Humans are omnivores that sit surprisingly low on the food web, at a trophic level of about 2.21 on a scale that tops out around 5.5 for apex predators like polar bears and killer whales. That puts us roughly on par with anchovies and pigs. But our true role in the food web goes far beyond what we eat. Through farming, fishing, hunting, and reshaping landscapes, humans redirect more of the planet’s energy and biomass than any other single species, fundamentally altering food webs everywhere on Earth.
Where Humans Rank on the Food Chain
Trophic levels are a way of measuring where a species sits in the food web. Plants and other organisms that make their own energy from sunlight are level 1. Pure herbivores are level 2. Carnivores that eat herbivores are level 3, and so on up to apex predators at levels 4.5 to 5.5. A species’ trophic level is calculated based on what proportion of its diet comes from plants versus animals.
A 2013 study published in the Proceedings of the National Academy of Sciences calculated the global human trophic level at 2.21, meaning our diet is heavily plant-based overall. This number varies by country. Burundi, where diets are roughly 97% plant-based, has a human trophic level of 2.04. Iceland, where about half the diet comes from meat and fish, sits at 2.57. Even at the high end, no human population reaches the trophic level of a true apex predator.
This might seem counterintuitive. We think of ourselves as top predators, and in many ecosystems we functionally are. But trophic level is strictly about diet composition, and most of what humanity eats is grain, vegetables, and other plant-based food. The distinction matters: our power over food webs comes not from our position in them, but from the sheer scale of our influence.
How Much Energy Humans Capture
Every ecosystem runs on energy from photosynthesis. The total amount of plant growth on Earth in a given year is called net primary production, and according to NASA estimates, humans require about 20% of all the net primary production generated on land each year. That figure includes the crops we eat, the feed we grow for livestock, the timber we harvest, and the plant material lost when we convert forests and grasslands to farms and cities.
No other single species comes close to claiming that share of the planet’s energy budget. This massive diversion of energy away from wild ecosystems is one of the main reasons wildlife populations have declined so dramatically. When one-fifth of all plant productivity is routed toward human use, there is simply less energy available to support wild food webs.
Humans and Livestock Dominate Mammal Biomass
The physical scale of human dominance is striking. Livestock account for roughly 630 million tonnes of body mass on Earth. Humans add another 390 million tonnes. Meanwhile, all wild terrestrial mammals combined weigh only about 20 million tonnes, which works out to around 3 kilograms of wild mammal per person on the planet. Domesticated mammals outweigh wild land mammals by a ratio of 30 to 1. Even domestic dogs alone, at about 20 million tonnes, match the total biomass of every wild land mammal species combined.
Cattle are the single largest contributors at around 420 million tonnes, followed by humans themselves. This lopsided distribution means the mammalian portion of the food web is now overwhelmingly shaped by human choices about which animals to breed, feed, and protect.
How Human Hunting Differs From Natural Predation
When wolves or sharks hunt, they typically target the young, old, sick, or small members of a prey population. Humans do the opposite. We preferentially target large, reproductive-aged adults, whether we’re fishing for the biggest tuna or hunting trophy-sized elk. We also kill at much higher rates than natural predators do, removing large proportions of prey populations rather than skimming a small percentage.
This pattern has measurable evolutionary consequences. When the largest, most reproductively successful individuals are consistently removed, prey species begin to shift toward smaller body sizes and earlier reproduction. Fish populations under heavy commercial pressure, for example, tend to mature at younger ages and smaller sizes over just a few decades. Natural predators exert selective pressure too, but human harvesting drives trait changes at an unusually fast pace because it is so intense and so precisely targeted at the wrong end of the size spectrum.
Fishing Down the Food Web
In the ocean, humans have progressively altered marine food webs through a pattern called “fishing down the food web.” It works like this: commercial fisheries first target the most valuable species, which tend to be large predatory fish high on the food chain. As those populations are depleted, the industry shifts to smaller, lower-level species like sardines and anchovies.
This can happen two ways. In the more destructive version, top predator populations collapse entirely and are replaced by fisheries targeting species further down the chain. In a slightly less dramatic version, fisheries for top predators continue while new fisheries for smaller species are added alongside them. Either way, the average trophic level of the global fish catch declines over time.
Both scenarios create serious problems. Overfished apex predator populations often have poor prospects for recovery, and removing large volumes of small forage fish undermines the food supply that remaining predators depend on. From a pure energy standpoint, fishing at lower trophic levels requires about 50% less plant production to sustain the same weight of catch, which sounds efficient until you realize it means competing directly with marine predators for their food base.
