diff --git a/src/game/engine/scenes/tests/worldsim_ecology_proof.gd b/src/game/engine/scenes/tests/worldsim_ecology_proof.gd
new file mode 100644
index 00000000..75c190fb
--- /dev/null
+++ b/src/game/engine/scenes/tests/worldsim_ecology_proof.gd
@@ -0,0 +1,197 @@
+extends Node2D
+## Increment 3a — Living-World Ecology Proof Scene.
+##
+## Drives the SAME Rust bridge the live `turn_manager.gd` loop ticks every turn
+## (`GdFaunaEcology.tick_populations` → `EcologyEngine::process_step`, which now
+## includes the Increment-2 carrying-capacity migration step alongside
+## emergence, Lotka-Volterra dynamics, dispersal, and tier advancement) against
+## a real terrain `GdGridState`, then renders fauna distribution BEFORE vs AFTER
+## N turns side-by-side. The visible spread of fauna across the map is the
+## "pixels" proof that the living world evolves through the playable path.
+##
+## Self-capturing (models climate_proof.gd): renders, screenshots
+## `user://screenshots/worldsim_ecology_proof_<ts>.png`, and quits.
+
+const CELL: int = 22
+const MARGIN: Vector2i = Vector2i(24, 48)
+const OUTPUT_DIR: String = "user://screenshots"
+
+const MAP_W: int = 26
+const MAP_H: int = 16
+const TURNS: int = 20
+const SEED: int = 0xC0FFEE
+const SPECIES_DIR: String = "res://public/resources/ecology/fauna/species"
+const SAMPLE_SPECIES: Array[String] = ["grey_wolf", "abalone", "red_deer"]
+
+var _grid: RefCounted = null
+var _fauna: RefCounted = null
+var _before: Dictionary = {}  # (col,row) → total population at turn 0
+var _after: Dictionary = {}   # (col,row) → total population at turn N
+var _before_tiles: int = 0
+var _after_tiles: int = 0
+var _peak_pop: float = 1.0
+var _captured: bool = false
+
+
+func _ready() -> void:
+	RenderingServer.set_default_clear_color(Color.BLACK)
+	get_viewport().size = Vector2i(1920, 1080)
+	DisplayServer.window_set_size(Vector2i(1920, 1080))
+	await get_tree().process_frame
+
+	_run_sim()
+	_print_stats()
+	queue_redraw()
+
+	for _i: int in range(10):
+		await get_tree().process_frame
+	_capture_and_quit()
+
+
+func _run_sim() -> void:
+	_grid = _make_terrain_grid()
+	_fauna = ClassDB.instantiate("GdFaunaEcology") as RefCounted
+	_register_and_seed()
+
+	# Snapshot BEFORE.
+	_before = _snapshot_populations()
+	_before_tiles = int(_fauna.call("populated_tile_count"))
+
+	# Tick the live continuous ecology path N turns.
+	for t: int in range(TURNS):
+		_fauna.call("tick_populations", _grid, SEED + t)
+
+	# Snapshot AFTER.
+	_after = _snapshot_populations()
+	_after_tiles = int(_fauna.call("populated_tile_count"))
+
+	# Peak population for color normalisation.
+	for v: Variant in _after.values():
+		_peak_pop = maxf(_peak_pop, float(v))
+	for v: Variant in _before.values():
+		_peak_pop = maxf(_peak_pop, float(v))
+
+
+func _make_terrain_grid() -> RefCounted:
+	var grid: RefCounted = GdGridState.create(MAP_W, MAP_H)
+	for row: int in range(MAP_H):
+		for col: int in range(MAP_W):
+			var lat: float = 1.0 - absf((float(row) - MAP_H / 2.0) / (MAP_H / 2.0))
+			var noise: float = fmod(float(col * 13 + row * 7) * 0.0173, 1.0)
+			grid.call("set_tile_dict", col, row, {
+				"temperature": 0.20 + lat * 0.50 + noise * 0.10,
+				"moisture": 0.30 + noise * 0.40,
+				"elevation": 0.20 + noise * 0.30,
+				"habitat_suitability": 0.4 + noise * 0.4,
+				"quality": 3,
+				"biome_id": "temperate_forest",
+			})
+	return grid
+
+
+func _register_and_seed() -> void:
+	for name: String in SAMPLE_SPECIES:
+		var raw: String = FileAccess.get_file_as_string("%s/%s.json" % [SPECIES_DIR, name])
+		if raw == "":
+			continue
+		var id: int = int(_fauna.call("register_species_from_json", raw))
+		if id < 0:
+			continue
+		for cell: Vector2i in [Vector2i(6, 5), Vector2i(7, 5), Vector2i(6, 6), Vector2i(18, 10)]:
+			_fauna.call("seed_population", cell.x, cell.y, id, 25.0)
+
+
+func _snapshot_populations() -> Dictionary:
+	var out: Dictionary = {}
+	for row: int in range(MAP_H):
+		for col: int in range(MAP_W):
+			var slots: Array = _fauna.call("populations_on_tile", col, row)
+			if slots.is_empty():
+				continue
+			var total: float = 0.0
+			for s: Dictionary in slots:
+				total += float(s.get("population", 0.0))
+			if total > 0.01:
+				out[Vector2i(col, row)] = total
+	return out
+
+
+func _print_stats() -> void:
+	print("=== Increment 3a — Living-World Ecology Proof ===")
+	print("Grid: %dx%d, %d turns, seed %d" % [MAP_W, MAP_H, TURNS, SEED])
+	print("Populated tiles: before=%d after=%d (delta +%d)" % [
+		_before_tiles, _after_tiles, _after_tiles - _before_tiles
+	])
+	print("Total slots after: %d" % int(_fauna.call("population_slot_count")))
+	print("Peak tile population: %.2f" % _peak_pop)
+
+
+func _draw() -> void:
+	var font: Font = ThemeDB.fallback_font
+	draw_string(
+		font, Vector2(MARGIN.x, 28),
+		"Increment 3a — Living World: fauna evolve through the live bridge "
+		+ "(emergence + Lotka-Volterra + dispersal + migration) — %dx%d, %d turns"
+		% [MAP_W, MAP_H, TURNS],
+		HORIZONTAL_ALIGNMENT_LEFT, -1, 18, Color.WHITE
+	)
+
+	_draw_panel(MARGIN.x, 56, "BEFORE — turn 0 (seeded clusters): %d tiles" % _before_tiles, _before)
+	var panel2_x: float = MARGIN.x + MAP_W * CELL + 60
+	_draw_panel(panel2_x, 56, "AFTER — turn %d (spread): %d tiles" % [TURNS, _after_tiles], _after)
+
+	# Verdict banner.
