Social distancing works – just ask lobsters, ants and vampire bats

Caribbean spiny lobsters normally live in groups, but healthy lobsters avoid members of their own species if they are infected with a deadly virus.
Humberto Ramirez/Getty Images

Dana Hawley, Virginia Tech and Julia Buck, University of North Carolina Wilmington

Social distancing to combat COVID-19 is profoundly impacting society, leaving many people wondering whether it will actually work. As disease ecologists, we know that nature has an answer.

Animals as diverse as monkeys, lobsters, insects and birds can detect and avoid sick members of their species. Why have so many types of animals evolved such sophisticated behaviors in response to disease? Because social distancing helps them survive.

In evolutionary terms, animals that effectively socially distance during an outbreak improve their chances of staying healthy and going on to produce more offspring, which also will socially distance when confronted with disease.

We study the diverse ways in which animals use behaviors to avoid infection, and why behaviors matter for disease spread. While animals have evolved a variety of behaviors that limit infection, the ubiquity of social distancing in group-living animals tells us that this strategy has been favored again and again in animals faced with high risk of contagious disease.

What can we learn about social distancing from other animals, and how are their actions like and unlike what humans are doing now?

Feed the sick, but protect the queen

Social insects are some of the most extreme practitioners of social distancing in nature. Many types of ants live in tight quarters with hundreds or even thousands of close relatives. Much like our day care centers, college dormitories and nursing homes, these colonies can create optimal conditions for spreading contagious diseases.

In response to this risk, ants have evolved the ability to socially distance. When a contagious disease sweeps through their society, both sick and healthy ants rapidly change their behavior in ways that slow disease transmission. Sick ants self-isolate, and healthy ants reduce their interaction with other ants when disease is present in the colony.

Healthy ants even “close rank” around the most vulnerable colony members – the queens and nurses – by keeping them isolated from the foragers that are most likely to introduce germs from outside. Overall, these measures are highly effective at limiting disease spread and keeping colony members alive.

Many other types of animals also choose exactly who to socially distance from, and conversely, when to put themselves at risk. For example, mandrills – a type of monkey – continue to care for sick family members even as they actively avoid sick individuals to whom they are not related. In an evolutionary sense, caring for a sick family member may allow an animal to pass on its genes through that family member’s offspring.

Mandrills live in large groups in the rainforests of equatorial Africa. They will often groom other group members, but actively avoid sick mandrills unless they are close family members.
Eric Kilby/Wikipedia, CC BY-SA

Further, some animals maintain essential social interactions in the face of sickness while foregoing less critical ones. For example, vampire bats continue to provide food for their sick groupmates, but avoid grooming them. This minimizes contagion risk while still preserving forms of social support that are most essential to keeping sick family members alive, such as food sharing.

These nuanced forms of social distancing minimize costs of disease while maintaining the benefits of social living. It should come as no surprise that evolution favors them in many types of animals.

Altruism makes us human

Human behavior in the presence of disease also bears the signature of evolution. This indicates that our hominid ancestors faced many of the same pressures from contagious disease that we are facing today.

Like social ants, we are protecting the most vulnerable members of our society from COVID-19 infection by ensuring that older individuals and those with pre-existing conditions stay away from potentially contagious people. Like monkeys and bats, we also practice nuanced social distancing, reducing non-essential social contacts while still providing essential care for sick family members.

A black garden ant queen (upper left), surrounded by adult ants, larvae (left), eggs (middle) and a cocoon (right).
Pan weterynarz/Wikipedia, CC BY-SA

There also are important differences. For example, in addition to caring for sick family members, humans sometimes increase their own risk by caring for unrelated individuals, such as friends and neighbors. And health care workers go further, actively seeking out and helping precisely those who many of us carefully avoid.

Altruism isn’t the only behavior that distinguishes human response to disease outbreaks. Other animals must rely on subtle cues to detect illness among group members, but we have cutting-edge technologies that make it possible to detect pathogens rapidly and then isolate and treat sick individuals. And humans can communicate health threats globally in an instant, which allows us to proactively institute behaviors that mitigate disease. That’s a huge evolutionary advantage.

