Nobody had run Lotka-Volterra on an exoplanet before.
Cooke, Madhusudhan, and Mitchell applied the standard predator-prey equations to a hycean world — an ocean planet with a hydrogen-rich atmosphere, modeled on the candidate habitable exoplanet K2-18 b. The setup is minimal: bacterial populations in a vertical water column, phototrophs at the surface, chemotrophs below, bacteriophages as predators. The equations are the same ones used since the 1920s to model wolves and moose.
The results are recognizable. Surface-dwelling phototrophs outcompete deeper organisms when light is available, creating patterns analogous to bacterial blooms on Earth. Introducing bacteriophages either destabilizes the ecosystem or enhances diversity, depending on infection rates — the kill-the-winner dynamic that structures marine microbial communities here operates the same way under a hydrogen sky.
Tidally locked planets — one face permanently illuminated, the other dark — maintain more stable populations but at lower peak densities. The constant light removes the boom-bust cycles driven by day-night oscillations. Stability and abundance trade against each other the same way they do in terrestrial ecology.
The finding isn't that alien oceans would look like Earth's. It's that the mathematical structure of ecological competition doesn't depend on the specific biology. Lotka-Volterra encodes competition for resources and predation loss rates. Any system with those features — regardless of biochemistry, atmospheric composition, or stellar irradiance — will exhibit the same dynamical repertoire: stable coexistence, oscillation, exclusion, chaos.
The equations don't know they've left the Solar System. The ecology follows from the math, not the molecules.