Resolving a conservation dilemma: Vulnerable lions eating endangered zebras.

Timothy G O’Brien,Steven Ekwanga,Christopher Wilmers,Terrie Williams,Laurence G Frank,Alayne Oriol-Cotterill,Daniel Rubenstein,Margaret F Kinnaird,Joseph K Bump

doi:10.1371/journal.pone.0201983

Abstract

When predators are removed or suppressed for generations, prey populations tend to increase and when predators are re-introduced, prey densities should fall back to pre-control levels. In cases of apparent competition where there are alternate abundant and rare prey species, rare species may decline further than expected or disappear altogether. Recently, concern about the impact of recovering predator populations on wildlife in Laikipia County, Kenya, has led to questions of whether lions (Panthera leo, IUCN Red List Vulnerable) exert top-down pressure on Grevy’s zebra (Equus grevyi, IUCN Red List Endangered). We examined effects of lion predation on Plain’s zebra (E. quagga, IUCN Red List Near Threatened) and Grevy’s zebra populations in a 2,105 km2 area defined by lion movements. We used line transect surveys to estimate density of Grevy’s (0.71/km2) and Plain’s (15.9/km2) zebras, and satellite telemetry to measure movements for lions and both zebras. We tracked lions to potential feeding sites to estimate predation rates on zebras. We compared field-based estimates of predation rates on both zebras to random gas models of encounters that result in predation to ask if lions prey preferentially on Grevy’s zebra at a sufficient rate to drive population declines. Lions preyed on Grevy’s zebra significantly less than expected in 15 of 16 (94%) scenarios considered and lions preyed on Plain’s zebras as expected or significantly less than expected in 15 of 16 scenarios. Population trend of Grevy’s zebra indicates that the Kenya population may be stabilizing. Recruitment rate to the population has tripled since 2004, making it unlikely that lions are having an impact on Grevy’s zebras. In Laikipia County, competitive displacement by livestock (Livestock: Grevy’s zebra ratio = 864:1) and interference competition for grass with Plain’s zebra (Plain’s zebra:Grevy’s zebra ratio = 22:1) are most likely the predominant threats to Grevy’s Zebra recovery.

Highlights

Large carnivores are known to influence the dynamics, distribution and behavior of ungulate prey populations [1, 2, 3]
In some systems where communities of prey populations include very common and very rare species, apparent competition and opportunistic predation can lead to disproportionate reduction in the density of the rarer species [8, 9]
We evaluated lion predation on Grevy’s and Plain’s zebras across a large, mixed-use landscape in Laikipia County using satellite telemetry to track lions and zebra movements, and to locate and identify lion kills

Summary

Introduction

Large carnivores are known to influence the dynamics, distribution and behavior of ungulate prey populations [1, 2, 3]. Removal of large predators may affect the behavior of prey populations. In ecosystems where humans have eliminated predators and allowed or assisted predator recovery, we often see reduction in prey populations as predator and prey densities return to pre-removal levels. In some systems where communities of prey populations include very common and very rare species, apparent competition and opportunistic predation can lead to disproportionate reduction in the density of the rarer species [8, 9]

Methods

Results

Conclusion