Kenyan white-bearded wildebeest (Connochaetes taurinus)

Determining the relative importance of dilution and detection for zebra foraging in mixed-species herds

Habitat selectivity influences the reactive responses of African ungulates to encounters with lions