What Is 'Mutualism' In Animals? A Biologist Explains Using Examples


What Is 'Mutualism' In Animals? A Biologist Explains Using Examples

In the open plains of the Namib in Southwest Africa, an unlikely alliance forms. Shy, reclusive ostriches hesitantly seek the support of antelope and zebra to remain safe from carnivores.

Despite moving in large herds of up to 100, ostriches are extremely vulnerable to predators. They have poor eyesight and can easily fall prey in parts of the plains where grasses are overgrown, or in unfamiliar territory.

The antelope and zebra on the other hand, have 20-20 vision.

In return, the ostriches offer the services of their acute sense of smell, which the herbivores lack. Before it went extinct, ostriches would be seen near the quagga (a subspecies of zebra) too, attracted by the beetles found in its dung.

Cooperation between ostriches and herbivores was observed even by Darwin in the 1800s, which he chronicled in Travels in the Interior of Southern Africa.

On African plains, such alliances between birds and mammals are abundant. Oxpeckers offer great grooming services in return for a nutritious diet of fleas and dead skin from herbivores. Paradise flycatchers fervently follow kudu and bushbuck, feeding on mosquitoes and other flying insects that mill around the antelope.

For centuries now, Indigenous people sharing spaces with wildlife have been observing such moments of camaraderie between different species across the world.

The behavior of honey badgers and honeyguide birds has the scientific community confused. Many anecdotes from indigenous honey-hunters in eastern Africa point to a remarkable association.

Birds are a part of the badgers' diet. But the honeyguide bird is an exception that actually calls to the badgers, despite the potential danger of predation. The former surreptitiously beckons the latter to bee hives they've located. The badgers devour the honey, making the bees and larvae within accessible to the birds. It's a win-win.

However, there is debate about this interaction. If it does occur, it's increasingly rare, given that the dry woodland habitats of badgers, birds and bees are declining fast, according to a June 2023 paper in Journal of Zoology. Could time be running out on a chance to document this unique behavior?

The honey hunters themselves interact with honeyguide birds the same way, following their chirps to the hives.

Traditional fishermen in Myanmar also work with wildlife in a mutually beneficial way. They rhythmically rap wooden sticks on their boats at sea, a signal to Irrawaddy dolphins who shepherd fish towards their nets. The dolphins are even kind enough to alert fishermen on when to throw the nets.

Unfortunately, commercial electrofishing is now breaking the dolphins' trust and threatening their future as they are frequently shocked and killed. Local initiatives are attempting to raise awareness and conserve the cultural practice.

In Southeast Asia, Hardwicke's woolly bats are looking for a much-needed place to rest, safe from danger. Bats use echolocation to identify roosting sites, and their senses usually lead them to an unlikely choice -- carnivorous pitcher plants.

These plants reflect their echoes to "call" the bats, in hopes of capturing their feces. The pitchers are able to trap and digest insects, but they're still deprived of nitrogen, as the soils they grow in tend to be deficient. Bat poop offers exactly this through a missing ingredient -- digested spiders.

After a long night of foraging, bats are offered a place to sleep, as pitchers are too narrow for them to fall into. In return, the pitchers receive valuable nutrients from arthropods eaten by the bats. In fact, this unique way of passing on nutrients is more efficient than if a pitcher had managed to actually trap a spider. A December 2023 paper in Journal of Ecology noted that pitchers met 95% of their nitrogen needs this way.

In forming cooperative relationships, different species effectively end up binding their fates together. When mutualism between two species is threatened, a few possible scenarios emerge, according to a December 2010 article published in Ecology Letters. A map of various trajectories predicts the risks of co-extinction, abandonment by one species or a shift to negative interactions.

In other words, when one species is endangered, so is the other. As anthropogenic pressures intensify and ecosystems decline, these interactions are being disrupted before we can fully understand them.

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