Overview: Megacarcasses, the massive carcasses of megaherbivores (elephants, rhinos, etc.), play a neglected, but potentially distinctive, role in the function of terrestrial ecosystems. Surprisingly, we know more about how megacarcasses in the deep sea (i.e., whale falls) impact nutrient cycling and species diversity than we do for megacarcasses on land. African elephants are the largest land animals, but we know almost nothing about how the nutrients from their massive carcasses (up to 6,000 kg) affect savanna ecosystems. Thus, we ask the overarching question: How do elephant megacarcasses create dynamic hotspots of ecosystem processes in African savannas? We will address this question using a chronosequence of elephant carcasses (up to 15+ years old) in Kruger National Park (KNP), South Africa. Combining soil (physical, chemical and biological properties), plant (productivity and diversity), and herbivore (vertebrate and invertebrate) surveys at 50 megacarcass sites along with mechanistic greenhouse experiments, we will assess how nutrient pulses from elephant carcasses drive integrated responses of ecosystem processes. Importantly, the chronosequence of elephant megacarcasses in KNP is distributed across gradients of rainfall (375-700 mm) and soil fertility (lessfertile sandy, granitic soils vs. more-fertile clayey, basaltic soils). The natural factorial design, rainfall crossed with soil nutrients, provides a robust experimental layout for testing how the abiotic template impacts the ecosystem-level legacy effects of terrestrial megacarcasses across space and time. Finally, by combining our empirical data on the effects of megacarcasses on ecosystem processes with a georeferenced database of elephant population across KNP, we will use simulation modeling to show how the distribution of megacarcasses generates spatiotemporal heterogeneity in ecosystem processes across the savanna landscape.
Our study would be the first examination of the ecological legacies of megacarcasses on terrestrial ecosystems. Understanding the long-term impact of megacarcasses on ecosystem processes will reveal the full influence of megaherbivores on terrestrial ecosystem function in the past, present, and future. Our central thesis is that the function of African savanna ecosystems is fundamentally entwined with the spatiotemporal distribution of megacarcasses. The continuing disappearance of megaherbivores across much of the African continent is likely resulting in a loss of ecosystem function that we still do not understand. These ideas are especially important for several reasons. First, the mass mortality events of hundreds of elephants due to drought, such as recent ones in Botswana and Zimbabwe, likely represent a massive pulse of nutrients that were likely common when megaherbivores occupied their historical ranges across Africa. Yet, we know little about the possible effects of these nutrient legacies on ecosystem function. Second, we are only starting to understand how the ‘extinction aftershock’ of losing large species impacts ecosystems. Most research focuses on the impacts of losing large species, triggering top-down cascades of trophic interactions. We are only beginning to understand what losing large species means for bottom-up processes involving nutrient dynamics, with very little known about how megacarcasses might affect those dynamics. Third, the spatiotemporal scale (across 20,000 km2 with carcasses 15+ years old), taxonomic spread (microbes, plants, insects, ungulates), and varied abiotic template (soil fertility, rainfall) of our project would create a powerful test of the integrated effects of carcasses on the landscape of ecosystem processes. Ultimately, our work may transform our understanding of the roles that megafauna play in ecosystem function, both in life and after death.
This project advances cross-disciplinary collaborations among multiple academic, government, and nonprofit institutions, including BI specialists, social scientists, artists, and STEM research scientists across partnerships in the United States and South Africa. The research will advance scientific discovery by helping understand the role of megacarcasses in terrestrial ecosystems. Knowledge will be disseminated to the scientific community, stakeholders and the general public via a variety of mechanisms (publications, conferences, and education materials). The PIs will mentor 2 graduate and 4 undergraduate students in ecology and science communication and outreach. Our team will codesign, produce, and evaluate a scientific documentary, The Legacy of Megaherbivores, which will be designed through iterative evaluation to increase public scientific literacy and public engagement with science. We will reach several thousand people via film festivals, broadcasting, and online distribution. We also will enhance STEM education infrastructure by having grad-undergrad teams produce openaccess educational products, including university-level lectures and educational children’s videos.