"Biodiversity as a whole forms a shield protecting each of the species that together compose it, ourselves included." — E.O. Wilson, "Half-Earth"

Earth is teeming with life, from huge blue whales and redwoods to tiny bacteria, archaea and fungi. It's not just the only planet known to host any life at all; it has so many species in so many places we still aren't even sure how many there are.

We do know, however, that Earth is losing species unusually quickly at the moment. We're seeing a mass extinction event, something that's happened at least five times before on Earth, albeit never in human history — and never with human help.

Extinction is part of evolution, but not like this. Species are vanishing more quickly than any human has ever seen; the extinction rate for vertebrate animals is now 114 times higher than the historical background rate. Humans are driving this in several ways, from poaching to pollution, but the No. 1 factor is habitat loss.

This is raising deep concerns about our planet's biodiversity, which, as biologist E.O. Wilson has pointed out, is like an ecological shield for us and other species. In fact, according to a new study, biodiversity loss has crossed the "safe" threshold in most of the world, leaving many ecosystems in danger of collapse.

biodiversity loss map A map of biodiversity loss in ecological hotspots around the world. (Image: Newbold et. al./Science)

"This is the first time we've quantified the effect of habitat loss on biodiversity globally in such detail," lead author and University College London researcher Tim Newbold says in a statement, "and we've found that across most of the world biodiversity loss is no longer within the safe limit suggested by ecologists."

Published in the journal Science, the study finds that 58 percent of Earth's land surface — an area home to 71 percent of all humans — has already lost enough biodiversity "to question the ability of ecosystems to support human societies."

That certainly sounds bad. But why is biodiversity so important? Can't technology keep civilization running, regardless of what happens to the wildlife in dwindling forests, grasslands or wetlands? Here's a closer look at why biodiversity is a big deal — and why it's in our own best interest to preserve what's left.

red-tailed bumblebee, Bombus lapidarius, on lavender The red-tailed bumblebee is an important crop pollinator in Europe. (Photo: Pippa Sanderson/Shutterstock)

1. Food

About 75 percent of our food supply comes from just 12 plant species, and more than 90 percent of global livestock production comes from just 15 species of mammals and birds. That's deceptive, though, because those 27 species — along with many others that also provide food for humans — couldn't exist without help from hundreds of thousands of lesser-known species working behind the scenes.

A wide range of wildlife makes agriculture possible, including bats, bees, birds, dragonflies, frogs, ladybugs, mantises, moles, nematodes, salamanders, spiders, toads and wasps, among countless others. Of 264 crops grown in the European Union, more than 80 percent depend on insect pollinators, while bees alone boost U.S. crop revenue by more than $15 billion per year. Worldwide, bats save corn farmers about $1 billion annually by eating pests like earworm larvae.

Wildlife doesn't just protect and pollinate food; it often is our food, too. Hundreds of millions of people rely on daily protein from wild-caught fish, for example, including many fish that depend on healthy coral reefs. And while we mostly eat just a few domesticated crops today, about 7,000 plant species have been cultivated as food in human history — and their wild relatives hold a cache of genetic diversity that may prove priceless as drought or disease threaten monoculture crops.

Semuc Champey Natural Monument, Guatemala About 70 percent of known plants with cancer-fighting properties exist only in rain forests. (Photo: soft_light/Shutterstock)

2. Health

Biodiversity is linked to human health in several ways. By having a diverse mix of plants, fungi and animals to eat, we ensure nutrition that buffers our bodies against disease and other hardships. Higher biodiversity has also been linked to lower instance of disease, with studies finding lower human rates of Lyme disease, malaria, acute respiratory infection and diarrhea around protected natural areas.

But even when we can't avoid getting sick, biodiversity still swoops in to the rescue.

Medical discoveries frequently begin with research on the biology or genetics of plants, animals, fungi and bacteria. This inspiration is especially prevalent in rain forests, biodiversity hotspots that contain half of all known species. The asthma drug theophylline comes from cacao trees, for example, and about 70 percent of plants with cancer-fighting properties occur only in rain forests. Yet medical insights can be found in other ecosystems, too, such as forests of eastern North America, where the eastern red cedar produces a compound that fights antibiotic-resistant bacteria.

