Eat, Poop, Die How Animals Make Our World

What a killer title. Rarely have I seen three snappy words so effectively capture the essence of a concept in biology. What concept is that? Zoogeochemistry. Many scientists have convincingly made the case that it is the small things that run the world. Though it is undeniably true that e.g. microbes and insects have shaped our planet, and continue to do so, it would be a mistake to think that larger animals are just along for the ride. I was stoked the moment the announcement for this book dropped and conservation biologist and marine ecologist Joe Roman did not disappoint. Eat, Poop, Die is fun, fascinating, while always keeping one eye firmly on the facts and complexities of ecology.

Given that this concept "is the beating heart of this book" (p. 214), what is zoogeochemistry? Physical forces shape the living world and living forces can shape the physical world right back—you may well have heard of biogeochemistry. Traditionally, research has focused on bottom-up interactions, revealing how e.g. microbes influence the climate and fungi and invertebrates help form soils. The phrase "ecosystem services" is often bandied about in this context, referring to how organisms keep our planet liveable by fertilizing soils, filtering water, or absorbing carbon dioxide from the atmosphere. Increasingly, however, it is becoming clear that larger animals similarly have the power to shape ecosystems, influencing the flow of chemical elements at large scales. Hence zoogeochemistry. How do animals do this? The title of the book says it all: rotting carcasses, deposited faeces, "and other unglamorous forces" (p. 52) can collectively move, concentrate, disperse, and recycle nutrients in ecosystems and influence the climate.

By visiting and interviewing fellow ecologists, and mixing in some of his own research, Roman introduces you to a variety of very interesting studies that are now uncovering these processes. He starts simply enough with the volcanic island Surtsey which appeared above the waves off the coast of Iceland in 1963. It has offered a unique opportunity for ecologists to study how a newly formed island gets colonized by plants and animals, with birds and seals enriching the initially scrappy plant communities through faeces, urine, carcasses, and eggshells. In the oceans, zooplankton move carbon and other elements from the surface to the deep, forming one component of the so-called biological pump. But whales, because of their sheer size, have the potential to counteract this. By bringing nutrients back from the deep, where they feed, to the surface, where they release nutrient-rich faecal plumes, they form what Roman calls a whale pump. (This happens to be his speciality, so expect a fair bit of lyrical waxing about whale poop.) In the Maasai Mara, wildebeest that die in river crossings provide an annual nutrient pulse, on top of the steady and intense input of hippos pooping in their pools. Coral-crunching parrotfish poop out the sand that covers the beaches of many tropical holiday destinations, and when periodical cicadas die in their trillions, they provide enormous but irregular nutrient pulses that have barely been studied. Roman appropriately concludes the book with James Estes's work on sea otters in Alaska that has become the poster child for the concept of trophic cascades. These and other examples form a delectable list of study systems, each more interesting and unbelievable than the last. No wonder Roman is often asked: "How did we overlook this for so long?"

What I particularly appreciated is that for some of the better-studied systems, Roman gets the nuances right. The story of wolf reintroduction in Yellowstone National Park suppressing elk overgrazing and leading to a restored ecosystem has almost become a meme in ecology. The details, however, are a bit more complicated than the idea that you can just sprinkle wolves over a broken ecosystem like some sort of magical fairy dust. Similarly, the notion that bears indirectly fertilize trees by littering the forest with salmon carcasses, which Suzanne Simard approvingly mentioned in Finding the Mother Tree, has a few detractors. Roman spends time in the field with Daniel Schindler who thinks that poorly executed science and overinterpreted stable-isotope data have created a good story. One of his students adds that, though the cycling of nutrients between different animals in this system is not in question, the idea that it also fertilizes trees with nitrogen is considered more shaky by some. When it comes to the Pleistocene extinction of megafauna, Roman again hits the nail on the head by acknowledging the debate about the relative contributions of human hunting and a changing climate.

Eat, Poop, Die avoids becoming an endless showcase of stories about animals moving nutrients around ecosystems in said fashion. Chapter 5 (Chicken Planet) could have easily concluded the book but instead sits smack in the middle, punctuating the flow nicely. These sombre crescendos partially answer Roman's earlier question of why we have overlooked the role of large animals for so long: because many have been driven to near-extinction by humans. The consequences of this have been studied in quite some detail for whaling, which resulted in impoverished marine ecosystems. But similar landscape changes resulted from the North American fur trade that saw the slaughter of bison, beavers, and otters. Humans have since become the prime mover of nutrients, with the mining of guano islands one sordid chapter in that history. The Haber–Bosch process might nowadays provide plentiful nitrogen, but phosphorus still has to be mined. Future shortage is one of those creeping problems that is often overlooked in environmental discourse.

Twice, Roman ruminates on whether rewilding our planet could help restore the nutrient flows that we have disrupted. It certainly has a better track record than geoengineering proposals. He is honest enough to highlight the downsides of large animals again roaming the land and acknowledges that certain scenes from the past would cause social upheaval today. He is quietly radical here, gesturing at veganism, degrowth, and overpopulation without explictly using these words. I could slate him for not developing this further, but understand that developing these complex topics would take us too far away from the main theme of the book.

Eat, Poop, Die is an absolute stonker that captivates from start to finish. The topic of zoogeochemistry is an incredibly fascinating development in ecological research and Roman recounts it here with flair.