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Food supply and poaching limit giraffe abundance in the Serengeti

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Population Ecology

Abstract

The iconic giraffe, an ecologically important browser, has shown a substantial decline in numbers across Africa since the 1990s. In Serengeti National Park, Tanzania, giraffes reached densities of 1.5–2.6 individuals km−2 in the 1970s coincident with a pulse of Acacia tree recruitment. However, despite continued increases in woody cover between the 1980s and the 2000s, giraffe recruitment and survival rates have declined and density has dropped to only 0.3–0.4 giraffes km−2. We used a decision table to investigate how four extrinsic factors may have contributed to these declines: food supply, predation, parasites, and poaching, which have all been previously shown to limit Serengeti ungulate populations. Lower recruitment likely resulted from a reduction in diet quality, owing to the replacement of preferred trees with unpalatable species, while decreased adult survival resulted from illegal harvesting, which appears to have had a greater impact on giraffe populations bordering the western and northern Serengeti. The Serengeti giraffe population will likely persist at low-to-moderate densities until palatable tree species regain their former abundance. Leslie matrix models suggest that park managers should meanwhile redouble their efforts to reduce poaching, thereby improving adult survival.

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Acknowledgments

We thank the Tanzania Commission for Science and Technology, Tanzania National Parks, and the Tanzania Wildlife Research Institute for permission to carry out the research, R. Hoare, F. Borner, S. Brown, D. Rosengren, and A. Swanson for assistance with aerial counts, SENAPA Veterinary Unit staff, particularly Yassin Rajabu for recording snare cases, T. Arnold and E. Thrane for assistance with modeling, and N. Owen-Smith and an anonymous reviewer for comments on an earlier draft of the manuscript. MS and the giraffe field studies were funded by the National Science Foundation Graduate Research Fellowship Program, the American Society of Mammalogists, Chester Zoo, Columbus Zoo, the Explorer’s Club, Minnesota Zoo, Riverbanks Zoo and Garden, and by the University of Minnesota’s Graduate School, GPS Alliance, and Bell Museum. Lion research was funded by NSF grant DEB-1020479 to CP.

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Correspondence to M. K. L. Strauss.

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Strauss, M.K.L., Kilewo, M., Rentsch, D. et al. Food supply and poaching limit giraffe abundance in the Serengeti. Popul Ecol 57, 505–516 (2015). https://doi.org/10.1007/s10144-015-0499-9

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