by Sam Ferreira and Paul Funston
Prey biomass, diversity, and availability dictate predator abundances and niche structure. Increased prey biomass and availability predicts that two apex predators, African lions and spotted hyaenas, should increase in abundance. Although elephant and rhino carcasses generated by poachers released prey biomass not previously available, individual lion prides or spotted hyaena clans may only have an additional fresh carcass for less than two weeks in a year. This predicts that predator changes primarily associate with prey biomass changes. We used a case study in Kruger National Park and showed that although African lion and spotted hyaena numbers increased, it did not associate with better availability of rhinoceros and elephant carcasses. Increases in the number of adult lionesses, instead, were linked with rises in prey biomass given competition with spotted hyaenas. Biomass of poached rhinoceros and elephant carcasses made trivial contributions to bottom-up changes in apex predator populations. Poachers, however, may induce top-down trophic cascades through the removal of keystone grazing and browsing species.
Dr Sam Ferreira is the large mammal ecologist of South African National Parks (SANParks) based in Kruger National Park, South Africa.
Dr Paul Funston is the African Lion Coordinator of Panthera based in the Caprivi Strip, Namibia.