diff --git a/guide/age-of-four/src/components/toc/TableOfContents.tsx b/guide/age-of-four/src/components/toc/TableOfContents.tsx
index 399576f6..0e5f65af 100644
--- a/guide/age-of-four/src/components/toc/TableOfContents.tsx
+++ b/guide/age-of-four/src/components/toc/TableOfContents.tsx
@@ -102,6 +102,7 @@ const NAV: NavGroup[] = [
       { to: '/climate/weather',     icon: '⛈',  label: 'Weather' },
       { to: '/climate/terrain',     icon: '🌿', label: 'Terrain Evolution' },
       { to: '/climate/survival',    icon: '🛡', label: 'Survival' },
+      { to: '/climate/ecosystem',   icon: '🦌', label: 'Ecosystem' },
       { to: '/climate/simulation',  icon: '🎬', label: 'Simulation' },
     ],
   },