The food chain you learned about in school isn’t the full picture. Yes, the rat eats your garden crops, the ermine snags the rat, and the eagle picks off the ermine. But that linear story misses a whole lot of nuance. Parasites like ticks and intestinal worms feed on the eagle and ermine. When those predators die, ants and other scavengers devour their carcasses. Oh, and rats are known to eat their own babies, so they’re predators of themselves.
Capturing the extraordinary complexity of species interactions has been a time-honored — and time-consuming — process of scientists getting out in the field and spying on birds’ nests, for instance, to see what the parents feed their young. Less romantically, they’ve had to sift through scat for the bones of prey animals.
Now they’ve got an even more powerful — and far less smelly — tool in the form of a citizen science project called Who Eats Whom. It taps into the nonprofit social network iNaturalist, which identifies species in photos that people upload and geotag. You can search for “brown rat,” for example, and find an image of an American ermine carting one off near Monty Drive in Ottawa, Canada. If that’s not metal enough for you, search for “red-tailed hawk” to see the raptors laying waste to snakes and squirrels all across the United States.
Who Eats Whom isn’t just engrossing — it could help inform conservation efforts on a rapidly warming planet. So far, it’s incorporated 17,000 interactions involving 5,700 species in more than 100 countries. “That’s just kind of the power of crowdsourcing,” said ecologist Bradley Allf, who developed the platform while at North Carolina State University but is now at Colorado State University. “You can generate a ton of valuable information in a way that you can’t if you’re just an individual scientist trying to follow snakes around and hope they eat something while you’re watching them, or waiting for them to poop and be able to take their scat.”
While the database literally offers snapshots in time, the idea is to amass data over the coming years, revealing how ecosystems are transforming alongside the planet as a whole. “Even if we look back, say, five years ago, there have been a lot of changes in the feeding patterns of these animals,” said Aditi Mallavarapu, a computer scientist at North Carolina State University and co-author of a new paper describing the work in the journal PLOS Biology. “So not only looking at what is being observed, but also noticing what is not being observed.”
Who Eats Whom, then, is more than a repository of captivating photos. If you click on “Interactive Food Web” at the top right of the site, it brings up a sprawling web of interactions. Search again for “red-tailed hawk” and you’ll see a plethora of small mammals that people have photographed them predating. (Arrows pointing to a species indicate the food going into it.) Look even closer and you’ll find that one of its meals, the American robin, eats the common buckthorn and yaupon holly.
And let’s not forget the pollinators. Search for “Western honey bee” in the interactive food web and you’ll see that it — among many other insects — ends up in the belly of the goldenrod crab spider, an absolutely gorgeous, ghostly white arachnid. But notice also all the plants that the bee feeds on — honeysuckles, thistles, buttercups — and helps reproduce by spreading their pollen around. “There’s all kinds of complicated ways that energy moves through real food webs, and we’re trying to document that messiness as much as we can,” said Allf, who is also the lead author of the new paper.
Who Eats Whom offers plenty of surprises. People have snapped New World vultures dining on all manner of carcasses, from wild boars to raccoons to groundhogs. On a beach in California’s San Luis Obispo County, though, at least one of the birds found itself a baby white shark, which had likely been stillborn.
With so many smartphone-wielding folks wandering beaches and forests and deserts, ecologists have gained an army of invaluable allies. “The biggest challenge is really data acquisition, because there’s so many species and so many interactions out there,” said Peter Roopnarine, curator of invertebrate zoology and geology at the California Academy of Sciences, who wasn’t involved in the project. “They sometimes can be ephemeral — like it happens once in a lifetime of a species, and that’s it. And they’re dispersed all over the place.”
By better understanding who eats whom, scientists and conservationists can better protect species. As the planet rapidly heats, species are marching toward the relative coolness of the poles. This is reshuffling ecosystems and changing how species interact. With a platform like Who Eats Whom, normal people with smartphone cameras may well be the first to document the arrival of a new animal in their area. “It’s obviously super engaging, I think, for the people who are participating,” said Rebecca Johnson, director of the Center for Biodiversity and Community Science at the California Academy of Sciences, who wasn’t involved in the project. “It gives you a new way of thinking about your nature observations that you might share.”
At the same time, invasive species — most notoriously, things like the lionfish — are shaking up ecosystems the world over. Left unchecked, hungry invaders can decimate native species, which may already be weakened by skyrocketing temperatures and worsening droughts. “We need to know who’s being consumed by these invasive species,” Roopnarine said, “and are there species on that menu that we really need to be worried about?”
To properly protect species in this topsy-turvy world, conservationists can’t just set aside some land or sea and call it a victory. They also need to ensure that carnivores and omnivores have the prey they usually hunt, and herbivores have the plants they usually graze. “Species don’t just need space — they don’t just need a habitat,” Allf said. “They need the relationships that allow them to survive.”
