Population trend and distribution of the Vulnerable common hippopotamus <i>Hippopotamus amphibius</i> in the Mara Region of Kenya

Kanga, Erustus; Ogutu, Joseph O.; Olff, Han; Santema, Peter

doi:10.1017/s0030605310000931

Cited by 46 publications

(77 citation statements)

References 38 publications

(69 reference statements)

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“…Hippos extended their grazing range further from water points in dry seasons, likely due to forage depletion near water as the dry season progresses (O'Connor and Campbell 1986), but this seasonal range expansion was more constrained in the pastoral areas, where herders graze livestock along rivers in dry seasons, thus depleting vegetation and interfering with the hippo ranging pattern from water (Belsky et al 1999;Thrash 2000). An earlier record of the hippo grazing range along the Mara River north of the SNP in the 1970s, of 1.5 km (Olivier and Laurie 1974), was smaller than the present estimate of 4 km, suggesting that the recent dramatic increase in the population of Mara hippos (Kanga et al 2011) or the progressive compression of the hippo distribution, due to changing land use over the last three decades and competition with livestock and other herbivores along the riparian-edge habitats (Reid et al 2003), probably compel hippos to travel further from water to satisfy their forage requirements. Unlike in the pastoral ranches, a sacrificial zone with heavily depleted grass cover due to repeated grazing and trampling by hippos leaving and returning to water (Thrash and Derry 1999) was well established in the MMNR and extended for about 250 m from river banks.…”

Section: Discussioncontrasting

confidence: 52%

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

et al. 2011

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Riparian savanna habitats grazed by hippopotamus or livestock experience seasonal ecological stresses through the depletion of herbaceous vegetation, and are often points of contacts and conflicts between herbivores, humans and their livestock. We investigated how hippopotamus and livestock grazing influence vegetation structure and cover and facilitate other wild herbivores in the Mara region of Kenya. We used 5 km-long transects, each with 13 plots measuring 10 9 10 m 2 , and which radiate from rivers in the Masai Mara National Reserve and adjoining community pastoral ranches. For each plot, we measured the height and visually estimated the percent cover of grasses, forbs, shrubs and bare ground, herbivore abundance and species richness. Our results showed that grass height was shortest closest to rivers in both landscapes, increased with increasing distance from rivers in the reserve, but was uniformly short in the pastoral ranches. Shifting mosaics of short grass lawns interspersed with patches of medium to tall grasses occurred within 2.5 km of the rivers in the reserve in areas grazed habitually by hippos. Hence, hippo grazing enhanced the structural heterogeneity of vegetation but livestock grazing had a homogenizing effect in the pastoral ranches. The distribution of biomass and the species richness of other ungulates with distance from rivers followed a quadratic pattern in the reserve, suggesting that hippopotamus grazing attracted more herbivores to the vegetation patches at intermediate distances from rivers in the reserve. However, the distribution of biomass and the species richness of other ungulates followed a linear pattern in the pastoral ranches, implying that herbivores avoided areas grazed heavily by livestock in the pastoral ranches, especially near rivers.

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Section: Discussioncontrasting

confidence: 52%

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

et al. 2011

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“…The Mara River ecosystem contains a population of over 4,000 hippos ( Hippopotamus amphibius ) (Kanga et al. ) and is on the route of the largest remaining overland migration in the world of 1.3 million wildebeest ( Connochaetes taurinus ; Hopcraft et al. ).…”

Section: Introductionmentioning

confidence: 99%

Organic matter and nutrient inputs from large wildlife influence ecosystem function in the Mara River, Africa

