Eight populations — a grazer and a hunter for each of the four corners, two populations per corner. Traits 0–10; body and mouth must be at least 1. A hunter needs a mouth at least as wide as its prey's body or it cannot eat at all, and any lineage you want to survive needs a count of at least two. Set a count to 0 to leave that slot empty.

Patch size is the correlation length in cells — small values give fine mottling, large values give broad prairies and barrens. Patch contrast 0 makes the land uniform; 1 uses the full growth range.

Provisioning is a species trait: f spends little on each newborn and F spends a lot, and the two do not interbreed. Disturbance hits a random patch on that interval - most events are small, a few are very large. Killing animals but sparing the grass rewards whoever recolonises fastest; stripping the grass too forces the colonists to live on what their parents gave them. The carnivore-on-carnivore size gap is the only thing that stops predators eating each other: a hunter's chance against another carnivore is zero when they are the same size (legs+body+mouth) and rises to its full concealment-limited value once it is this many units bigger — so a species can never eat itself, and newborns are safe from their parents. Strike reach is how far a hunter can take prey without moving: with the eyes rule it is max(1, hunter eyes − prey eyes), so sharp eyes reach further and sharp-eyed prey are harder to reach. The allometry span couples body and mouth — a big digestive system needs a big body to hold it — while legs and eyes are free.

Every step an animal burns basal = 0.75×legs + 1.8×body + 0.3×mouth + 0.15×eyes, tenths of a fat unit per basal unit; a newborn costs its parents build = 3.8×legs + 4.5×body + 0.7×mouth + 0.07×eyes plus its starting fat; and a kill returns a fixed fraction of what each prey tissue cost to build (legs 0.85, body 0.65, mouth 0.15, eyes 0.17, fat 0.92). All from mammal tissue physiology, 2026‑09‑01. A hunter can take any prey whose body is no wider than its mouth (mouth ≥ body).

Everything here reproduces the model as it stood before 2026‑09‑01, for comparison runs. Legacy economics restores the flat costs (basal = legs + body + eye upkeep×eyes, build = legs + body + mouth, a kill worth legs + body + fat) and the predator-side conversion discount 0.9 − eyes cost×eyes − legs cost×legs; the three numbers act only when it is ticked. Strict gape requires mouth > body rather than ≥; it was found to starve derived carnivores whenever the dominant herbivore's mouth equalled its body, and cannibalism is already prevented by the size gap above.