From sloths to clownfish: 20 examples of teamwork across the animal kingdom
When Charles Darwin presented the theory of evolution in the late 19th century, other biologists began to idealize the natural world as a realm driven by competition. Every living creature is striving to survive by any means necessary, these scientists thought, and it will happily push out, feed on, or otherwise out-compete any other creature that stands in its way. In actuality—as anyone who’s fallen down a “cute animals become friends” YouTube rabbit hole knows—the natural world is far kinder and far more complicated than the basic tenets of evolution would have it seem.
From the biggest whales to the tiniest fungi, living creatures depend upon each other to survive. Sure, one species “depending on” another can often mean that the first species needs to eat the second. But there are also flowering plants depending upon honeybees to spread their seeds, ants depending upon trees to provide homes for their colonies, corals depending upon microscopic algae to give them energy through photosynthesis, and even sea worms depending upon bacteria to help break down the bones of dead animals.
Scientists call a dependent relationship like this mutualism: two or more species that mutually benefit each other. Sometimes these relationships are more like casual friendships, where one species can help each other out occasionally, and other times they’re more like intense marriages, where both species need each other to survive. Mutualisms are important to biologists who look to the past and those who look to the future because studying these behavioral interactions can both provide clues as to how species evolved and help conservation researchers understand how to best protect endangered populations.
For this story, Stacker scoured the scientific literature (and surveyed a few of our science communication friends) to compile a list of 20 incredible mutualisms showcasing how different life forms can work together. Read on to learn about friendships from the plains of the Serengeti to the bottom of the ocean.
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Zebra and wildebeests
Banding together to avoid predators is a useful tactic, even for animals as big as zebras and wildebeests. On the Serengeti, these two herbivores can graze together without getting competitive, because zebras like to eat longer, tougher grasses while wildebeests prefer shorter, more tender specimens. Plus, zebras, wildebeests, and impalas, a type of antelope, can all recognize each other’s warning calls and help each other escape danger. Scientists are still investigating this relationship to determine whether it is truly a mutualism or simply a convenient habitat-sharing interaction, but either way, it’s clear that the Serengeti’s plant-eaters are able to live in harmony.
Langur monkeys and chital deer
In central India, langur monkeys and chital deer help each other avoid tigers and other predators. The langurs, long-haired gray monkeys with great eyesight, keep a look-out in the trees while the chital deer, brown spotted deer with an impressive sense of smell, watch out for predators on the ground. The deer also eat fruit that the langurs drop from the canopy.
Galápagos birds and flowering plants
In oceanic island habitats like the Galápagos, biodiversity is often limited—in other words, there just aren’t that many different species present. Plants in such environments often invite lots of pollinators to help them reproduce while pollinators benefit from less picky eating. This trend leads some bird species on the Galápagos islands to act as double mutualists: These birds consume nectar from plants’ flowers, and then later consume the very fruit that resulted from their own pollination.
Jens Olesen and colleagues, who described these interactions in a 2018 Nature paper, suggest that the conservation focus for island biologists should be on whole environments, rather than on particular species, in order to preserve these complex networks.
Pawpaw trees and zebra swallowtail butterflies
Zebra swallowtails, beautiful black-and-white-striped butterflies native to the eastern U.S. and Canada, are the state butterfly of Tennessee. For reproduction, these butterflies rely on pawpaws, a group of understory trees with large, yellow-green fruit. Zebra swallowtail caterpillars exclusively live on pawpaws, because they ingest compounds in the trees’ leaves that are poisonous to many predators. In return, the butterflies help the trees reproduce through pollination.
Duroia trees and lemon ants
While acacia ants protect acacia trees, lemon ants protect duroia trees, flowering plants in the understory of the Amazon rainforest. A particular species of lemon ant, called Myrmelachista schumanni, nests in a particular species of duroia tree, called Duroia hirsuta. The ants are so determined not to let competitors threaten their nests that they produce formic acid, a deadly compound, and poison any other trees that come into the area. This deadly partnership creates areas of the forest that are populated solely by duroia trees. Indigenous people living in the Amazon called these strands “devil’s gardens” and believed they were created by evil forest spirits.
[Pictured: The swollen leaves and thin stem of a myrmecophyte from the forests of the Andaman Islands. One of the leaves has been sectioned.]
Acacia trees and acacia ants
Like the yucca moths, acacia ants evolved alongside a group of trees. These ants depend on acacia trees for shelter; in fact, queen ants burrow into the large thorns at the base of acacia leaves, lay their eggs inside, and take nectar from the nearby leaves. When an ant colony grows large enough, every thorn of an acacia can become inhabited. In return, the ants defend their trees against rival insects and other predators.
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Yucca plants and yucca moths
You know a friendship is special when two species groups share the same name. Yuccas, a group of tropical trees and shrubs known for their tough, sword-shaped leaves, and yucca moths, a group of small, nondescript moths, actually developed through natural history together in a process biologists call coevolution. The yucca plants rely on the moths for pollination, while the larvae of some moth species feed exclusively on yucca seeds.
Oxpeckers, rhinos, and zebra
Another small bird, big eater relationship can be found on the plains of sub-Saharan Africa: Oxpeckers perch on the backs of big herbivores, namely rhinoceroses and zebras, and eat the ticks and flies they find. While this relationship has long been hailed as a classic mutualism example, recent research reveals that it’s actually more sinister, as Kat Eschner reported in the Smithsonian. Oxpeckers not only eat ticks from their hosts’ backs, they also drink blood from the animals’ sores—making it harder for those wounds to heal.
Plover birds and Nile crocodiles
While wrasse fish have some preferences for which larger animals they’d like to clean, they are generally equal-opportunity feeders. Egyptian plover birds, on the other hand, have a mutualistic relationship with one specific predator: the Nile crocodile. When a Nile crocodile gets food stuck in its teeth, it will sit in the sun with its mouth open, and a Plover bird will swing by to pick the extra food out. The crocodile is thus protected from rotting food and infections.
Cleaner wrasses and larger fish
Exploring a coral reef is a hazardous task; not only do fish have to avoid big predators, they also risk having their scales clogged by smaller, parasitic creatures and ocean gunk. When the situation gets particularly dire, reef fish visit “cleaning stations” run by blue-streaked cleaner wrasses and other similar species. At these “cleaning stations,” basically the aquatic equivalent of a dentist’s office, wrasses eat the parasites, displaced scales, and other gunk from their so-called clients. The larger fish get spa treatment while the wrasse gets a meal.2018 All rights reserved.