In his new book, Serendipity: An Ecologist's Quest to Understand Nature (UC Press, May 2016), marine ecologist James Estes recounts the simple twists of fate that sent him to the Aleutian Islands in 1970 to study the distribution and abundance of sea otters. It was the start of a remarkable journey of discovery that led to profound insights about the complexity of ecological interactions and the importance of predators in natural ecosystems.
Now a professor of ecology and evolutionary biology at UC Santa Cruz, Estes has returned to the Aleutian Islands nearly every year after that first visit, developing a deep knowledge of the area's natural history and witnessing dramatic changes in its ecosystems. In Serendipity, he starts with his research on sea otters and kelp forests, shows how one question led to another, and explains the broader principles of ecology illuminated by his findings.
"I try to not only tell the story of the science, but also give an explanation of how it came about and highlight why it's important to the science of ecology," Estes said.
Keystone species
His research showed that sea otters are a "keystone species" that maintains kelp forest ecosystems by controlling populations of kelp-grazing sea urchins. Sea otters had been hunted to near extinction for the fur trade, and the recovery of their populations was uneven and fragmented across the Aleutian Archipelago. This enabled Estes to compare coastal ecosystems around islands with and without sea otters, and he found that there were no kelp forests without sea otters.
His findings have become a classic example of how apex predators shape ecosystems. Estes continued to build on his early observations over the following decades, carefully documenting the interactions among sea otters, sea urchins, and other elements of kelp forest ecosystems. He conducted long-term studies tracking the changes at sites where sea otters recolonized an island and expanded their numbers, and at other sites where once thriving populations underwent sudden declines.
Unexpected collapse
The unexpected collapse of sea otter populations in parts of the Aleutian Archipelago in the 1990s led the research in new directions. Estes concluded that the likely cause of the decline was predation by killer whales. But why had killer whales begun preying on sea otters? It appeared to be part of a broader "megafaunal collapse" that included several species of seals and sea lions.
Estes and others proposed that industrial whaling had forced a dietary shift in killer whales that had previously preyed on large whales. As the great whales became scarce, the killer whales turned to smaller marine mammals, including seals, sea lions, and sea otters, all of which underwent marked population declines. This remains a controversial hypothesis, and Estes devotes a chapter of the book to the ongoing debate.
In recent years, he has led international teams of scientists investigating how a broad range of ecosystems have been disrupted by the decline of large predators and other "apex consumers" at the top of the food chain.
"Natural ecosystems are strongly influenced by these big predators," Estes said. "The top predators have really important roles in the way ecosystems are structured and how they operate, and the loss of these animals as part of the erosion of biodiversity is an issue of global significance."
Serendipity
The book's title, Serendipity, reflects the unpredictable and often surprising course of his research career, Estes said. "So much of the process of science has to do with fortuitous events, the people you meet, and the ideas that surface during informal conversations."
A crucial encounter for Estes was a brief conversation in 1971 with the pioneering ecologist Robert Paine during a visit Paine made to Amchitka Island, where Estes was based. Estes had been observing a thriving sea otter population around Amchitka Island, diving in the kelp forests, and trying to come up with an idea for a Ph.D. thesis. Inspired by Paine, he organized a trip to another island in the Aleutian archipelago where the sea otter population had never recovered.
"That was probably the most exciting moment in my career, when I first went to an island that lacked sea otters and stuck my head in the water, and I saw how incredibly different it was," Estes said. "That was such a powerful experience, probably the most defining moment of my life, and it happened in less than a second."
Estes, who joined the UCSC faculty in 1978, was elected to the National Academy of Sciences in 2014. He is also a fellow of the California Academy of Sciences and has received the Western Society of Naturalists' Lifetime Achievement Award, a Pew Marine Conservation Fellowship, and the C. Hart Merriam Award of the American Society of Mammalogists.
