Conservation pioneer Russell A. Mittermeier started this year’s Roger Tory Peterson Memorial Lecture (April 5) with a quiz. In front of several hundred listeners at Harvard’s Science Center he turned on a small recorder.

The sudden call of an animal — piercing and reedy — shot like an alarm across the expanse of Lecture Hall B.

Mittermeier, president of the biodiversity protection group Conservation International, asked: What is it?

From some of the hundreds there came shouted answers. A whale? A river otter? But few got the right answer: the eerie forest voice of the indri.

The indri is the largest species of lemur, a kind of primate found only on Madagascar, a lushly biodiverse island off the southeast coast of Africa.

This lean, saucer-eared black-and-white primate is “symbolic of the challenge” confronting humankind, said Mittermeier: a period of catastrophic extinction that could strip the world of 30 percent of its plant and animal species by the end of this century. Among primates alone, he said, one in three is at risk.

Biodiversity, even in just the “ecological services” it provides, like pollination, underpins the well-being of humankind, he said. Yet despite the extinction challenge, humans at large remain largely ignorant, said Mittermeier, “and our ignorance extends to our largest living relatives, non-human primates.”

Lemurs — some weighing just 30 grams — are related to the evolutionary branch that produced humans.

The world’s diversity of plants and animals — about 10 million species, most of them unrecorded — face accelerating pressures of human origin. Those that are regional include mining, invasive species, the pet trade, hunting, and logging.

“Logging of tropical forests is a 19th century activity that has no place in the modern world,” said Mittermeier. His slides included a seeming moonscape on Madagascar — treeless slopes that turn the nation’s rivers red with eroded topsoil.

Hunting for “bush meat” takes its toll too, he said, showing a disturbing image: the severed head of a great ape in a marketplace dish, next to a bunch of bananas. In another image, radiated tortoises were lined belly-up on a Madagascar beach. Their livers are coveted as a tasty pâté.

Other extinction pressures — climate change and deforestation — are global, he said.

But think of climate change as both a threat and an opportunity, said Mittermeier, whose lecture was titled “Conserving the World’s Biodiversity: How the Climate Crisis Could Both Hurt and Help.”

About 20 percent of the carbon emissions altering the atmosphere come from the burning of tropical forests. Putting a halt to this, he said, is the most cost-efficient way to cut down on Earth-warming gases.

Beyond climate change, Mittermeier added three other important conservation concepts: hot spots, “megadiversity” countries, and high-biodiversity wilderness areas.

All biodiversity is important, he said, but the world’s 35 “hot spots” contain a high number of species and face a high level of threat. (Madagascar is one example.)

These resource-dense areas have shrunk to 2.3 percent of the Earth’s land surface, an area about the size of India. But compressed within are 50 percent of the world’s plants and 40 percent of its vertebrates.

“Megadiversity” countries number 18, with Brazil and Indonesia at the top of the list for abundant biodiversity. Contained within are two-thirds of the planet’s terrestrial, freshwater, and marine species.

The world’s high-biodiversity wilderness areas, including the Amazon region of South America, cover 6 percent of Earth’s land surfaces, but remain largely intact.

Taken together, these three geographical areas of biodiversity also contain the world’s biggest share of linguistic and cultural diversity. Spoken there are 74 percent of the Earth’s 6,900 languages.

After seven years of graduate study, Mittermeier left Harvard in 1977 with a Ph.D. in biological anthropology. His dissertation was on the eight primate species known to inhabit Surinam, South America’s smallest sovereign state.

In his decades of fieldwork after that, the polymathic Mittermeier acquired fluency in German, Spanish, Portuguese, French, and Sranan Tongo, a creole language widely used in Surinam.

He also took the time to write 225 scientific and popular articles, along with eight books.

Since 1989, Mittermeier has been president of Conservation International, a Washington, D.C.-area group devoted to protecting global biodiversity and the environmental, economic, and cultural values represented by the natural world.

In 1998, he was named by Time magazine as one of the “EcoHeroes for the Planet.”

It was all that writing and all that fieldwork and all that advocacy on behalf of the Earth’s threatened biodiversity that landed Mittermeier back at Harvard as the 12th recipient of the Roger Tory Peterson Medal. The award is sponsored every year by the Harvard Museum of Natural History.

The medal comes with one obligation — to deliver a lecture in memory of Peterson. He was the American naturalist, artist, and ornithologist (1908-1996) credited with writing the first modern field guide. (“A Field Guide to the Birds” appeared in 1934, and spawned decades of guides to birds, insects, plants, and other living things.)

Previous recipients of the Peterson medal include Jane Goodall, Richard E. Leakey, and Edward O. Wilson, Pellegrino University Professor Emeritus of biology at Harvard — a man Mittermeier called “the Darwin of the 20th century, and the 21st century.”