Subalusky

Dutton

Njoroge

et al. 2018

Ecology

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Animals can be important vectors for the movement of resources across ecosystem boundaries. Animals add resources to ecosystems primarily through egestion, excretion, and carcasses, and the stoichiometry and bioavailability of these inputs likely interact with characteristics of the recipient ecosystem to determine their effects on ecosystem function. We studied the influence of hippopotamus excretion/egestion and wildebeest carcasses, and their interactions with discharge, in the Mara River, Kenya. We measured nutrient dissolution and decomposition rates of wildlife inputs, the influence of inputs on nutrient concentrations and nutrient limitation in the river and the influence of inputs on biofilm growth and function in both experimental streams and along a gradient of inputs in the river. We found that hippopotamus excretion/egestion increases ammonium and coarse particulate organic matter in the river, and wildebeest carcasses increase ammonium, soluble reactive phosphorus, and total phosphorus. Concentrations of dissolved carbon and nutrients in the water column increased along a gradient of wildlife inputs and during low discharge, although concentrations of particulate carbon decreased during low discharge due to deposition on the river bottom. Autotrophs were nitrogen limited and heterotrophs were carbon limited and nitrogen and phosphorus colimited upstream of animal inputs but there was no nutrient limitation downstream of inputs. In experimental streams, hippo and wildebeest inputs together increased biofilm gross primary production (GPP) and respiration (R). These results differed in the river, where low concentrations of hippo inputs increased gross primary production (GPP) and respiration (R) of biofilms, but high concentrations of hippo inputs in conjunction with wildebeest inputs decreased GPP. Our research shows that inputs from large wildlife alleviate nutrient limitation and stimulate ecosystem metabolism in the Mara River and that the extent to which these inputs subsidize the ecosystem is mediated by the quantity and quality of inputs and discharge of the river ecosystem. Thus, animal inputs provide an important ecological subsidy to this river, and animal inputs were likely important in many other rivers prior to the widespread extirpation of large wildlife.

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“…have increased dramatically in recent years (Kanga et al 2011), may have forced buffaloes to travel longer distances to and from water along the Mara river during and after the 1993-94 drought.…”

Section: Discussionmentioning

confidence: 99%

Population regulation of African buffalo in the Mara–Serengeti ecosystem

Dublin

Ogutu

2015

Wildl. Res.

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Context. The processes regulating ungulate populations have been the focus of numerous studies. For the African buffalo (Syncerus caffer Sparrman) population inhabiting the Mara-Serengeti ecosystem, rinderpest was the primary regulatory factor up to the mid-1960s. Following reduction of rinderpest and buffalo population increase, interspecific competition for food, notably with cattle and wildebeest (Connochaetes taurinus Burchell), was thought to be the primary regulatory factor in the ecosystem.Aims. We analysed buffalo population trends and the relationship between buffalo population growth and rainfall and density dependence in the Mara-Serengeti ecosystem and discuss the findings in the context of the key ecosystem processes governing buffalo population dynamics in African savannas, namely, food limitation, competition, predation, disease and land use changes.Methods. We analysed buffalo population dynamics in the Mara-Serengeti ecosystem in relation to rainfall and density dependence feedback between 1984 and 2010.Key results. Buffalo population growth was both significantly density-dependent and positively correlated with the dry season rainfall after, but not before, a severe drought in 1993. Buffalo numbers crashed by 48.6% in 1984-85 and by 76.1% in 1993-94 during severe droughts when food availability was lowest and competition with the more numerous cattle and wildebeest was highest.Conclusions. Recovery of buffalo numbers to pre-drought levels took 8-9 years after the 1984-85 drought but was much slower, with buffaloes numbering merely 36% of their 1993 population (12 895 animals) 18 years after the 1993-94 drought despite intermittent periods of high rainfall, probably due to demographic and/or reproductive factors, heightened competition with livestock, land use changes in the adjoining pastoral ranches, lion predation and recurrent severe droughts.Implications. Our findings demonstrate how food limitation caused by droughts associated with the hemispheric El Niño-Southern Oscillation can cause severe declines in and threaten the persistence of large ungulate populations. The findings also portray how density-dependent food limitation, competition, predation, land use changes and other factors can accentuate the effect of droughts and greatly prolong population recovery.

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Population trend and distribution of the Vulnerable common hippopotamus Hippopotamus amphibius in the Mara Region of Kenya

Cited by 46 publications

References 38 publications

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

Organic matter and nutrient inputs from large wildlife influence ecosystem function in the Mara River, Africa

Population regulation of African buffalo in the Mara–Serengeti ecosystem

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