Nature clearly benefits human health. Research shows how trees clear the air, wetlands filter water and insects pollinate food.
But moving beyond these generalities to specifics is hard, says Thomas Timberlake, an ecologist at the University of York. Figuring out which parts of an ecosystem are most important, and how much they bolster the health of people and communities is difficult to quantify.
"Ecological systems are complex and messy," he says. Making sense of that mess to draw distinct lines from biodiversity to human nutrition takes painstaking work — tracing people's diet to individual crops and then, the pollinators that support them. But doing that work is crucial for understanding how the loss of biodiversity across the globe is affecting human health on the ground.
In Nepal, they found a picture that is both worrying, and hopeful.
In rural communities, pollinating bees and hoverflies are responsible for more than 20% of people's intake of key vitamins, and more than 40% of their income, the researchers report Wednesday in Nature. Insect decline, driven by climate change and habitat loss, could result in more hardship for people, the researchers project. But they find those losses could be reversed by simple actions to support pollinators, like planting wildflowers.
"Biodiversity isn't just about saving bees or wild animals. It's for the benefit of humans and sometimes the most vulnerable populations," says Kelvin Mulungu, an agricultural economist at the International Maize and Wheat Improvement Center in Lusaka, Zambia who wasn't involved in the study. "It promotes income, it promotes nutrition, it promotes health."
Drawing connections
In rural Nepal, almost three quarters of the population depend directly on smallholder farming, says Timberlake. These communities are surrounded by the food they grow, and the ecosystem that supports that food. That ecosystem is the insects that pollinate the plants, the soil that nourishes it.
"That link between the biodiversity around them, and their health, their nutrition, their livelihoods is very, very direct," he says, much more so than people in wealthier countries who buy their food from the grocery store.
That proximity makes these communities especially vulnerable to pollinator decline. In parts of Nepal, native honeybee populations have dropped by nearly 50% over the past decade or so, due to climate change, habitat loss and pesticide use. But that proximity also makes it easier for researchers to study the links between health and biodiversity.
To start, they tracked the diets of 776 people over the course of a year. Twice a week, researchers would visit their homes, and ask about everything people had eaten in the previous 24 hours. That allowed the researchers to figure out how much of key nutrients people were getting, and what foods those nutrients were coming from.
"So for vitamin A, how much of that is coming from carrots?," says Timberlake. "How much from beans? How much from green leafy vegetables?"
The next step was tying those nutrients to pollinators. That required collecting a lot of insects. The team surveyed the farms around these villages, noting which insects visited which plants. They even looked to see how much pollen individual bugs carried on their bodies. "It's a huge amount of work," for the team, says Timberlake.
With all that data, the team could start to measure the weight of the connections between each insect, each crop, and each human.
Those connections were strong, they found. Insects, and especially native honeybees, helped produce more than 20% of total vitamin E, vitamin A and folate intake. Insects also pollinated the crops that accounted for 44% of the farmers income.
"The magnitude of the effect surprises me" says Taylor Ricketts, an ecologist at the University of Vermont who wasn't involved in the study. He says biodiversity's impact isn't "a rounding error, it's not a little effect. It is really in the ball game in keeping people healthy."
If insect decline continues on its current trajectory, these communities could become less healthy. By 2030, vitamin A and folate intake could decline by about 7% because of fewer pollinators, the researchers estimate. A complete loss of pollinators — an unlikely scenario, but one that's played out in some areas with heavy pesticide use — could lead to an almost 50% cut in farming income, and a 20% decline in vitamin A and folate intake.
But insect declines can be reversed. "Helping bees isn't hard," says Ricketts.
Relatively simple interventions, like planting wildflowers that give extra food for insects, providing bee nesting sites, and reducing pesticides, can help insects recover. The researchers estimate such actions could raise farmer income up to 30%. Additionally, diets would improve enough to raise 9% of the population out of a nutrient deficiency.
Ricketts has minor quibbles with some of the assumptions behind these projections. For example, the researchers assume that as pollinator visits decline, crop yields drop proportionally, when the data suggests that relationship is a little more complicated. But overall, he says the picture here is clear.
"Conserving biodiversity is a public health investment. And not only a statistically significant one, but a substantial one," he says. "The effects are big."
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