Large carnivores make savanna tree communities less thorny

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Science  17 Oct 2014:
Vol. 346, Issue 6207, pp. 346-349
DOI: 10.1126/science.1252753

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Understanding how predation risk and plant defenses interactively shape plant distributions is a core challenge in ecology. By combining global positioning system telemetry of an abundant antelope (impala) and its main predators (leopards and wild dogs) with a series of manipulative field experiments, we showed that herbivores’ risk-avoidance behavior and plants’ antiherbivore defenses interact to determine tree distributions in an African savanna. Well-defended thorny Acacia trees (A. etbaica) were abundant in low-risk areas where impala aggregated but rare in high-risk areas that impala avoided. In contrast, poorly defended trees (A. brevispica) were more abundant in high- than in low-risk areas. Our results suggest that plants can persist in landscapes characterized by intense herbivory, either by defending themselves or by thriving in risky areas where carnivores hunt.

A thorny defense keeps grazers at bay

Fear and avoidance of predators are known to influence how and where herbivore prey species, such as impala, forage. This in turn has cascading effects on plant morphologies and communities. Plants, however, have their own defenses, and so may not just be hapless victims of the predator-prey “dance.” Ford et al. found that thorny Acacia trees are more common in areas where impala experience a low risk of predation by wild dogs. A related Acacia, without thorns, is most abundant in areas where risk of predation is high, and so the number of hungry impala is low.

Science, this issue p. 346

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