Niche Partitioning by Time and Grass Height
One type of niche partitioning in the savanna is shown in Figure 1. The resource partitioned in this example is a typical savanna grass called Panicum maximum. This grass’s growing season starts after the peak rain and continues for six months. When the grass is tall, it has lots of stems, which are relatively low-quality food for herbivores. The more nutritious parts of the grass are closer to the ground. If a grass-eating herbivore, or grazer, eats the top of the grass, the new parts of the grass that grow back are also more nutritious.
Figure 1 shows three types of grazers — zebra, wildebeest, and Thomson’s gazelle — that graze, or eat, this grass over time. Zebras, the first grazers to use this resource, thrive when the grass is tall and abundant, even if it is less nutritious. The zebras have paired upper and lower teeth that help them bite off tall stems on the tops of the grass.
Zebras can also digest food much more quickly than the other two grazers. This is because wildebeests and Thomson’s gazelles are ruminants, mammals with four-chambered stomachs that take longer to digest food. Sometimes ruminants must also regurgitate and rechew partly digested food before they can fully digest it.
However, when the ruminants digest their food (via fermentation in the foregut), they take up more nutrients and proteins than when zebras digest food (via fermentation in the hindgut). So, a ruminant can extract more energy from a smaller amount of food if that food is more nutritious. Smaller ruminants, such as Thomson’s gazelles, need less energy than larger ruminants, such as wildebeests.
