The lion’s share: implications of carnivore diet for threatened herbivores in Tsavo, Kenya

Introduction

The charisma of carnivores and their connection with the human psyche, coupled with their important functional roles in ecosystems, often make carnivores suitable flagship species for conservation (Gittleman et al., Reference Gittleman, Funk, MacDonald and Wayne2001; Dalerum et al., Reference Dalerum, Somers, Kunkel and Cameron2008; Ducarme et al., Reference Ducarme, Luque and Courchamp2013; Ripple et al., Reference Ripple, Estes, Beschta, Wilmers, Ritchie and Hebblewhite2014). The tiger Panthera tigris, lion Panthera leo, grey wolf Canis lupus and cheetah Acinonyx jubatus have been the face of projects focused on habitat conservation, ecosystem revival and conservation introductions (Bangs & Fritts, Reference Bangs and Fritts1996; Jhala et al., Reference Jhala, Banerjee, Chakrabarti, Basu, Singh, Dave and Gogoi2019; Packer, Reference Packer2019; Jhala et al., Reference Jhala, Gopal, Mathur, Ghosh, Negi and Narain2021). Although such conservation policies currently aim to restore carnivores through protection and/or augmentation, carnivore recovery can lead to increased conflicts with people (e.g. with brown bears Ursus arctos in the Pyrenees mountains; Piedallu et al., Reference Piedallu, Quenette, Mounet, Lescureux, Borelli-Massines and Dubarry2016) and reduction of threatened prey species (e.g. predation of bighorn sheep Ovis canadensis by pumas Puma concolor; Johnson et al., Reference Johnson, Hebblewhite, Stephenson, German, Pierce and Bleich2012). The depletion of threatened or rare prey through predation is particularly important in systems where predators have abundant primary prey. As a result of this, predator densities in such systems can remain high and are not restricted by the availability of rare or secondary prey. Such high predator densities can, however, result in high predation on rare prey, trapping them in a predator pit that can lead to further population declines (Allee et al., Reference Allee, Park, Emerson, Park and Schmidt1949; Messier, Reference Messier1994; Sinclair et al., Reference Sinclair, Pech, Dickman, Hik, Mahon and Newsome1998; Schmidt, Reference Schmidt2004; Johnson et al., Reference Johnson, Hebblewhite, Stephenson, German, Pierce and Bleich2012). Because of such layered effects mediated by carnivores, knowledge of their ecology and behaviour remains key for effective management of ecosystems (Boitani & Powell, Reference Boitani and Powell2012).

Lions are iconic for their connection to human culture and their apex position in ecosystems, often making them symbols of conservation (Roemer et al., Reference Roemer, Gompper and Van Valkenburgh2009). However, lions are also one of the top species involved in conflict, severely threatening human lives and livelihoods (Ray et al., Reference Ray, Hunter and Zigouris2005). Direct persecution and detrimental habitat alteration have reduced their numbers by > 75% since 1970, with a range contraction of > 90% (Ripple et al., Reference Ripple, Estes, Beschta, Wilmers, Ritchie and Hebblewhite2014; Loveridge et al., Reference Loveridge, Sousa, Cushman, Kaszta and Macdonald2022). The Tsavo Conservation Area (hereafter Tsavo) in south-east Kenya is a semi-arid, drought-prone landscape that hosts one of the largest populations of lions in East Africa (Henschel et al., Reference Henschel, Petracca, Ferreira, Ekwanga, Ryan and Frank2020). This landscape is also an important connection between two major African biomes: mesic grassland savannah to the south and semi-arid bush savannah to the north (Henschel et al., Reference Henschel, Petracca, Ferreira, Ekwanga, Ryan and Frank2020). Nearly 450 lions live in the Tsavo landscape (covering both East and West Tsavo National Parks; Elliot et al., Reference Elliot, Broekhuis, Omondi, Ngene, Kariuki and Sankan2021), yet lion ecology has been understudied in this landscape (barring mane growth, Kays & Patterson, Reference Kays and Patterson2002, and the human-eating tendencies of two infamous male lions, DeSantis & Patterson, Reference DeSantis and Patterson2017). This contrasts with other well-studied East African lion populations in Serengeti and Ngorongoro (Packer et al., Reference Packer2019).

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Tsavo is also home to one of the last remaining populations of the Critically Endangered hirola Beatragus hunteri. The hirola is restricted to a small area of its natural range on the Kenyan-Somali border, but was introduced to Tsavo East National Park in 1962 and 1996 as insurance against extinction in its natural range (Probert et al., Reference Probert, Evans, Andanje, Kock and Amin2014). The hirola population in Tsavo has remained small, and such small herbivore populations can be prone to the detrimental effects of predator mediated apparent competition when primary prey is abundant (Johnson et al., Reference Johnson, Hebblewhite, Stephenson, German, Pierce and Bleich2012). The Endangered Grevy’s zebra Equus grevyi was also introduced to Tsavo, in 1964 and 1977, but the population has also remained small (Githiru, Reference Githiru2017). Multiple factors can impede recovery of introduced herbivores, and predation is a plausible cause for the lack of population growth in these two species of conservation concern in Tsavo (Evans, Reference Evans2011; Probert et al., Reference Probert, Evans, Andanje, Kock and Amin2014).

To examine the ecology of this important population of lions and their potential predation impacts on the hirola and Grevy’s zebra, we present information on lion diet and preferences in Tsavo, determined from scat analysis using biomass models. Our findings have important implications for predation ecology of threatened herbivores in an important conservation landscape.

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