A new study focused on Mozambique's Gorongosa National Park, where entire populations of large-mammal predators were nearly extinguished during the Mozambican Civil War, illustrates how the loss of an ecosystem's top carnivores can have far-reaching consequences for prey and plant populations, turning "landscapes of fear" into "landscapes of fearlessness" in which emboldened herbivores graze and suppress plants. While the results of this study illustrate the cascading ecosystem impacts of human-mediated predator extinction, they also show that carnivore restoration in these areas could help reverse any ill effects of human activity, the authors say. The Mozambican Civil War (1977-1992) ravaged the populations of large mammals throughout Gorongosa and resulted in declines greater than 90% across all monitored species. To date, the region remains nearly devoid of carnivorous predators like leopards, wild dogs and hyenas. Apex predators, however, play a central role in defining an ecosystem through trophic cascades - an ecological concept that describes the complex and often indirect interactions between all members of an ecosystem's food web. One way in which predators can reduce prey abundance is by creating landscapes of fear, resource-rich yet risky habitats that prey tend to avoid to reduce their chances of being eaten. By changing the behavior of herbivores in this way, predators can create habitats where certain food plants can thrive. However, in the absence of carnivores, these once-risky habitats could become landscapes of fearlessness, where emboldened herbivores graze and suppress plant abundance. According to the authors the war-ravaged animal populations of Gorongosa provide a valuable opportunity to evaluate trophic cascades in large mammals that are otherwise difficult to study. Justine Atkins and colleagues observed the behavior of the bushbuck, an antelope that largely keeps to the cover of trees to avoid predators. However, in Gorongosa by at least 2002, Atkins et al. noticed a shift in its behavior; GPS-collared bushbuck, recognizing predators were less abundant, ventured into the treeless floodplain to feed - a decision that would otherwise be dangerous. Critically, the authors demonstrated that these shifts were reversible. By mimicking the presence of predators through recorded sounds and urine, fearless bushbuck became fearful and shifted their behavior accordingly, despite the decades-long absence of predators.
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Journal
Science