Humans are not the only animals that practice agriculture. Leaf-cutter ants, for example, painstakingly carry leaves back to their nest to cultivate a fungus that they feed upon. Some beetles also raise fungi inside rotten trees. Damselfish tend to areas where their favorite algae grows and weed out the undesirable types.
Now, researchers have found evidence that small mammals called pocket gophers manage, fertilize, and harvest roots for food too. This meets the definition of agriculture, according to the researchers of a study published July 11 in Current Biology.
“Gophers are shaping the plants, as well as the soil,” says Francis (Jack) Putz, a professor of biology at the University of Florida, and the researcher behind this project. “So they're managing crops. If farming is the management of crops, that’s what they're doing.”
Although further work is needed to definitively prove this behavior amounts to a type of agriculture or “farming,” the finding raises fascinating questions about the ecological role of these creatures and suggests that animal-plant interactions are often much more complex than first thought. It also shows gophers are ecological engineers, not just pests.
Southeastern pocket gophers (Geomys pinetis) spend most of their lifetime alone, burrowing underground. Although they’re common across North and Central American grasslands, you’re unlikely to see one—their presence is usually only noticeable thanks to the mounds of sandy soil they leave behind upon digging sprawling underground tunnel systems stretching more than 500 feet, usually about 50 inches below the ground.
Their anatomy suits such a life: They can close their mouths behind their incisors, using teeth to dig without swallowing dirt. Fur-lined pockets on both sides of their faces carry seeds and plant material while plowing. Recent research has discovered that they glow in the dark too, another skill that comes in handy when living deep below—perhaps for communicating or evading predators.
Previously, gophers were thought to feed themselves mainly by munching away at the roots they encounter while constructing new tunnel systems. Yet, digging tunnels is energetically costly—up to 300 to 3000 times more tiring than walking on a surface—and the researchers show that solely eating the roots found while excavating just doesn’t make up for the energy spent.
“If they were burrowing a meter and they were encountering this many roots in that meter, would they gain enough energy from those roots to offset the cost of burrowing that meter?” ask Veronica Selden, the student researcher at the University of Florida behind this study. “In all but one case we looked at, the answer is no.”
To understand how else these mammals get access to enough roots to survive, Putz and Selden observed the behavior of gophers in a longleaf pine savanna in northern Florida. The researchers manually excluded the gophers from parts of their tunnel systems by using an open-ended barrel as a small dam, cutting access to parts of their home for varying amounts of time. They observed that, in the dark, wet subterranean tunnels the gophers had dug, new, soft, digestible roots grew like stalactites and stalagmites covering the surfaces.
The gophers seem to be actively tending to the roots to ensure they grow, the scientists contend. By maintaining and defending these long networks of tunnels, gophers are creating the perfect humid environment for roots to thrive, and causing soil aeration by loosening the ground in which plants grow in the first place.
Importantly, the gophers scatter and distribute their feces and urine throughout the tunnels.
This waste fertilizes the soil and the roots, Selden says. This is rather unlike other gopher species, which tend to have designated waste areas, and sets them apart from other herbivores on the surface who may incidentally fertilize patches of grass or brush with their excrement.
“Gophers seem to be employing a version of a food production system by providing this optimal space for roots to grow,” Selden says.
By nibbling at the roots, the gophers also seem to be encouraging new growth.
“You’re a small mammal going along and you encounter a large root, and you bite it off but it’s not very digestible because it has a lot of lignin or celluloses, it’s tough, it’s hard,” says Putz. “But in response to being cropped, that root will make many small roots, and those will be really tasty and more digestible.”
The study found that the gophers’ daily harvest of root crops can supply from 21 to 62 percent of their caloric needs—making up the rest of the calories the animals need to continue burrowing systems of tunnels.
“They have these long tunnels that [cannot] be explained. It is risky digging tunnels… energetically costly,” Putz says. So why do it? If it’s not to “farm food,” he says, “I can't think of any other reason.”
The ‘farming’ debate
“I have often thought of gophers as ‘farmers,’” says Brittany Brito, a habitat biologist for the Wyoming Game and Fish Department, who was not involved in the study. “I think this [is] a compelling argument that gophers could be considered farmers because they aerate the soil, increase nutrient mineralization, and fertilize the soil. Those activities are, in a sense, growing crops [that] they consume.”
But other researchers wonder if “farming” is an appropriate term for the gophers’ activities.
“I am not sure they are actively ‘tending’ or just actively harvesting with the effect of stimulating growth. It’s a subtle difference,” says James Demastes, a professor of biology at the University of Northern Iowa who studies pocket gophers but who wasn’t involved in the paper.
He notes that the observations of fertilization are interesting and “definitely unusual” for this family of animals, but the idea that pocket gophers could potentially be practicing agriculture resonates with what is known about gophers overall. “I think it is pretty cool,” says Demastes.
Yet, pocket gophers aren’t sowing or weeding their crops, two elements traditionally understood as necessary for farming, and which some other “farming” animals such as the fungus-inoculating ants and beetles are thought to do.
“To describe the gopher activity as farming seems like a stretch,” says Kimberly Asmus Hersey, from the Mammal Conservation Coordinator Utah Division of Wildlife Resources, who was not involved in the study. “I don't see this as all that different from many other plant and herbivore interactions.”
There are many cases where grazing can stimulate productivity in plants, she adds, which is why she finds this not much different than a deer pruning a shrub.
It's controversial to claim that gophers are farming because people have different definitions of the term farming, according to Putz. “They're certainly agricultural engineers because they’re doing everything they can to enhance crop growth.”
Of course, the researchers note that there are several other ways gophers could be satiating their energy requirements which haven’t been explored in depth yet. Gophers could be foraging in areas with more roots than those tested; they could be relying heavily on tubers for their nutrition in addition to roots; or they could occasionally be eating above ground too, or pulling plants underground by their roots and eating them whole.
Although gophers are usually thought of as pests, studies have shown that they are often invaluable ecosystem engineers for the habitats they inhabit. For example, they have been shown to help maintain prairies and mountain meadows by keeping out significant numbers of encroaching tree seedlings, and they even helped colonizing plants gain a foothold in the barren landscape following the eruption of Mount St. Helens in May 1980.
“Learning that gophers themselves are farmers … may hopefully shift the narrative from them being agricultural pests to agricultural partners that we can learn from,” Selden says.