In defence of rodents – why wholesome ecosystems want them

You might think you have the measure of the rodent family. Perhaps the very word “rodent” conjures up images of invasive rats, the city dwellers accused of spreading pathogens and parasites, chewing through wires and spoiling food.

Most rodents are indeed more elusive, inhabiting quiet corners of rainforests, mountains, deserts, and rivers. These small mammals have occupied a niche in nature for at least the last 56 million years, and from shrews to rats and hamsters to beavers, rodents play important roles in ecosystems worldwide.

Nevertheless, numerous rodent species are threatened with extinction. Rodents, who eke out an existence in declining habitats and are threatened by persecution, pollution and climate change, are largely neglected by research and funding that could help protect them. We’re three conservation scientists determined to show this is a mistake – and change the way you think about these misunderstood creatures.

More than bugs

About 40% of all mammalian species are rodents. There are around 2,375 living species including mice, rats, squirrels, hamsters, voles, porcupines, lemmings, beavers, chinchillas, chipmunks and more. The number of recognized rodent species is still growing, and seemingly faster than other groups of mammals, including bats, primates, and carnivores. Between two comprehensive checklists of global mammal species produced in 2005 and 2018, an additional 371 rodents were officially recognized.

New discoveries are often the result of genetic research that has identified multiple similar-looking species previously described as one. Nonetheless, rodents, from the 3-gram jerboa to the 50-kg capybara, are a remarkably diverse group.

Edible dormouse can hibernate for six months or longer.
Slowmotiongli/Shutterstock

This diversity allows rodents to play numerous roles in Earth’s ecosystems. Rodents have a hand (or rather paw) in determining which plants to reproduce and where, by eating and dispersing their seeds. Beavers build entire ecosystems with their dams that help clean water systems and mitigate floods and droughts, while burrowing kangaroo rats create underground habitats used by other wildlife. Rodents are also an invaluable link in the food chain, feeding on predators such as birds of prey, wolves, snakes and even spiders.

We should not forget that humans have long benefited from relationships with rodents. Agoutis in South America are one of the few animal groups capable of breaking open the capsules of the Brazil nut fruit. By hoarding surplus seeds, agoutis help disperse their trees throughout the Amazon rainforest and support the world’s Brazil nut production, which depends almost entirely on wild collection. African possums can detect tuberculosis in saliva, hidden landmines, survivors trapped under rubble and pangolins smuggled in shipping containers. By studying the resistance of naked mole rats to cancer, the scientists hope to improve our understanding of the disease and its potential treatment. It is clear that the loss of a species of rodent – even the smallest – can have far-reaching consequences for people and the environment.

Underfunded, understudied and disappearing

Worryingly, at least 15% of rodent species are threatened with extinction. More than 100 are among the top 560 evolutionarily diverse and globally endangered (EDGE) mammals, meaning that while they are threatened, they also have few or no close relatives. If an EDGE species were to disappear, there would be nothing quite like it.

For many other species, scientists just don’t know enough to understand how they’re doing: the population trends (whether stable, declining, or increasing) of at least a thousand rodents are unknown. Even when it comes to zoonoses, there are significant gaps in knowledge about viruses in rodents and how outbreaks can be influenced by their ecology or population dynamics. The reality is that rodents receive very little scientific attention beyond their discovery and naming.

Rodents are also hard to sell outside of science. Studies on public perceptions of wildlife show that rodents are generally the least favored group. Compared to larger-bodied mammals, rodents and small mammals are mentioned far less often on Twitter, are viewed as uninteresting by zoo visitors, and are less likely to inspire donations to conservation programs. Even the larger rodents like beavers are outperformed in public preference polls by large carnivores, birds, moths and bees.

Even beavers cannot overcome the anti-rodent bias.
WildMedia/Shutterstock

So it’s no surprise that some species have already fallen through the cracks. The tiny swan island of Hutia, a rodent once endemic to the Caribbean islands of the same name, was driven to extinction by introduced cats in the 1960s. The candango mouse disappeared during a similar period in central Brazil, where its forest habitat was almost completely paved over. Australia’s Bramble Cay Melomys was only declared extinct in 2016 after rising sea levels gradually degraded the tiny coral cay it lived on. The loss of this rodent is believed to be the first modern mammalian extinction caused by climate change.

Some rodents remain unstudied for so long that it is not known if they still exist. Gould’s mouse, also a species native to Australia, was thought to be extinct for 150 years before it was recently rediscovered, surviving on islands off Western Australia. Another, the flying squirrel Namdapha, was thought to be extinct in the wild until a single specimen was collected from northeast India in 1981. The species is now classified as Critically Endangered and is currently known only from informal sightings that date back decades. Of the world’s rediscovered species, data shows rodents are the longest-missing species, likely because not enough people are looking for them.

Even well-monitored or known rodents are not safe. The common hamster is classified as critically endangered and could become extinct in the coming decades if its decline is not reversed. Its beloved cousin, the golden hamster (or Syrian hamster) is also endangered in the wild, clinging to its last fragment of habitat.

Many rodents can adapt well to landscapes modified by humans, but others cannot adapt to this hamster wheel and only exist in dwindling and deteriorating wildernesses. It’s likely that we’ve already lost many species that we didn’t even know existed.

Changing our own perceptions and behaviors could be the first step in restoring many threatened but overlooked species. For the little fellows like rodents, this means understanding that while they may not be as glamorous or powerful as many conservation showcase species, we are far more dependent on their biodiversity than we can imagine.

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