Ruling the Rock

On the 60th Anniversary of Keystone Species

Keystone Predator, one of SimBio’s most popular ecology tutorial labs, allows students to conduct experiments to figure out the underlying dynamics controlling the structure of an intertidal community. 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.

Thirty years ago, when I first started working on the Keystone Predator module, I was a graduate student sitting two doors down from the lab of Robert T. Paine, the University of Washington ecologist who wrote that paper. Thirty years prior, Paine had conducted a revolutionary experiment that involved periodically visiting a stretch of rocky intertidal off the coast of Washington where he systematically removed all of the starfish from one area while leaving a neighboring area intact. After just one year, it was clear that the community in his plot without starfish was changing to favor a single species that dominated space on the rocks. His groundbreaking paper resulting from this work 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 demonstrated the power of conducting controlled field experiments to better understand ecological systems.

In learning about this story and 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.

I sought to replicate Paine’s experiment on a virtual level by building an interactive model of his system with the capacity for students to place simulated sessile species (defined by preset rules) on a virtual rock face and allowed them to introduce simulated mobile species to wander around eating them. Each individual appeared as a small colored square (designating its species) on the screen. With simple mouse actions, students could either remove species from or transplant species to the rock, allowing them to set up competition experiments. They could also determine who ate whom and, with a click, mimic Paine and remove all of the starfish from an area. Once their simulated experiments were set up, they could run them for virtual years. Data analogous to that collected in Paine’s long-term experiment was thus 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’ve heard from students decades later as they puzzled out their predictions of what will happen when they remove the starfish 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 like scientists.