Triggering Trophic Cascades
Some of humanity’s most far-reaching effects on food webs are indirect. When humans eliminate apex predators from an ecosystem, the consequences ripple downward through every trophic level in what ecologists call a trophic cascade.
Wolf extirpation is the most well-documented example. When wolves were removed from European and American landscapes, deer populations erupted. Without predation keeping their numbers in check, deer overgrazed vegetation, which in turn affected insects, birds, and soil organisms that depended on those plants. Similar cascades have followed the removal of bears, large cats, and sharks from their respective ecosystems. The loss of lynx from parts of Europe, driven by human pressures, triggered what’s known as mesopredator release: populations of medium-sized predators like foxes expanded, which then suppressed smaller prey species that the lynx had never threatened.
These cascades demonstrate that humans don’t need to interact directly with every species in a food web to reshape it. Removing or suppressing a single key predator can restructure the entire system.
Spreading Species Into New Food Webs
Humans also reshape food webs by moving species, intentionally or accidentally, into ecosystems where they didn’t evolve. When an invasive predator or competitor arrives in a new habitat, native species are forced to change what they eat, where they feed, and how they behave.
A detailed study of lake trout invasion into lakes where they weren’t native illustrates the process clearly. The invasive lake trout forced native fish species to abandon their usual prey and shift to less nutritious food sources in different habitats. Over time, this reorganized not just the fish community but also the invertebrate populations they fed on. The native top predator, bull trout, was functionally eliminated. Native species that were diet specialists, accustomed to eating specific prey, were pushed toward becoming generalists eating whatever they could find. This kind of trophic displacement and dispersion, repeated across thousands of ecosystems worldwide, progressively unravels the food web structures that evolved over millennia.
Agriculture and Simplified Food Webs
Farming occupies about 40% of Earth’s land surface, making agricultural land management the single most impactful human activity on global ecosystems. Industrial monoculture, where thousands of acres are planted with a single crop, replaces the complex web of species interactions found in natural ecosystems with a radically simplified system.
In a natural landscape, diverse plant species support diverse insects, which support diverse birds and small mammals, which support predators. A monoculture field strips away almost all of that. With only one plant species present, the intricate root systems that build healthy soil are replaced by shallow, uniform root structures. The soil food web, a vast community of bacteria, fungi, and invertebrates that cycle nutrients and support plant health, is dramatically reduced. Pesticide application has contributed to what some researchers call an “insect apocalypse,” further severing food web connections. Tillage disrupts the soil’s ability to store carbon, filter water, and cycle nutrients.
The result is an ecosystem that cannot sustain itself without constant artificial inputs: synthetic fertilizer replaces nutrient cycling, pesticides replace natural pest control, and irrigation replaces the water-holding capacity that healthy soil and diverse plant cover would otherwise provide.
Toxins Climbing the Food Chain to Humans
Humans are also on the receiving end of food web dynamics through a process called biomagnification. When toxic substances enter an ecosystem, they concentrate as they move up the food chain. Small organisms absorb pollutants from the water or soil around them. When those organisms are eaten, the toxins transfer to the predator. Because each predator eats many prey items over its lifetime, the concentration of the toxin increases at each step.
Mercury in seafood is the classic example. Tiny aquatic organisms absorb mercury from water. Small fish eat thousands of those organisms and accumulate the mercury in their tissues. Larger fish eat the smaller fish, concentrating the mercury further. By the time a tuna or swordfish reaches your plate, mercury levels can be millions of times higher than in the surrounding water. Humans, eating at the top of that particular chain, receive the most concentrated dose. The same pattern applies to persistent pesticides, industrial chemicals, and increasingly to microplastics.
Restoring Food Web Complexity
The scale of human impact on food webs is enormous, but some of the damage is reversible through changes in land management. Regenerative agriculture practices, including reducing tillage, planting diverse crop rotations, using cover crops, and minimizing synthetic chemical inputs, have been shown to increase soil microbial diversity and rebuild soil food web complexity. Greater microbial diversity improves nutrient cycling, which supports more plant growth, which in turn supports more insects, birds, and other wildlife. These techniques aren’t new. Indigenous communities around the world have practiced them for centuries or longer.
Predator reintroduction programs have demonstrated that trophic cascades can work in reverse. Bringing wolves back to ecosystems where they were extirpated has, in some cases, allowed vegetation to recover, stream banks to stabilize, and bird and fish populations to rebound. These successes suggest that while humans have profoundly disrupted food webs at every level, the webs retain some capacity to reassemble when the pressure is reduced.