Hippo teeth reveal environmental change

Changed plant types associated with loss of elephants in Ugandan national park

Date: September 12, 2016

Source: University of Utah

Loss of megaherbivores such as elephants and hippos can allow woody plants and non-grassy herbs and flowering plants to encroach on grasslands in African national parks, according to a new University of Utah study, published Sept. 12 in Scientific Reports. The study used isotopes in hippopotamus teeth to find a shift in the diet of hippos over the course of a decade in Uganda's Queen Elizabeth National Park following widespread elephant poaching in the 1970s.

Study first author and U postdoctoral scholar Kendra Chritz says that her method of using hippo enamel isotopes could help scientists reconstruct past changes in vegetation in Africa's national parks, areas with relatively little ongoing scientific observation. The results could give ecologists an idea of what could happen to Africa's grasslands if elephants, whose populations are steeply declining, went extinct or reached near-extinction.

"We have a window into what these environments could look like without megaherbivores, and it's kind of grim," Chritz says.

Competing plant classes

Grasslands are an important ecosystem in Africa, hosting many animals and serving as corridors for wildlife movement. Lowland tropical grasses, such as those in elephant ecosystems, are part of the C4 class of plants, a reference to the enzyme used to process carbon dioxide into sugars during photosynthesis. Corn and sugarcane are also C4 plants. C3 plants, which use a different enzyme, include trees, shrubs, flowering plants and herbs. C3 plants compete for resources with C4 grasses in African savannas, including sunlight. Elephants and other megaherbivores help keep woody plant encroachment in check by browsing seasonally on shrubs and trees. But without that herbivore control, C3 plants can advance on grasslands unimpeded.

The presence of shrubs and trees, which can be seen in aerial photographs, give only a partial picture of the balance of power between C3 and C4 plants. Observing herbs and flowering plants requires ground-level observation, and records of such observations in Uganda's Queen Elizabeth National Park, and many national parks in Africa, is sparse.

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