Elephant influence on the landscape of fear
African lions exert profound cascading effects on their ecosystems through both predation and the threat of predation. Herbivore species such as impala and kudu must make adjustments to their own behavior in order to avoid becoming prey, by herding in larger numbers, being more vigilant while eating, and selecting different grazing patches. The movements and behavior of both predator and prey affect where grass and trees grow, creating what ecologists term a ‘landscape of fear’.
However, owing to their enormous size, adult megaherbivores like African elephants are largely immune to predation, even from lions. Although elephant impacts on trees have been widely studied, little is known about their effects on the landscape of fear. Elephants are known to forage and distribute nutrients across the landscape without respect to predators, and lions with young cubs may actually adjust their behavior to avoid elephants, so spatiotemporal dynamics between megaherbivores and predators could alter the effects of the landscape of fear on ungulates and woody vegetation.
The movement of all of these species in relation to each other and to their environment has profound implications for overall biodiversity at several trophic (food web) levels. Prey vulnerable to predation by lions may also face constraints from aggressive elephant behavior and elephant patch selection, particularly around waterholes, where ungulate species are most vulnerable. Elephant monopolization of waterholes or other resources may lead to shifts in spatial or temporal overlap by other herbivores and even modify ungulate abundances. Changes in herbivore assemblages will exert strong cascading effects on diversity and productivity of the vegetative layer as well.
Previous studies in terrestrial systems have found that restorations of apex predators can increase diversity and tree recruitment to maturity via reductions in herbivore abundance and feeding. High diversity within plant communities promotes stability and sustains positive reciprocal effects with herbivores, important considerations for conserving rare and threatened plant species and the animals that depend on them. However, elephant restorations are typically associated with a reduction in diversity and maturity among trees, so cascading effects from lions and elephants may interact along multiple pathways to produce a net result different from the restoration of either lions or elephants alone.
By measuring the effects of elephants on the landscape of fear across a variety of protected areas, Sarah’s research will provide relevant data and guidance for reserve managers and ecologists as they consider conservation strategies, particularly in regard to restoring large mammals.