Finally, thanks to virtual platforms, humans can maintain social connections without direct physical contact. This means that unlike other animals, we can practice physical rather than social distancing, which lets us preserve some of the important benefits of group living while minimizing disease risk.

Worth the disruption

The evidence from nature is clear: Social distancing is an effective tool for reducing disease spread. It is also a tool that can be implemented more rapidly and more universally than almost any other. Unlike vaccination and medication, behavioral changes don’t require development or testing.

However, social distancing can also incur significant and sometimes unsustainable costs. Some highly social animals, like banded mongooses, do not avoid group members even when they are visibly sick; the evolutionary costs of social distancing from their relatives may simply be too high. As we are currently experiencing, social distancing also imposes severe costs of many kinds in human societies, and these costs are often borne disproportionately by the most vulnerable people.

Given that social distancing can be costly, why do so many animals do it? In short, because behaviors that protect us from disease ultimately allow us to enjoy social living – a lifestyle that offers myriad benefits, but also carries risks. By implementing social distancing when it’s necessary, humans and other animals can continue to reap the diverse benefits of social living in the long term, while minimizing the costs of potentially deadly diseases when they arise.

Social distancing can be profoundly disruptive to our society, but it can also stop a disease outbreak in its tracks. Just ask ants.

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Dana Hawley, Professor of Biological Sciences, Virginia Tech and Julia Buck, Assistant Professor of Biology, University of North Carolina Wilmington

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Lemurs are the world’s most endangered mammals, but planting trees can help save them

Black-and-white ruffed lemurs are important indicators of rainforest health.
Franck Rabenahy, CC BY-ND

Andrea L. Baden, Hunter College

Madagascar, the world’s fourth-largest island, is a global biodiversity hotspot.
Andrea Baden

The island of Madagascar off the southeastern coast of Africa hosts at least 12,000 plant species and 700 vertebrate species, 80% to 90% of which are found nowhere else on Earth.

Isolated for the last 88 million years and covering an area approximately the size of the northeastern United States, Madagascar is one of the world’s hottest biodiversity hotspots. Its island-wide species diversity is striking, but its tropical forest biodiversity is truly exceptional.

Sadly, human activities are ravaging tropical forests worldwide. Habitat fragmentation, over-harvesting of wood and other forest products, over-hunting, invasive species, pollution and climate change are depleting many of these forests’ native species.

Among these threats, climate change receives special attention because of its global reach. But in my research, I have found that in Madagascar it is not the dominant reason for species decline, although of course it’s an important long-term factor.

As a primatologist and lemur specialist, I study how human pressures affect Madagascar’s highly diverse and endemic signature species. In two recent studies, colleagues and I have found that in particular, the ruffed lemur – an important seed disperser and indicator of rainforest health – is being disproportionately impacted by human activities. Importantly, habitat loss is driving ruffed lemurs’ distributions and genetic health. These findings will be key to helping save them.

Deforestation from slash-and-burn agriculture in the peripheral zones of Ranomafana National Park, Madagascar.
Nina Beeby/Ranomafana Ruffed Lemur Project, CC BY-ND

The forest is disappearing

Madagascar has lost nearly half (44%) of its forests within the last 60 years, largely due to slash-and-burn agriculture – known locally as “tavy” – and charcoal production. Habitat loss and fragmentation runs throughout Madagascar’s history, and the rates of change are staggering.

This destruction threatens Madagascar’s biodiversity and its human population. Nearly 50% of the country’s remaining forest is now located within 300 feet (100 meters) of an unforested area. Deforestation, illegal hunting and collection for the pet trade are pushing many species toward the brink of extinction.

In fact, the International Union for Conservation of Nature estimates that 95% of Madagascar’s lemurs are now threatened, making them the world’s most endangered mammals. Pressure on Madagascar’s biodiversity has significantly increased over the last decade.

