Ruling the Rock

On the 60th Anniversary of Keystone Species

Keystone Predator, one of SimBio’s most popular ecology tutorial labs, allows students to experiment with the dynamic systems among the rocks in the intertidal zone. I was recently reminded of the relevance of Keystone Predator, as 2026 marks the 60-year anniversary of Food Web Complexity and Species Diversity, the seminal paper on which our tutorial is based.

When I authored Keystone Predator, I was sitting two doors down from the lab of the ecologist who wrote the paper, Dr. Robert Paine. In the early 1960’s, Paine periodically visited a stretch of rocky intertidal coastline near the University of Washington where he worked, picking up all the starfish and throwing them away from his study area. Simultaneously, a neighboring area was left alone. After just a year, it was clear that the community without starfish was changing to favor a single species that dominated space on the rocks. His groundbreaking paper covering this experiment led to several ideas that are now core to the ecological sciences, including keystone species, indirect effects, trophic cascades, and more. Just as importantly, his work showed the possibility of doing controlled field experiments to learn about ecological systems.

In learning about this story and the subsequent work from his students, I was intrigued by how simple the experiments were, and how an undergraduate could, conceptually, repeat Paine’s actions and make the discovery of keystone species for themselves.

Using Paine’s work, I sought to replicate the experiment on a virtual level. The result, a nascent simulated environment called EcoBeaker, had the capacity to put different species on a virtual rock face and allowed other species to wander around eating them. Each individual appeared as a small colored square on the screen. Moving the mouse on the screen could clear areas of the rock or transplant species, allowing students to figure out where competition occurred. They could also measure what each species was eating and, with a click, follow Paine and remove the virtual starfish to observe the results. The data from Paine’s long-term experiment was available for students to collect in a typical class period, during which they could just about write their own version of Paine’s seminal paper.

Of course, for anyone who has gone tide pooling, clicking squares on a screen (even with the much fancier graphics we have nowadays) doesn’t compare to grabbing an actual starfish off a rock and turning it over, or seeing the fans of a barnacle moving in and out as they feed, and certainly doesn’t have the complexity of a true ecological system. But the conversations I had with Paine and his students about ecology are not all that different than the conversations I heard from students as they puzzled out their predictions of what will happen when they remove Pisaster in the Keystone Predator tutorial. Today, where critical thinking and skills like experimental design are among the most important learning students gain from a science education, it’s satisfying to see the simulation I built consulting with a master ecologist continuing to help students learn to think ecologically.