Conservation conundrum: Endangered predators eating endangered prey

Abstract

As populations of wildlife dwindle in number, and as ecosystems suitable for animals disappear, conservation conundrums emerge that have no easy solutions. One such issue involves predators and prey. What can be done when an endangered species of predators might be hastening the extinction of an endangered species of prey by including it in their diet? Evaluating potential solutions requires a solid framework incorporating the complex labyrinthine ecological dynamics regulating predatory/prey interactions. In the same way in which a body operates as a set of integrated components dependent upon each other for the maintenance of life, ecosystems operate as a set of integrated components. Sometimes compensatory mechanisms can blossom, but sometimes the damage is fatal. At least six factors mould the trajectory of predator/prey interactions: (a) atmospheric influences on vegetation that provide food, shelter and protection to prey, (b) soil impacts on vegetation types and growth, (c) plant phenology and identity mediating the abundance and distribution of prey species and of individuals, (d) variable foraging strategies influencing the movement patterns, body condition, health, parasite load and reproductive rates of prey, (e) prey location modulating the movement and location of predators, (f) prey selection by predators, which is affected by the distribution and abundance of multiple prey species, as well as the age and health of both targeted animals and predator. Consider some cases revealing the complexity of predator/prey interactions. In Kruger National Park, South Africa, over a 70 year period, lion (Panthera leo) predation on giraffe (Giraffa camelopardalis) was more dependent upon a low abundance of Cape buffalo (Syncerus cafer) than on a high abundance of giraffe (Owen-Smith & Mills, 2008), while in the Tarangire Ecosystem, predation rates on giraffe calves were reduced when wildebeest (Connochaetes taurinus) calves and zebra (Equus quagga) foals were plentiful (Lee, Kissui, Kiwango, & Bond, 2016). In Karoo National Park, South Africa, when springbok (Antidorcas marsupialis) numbers were artificially increased, their appearance in black-backed jackal (Canis mesomelas) scats became elevated, while boosting the lion population in the same location resulted in more large ungulates, such as kudu (Tragelaphus strepsiceros), in jackal scats, probably due to scavenging (Fourie, Tambling, Gaylard, & Kerley, 2015). Among wildlife ranches in Limpopo Province, South Africa, the removal of predators did not reduce predation rate on some ungulates, probably because of a “vacuum effect,” whereby an influx of predators undermined the removal strategy (Schepers, Matthews, & van Niekerk, 2018). Prey species will shift from preferred habitats with high predation to less preferred habitats with low predation and can become “invasive species” that degrade habitats and adversely influence the flora and fauna in their newly adopted ranges (Winnie & Creel, 2017). Predators and prey both influence the distribution and abundance of each other, and are impacted by landscape features combined with atmospheric conditions. As both predator and prey within an ecosystem are involuntarily herded by people towards an extinction vortex, what can we do? Consider the case of giraffes and lions. Lions are classified on the IUCN Red List as “Vulnerable,” with about 20,000–30,000 individuals remaining on the African continent (Bauer, Packer, Funston, Henschel, & Nowell, 2016). Giraffes are classified on the IUCN Red List as “Vulnerable,” with less than 100,000 individuals roaming the continent (Muller et al., 2016). Lion predation is probably the major cause of giraffe mortality, with about half of the giraffes born in the wild not surviving the first year of life. A giraffe gives birth to a calf about every 20–22 months beginning when she is about 6 or 7 years old (Bercovitch & Berry, 2010). With an average age of death of 17 years old (Bercovitch & Berry, 2017), a female might produce about five or six calves during her lifetime. Sons and daughters are born, as well as killed by lions, in equal proportions. Therefore, on average, a female giraffe might leave two to three descendants. That amounts to zero population growth in a species that is declining in number across the continent. Most populations of giraffes in Africa contain about 30% immature animals, but in one reserve in Kenya, where lions are plentiful, the youngsters only make up about 6% of the population (Muller, 2018) which is a recipe for disaster. What are the solutions to the dilemma of endangered species eating endangered species? One possibility is an anathema to some conservation biologists, but a panacea to others: hunting. While furiously debated within the conservation community, Stuart and Bas (2016) concluded “legal, well-regulated trophy hunting programmes can – and do – play an important role in…wildlife conservation.” Probably few things are as contentious as the paradoxical notion that hunting an endangered species is a solution to saving that same endangered species, or even other species. A second approach involves the translocation of animals. Moving lions, and other predators, raises hackles because no matter where they are released, the prospect of preying on domestic animals, or even people, becomes a rallying cry for the opposition. Moving giraffes is difficult because their size, shape and physiology present a challenge to capture and transport. Nevertheless, giraffes are regularly moved from place to place in South Africa. But some of these giraffes are moved to areas where giraffes have never lived, making them an invasive species that could have detrimental consequences for local species, some of which might be endangered. A third solution is to do nothing; let nature take its course. As giraffe numbers decline, the probability of lions preying on giraffes should decrease, so giraffe numbers might rebound, but what if giraffe numbers are too low for a recovery? Some conservationists lean towards a hands-off approach partly from a viewpoint that conservation management by manipulation is a very species-chauvinist approach adopted by those who think that humans are superior beings that can control other animals. But is it reasonable to decide that handcuffing ourselves behind our backs is a solution to a problem we created when our hands were free and in front of us? A fourth solution would be to saturate a reserve or park with other potential lion prey species causing a shift in predation profiles. Introducing impala or zebra as lion bait might trigger not only protests among animal ethics boards, but could result in detrimental effects to the habitat, and what happens if lions do not shift prey preferences? One size will not fit all. Evolution has yielded a planet composed of interacting context-dependent forces. Tinkering with any part of it is like playing the classic game of Jenga®. The removal of one wooden block destabilizes the structure, and the collapse comes when too many block removals result in a complete imbalance. It is the same with ecosystems. Wildlife has evolved an adaptive flexibility in foraging and reproductive strategies enabling individuals within a population to pursue alternative life history strategies yielding comparable goals, but animal trajectories are not unbounded. The versatility of animal adaptations, coupled with the dynamic nature of predator/prey interactions, hinders developing a simple solution to a complex conundrum. Whether confined in a fenced area, or roaming in a large national park, the number of giraffes and lions will both depend upon the number and types of other animals, which will depend upon the carrying capacity of the area, which will depend upon the distribution and availability of resources, which will depend upon both the natural cycle of the planet, as well as human-induced influences. What is the best policy to pursue to ensure that lions and giraffes, as well as other species, will persist in time? Not only so that our descendants can marvel at these incredible animals, but so that the descendants of the lions can still eat the descendants of the giraffes, who will still be able to continue to wander across the plains of Africa.