A red ruffed lemur, one of two Varecia species endemic to Madagascar.
Varecia Garbutt, CC BY-ND

Deforestation threatens ruffed lemur survival

In a newly published study, climate scientist Toni Lyn Morelli, species distribution expert Adam Smith and I worked with 19 other researchers to study how deforestation and climate change will affect two critically endangered ruffed lemur species over the next century. Using combinations of different deforestation and climate change scenarios, we estimate that suitable rainforest habitat could be reduced by as much as 93%.

If left unchecked, deforestation alone could effectively eliminate ruffed lemurs’ entire eastern rainforest habitat and with it, the animals themselves. In sum, for these lemurs the effects of forest loss will outpace climate change.

But we also found that if current protected areas lose no more forest, climate change and deforestation outside of parks will reduce suitable habitat by only 62%. This means that maintaining and enhancing the integrity of protected areas will be essential for saving Madagascar’s rainforest habitats.

Warm colors indicate areas where lemurs can move about readily, which promotes genetic diversity; cool colors indicate areas where they are more constrained and less able to mate with members of other population groups.
Baden et al. (2019), Nature Scientific Reports, CC BY-ND

In a study published in November 2019, my colleagues and I showed that ruffed lemurs depend on habitat cover to survive. We investigated natural and human-caused impediments that prevent the lemurs from spreading across their range, and tracked the movement of their genes as they ranged between habitats and reproduced. This movement, known as gene flow, is important for maintaining genetic variability within populations, allowing lemurs to adapt to their ever-changing environments.

Based on this analysis, we parsed out which landscape variables – including rivers, elevation, roads, habitat quality and human population density – best explained gene flow in ruffed lemurs. We found that human activity was the best predictor of ruffed lemurs’ population structure and gene flow. Deforestation alongside human communities was the most significant barrier.

Taken together, these and other lines of evidence show that deforestation poses an imminent threat to conservation on Madagascar. Based on our projections, habitat loss is a more immediate threat to lemurs than climate change, at least in the immediate future.

In 1961 naturalist David Attenborough filmed ruffed lemurs for the BBC.

This matters not only for lemurs, but also for other plants and animals in the areas where lemurs are found. The same is true at the global level: More than one-third (about 36.5%) of Earth’s plant species are exceedingly rare and disproportionately affected by human use of land. Regions where the most rare species live are experiencing higher levels of human impact.

Crisis can drive conservation

Scientists have warned that the fate of Madagascar’s rich natural heritage hangs in the balance. Results from our work suggest that strengthening protected areas and reforestation efforts will help to mitigate this devastation while environmentalists work toward long-term solutions for curbing the runaway greenhouse gas emissions that drive climate change.

A young woman participates in reforestation efforts in Kianjavato, Madagascar.
Brittani Robertson/Madagascar Biodiversity Partnership, CC BY-ND

Already, nonprofits are working hard toward these goals. A partnership between Dr. Edward E. Louis Jr., founder of Madagascar Biodiversity Partnership and director of Conservation Genetics at Omaha’s Henry Doorly Zoo, and the Arbor Day Foundation’s Plant Madagascar project has replanted nearly 3 million trees throughout Kianjavato, one region identified by our study. Members of Centre ValBio’s reforestation team – a nonprofit based just outside of Ranomafana National Park that facilitates our ruffed lemur research – are following suit.

At an international conference in Nairobi earlier this year, Madagascar’s president, Andry Rajoelina, promised to reforest 40,000 hectares (99,000 acres) every year for the next five years – the equivalent of 75,000 football fields. This commitment, while encouraging, unfortunately lacks a coherent implementation plan.

Our projections highlight areas of habitat persistence, as well as areas where ruffed lemurs could experience near-complete habitat loss or genetic isolation in the not-so-distant future. Lemurs are an effective indicator of total non-primate community richness in Madagascar, which is another way of saying that protecting lemurs will protect biodiversity. Our results can help pinpoint where to start.

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Andrea L. Baden, Assistant Professor of Anthropology, Hunter College

This article is republished from The Conversation under a Creative Commons license. Read the original article.