A statement in this article from Amanda Korstjens, a professor of behavioral ecology at Bournemouth University in the United Kingdom, was incorrectly attributed to Andrew Bernard, a doctoral candidate in anthropology at the University of Michigan. It has been updated.
More than 100 scientists who spent some 151,000 hours observing animals across Madagascar and Central and South America found that the primates are risking exposure to new predators to escape the heat and find food, though they still spend the vast majority of their time in trees.
Those species most inclined to adapt to spending time on the ground — whether because they have more diverse diets, live in the relative safety of large groups or are physiologically more capable of ambling on the forest floor — are most likely to descend from the trees, and thus may be more likely to survive into the future, said Tim Eppley, a postdoctoral associate at the San Diego Zoo Wildlife Alliance. Eppley is lead author of the study, which was published in the Proceedings of the National Academy of Sciences.
As global warming accelerates and deforestation and wildfires spread, those primates less advantaged for such a transition will be increasingly imperiled.
“They’re not going to be able to live for long,” Eppley said. That could compound ecological challenges in vulnerable forest habitats, because animals such as lemurs play an important role dispersing tree seeds. “Once you get rid of the lemurs, there’s this whole cascade effect.”
Scientists said the research shows signs of hope for the resilience of vulnerable creatures and ecological systems, while also stressing the need to slow or prevent warming and habitat loss.
“Primates in Madagascar are already the most threatened in the world, but studies like this show us that they may be able to find refuge from the worst climate changes by flexibly adapting to spending more time in areas with lower temperatures,” Amanda Korstjens, a professor of behavioral ecology at Bournemouth University in the United Kingdom, wrote in an email. “But the study also highlights the importance of preserving healthy forest habitats to allow primates to use the limited options they have to manage global warming.”
Helen Slater, a research associate at Newcastle University in the United Kingdom, said the study suggests “a pretty daunting task” to predict how various primate species will respond to climate change, and to determine how best to promote their conservation.
“There isn’t going to be a one-size-fits-all solution, and we’ll probably have to develop strategies that are site and species-specific,” she said in an email.
The research began with Eppley’s own observations. He spent a year observing southern bamboo lemurs in southeastern Madagascar and collecting data on their nutrition. He was surprised to find that in degraded forest habitats, the animals were willing to risk their lives to come down to the forest floor, where they gathered more nutritious food and sometimes even slept. In a healthy, continuous rainforest, the lemurs would “almost always” be found in trees or bamboo stands, Eppley said.
Then, a discussion at a 2016 conference about his observations and questions, which other researchers shared, became the genesis for the study. Eppley began contacting anyone he could find who had spent time tracking primates, and eventually connected with 118 co-authors at 124 different institutions. The study is based entirely on raw observations of monkeys and lemurs, as opposed to an analysis of a sampling, taken starting in 1985.
The study came to various conclusions on what makes primates more likely to leave their natural habitat in the trees. Those who live in large groups can descend to the ground more often because there is safety in numbers, as can those willing and able to eat more than just fruit. The warmer the climate and the sparser the tree cover at any given site, the more likely the animals were to descend to the ground.
But in areas close to roads and other human infrastructure, the primates were less likely to spend time on the forest floor, perhaps because that often means proximity to feral dogs, the study found.
Researchers not involved with the study said it supports literature that has shown the effects of climate change on primates, including that primates will increasingly depend on the availability of shade in forests as global temperatures rise, according to Korstjens.
Researchers said more investigation is needed to parse in detail what is driving the changes in the primates’ habits. For example, comparing temperatures on the ground versus in the canopy at observation sites could better demonstrate what role warming temperatures play, Slater said.
It’s not clear how important the variation in the primates’ ability to adapt to a ground-based habitat will be in the long run. The study found that among the 15 lemur species and 32 monkey species observed, they spent less than 5 percent of their time on the ground, on average, a level low enough that made Korstjens question how important the habit may be to a primate’s survival.
And it’s not safe to assume that some species will thrive just because they might be more adaptable to spending time on the ground, said Andrew Bernard, a doctoral candidate in anthropology at the University of Michigan whose research focuses on primate behaviors.
“Plenty of primates spend considerable time in low-quality habitats that could not independently sustain viable populations,” he said.
But the study still emphasizes the effects of global warming on animals, and the adaptations it’s requiring of them.
The study focused on primates in Madagascar and the Americas because similar species in Africa and Asia already underwent similar transitions millions of years ago, adapting from living primarily in trees to spending time on the ground. It’s a relatively common evolutionary transition among primates, though what the researchers observed appears different.
“What we’re seeing now is largely anthropogenically induced,” Eppley said. “This is happening so fast.”
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