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Kruger Ecology 6: The Grazers

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Wed Jul 25, 2012 10:09 pm Unread post
The Kruger National Park has a spectacular variety of grazing mammals. This variety points to the fact that each species is adapted in a unique way to fill a specific niche in Africa’s savannas and grasslands. Let’s now look at the different types (guilds) of grazers and discuss their unique roles in their environment. Please note that mixed feeders (animals which both browse and graze) such as elephant and impala will not be discussed here as they will be the focus of upcoming posts.

Grazing guilds
The first guild is the bulk feeders with a tolerance for fibrous grasses. Buffalo and waterbuck falls in this group. These animals are not overly selective of the grasses they eat. Buffaloes specifically, have to eat a lot to maintain their huge bodies and can therefore not afford to be very picky! These animals play a very important role by eating tall and tough grasses and thereby opening up grazing areas to other more selective grazers who prefer shorter grass of higher quality. Large buffalo herds are key drivers of nutrient cycling in savannas. Through their dung they help to return nutrients (that have been locked up in unpalatable perennial grasses) to the soil, aided of course by dung beetles! Due to their high fibre diets, buffalo and waterbuck have one key habitat requirement: Continuous access to water.

Image
Buffalo and Waterbuck - bulk grazers with tolerance for fibrous grass

The next grazing guild is the bulk feeders with a preference for short grasses which are high in nitrogen. Examples of grazers in this group are: white rhino, hippo, burchell’s zebra and blue wildebeest. Hippos create grazing lawns next to rivers which they maintain during their nocturnal foraging. Likewise, white rhino create lawns amongst areas of taller grasses. This suites grazing with their square-lipped mouths and provides them with a constant supply of fresh new growth, high in nitrogen. These lawns of creeping grasses bring variety to the bush and create new opportunities for animals and plants specifically adapted to these habitats and which would not have been present without these open areas.

Zebra can be seen as an intermediate species between the bulk-fibrous feeders and the bulk-short grass feeders. They can eat grass of a medium to short length but prefer shorter grasses which are high in nutrients such as nitrogen.

As all three above mentioned short grass feeders are not ruminants (unlike antelope), their digestive systems are not as effective in dealing with plant material. Therefore they need to eat a lot of food to obtain enough nutrients for survival. That is the reason why these animals always look healthy and fat due to their large stomachs full of grass!

Blue wildebeest are the pickiest animals in this grazing guild. They prefer to eat short grass of the highest quality, which are packed with nitrogen. For this reason they are mainly found in sweetveld areas (see “Kruger Ecology 5” for description of sweetveld). The mass migration of wildebeest in the Serengeti is a prime example of these animals’ constant search for high quality grazing.

Image
Zebra and blue wildebeest - Short grass bulk grazers

An interesting phenomenon in savannas is grazing succession. This is the process whereby different grazing species visit feeding grounds in a specific order depending on their feeding preferences and as a result of past feeding practices of other species. An example would be where buffalo first enters an area with tall, fibrous grass. When they have opened up the area by removing the tough, tall-growing grasses, zebra enters the area and further crops the remaining grass stands. Lastly, blue wildebeest comes along to utilize the fresh new growth brought about by the buffalo and zebra.

The last grazing guild is the selective feeders with the key dietary requirement of grass with high quality carbon (normally medium to tall grasses), especially in the dry season. Examples of species in this guild are most of the rare antelope species in Kruger: Sable, roan, tsessebe and eland. This requirement serves as a clue as to the main reason why all of these antelope have become so scarce in the last couple of decades… But more about this in the next post where we will deal with the impact of the 4 drivers of savannas on grazer populations.

References:
Estes, Richard. The Behavior Guide to African Mammals: Including Hoofed Mammals, Carnivores, Primates. Los Angeles, USA: University of California Press Ltd, 1992. Print.

Seydack, A.H., Grant, C.C., Smit, I.P., Vermeulen, W.J., Baard, J. & Zambatis, N., 2012, ‘Large herbivore population performance and climate in a South African semi-arid savanna’, Koedoe54(1), Art. #1047, 20 pages. http://dx.doi.org/10.4102/ koedoe.v54i1.1047
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Re: Kruger Ecology 6: The Grazers

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Thu Jul 26, 2012 6:20 am Unread post
Excellent read. Thanks, Ifubesi. :thumbs_up: :clap: :clap:


Re: Kruger Ecology 6: The Grazers

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Location: Pretoria, South-Africa
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Sat Jul 28, 2012 4:23 pm Unread post
Ifubesi, a great read as usual. Keep it up!


Re: Kruger Ecology 6: The Grazers

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Sat Jul 28, 2012 4:28 pm Unread post
I agree, very interesting. It also demonstrates why certain animals flock to specific areas.. and why I am always seeing so many pregnant Zebras. :roll:
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