Criteria: B1a(i)b(iii); B2a(i)b(iii)
Categories & Criteria version: 3.1 · Guidelines version: 16 (March 2024)
Sensitivity analysis using island-adapted thresholds (González-Mancebo et al. 2012): AOO = 21 cells of 0.25 km²; EOO thresholds CR < 5 / EN < 50 / VU < 500 km².
This species is assessed as Endangered (B1a(i)b(iii); B2a(i)b(iii)) because the extent of occurrence (EOO) is 841.7 km² (below the EN threshold of 5,000 km²) and the area of occupancy (AOO) is 56 km² (below the EN threshold of 500 km²). It is known from 11 locations on a single island (Tenerife), and the population is severely fragmented [subcriterion a(i)] — each lava tube constitutes an isolated subpopulation with no gene flow, owing to the species’ troglobitic habits and zero dispersal capacity between caves. A continuing decline is inferred in the extent and quality of its habitat [subcriterion b(iii)] based on documented threats: urbanisation near cave entrances, uncontrolled speleotourism, pollution (solid waste, stormwater contamination), the invasive congeneric Dysdera crocata (recorded in caves; Macías-Hernández et al. 2016), and climate change progressively altering the cave microclimate on which troglobitic fauna depends.
Sensitivity analysis: Under island-adapted thresholds (González-Mancebo et al. 2012), designed to account for the inherently restricted geographic ranges of Canarian endemics (Martín 2009), this species is reclassified as Vulnerable (VU). The EOO (841.7 km²) exceeds the adapted EN threshold of 50 km², and the 21 cells of 0.25 km² fall at the VU threshold of ≤20 cells. This suggests that part of the standard EN classification may reflect the “island effect” rather than genuine heightened extinction risk, though the documented habitat threats remain a genuine concern.
The species is endemic to the Canary Islands (Spain), known from a single island (Tenerife). The extent of occurrence (EOO) is estimated at 841.7 km² (minimum convex polygon) and the area of occupancy (AOO) at 56 km² (2 × 2 km grid cells).
Biogeographic realm: Palearctic
| Country | Presence | Origin | Seasonality |
|---|---|---|---|
| Spain | Extant | Native | Resident |
| Spain → Canary Islands (Tenerife) | Extant | Native | Resident |
Red circles: occurrences (click for coordinates); orange cells: AOO (2×2 km); blue dashed: EOO (MCP). Layer control top-right.
| Parameter | Value |
|---|---|
| Total records | 326 |
| Unique coordinates | 21 |
| EOO (MCP) | 841.7 km² |
| AOO (2×2 km, IUCN standard) | 56 km² (14 cells) |
| AOO (0.5×0.5 km, GM2012) | 5.25 km² (21 cells) |
| Locations (IUCN sense) | 11 |
| Islands | 1 (Tenerife) |
| Criterion | Threshold | Value | Meets? |
|---|---|---|---|
| B1 CR: EOO < 100 km² | 100 | 841.7 | No |
| B1 EN: EOO < 5,000 km² | 5,000 | 841.7 | Yes |
| B2 CR: AOO < 10 km² | 10 | 56 | No |
| B2 EN: AOO < 500 km² | 500 | 56 | Yes |
| D2: AOO < 20 km² or locs ≤ 5 | 20 / 5 | 56 / 11 | No |
Subcriteria check (need ≥ 2 of a, b, c):
→ Two subcriteria met → B1a(i)b(iii); B2a(i)b(iii) = EN
| Criterion | Adapted threshold | Value | Meets? |
|---|---|---|---|
| B1 CR: EOO < 5 km² | 5 | 841.7 | No |
| B1 EN: EOO < 50 km² | 50 | 841.7 | No |
| B1 VU: EOO < 500 km² | 500 | 841.7 | No |
| B2 CR: AOO ≤ 1 cell | 1 | 21 | No |
| B2 EN: AOO ≤ 5 cells | 5 | 21 | No |
| B2 VU: AOO ≤ 20 cells | 20 | 21 | Yes (= threshold) |
| NT: EOO < 1,000 km² or AOO ≤ 80 cells | 1000 / 80 | 841.7 / 21 | Yes |
→ B2 meets VU threshold (≤ 20 cells) with a(i) + b(iii) → VU under GM2012
| Framework | Category | Criteria |
|---|---|---|
| IUCN standard (v16) | EN | B1a(i)b(iii); B2a(i)b(iii) |
| Island-adapted (GM2012) | VU | B2a(i)b(iii) |
The species drops one category under the adapted framework because its EOO (843.8 km²) exceeds the adapted EN threshold of 50 km², and its 20 cells of 0.25 km² sit exactly at the VU boundary. This suggests that the EN classification under standard thresholds partly captures the “island effect” — restricted range inherent to being an island endemic — rather than exclusively reflecting genuine elevated extinction risk. However, documented habitat threats (especially pollution in Cueva Felipe Reventón and invasive D. crocata) support that this species faces real, ongoing habitat degradation.
Known from 326 specimen records across 21 unique localities on Tenerife. No quantitative population estimates available. Current population trend: Decreasing (inferred from habitat decline).
Dysdera cribellata is a troglobitic endemic spider of the Canary Islands. Canarian Dysdera have undergone an adaptive radiation into subterranean habitats (volcanic lava tubes and MSS), with many species showing troglomorphism (eye reduction, depigmentation, elongated appendages). Specialised predator of cave-dwelling isopods.
| Habitat (IUCN) | Season | Suitability | Major importance |
|---|---|---|---|
| 7.1 Caves & Subterranean Habitats → Caves | Resident | Suitable | Yes |
| 7.2 Caves & Subterranean Habitats → Other (MSS) | Resident | Suitable | Yes |
System: Terrestrial · Generation length: Unknown (estimated 2–4 years)
| Code | Threat | Timing | Scope | Severity |
|---|---|---|---|---|
| 1.1 | Housing & urban areas | Ongoing | Minority (<50%) | Slow, significant declines |
| 1.3 | Tourism & recreation areas | Ongoing | Minority (<50%) | Slow, significant declines |
| 6.1 | Recreational activities (caving, speleotourism) | Ongoing | Minority (<50%) | Slow, significant declines |
| 7.3 | Other ecosystem modifications (entrance sealing, quarrying) | Ongoing | Minority (<50%) | Rapid declines |
| 8.1.2 | Invasive non-native: Dysdera crocata (in lava tubes) | Ongoing | Minority (<50%) | Unknown |
| 9.1.1 | Sewage (stormwater run-off into caves) | Ongoing | Minority (<50%) | Slow, significant declines |
| 9.4 | Garbage & solid waste (illegal dumping in caves) | Ongoing | Minority (<50%) | Slow, significant declines |
| 11.1 | Climate change: habitat shifting & alteration (cave microclimate) | Ongoing | Whole (>90%) | Slow, significant declines |
| 11.2 | Climate change: droughts | Ongoing | Whole (>90%) | Unknown |
Parts of the range may fall within Parque Rural de Anaga or Parque Rural de Teno (Tenerife). No specific management plans exist for cave-dwelling arachnid fauna. Not listed in the Catálogo Español de Especies Amenazadas.
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