diff --git a/src/simulator/api-gdext/src/lib.rs b/src/simulator/api-gdext/src/lib.rs
index bc5a3a00..a26561c2 100644
--- a/src/simulator/api-gdext/src/lib.rs
+++ b/src/simulator/api-gdext/src/lib.rs
@@ -20,6 +20,8 @@ use mc_climate::spec;
 use mc_core::grid::GridState;
 use mc_ecology::EcologyEngine;
 use mc_ecology::fauna_product::{fauna_product_supply, FaunaProduct};
+use mc_ecology::population::PopulationSlot;
+use mc_ecology::species::Species;
 use mc_mapgen::MapGenerator;
 
 struct MagicCivPhysicsExtension;
@@ -334,6 +336,42 @@ impl GdFaunaEcology {
         }
         out
     }
+
+    /// Register a fauna species from its canonical JSON definition (the same
+    /// shape consumed by `mc_ecology::species::Species::from_json`, matching
+    /// `public/resources/ecology/fauna/species/*.json`). The numeric
+    /// `species_id` is derived from a hash of the string `id` field; the
+    /// caller passes that returned id to `seed_population`.
+    ///
+    /// Returns `-1` on parse error. Used by proof scenes and integration tests
+    /// to construct controlled fauna populations against the live engine.
+    #[func]
+    fn register_species_from_json(&mut self, species_json: GString) -> i64 {
+        match Species::from_json(&species_json.to_string()) {
+            Ok(species) => {
+                let id = species.id as i64;
+                self.inner.register_species(species);
+                id
+            }
+            Err(e) => {
+                godot_error!("GdFaunaEcology::register_species_from_json: {e}");
+                -1
+            }
+        }
+    }
+
+    /// Seed a population slot onto a tile. `species_id` must be the value
+    /// returned by a prior `register_species_from_json` call. Negative or
+    /// out-of-range ids are silently ignored. Multiple seed calls on the
+    /// same tile push additional slots (matches `EcologyEngine::seed_population`).
+    #[func]
+    fn seed_population(&mut self, col: i32, row: i32, species_id: i64, population: f64) {
+        if !(0..=u32::MAX as i64).contains(&species_id) {
+            return;
+        }
+        let slot = PopulationSlot::new(species_id as u32, population as f32);
+        self.inner.seed_population(col, row, slot);
+    }
 }
 
 // ── GdAtmosphericChemistry ──────────────────────────────────────────────