"Every time a species goes extinct or genetic diversity is lost, we will never know whether research would have given us a new vaccine or drug," points out the National Wildlife Federation. And as The Economics of Ecosystems and Biodiversity (TEEB) initiative notes, "all ecosystems are a potential source of medicinal resources."

Red Cloud Peak Wilderness Study Area, Colorado Soil biodiversity is key to the health of grasslands, like this one in Colorado. (Photo: U.S. Bureau of Land Management)

3. Ecosystem services

Food and medicine are just two of many "ecosystem services" humans can expect from biodiverse habitats. Here are a few other examples:

  • Clean air: From old-growth forests to ocean phytoplankton, the oxygen we breathe is generated by photosynthesizing members of ecosystems around the world. Plants also absorb a variety of pollutants from the air, and sequester the excess carbon dioxide emissions that fuel climate change.
  • Clean water: Forests help soil absorb more water, which can reduce flooding, limit erosion, filter out contaminants and refill aquifers. Wetlands also excel at "phytoremediation," or cleaning hazardous chemicals from water and soil. Different species bring different skills, so the more the merrier.
  • Healthy soil: Soil naturally bustles with lots of arthropods and microorganisms, which are easy to overlook but provide a wide range of benefits. They provide food for slightly larger creatures, help nutrients cycle through soil, boost nutrient availability to roots and enhance plant health, among other things.
  • Raw materials: Biodiverse ecosystems supply us with a diversity of raw materials, including wood, biofuels and plant oils that come from both wild and cultivated species. Materials from different plants offer different properties, such as harder or softer wood, or oils with varying smoke points.

As biodiversity falls below safe limits, these services are in jeopardy for a growing number of people. "Decision-makers worry a lot about economic recessions, but an ecological recession could have even worse consequences — and the biodiversity damage we've had means we're at risk of that happening," says Andy Purvis, a researcher at Imperial College London and co-author of the new study. "Until and unless we can bring biodiversity back up, we're playing ecological roulette."

fishing boat near Flores, Indonesia Anglers work near a coral reef in Indonesia, where people rely heavily on wild fish. (Photo: Ethan Daniels/Shutterstock)

4. Resilience

One of the single most important aspects of biodiversity is that it provides insurance. According to the insurance hypothesis: "Biodiversity insures ecosystems against declines in their functioning because many species provide greater guarantees that some will maintain functioning even if others fail."

When an ecosystem has lots of different species, they can fill an array of different ecological niches, while in a monoculture they're all competing for the same niche. Biodiversity tends to increase overall rates of photosynthesis, and it also buffers the community against illness. Plant viruses often specialize in a certain species, genus or family of plants, so one viral strain can obliterate all members of a monoculture. In a biodiverse ecosystem, on the other hand, all the eggs are not in a single basket.

"Biodiversity allows for ecosystems to adjust to disturbances like extreme fires and floods," the NWF adds. "If a reptile species goes extinct, a forest with 20 other reptiles is likely to adapt better than another forest with only one reptile."

sunrise over rainforest in Sri Lanka Sunrise illuminates the canopy of a rain forest in Sri Lanka. (Photo: Sergieiev/Shutterstock)

5. Ethics, aesthetics and awe

There are many practical reasons to preserve biodiversity. It saves us money and effort, protects our lives and livelihoods, and ensures we have enough to eat. It's also worth noting, however, that biodiversity is bigger than any one species, including us.

By leaving biodiversity intact, we let natural evolutionary processes continue. That's a long-term benefit beyond the scale of human lifetimes, but that doesn't mean it's not important. Evolution lets organisms adapt to environmental change, and who are we to interfere with that? Since it's possible for humans to thrive without destroying the ecosystems — and lives — around us, why destroy them? As a species capable of ruining ecosystems, we have a moral obligation not to screw everything up.

And, finally, the most basic beauty of biodiversity is the beauty itself. Spending time in nature offers many perks for people, like more creativity, better memory and faster healing. Feeling awe at the sight of nature can even reduce pro-inflammatory proteins in the body. But we don't need science to tell us that. All it takes is one step into an old-growth forest, or one paddle into an ancient estuary, to make clear that we aren't just lucky to be alive — we're lucky the world around us is, too.

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.