Elephant Dung Piles are Crucial to Biodiversity, Study Shows

Key Points:

• Elephants function as a keystone species, producing large amounts of nutrient-rich dung that sustain diverse dung beetle populations and support wider ecosystem health.

• A 15-year field experiment showed that removing elephants leads to sharp declines in dung beetle abundance, biomass, and species diversity, and other herbivores cannot replace their role.

• The findings provide rare real-world evidence that losing a single, highly connected species can trigger cascading effects across ecosystems, reinforcing the importance of protecting key ecological "hubs."

For decades, ecologists have relied on mathematical models to predict what happens when a species disappears. Those models consistently suggest a troubling possibility: Removing a single species from an ecosystem can trigger a cascade of additional extinctions.

But proving that idea in the real world has been far more difficult, said Department of Life and Environmental Sciences Professor Matthew Hutchinson, who collaborated on an innovative study led by researchers at Princeton University.

"Those predictions … rang true in computer simulations but had been really hard to prove in the real world," he said.

The study, published in Science, offers rare, concrete evidence for this phenomenon - and it centers on one of Earth's largest animals. The research shows that elephants act as a keystone species, an organism that has a disproportionately large impact on its natural environment relative to its population size, serving as the ecological "glue" that holds an ecosystem together. The enormous amount of waste elephants produce supports dung beetle abundance and diversity in East African savannas, which safeguards the ecological services dung beetles provide.

The findings suggest that losing even a single, well-connected species can ripple through an ecosystem in ways scientists have long expected but seldom demonstrated.

Clear Effects on Biodiversity

The study draws on a 15-year field experiment in Kenya, where researchers constructed large, fenced plots to exclude animals based on their size. By keeping elephants and other large herbivores out of some areas while allowing them into others, scientists could track what happens when those animals disappear - without actually removing them from the landscape.

The results were striking. When elephants were excluded, dung beetle abundance, biomass and species richness all plummeted.

Crucially, the presence of more numerous, smaller herbivores did not compensate for the absence of elephants.

Dung beetles depend on feces for food and reproduction. Elephants provide a particularly valuable resource: large quantities of nutrient-rich dung (up to 150 kg per adult per day) that many beetle species prefer.

Even when dung quantity was controlled, beetles were drawn disproportionately to elephant dung, which supported far more individuals and species than other herbivores.

That makes elephants central nodes in what scientists call an ecological network - a depiction of how species are connected to and dependent upon one another in an ecosystem.

But unlike classic examples of keystone species, such as sea otters controlling urchin populations and maintaining kelp forest ecosystems, elephants play a different role.

"In our case, the elephants are not controlling anything; they're providing a critical resource," Hutchinson said. "Without all that dung, the dung beetle biodiversity isn't maintained at the same level."

That resource fuels not just beetles but the broader ecosystem. By breaking down and burying dung, beetles recycle nutrients, improve soil health and reduce pest populations.

"Dung beetles provide this really important ecosystem service, clearing away all of the dung that these large animals put on the landscape," Hutchinson said.

He said the experiments used in the study are particularly insightful and innovative.

"These really large animals are disproportionately at risk of extinction from several different factors. Yet, by virtue of their size, they have huge impacts on ecosystems. Those two factors together make it crucial to study how ecosystems respond to their loss," Hutchinson said. "But because of their size, they're really hard to study, especially when you want to answer that question: What happens when they're gone?"

Scaling up the Experiments

One common criticism of enclosure experiments, even the 1-hectare plots used in this study, is scale. Experimental plots, it is argued, may capture animal behavior - such as dung beetles making their rare long-distance flights into or out of the plot - rather than true ecosystem change, Hutchinson explained.

To address this, the researchers expanded their analysis, comparing sites with different levels of wildlife abundance. At one location, wildlife populations - including elephants - remained high. At two nearby sites, livestock dominated and elephants were largely absent.

The pattern held. Dung beetle abundance and biomass were significantly lower in livestock-dominated areas, even though more dung piles were present on those landscapes compared to the site with the highest wildlife abundance.

That suggests the experimental results reflect real-world dynamics and strengthens the case that elephants underpin dung beetle communities at both small and large scales.

"Elephants are the big ecosystem engineers, uprooting trees and throwing them around, which keeps the landscape open, whereas dung beetles are the little ecosystem engineers, moving and burying the nutrient-rich dung piles elephants produce, which reduces pest and parasite abundance while dispersing seeds and nutrients into the soil," Hutchinson said.

"I think the key takeaway is that the loss - or even just the decline - of a single species can ripple through an ecosystem and cause the loss of other species that depend on it," he said.

Real-world Data

Usually, conservation focuses on species that are charismatic, evolutionarily unique, or already endangered, but the study suggests there is another way to prioritize: How many other species depend on a given species?

"A species might be common and not especially at risk," he said, "but if it supports a large share of the ecosystem's diversity … it could be critical to protect before it declines."

At Mpala Conservancy, Kenya, where this study was conducted, there are 20 to 30 large herbivore species. All of them are smaller than elephants but some are far more abundant - and still, their impact doesn't come close, Hutchinson said.

"You could remove almost any other herbivore in this system and expect to see relatively minor changes to dung beetles and the services they provide. But when you remove elephants, you see a dramatic drop in beetle abundance and function," he said. "The idea of a keystone species in ecology has echoes of Orwell's 'Animal Farm:' All species contribute to an ecosystem, but some contribute more. Losing those keystones risks unraveling the entire system."

What sets the study apart is its breadth. Researchers combined long-term experiments, field surveys, detailed taxonomy, DNA analysis and computer simulations - each reinforcing the same conclusion.

"I think one of the real strengths of this study is how many different approaches it brings together," Hutchinson said. "Any one of those on its own would be intriguing, but together they are definitive."

By aligning theory with real-world data, the study offers one of the clearest demonstrations yet of how ecosystems are shaped by keystone species, how ecological networks can identify the species likely to be keystones, and how the loss of those species leads to collapse.

Lorena Anderson