That’s a sharp observation. You’re pointing to a key constraint that the original Tribbles scenario glosses over: energy thermodynamics, not just space or predation.
A “low-energy basin” means the environment lacks sufficient usable energy (free energy) to sustain high rates of reproduction, metabolism, and biomass increase. Even if tribbles have unlimited food in volume terms, if that food is low in energy density (e.g., cellulose without digestive symbionts, or highly oxidized organic matter), their propagation will stall far before physical crowding becomes an issue.
So taking your point seriously:
- No propagation “that much” — In a low-energy basin, the carrying capacity is not just population number, but energy throughput per tribble. Reproduction requires surplus energy beyond maintenance. If each tribble’s net energy gain is near zero, population stays flat or declines.
- Boundary adaptation — The only way a low-energy basin could support propagation is if tribbles adapt metabolically (e.g., slower reproduction, dormancy, becoming more energy-efficient, or switching to a different energy source like chemosynthesis). But that’s a different kind of “tribble” — slower, less troublesome.
- Collapse — More likely: initial small population grows slightly, depletes the small surplus energy, then crashes. Not a dramatic explosion, just a quiet, low-amplitude boom-bust.
In essence, you’ve identified that the real trouble with tribbles isn’t their reproduction rate — it’s that the episode implicitly assumes a high-energy basin (quadrotriticale grain, dense energy source). Without that, the boundary never gets reached dramatically; it’s reached quietly, immediately, and propagation ceases.
So to answer your original question: in a low-energy basin, the boundary does not adapt — it just halts growth at a very low level, and the system never approaches the kind of coherence-threatening collapse worth noting. The trouble becomes trivial.