Nicolas Brown adapts Sean B. Carroll’s book The Serengeti Rules, at once paying homage to the five scientists at the heart of it, and explicating their theories in a handsome, engaging documentary. Like so many environmental docs that have come before it, it identifies a threat to our planet, in this case, the degradation to our natural world that ensues with the loss of biodiversity. But unlike so many films of its nature, it is more hopeful in tone. The scientists know what needs to be done to cure this particular malady; the trick is getting it done. The Serengeti Rules serves as a clarion call for action.

Working in disparate corners of the natural world—Bob Paine in the Pacific Ocean off Washington state, Jim Estes in the Aleutian Islands, Mary E. Power in the rivers and streams of Oklahoma, Tony Sinclair in Africa’s Serengeti, and John Terborgh in the Amazonian rainforest—the five scientists observed the same phenomenon: That when certain species are removed from an ecosystem, collapse follows. Paine, for example, constructed an experiment in which he removed starfish from an area of the seabed. With the predator gone, mussels proliferated while the overall diversity of species in the area dropped by half.

It was Paine who explicated the theory that the scientists ascribe to: That certain species, referred to as “keystones” and often predators, are vital to the health of communities. When they are removed from a system or die off for whatever reason, it upsets the balance and the entire system suffers.

Brown employs reenactments to illuminate his subjects’ work as young scientists. To this he adds interviews with the five, including Paine literally on his death bed, and commentary from Carroll to illustrate the keystone theory. It is not all doom and gloom. In particular, Sinclair has watched the renewal of the Serengeti after the wildebeest population rebounded with the eradication of the rinderpest disease.

The Serengeti Rules is also a spectacularly beautiful film. Tim Cragg and Simon De Glanville’s cinematography is gorgeous whether exploring the ocean floor, observing otters bobbing atop the current, following big mouth bass darting through murky water, peeking through foliage in the Amazon or Yellowstone National Park, or regarding the wildlife of the Serengeti. Those images are affirming—it really is a beautiful world we inhabit. But Brown is also making a point with such glorious depictions—it is a beautiful world and it is urgent that we pay more attention to it and the keystone species that support it. –Pam Grady