Three coupled equations, one big lesson: pull a single predator out of a food web and the effects don't stop with its direct prey. Click "Remove Keystone Predator" and watch the cascade unfold in real time — urchins that were being kept in check explode in number, graze the kelp forest down to bare rock, and the once-green spatial map turns to grey — a live demonstration of why keystone species matter far more than their raw numbers suggest.
A three-level trophic chain — sea otter, sea urchin and kelp — integrated as coupled differential equations, visualised as both a population time-series and a spatial kelp-forest map that visibly collapses into an urchin barren when the keystone predator is removed.
Adjust Otter Predation Rate, Urchin Grazing Rate and Kelp Regrowth Rate to change the balance of the food web, click Remove Keystone Predator to trigger a trophic cascade, then Reintroduce Otters to see how much of the kelp forest recovers.
The sea otter-urchin-kelp system is one of the best-documented keystone predator relationships in ecology: after otters were hunted to near extinction along parts of the Pacific coast, urchin barrens replaced lush kelp forests across large stretches of coastline.
A keystone species is an organism whose impact on its ecosystem is disproportionately large relative to its abundance; removing it triggers cascading changes throughout the food web, as sea otters do for kelp forests.
Sea otters prey heavily on sea urchins, keeping urchin numbers low enough that urchins cannot graze kelp faster than it regrows; without otters, urchin populations explode and strip the kelp forest bare.
A trophic cascade is a chain reaction that runs down a food web when a predator population changes, altering the abundance of the species it eats and, in turn, the species those prey eat, here otters, then urchins, then kelp.
The otter population is set to zero, removing predation pressure on urchins; over the following seconds urchins boom, graze down the kelp, and the spatial map shifts from lush green kelp forest to a bare grey urchin barren.
Reintroducing a small seed population of otters lets predation resume, gradually suppressing the urchin population and allowing kelp regrowth, though recovery is slower than the original collapse and depends on the otter predation rate, urchin grazing rate and kelp regrowth rate sliders.