In the Mojave and Sonoran deserts of North America, donkeys(驴) walk freely. They travel in groups, seeking out water sources in small wetlands, often trampling (践踏) vegetation in the process.

The donkeys are considered an invasive (入侵的) species, and many conservationists(保护主义者) advocate for killing or relocating them as they are thought to lack predators(捕食者) that could keep their populations in control. But a recent study, a team of ecologists found that these donkeys have become a favorite snack for hungry cougars(美洲豹).

Using cameras to record videos whenever an animal walks by, the researchers surveyed donkey activity in 14 different wetlands throughout Death Valley National Park in California. They were thus able to identify eight wetlands with clear evidence of cougars killing donkeys. They also visited each site in person to look for donkey bodies, which cougars will often hide and return to later on. “Some of these hiding sites were used over and over again, so that every time we went, there would be three or four fresh kills,” says Erick Lundgren, ecologist at Aarhus University and lead author on the study.

In the sites that lacked cougars, donkeys were frequently caught on camera during the day and night. But in sites with active cougar predation, the donkeys were only seen during the day. At night, the donkeys avoided any wetlands where cougars had recently killed other donkeys.

In addition, the study showed that the donkey presence in desert wetlands was associated with striking changes to the local plant life. “These sites where they’re all day, they’re trampling and eating the vegetation,” says Lundgren. “It really strongly leads to a lot of bare(光秃的) open ground and then a really strong reduction in plant cover.” These findings highlight how important top predators like cougars can influence the stability of an ecosystem.

Julie K. Yong, a wildlife ecologist at Utah State University, says that documenting the beneficial role of cougars in the environment could help bolster their image. “It could increase social tolerance for them on the landscape,” she says. Especially among farmers who worry about their cattle’s safety, Young explains, highlighting that the benefits of keeping cougars around might go a long way in conserving this predator.

Lundgren, on the hand, worries that if conservation managers remove donkeys from the desert ecosystem, it could have unintended consequences. “If the donkeys disappear, the cougars in Death Valley may simply switch to feeding on bighorn sheep or other native wildlife,” he says.

The world is getting greener, according to a new study published in Nature this week.

Chi Chen, lead author of the study, and his colleagues have been mining data collected by an orbiting NASA camera that monitors green vegetation on Earth’s surface, day by day. Even more interesting: They are able to show the exact causes of increasing or decreasing leaf cover in particular areas.

In some cold places, increase in leaf cover apparently resulted from global warming. Since the climate is becoming more and more temperate and the growing season is getting longer and longer, the plants are growing bigger and leafier there.

“One large area of Brazil lost vegetation. I personally checked the data, and that’s because of lack of rain,” Chen said.

The most striking changes, though, were the result of human decisions in China and India. Both countries have been getting a lot greener.

The greening of India, Chen says, comes from a huge expansion of irrigated agriculture. “Instead of having just crops when it’s raining, they also have a whole six months of cropping and greenness when it’s not raining,” he says. “This version of greening isn’t really so great for the environment, though. The irrigation drains groundwater, vegetation is wiped away at harvest time and the extra chemicals farmers use produce greenhouse gases.”

In China, though, about half of the new leaf cover that Chen detected appears to be the result of a massive reforestation effort. It’s a government-supported attempt to prevent disastrous dust storms that resulted from earlier deforestation. “They are really doing a good job,” Chen says. “They have a large and comprehensive tree planting program. Those trees will stay in place, capturing (捕捉) dust and also CO₂, the greenhouse gas. They’ll store it in wood, roots and soil, doing their part to slow global warming.”

As a new mother in 2016, Tash Gorst was scrolling (翻阅) through her phone when she fell down the rabbit hole of reading about plastic pollution. Fast-forward to 2019 and she had opened Gather, an organic zero-waste shop.

Customers come to Gather to refill their own containers with everything from rice to beauty products. And it’s not only the produce that is sustainable — the shop is powered by renewable energy and financed by a more sustainable bank, while all the units inside have been made from waste materials, mostly by Gorst herself.

Zero-waste shops have become an increasingly common feature on the streets in recent years. Where they have gone, supermarkets now look set to follow, with Morrisons, Marks & Spencer and Waitrose all recently agreeing to add refill stations in shops by the end of this year. Meanwhile, Asda has introduced refill aisles (过道) to more of its supermarkets following successful trials.

As small startup businesses aiming to make responsible decisions without cutting ethical (道德上的) corners, refill shops tend to be more expensive than supermarkets and chains. Gorst acknowledges that not everyone can afford to buy from them.

“But if you can, you should. You’ll feel good about the small decision that you’ve made in contributing to your local economy and doing something that’s better for the planet,” she says.

Emily, Drabble is a regular Gather customer. She buys everything that would “normally be encased in plastic”, from cleaning products to food like pasta, which she puts into glass containers. “When I get home, I love unpacking my shopping, throwing nothing in the bin,” Drabble says.

And customers at refill shops get more than just physical goods, notes Gorst. Besides employing four local people, Gather, for example, holds free events, including a monthly book club for reading about sustainability, workshops for kids and so on. “I also see it as a place to bring people together,” she says.