Karen Lips has never forgotten the silence. It was the early 1990s; she was finishing her PhD in tropical biology, and had come back to a research site in Costa Rica, a protected reserve high up in the mountains, after a short break. On her previous visit, the air had been full of the sounds of the frog species she was studying. Now, inexplicably, almost all the frogs were gone.
She was mystified and alarmed, but she arranged to move her research sites further south in Central America, into the mountains of Panama and eventually as far south as the border with Colombia. Wherever she and her colleagues went, though, they found a wave of death preceding them. “By the time we got there,” she recalls, “it was already too late.”
What Lips was seeing as a graduate student—she is now a tropical ecologist and a professor of biology at the University of Maryland College Park—was the arrival in the Americas of a fungal pandemic that had been sweeping the globe. Batrachochytrium dendrobatidis, a virulent spore-forming pathogen generally known as Bd, originated in Asia and probably spread for decades before its damage began to be noticed in the 1980s. Since then, scientists estimate, 90 amphibian species have been made extinct by the fungus, and more than 400 were severely harmed by it, losing up to 90 percent of their populations. Altogether, more than 6 percent of all amphibian species in the world were decimated or destroyed, a catastrophe that one research group has called “the greatest loss of biodiversity attributable to a disease.”
Over the years, Lips and other scientists were able to document what happened to the ecosystems that lost those frogs and other amphibian species: surges in populations of insects (which the frogs would have eaten) and drops in populations of snakes (which would have eaten the frogs). But what looked to ecologists like profound environmental disruption was invisible to most of society, because it occurred far from human habitation, in locations where surveillance is patchy and expensive.
Now, though, there’s evidence that the damage caused by Bd has rippled into the human world.
In the journal Environmental Research Letters, Lips and several other researchers report that the devastation of frog species in Costa Rica and Panama caused an unforeseen surge in human malaria cases lasting eight years after the pathogen arrived—likely because, with no tadpoles to eat their larvae, mosquito populations boomed. It’s the first published evidence that the worldwide amphibian die-off has had implications for people.
“This paper is a wake-up call,” says John Vandermeer, a professor of ecology and evolutionary biology at the University of Michigan, who was not involved in the study. “It makes the point that the problem is not just that we're losing biodiversity, and biodiversity is wonderful and pretty and beautiful. It’s that the loss of biodiversity does have secondary consequences on human welfare—in this particular case, human health.”