Abstract
The fear large carnivores inspire in large ungulates has been argued to have cascading effects down food webs. However, a direct link between ungulate habitat use and their fear of large carnivores has not been experimentally tested. To fill this critical gap, we conducted a bi-factorial experiment in an African savanna. We removed shrub cover and broadcast large carnivore vocalizations (leopard, hyena, dog) or non-threatening control vocalizations in both experimentally cleared and shrubby control sites. We recorded the proactive (frequency of visitation) and reactive (fleeing or vigilance) responses of multiple prey (impala, warthog, nyala and bushbuck). Critically, we found a significant proactive–reactive interaction. Ungulates were 47% more likely to run after hearing a predator vocalization in shrubby control sites than experimental clearings, demonstrating that ungulates perceived less fear from large carnivores in open habitat (clearings). Consistent with this finding, ungulates visited clearings 2.4 times more often than shrubby control sites and visited shrubby control sites less often at night, when large carnivores are most active. Combined with results from previous experiments demonstrating that the disproportionate use of available habitats by large ungulates can alter ecosystem properties, our experiment provides critical evidence that the fear large carnivores inspire in large ungulates can cause trophic cascades.
Highlights
The fear large carnivores inspire in large ungulates has been argued to have cascading effects down food webs
The overarching goal of this study was to fill the gaps in our current understanding of how the fear large carnivores inspire in large ungulates may contribute to causing trophic cascades. To accomplish this goal we conducted a bi-factorial experiment in which we manipulated both habitat characteristics and fear. Measuring both proactive and reactive antipredator responses, we evaluated how ungulate species in an African savanna responded to large carnivore vocalizations, or non-threatening control vocalizations, in both experimentally cleared and shrubby control sites
Manipulating both fear and shrub cover, we demonstrated interactive proactive–reactive responses, establishing a clear link between fear of large carnivores and ungulate habitat use
Summary
The fear large carnivores inspire in large ungulates has been argued to have cascading effects down food webs. A direct link between ungulate habitat use and their fear of large carnivores has not been experimentally tested To fill this critical gap, we conducted a bi-factorial experiment in an African savanna. Landscapes are increasingly devoid of large carnivores, often due to human-large carnivore conflict[1] The loss of these apex predators has often coincided with considerable alterations in community composition at multiple lower trophic levels[1,2]. Field experiments manipulating vegetation cover have demonstrated that ungulates’ preferential use of open habitats cannot be explained by foraging r esources[13] It follows that if fear of large carnivores shapes habitat use by large ungulates, cascading effects on the vegetation in these areas should occur[3,13,15]. This creates extensive woody patches that are avoided by many of the region’s mid-sized ungulate grazers and browsers[17,20]
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