Nutrient legacies from elephant megacarcasses create coldspots of biodiversity and hotspots of ecosystem processes.

Abstract

Terrestrial megafauna (animals >1,000 kg) have substantial impacts on ecosystems while alive; yet, we know little about the impacts of these ecosystem engineers after they die. Like whale carcasses in the ocean, terrestrial megacarcasses may leave ecological legacies via the nutrient pulses they create on the landscape. Here, we investigated the impact of elephant megacarcasses on savanna ecosystems in Kruger National Park, South Africa. To determine how elephant carcasses affect below- and aboveground biodiversity and ecosystem processes, we collected soil and plant samples from 40 carcass sites (pairing "on carcass" and "off carcass" samples) ranging from 8 d to 7.7 y postmortem. We found that elephant carcasses released enormous pools of nutrients into savanna soils, increasing ammonium by 31×, nitrate by 7×, and phosphorus by 3× on average. These extreme ammonium concentrations were negatively correlated with the biodiversity of bacteria and plants, which were both suppressed at elephant carcass sites. Despite these decreases in biodiversity, ecosystem processes were strongly elevated at elephant carcass sites, with soil microbial respiration elevated for 1 to 2 y and herbivore grazing >3× higher for 7+ y postmortem. These results demonstrate that elephant megacarcasses generate coldspots of biodiversity but hotspots of ecosystem processes, unveiling a cryptic ecological function of megaherbivores that is extreme in both magnitude and duration relative to carcasses of smaller animals. As humans drive terrestrial megafauna toward extinction, we risk losing not only their ecosystem engineering abilities while they are alive but also the ecological legacies their carcasses create after death.