Wherever a habitat patch borders a different land use, altered wind, light and moisture penetrate inward from the boundary a fixed distance d (the edge-penetration depth). Only the habitat farther than d from every edge keeps the stable, buffered "core" microclimate that interior specialists need — the rest is edge-affected habitat, tolerated mainly by generalists.
core side = max(0, patchSide − 2d)
core area = coreSide²
edge area = patchArea − coreArea
Splitting one large patch into several small ones of the same combined area multiplies the total perimeter, so the edge band eats a much bigger share of each fragment. Push the depth slider up or the fragment count up and watch the fragmented core bar collapse toward zero while the single patch still holds a solid core.
- Edge penetration depth — how far degraded microclimate reaches inward from any boundary; deeper-penetrating edges (open farmland, wide roads) shrink core habitat fastest.
- Fragments — breaks the same total area into an n×n grid of smaller patches, holding total area fixed while perimeter-to-area ratio rises sharply.
- Total habitat area — the combined footprint shared identically by both scenarios, so any core-area gap is due purely to shape, not to losing land.
Real-world relevance: this is why a single 100-hectare forest reserve protects far more true interior-forest bird and amphibian habitat than ten 10-hectare fragments of the same combined area — even though no land was "lost," most of the small fragments' area is edge-affected.