+	var verdict_y: float = 56 + 28 + MAP_H * CELL + 36
+	var grew: bool = _after_tiles > _before_tiles
+	draw_string(
+		font, Vector2(MARGIN.x, verdict_y),
+		"VERDICT: %s — populated tiles %d → %d (%+d). The world is alive and evolving each turn."
+		% ["PASS" if grew else "FAIL", _before_tiles, _after_tiles, _after_tiles - _before_tiles],
+		HORIZONTAL_ALIGNMENT_LEFT, -1, 16,
+		Color(0.4, 0.9, 0.4) if grew else Color(0.9, 0.4, 0.4)
+	)
+	draw_string(
+		font, Vector2(MARGIN.x, verdict_y + 26),
+		"Colour = total fauna population on tile (dark green → bright yellow). "
+		+ "Grey grid = land tiles with no fauna.",
+		HORIZONTAL_ALIGNMENT_LEFT, -1, 13, Color(0.75, 0.75, 0.75)
+	)
+
+
+func _draw_panel(ox: float, oy: float, label: String, pops: Dictionary) -> void:
+	var font: Font = ThemeDB.fallback_font
+	draw_string(font, Vector2(ox, oy - 6), label, HORIZONTAL_ALIGNMENT_LEFT, -1, 15, Color.WHITE)
+	for row: int in range(MAP_H):
+		for col: int in range(MAP_W):
+			var x: float = ox + col * CELL
+			var y: float = oy + row * CELL
+			var key: Vector2i = Vector2i(col, row)
+			var color: Color = Color(0.18, 0.18, 0.18)  # empty land
+			if pops.has(key):
+				var frac: float = clampf(float(pops[key]) / _peak_pop, 0.0, 1.0)
+				# dark green → bright yellow ramp
+				color = Color(0.15 + frac * 0.80, 0.35 + frac * 0.55, 0.10)
+			draw_rect(Rect2(x, y, CELL - 2, CELL - 2), color)
+
+
+func _capture_and_quit() -> void:
+	if _captured:
+		return
+	_captured = true
+	DirAccess.make_dir_recursive_absolute(ProjectSettings.globalize_path(OUTPUT_DIR))
+	var image: Image = get_viewport().get_texture().get_image()
+	if image == null:
+		push_error("WorldsimEcologyProof: failed to get viewport image")
+		get_tree().quit(1)
+		return
+	var ts: String = Time.get_datetime_string_from_system().replace(":", "-").replace("T", "_")
+	var abs_path: String = ProjectSettings.globalize_path(
+		"%s/worldsim_ecology_proof_%s.png" % [OUTPUT_DIR, ts]
+	)
+	var err: Error = image.save_png(abs_path)
+	if err == OK:
+		print("SCREENSHOT_PATH:%s" % abs_path)
+		print("Screenshot: %dx%d saved" % [image.get_width(), image.get_height()])
+	else:
+		push_error("WorldsimEcologyProof: save failed: %s" % error_string(err))
+	get_tree().quit()
diff --git a/src/game/engine/scenes/tests/worldsim_ecology_proof.gd.uid b/src/game/engine/scenes/tests/worldsim_ecology_proof.gd.uid
new file mode 100644
index 00000000..5457fb63
--- /dev/null
+++ b/src/game/engine/scenes/tests/worldsim_ecology_proof.gd.uid
@@ -0,0 +1 @@
+uid://bf47tl87kj58y
diff --git a/src/game/engine/scenes/tests/worldsim_ecology_proof.tscn b/src/game/engine/scenes/tests/worldsim_ecology_proof.tscn
new file mode 100644
index 00000000..bbd91442
--- /dev/null
+++ b/src/game/engine/scenes/tests/worldsim_ecology_proof.tscn
@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=3 uid="uid://c7w0rld5imec0pr0"]
+
+[ext_resource type="Script" path="res://engine/scenes/tests/worldsim_ecology_proof.gd" id="1_script"]
+
+[node name="WorldsimEcologyProof" type="Node2D"]
+script = ExtResource("1_script")