# Biota — Flora · Fauna · Funga (density + slot/point population)

> Status: **implemented.** This supersedes the original density-only sketch. The discrete
> slot/point design comes from `docs/fauna_generation_plan.md`; this doc records the unified,
> shipped design. Code: `src/sim/PlanetBiota.{hpp,cpp}` + `PlanetFloraGen/FaunaGen/FungiGen.cpp`;
> test `test_biota.cpp`; controls `8`/`9`/`0` (density views) + `L` (generate population).

## Three kinds (Biota)

Living things are split into **Flora** (plants), **Fauna** (animals) and **Funga** (fungi).
Funga is *not* a plant but is generated with a flora-like environmental system and its own
rules; all three share the same per-cell slot/point logic.

## Two layers

1. **Density scalars** (`sFloraDensity`/`sFaunaDensity`/`sFungaDensity` ∈ [0,1]) — derived from
   the climate fields each tick (like biomes/climate), drive the colour views. 0 on water/Ice.
   - Flora = NPP-style **Liebig minimum** of a temperature factor
     `clamp((T−bioVegTempMin)/(bioVegTempOpt−bioVegTempMin),0,1)` and a moisture factor
     `clamp(sMoist/bioVegMoistRef,0,1)`.
   - Fauna = herbivore carrying capacity `clamp(floraDensity·bioFaunaProductivity,0,1)`;
     carnivores in the *population* are gated on neighbourhood prey ≥ `bioCarnPreyMin`.
   - Funga = `min(moistFactor, bioFungaFloraWeight·floraDensity + (1−w)) · coldTolerance`
     (`bioFungaMoistRef`, `bioFungaTempMin`) — thrives moist + with organic matter, persists in
     cold shade where flora thins, ~0 in hot dry desert.
2. **Discrete slot/point population** (`sBiota`, saved v7) — generated **on demand**
   (`generateBiota()`, key `L`, settled world). Each land cell draws broad **archetypes** (NOT
   real species) from the comprehensive append-only table `biotaArchetypes()` — each carries a
   Class/Order/Family + Size (Tiny..Huge), a biome mask and a climate tolerance. A cell has a
   per-kind **slot** cap (distinct types) and a density-scaled **point** budget (size → cost
   Tiny=1…Huge=5); archetypes are added until slots full or points exhausted. Selection is
   weighted by biome/climate suitability × a **regional bonus** for archetypes already placed in
   already-filled, same-biome neighbours (homogeneous regions, variety at boundaries). Organisms
   are **named by taxonomy** — Family + Size + role (full `Class > Order > Family` available),
   never an informal common name ("Felidae", not "cat"; Felidae is the family, cat a common
   name). Generalist families get a biome adjective ("Desert Muridae" / "Forest Muridae").

## Config knobs (`bio*`, in `planet.cfg`)

`bioVegTempMin(-5)`, `bioVegTempOpt(15)`, `bioVegMoistRef(0.5)`, `bioFaunaProductivity(0.9)`,
`bioCarnPreyMin(0.30)`, `bioCarnScale(1.0)`, `bioFungaMoistRef(0.4)`, `bioFungaFloraWeight(0.6)`,
`bioFungaTempMin(-15)`, `bioRegionBonus(0.5)`, slot caps `bioFlora/Fauna/FungaSlots(12/10/8)`,
point budgets `bioFlora/Fauna/FungaPoints(20/16/14)`.

## Determinism & persistence

`generateBiota()` uses a **separate RNG seeded from `cfg.seed`** (not `Planet::rngState`), so it
never perturbs tectonic determinism (asserted in `test_biota.cpp`). The population is **saved**
(save **v7**); densities are derived/not-saved. Older saves load with an empty population (press
`L`). The archetype table is **append-only** — indices are serialized.

## Out of scope (future / Live World)

Time-evolving populations (growth, migration, predator-prey dynamics, extinction), seasons, and
true species/typed organisms — reserved for the **Live World** real-time mode. This stage
answers *"what could live here"*, not *"what is living/evolving here"*.