Fluctuations in food supply in an insularized and heavily grazed savanna ecosystem in Kenya

Mwangi, Evans Mungai; Western, David

doi:10.1046/j.1365-2028.1998.00121.x

Cited by 11 publications

(18 citation statements)

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“…Higher N concentrations of >12 mg g −1 also seem to occur in grass forage on basaltic and granitic soils in Kruger National Park, South Africa (Grant & Scholes 2006;Skidmore et al 2010). Studies from Lake Nakuru National Park, Kenya, have provided values similar to those in our study (7.7-9 mg g −1 N), but these were for all forage grasses rather than only to the most nutritious species (Mwangi & Western 1998). Grazers in open woodland of southern India also consumed grasses of considerably higher quality than were available in our savanna (10-28 mg g −1 N; Ahrestani et al 2012).…”

Section: The Importance Of Forage Qualitysupporting

confidence: 82%

“…During the dry seasons, the nitrogen concentrations of most savanna grasses decrease, and even in shortgrass savannas, they may fall below the levels that wild ruminants require for body maintenance (Sinclair 1975;Mwangi & Western 1998). These threshold levels vary according to herbivore species, body size and growth stage, but for smaller and mid-sized grazers, they are commonly estimated to be 4-9% crude protein concentration (i.e.…”

Section: The Importance Of Forage Qualitymentioning

confidence: 98%

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Convergent grazing responses of different‐sized ungulates to low forage quality in a wet savanna

Stähli

Edwards²,

Venterink

et al. 2015

Austral Ecology

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We studied how grazing intensity by small and mid-sized ungulate grazers varied with nutritional quality and grass species composition in wet oligotrophic tallgrass savanna of coastal northern Tanzania. Average grazing intensity was low (3-15% by cover), and most grass species were scarcely used by herbivores. Only two grasses, Panicum infestum and Digitaria milanjiana, had nitrogen and phosphorus concentrations that were consistently above the minimum levels (e.g. nitrogen concentrations <7 mg g −1 ) required by the three commonest grazers, Bohor reedbuck, waterbuck and wildebeest. The best predictors of grazing intensity were cover of P. infestum (the most abundant grass, with a mean cover of 15%) and canopy height of ungrazed vegetation. Models did not contain separate predictors for nutritional quality, presumably because quality varied mainly at the grass species level and therefore was fully represented by the variable 'cover of P. infestum'. Given that the three grazers differed greatly in body size and muzzle width (parameters known to influence nutrient requirements and the ability of grazers to feed selectively at the smallest spatial scale), we expected there to be strong resource partitioning that would be detectable in terms of grazing strategies and feeding sites. However, apart from minor differences in canopy height, greenness and diameter of grazed patches (albeit consistent with our expectations), feeding stations of the three grazers were similar and strongly dominated by P. infestum. We conclude that the low quality of herbage in wet oligotrophic savannas restricts foraging choices, which produces a characteristic yet impoverished grazing community that exhibits only limited resource partitioning.

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Section: The Importance Of Forage Qualitysupporting

confidence: 82%

Section: The Importance Of Forage Qualitymentioning

confidence: 98%

Convergent grazing responses of different‐sized ungulates to low forage quality in a wet savanna

Stähli

Edwards²,

Venterink

et al. 2015

Austral Ecology

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“…Buffalo diet is also dominated by grasses (Halley and Minagawa 2005) whereas zebra are non-ruminant grazers able to rapidly process large quantities of low quality forage (Owaga 1975). Since habitats utilized by buffalo, waterbuck and zebra in LNNP overlap extensively throughout the year (Mwangi and Western 1998), this increases chances of exploitative competition for forage in times of scarcity, as well as for space and water. In particular, herbivores in LNNP concentrate on grasslands on the lake shore during dry periods but disperse from the lake during the wet periods (Kutliek 1979;Wirtz and Kaiser 1988).…”

Section: Trends In Population Abundancementioning

confidence: 99%

“…Buffalo, waterbuck and zebra likely competed for forage due to extensive overlaps in their habitat utilization in LNNP (Mwangi and Western 1998) and similarity of their diets. Fig.…”

Section: Trends In Population Abundancementioning

confidence: 99%

“…The other species showed relatively stable populations despite the small park size and presence of predators. The capacity of LNNP to support this high biomass reflects the nutrient-rich status of its location on the Rift Valley floor (Bell 1982;East 1984), with soils derived from sediments of volcanic and lacustrine origin (Maskall and Thornton 1991), high terrestrial habitat diversity (Kutliek 1979;Mwangi and Western 1998), and the contribution by expanded lakeshore grasslands during low rainfall periods (Kutliek 1979).…”

Section: Trends In Population Abundancementioning

confidence: 99%

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Dynamics of ungulates in relation to climatic and land use changes in an insularized African savanna ecosystem

et al. 2012

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Land use change and human population growth are accelerating the fragmentation and insularization of wildlife habitats worldwide. The conservation and management of wildlife in the resultant 'island' ecosystems in the context of global warming is challenging due to the isolation and reduced size of the ecosystems and hence the scale over which ecosystem processes can operate. We analyzed trends in numbers of nine large herbivores in Kenya's Lake Nakuru National Park to understand how rainfall and temperature variability, surrounding land use changes, and boundary fencing affected wildlife population dynamics inside the park during 1970-2011. Buffalo, zebra and Thomson's gazelle numbers increased persistently. Grant's gazelle and impala increased initially then gradually declined. Waterbuck and warthog numbers progressively declined to levels that potentially threatened their local population persistence. The total biomass of ungulates tripled from 1970 to 2011, with buffalo replacing waterbuck as the predominant species in biomass. Increased competition from buffalo and zebra, heightened predation and illicit human harvests probably all contributed to the declines by waterbuck and warthog.Density-dependent limitation of population growth within the park confines was evident for buffalo, impala, eland, giraffe, Grant's and Thomson's gazelles. Fluctuations in the lake level related to varying rainfall affected changes in animal abundance through expansion of the lake area and flooding of grasslands bordering the lake. Unusually, the most stressful conditions were associated with high water levels following high rainfall. There was also evidence of carry-over effects from prior habitat conditions affecting all species. The relatively stable populations of all species except warthog and waterbuck demonstrate the remarkable capacity of this small, insularized park to retain viable populations of most of the large herbivores, without much management intervention.

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Seasonal interactions of pastoralists and wildlife in relation to pasture in an African savanna ecosystem

Russell¹,

Tyrrell²,

Western

2018

Journal of Arid Environments

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Fluctuations in food supply in an insularized and heavily grazed savanna ecosystem in Kenya

Cited by 11 publications

References 0 publications

Convergent grazing responses of different‐sized ungulates to low forage quality in a wet savanna

Convergent grazing responses of different‐sized ungulates to low forage quality in a wet savanna

Dynamics of ungulates in relation to climatic and land use changes in an insularized African savanna ecosystem

Seasonal interactions of pastoralists and wildlife in relation to pasture in an African savanna ecosystem

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