Rarity-weighted Species Richness
This layer highlights places dominated by range-restricted and endemic species.
Category: Transition risks · Invasive Species Coverage: Global Format: Raster grid Used in risk analysis: Yes — gates Invasive species
What it shows
This layer highlights places dominated by range-restricted and endemic species. Rather than simply counting how many species occur in a location, it gives more weight to species with small global ranges, so areas rich in narrowly distributed species stand out. It is widely used as a proxy for biodiversity sensitivity and conservation value, flagging regions where biological impacts — such as biological invasions or habitat loss — would carry disproportionately high consequences.
How it is built
The index is a global spatial dataset in which each species' contribution to local richness is weighted by the inverse of its geographic range size. Species with very small ranges therefore contribute strongly to the score where they occur, while wide-ranging species contribute little. Summed across all species present, this produces a continuous surface that emphasises endemism and irreplaceability. The result is delivered as a global grid of values.
How to read it
Higher values indicate a concentration of range-restricted and endemic species, meaning greater biodiversity sensitivity and a higher potential cost of disturbance at that location. Lower values indicate areas dominated by more widespread species. In this layer the score is used as an inverse proxy for vulnerability to invasive species: places richest in rare, range-restricted species are treated as most sensitive to disruption.
Source
Rarity-Weighted Species Richness (RWSR), a global spatial dataset weighting species by the inverse of their geographic range size. (No explicit attribution provided with the layer.)
Comparison with the WWF Risk Filter Suite
This layer maps to WWF Biodiversity Risk Filter indicator S14_6 Range Rarity, with which it is aligned (both draw on the IUCN Red List range-rarity family). Darwin additionally uses it as an inverse proxy for S13_3 Invasive Species. That second use is a deliberate proxy mismatch: Darwin gates on habitat rarity and vulnerability, whereas WWF's S13_3 measures actual invasive-species presence (from CABI, 2024). The invasive-species reading should therefore be understood as indicative rather than a direct equivalent.
Risk analysis
A site is flagged on a dimension by combining a proximity trigger (this layer) with an activity trigger (the entity's ENCORE pressure/service). Proximity only → Potentially material; proximity and the matching ENCORE pressure/service is material → Very material; neither → Not material.
| Dimension | ENCORE service / pressure | Proximity trigger (this layer) | Activity trigger (entity) |
|---|---|---|---|
| Invasive species | Introduction of invasive species | Layer value above 0.05 | “Introduction of invasive species” pressure ≥ 4 |
Legend
Symbolised field: Rarity score
| Class | Colour |
|---|---|
| Low | #add8e6 |
| High | #ff0000 |
Generated from darwin/layers/layer-rarity-weighted-species-richness.toml and risk_indicator_pairs.toml (develop).