Predator and Prey

In every ecosystem there are predators (animals that hunt other animals for food) and prey (the animals they hunt). The relationship between the two is one of the most important forces shaping life on Earth. Predators have evolved sharper claws, faster speeds, better camouflage and cleverer hunting techniques to catch their prey. Prey have evolved stronger defences, faster escapes, better hiding places and warning systems to avoid being caught. Each side keeps pushing the other to evolve further. It is one of the great driving forces of nature.

  • Predator examplesLion, eagle, shark, spiderAlmost every meat-eating animal
  • Prey examplesZebra, mouse, herring, flyAlmost every plant-eating animal
  • Apex predatorHas no natural predatorsLions, killer whales, polar bears
  • Predator-prey cyclePopulation goes up and downFamously in lynx and snowshoe hare
  • Best hunter (success rate)Dragonflyapprox. 95% of hunts succeed
  • Worst hunter (success rate)Tigerapprox. 5 to 10% of hunts succeed

What is a predator?

A predator is any animal that hunts, kills and eats other animals. Predators come in all shapes and sizes:

  • Big cats: lions, tigers, leopards, cheetahs.
  • Wolves and wild dogs: hunt in packs with great teamwork.
  • Birds of prey: eagles, hawks, falcons, owls.
  • Marine predators: sharks, killer whales, dolphins, barracuda.
  • Small predators: spiders, dragonflies, frogs, snakes, mongooses.
  • Even plants: Venus flytraps and pitcher plants are technically predators of insects.

Predator adaptations

Predators have evolved many tools for the hunt.

  • Sharp teeth and claws: for biting and gripping prey.
  • Speed: cheetahs can sprint at 100 km/h; peregrine falcons dive at over 350 km/h.
  • Excellent senses: eagle eyesight, owl hearing, shark smell, snake heat detection.
  • Camouflage: tigers have stripes that blend with jungle grass; great white sharks are dark above and light below to match the sea above and below them.
  • Intelligence: many predators learn complex hunting techniques. Killer whales work together to make waves that wash seals off ice floes.
  • Venom: snakes, spiders, scorpions and stingrays use chemicals to immobilise prey.

Prey adaptations

Prey animals have not stood still. They have evolved equally clever defences.

  • Camouflage: rabbits in brown leaves, snowshoe hares in snow, leaf insects in plants.
  • Speed: gazelles outrun cheetahs over distance; flying fish leap from the water.
  • Safety in numbers: herding animals like wildebeest are hard to single out in a crowd of thousands; small fish swim in schools that confuse predators.
  • Warning colours: poison frogs, monarch butterflies and many insects use bright colours to warn predators they are toxic.
  • Armour: tortoises have shells; pangolins have scales; porcupines have spines.
  • Mimicry: some non-toxic species (like the harmless king snake) mimic the colours of toxic ones (like the coral snake), gaining protection without the poison.
  • Eyes on the side of the head: most prey animals have wide-angle vision to spot predators coming from any direction. Most predators have forward-facing eyes for accurate distance judgement.

The predator-prey cycle

In the wild, predator and prey populations often rise and fall together in a regular cycle. The most famous example is the Canadian lynx and the snowshoe hare. Records kept by the Hudson's Bay Company over almost 100 years showed the populations of both species cycling up and down on a roughly 10-year cycle:

  1. When there are lots of hares, the lynx have plenty to eat, and their numbers grow.
  2. As lynx numbers rise, they kill more hares than the hares can replace.
  3. Hare numbers crash.
  4. With few hares to eat, many lynx starve and lynx numbers crash too.
  5. With few lynx around, hare numbers slowly recover.
  6. And the cycle starts again.

This kind of cycle is one of the cleanest examples of how predators and prey shape each other's populations over time.

Fact The most successful hunter on Earth is not a lion or a tiger but the humble dragonfly. Recent studies have found that dragonflies catch their prey on around 95% of all attempts: a higher hit rate than any other known predator. They achieve this by using two giant compound eyes (with up to 30,000 lenses each), four independently controlled wings that let them fly in any direction, and a brain that calculates exactly where to intercept a flying insect long before it gets there.

Why predators matter for ecosystems

People sometimes think of predators as cruel or unnecessary. The opposite is true: predators are essential for healthy ecosystems. They control prey populations, prevent over-grazing, and keep ecosystems in balance. Without predators, herbivore populations can explode, eating themselves out of food, damaging vegetation, eroding soil and even spreading disease.

Famous examples include:

  • Wolves controlling elk in Yellowstone (with positive knock-on effects through the whole ecosystem).
  • Sea otters controlling sea urchins (and so keeping kelp forests alive).
  • Sharks keeping fish populations in balance on coral reefs.
  • Foxes keeping rabbit populations from over-grazing British meadows.

This is one of the strongest reasons to protect top predators, even if they sometimes scare livestock or compete with human hunters.

Did you know? Even the fastest predators do not catch every meal. Tigers succeed on only about 5 to 10% of their hunts. Lions are more like 20 to 30%. Cheetahs succeed on around 25 to 40%. Many wild predators go several days without a kill and have to be patient. The image of the unstoppable predator is a myth: most predators are far more often hungry than well-fed.
Deeper dive: the evolutionary arms race

The relationship between predators and prey is one of the most intense examples of co-evolution in nature. As predators evolve to be better hunters, prey evolve to be better at escaping, which puts more pressure on predators to evolve more new tricks, and so on. This kind of mutual back-and-forth is sometimes called an evolutionary arms race, by analogy with the way human armies keep developing better weapons in response to each other.

Examples are everywhere. Cheetahs are the fastest land animals at 100 km/h; gazelles can hit 80 km/h and have evolved sharp turning ability that cheetahs struggle to match. Owls evolved silent flight and acute hearing for catching mice; mice in turn evolved better hearing and an instinct to freeze when they hear a wing-beat. Newts in some parts of North America have evolved skin so toxic that one would kill a person; in response, local garter snakes have evolved resistance to the poison.

Sometimes the arms race goes one step too far. The famous "extinct giant ground sloths" of the Americas survived for millions of years against most predators, but when humans arrived around 13,000 years ago with weapons and group hunting techniques, the giant sloths had no defence and went extinct within a few thousand years. Many of the world's big mammals (mammoths, woolly rhinos, sabre-toothed cats) faced the same fate.

Today the most disturbing arms race may be against bacteria. Modern medicine's antibiotics are our weapons; bacterial mutations are the bacteria's defences. Antibiotic resistance is rising worldwide as bacteria evolve to defeat one drug after another. The arms race between us and our microbial predators is one of the biggest health challenges of the 21st century.

For how predators fit into food chains, see food chains. For helpful biological relationships, see symbiosis.