Surprisingly small animals are powerful grassland engineers

When people imagine grasslands, they often picture bison herds stretching to the horizon. These giant animals once ruled the Great Plains, shaping the land with their grazing. But size is not everything.

A new study shows that the smallest herbivores, prairie dogs and grasshoppers, do more for nutrient cycling than the mighty bison or cattle.

The research, led by scientists from the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI), reveals a surprising truth. The tiniest animals can have the biggest impact on how nutrients move through grassland soil and plants.

Why grasslands matter

Grasslands cover 40 percent of Earth’s land. They store carbon, protect soil, and support biodiversity. Yet they remain among the planet’s most threatened ecosystems.

Farming and ranching have taken over large areas. Development has carved up habitats and replaced native grasses with crops or invasive plants. The result is fragile soil, fewer species, and land that struggles to recover after droughts or fires.

In North America, the Great Plains once stretched endlessly. Bison herds darkened the horizon. Prairie dogs dug their towns across vast distances. Today, those numbers have collapsed. Both species survive at just one or two percent of their former abundance.

This loss changed how the grasslands function. Without constant grazing or burrowing, the soil misses some of the recycling and mixing it once relied on. Plants grow differently. Nutrients move more slowly. The system no longer works the same.

Which animals support grasslands?

To see what remains, the researchers focused on northeast Montana. This region still holds stretches of shortgrass prairie. It also shows how people use the land in many ways.

Some areas are set aside for conservation. Others support ranching or crop farming. Together, they form a patchwork landscape. That mix gave scientists a chance to study real conditions rather than isolated sites.

The team selected 15 locations. By comparing them, the researchers could see how herbivores – from prairie dogs to cattle – shape soil and grass today.

The green food web

“Herbivores contribute to the green food web by turning plant tissues into urine and dung that provide new plant growth with readily available nutrients,” said Ellen Welti, NZCBI community ecologist and the study’s senior author.

“This cycles nutrients at a faster rate than the brown food web, where plant tissues slowly senesce and degrade before nutrients become available for uptake by future plants.”

The cycle is faster and more direct when small animals do the work. Prairie dogs and grasshoppers, in particular, push nutrients back into the soil quickly, changing the landscape in ways the larger grazers do not.

Prairie dogs have a big influence

Prairie dogs had the biggest influence. Their colonies held higher levels of carbon and nitrogen in the soil than surrounding grasslands.

Their burrows moved nutrients deeper into the ground, while their waste enriched plants with nitrogen, potassium, and magnesium.

These animals don’t just nibble on grass. By digging, depositing, and living in dense groups, they create hot spots of fertility. The land around a prairie dog town becomes richer and more productive than areas without them.

Tiny animals that shape grasslands

Grasshoppers also left their mark. Their feeding increased phosphorus in the soil, an essential nutrient for plant growth. But they also shaped the rhythm of the prairie. Plant biomass peaked in mid-summer, then declined sharply. That pattern lined up with the grasshopper life cycle.

Nymphs hatched in spring, barely eating at first. By late summer, they had grown into hungry adults, devouring plants at a much higher rate.

Bison and cattle grazed more steadily through the season, but grasshoppers created these dramatic seasonal swings – influencing not only plant growth but also food availability for other prairie species.

Interactions that matter

“This study shows there are many different interactions occurring between herbivores and the greater grassland ecosystem,” said Julie Rebh, the study’s lead author who conducted the research as an intern at NZCBI.

“While the presence of some smaller herbivores such as prairie dogs and grasshoppers may not be as obvious, the impact they have on grassland ecology is considerable.”

The research makes one point clear: ecosystems rely on many actors, not just the most visible ones. Big animals shape the landscape in one way, but the smallest can speed up cycles and create pockets of fertility that keep the system running.

A broader view of healthy grasslands

Conservation often centers on iconic species like bison. But this study argues for a more complete approach.

Prairie dogs and grasshoppers may not inspire awe, but they keep nutrients flowing. Without them, grasslands risk losing part of their engine.

Healthy grasslands need both large grazers and small recyclers. Together they keep soil, plants, and animals in balance. Protecting them protects the whole system. It also ensures resilience, biodiversity, and survival under pressure.

The study is published in the journal Ecology.

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