IUCN SSC Mid-Atlantic Island Invertebrates Specialist Group

Species

BackOecobius selvagensis Wunderlich, 1995

Oecobius selvagensis Wunderlich, 1995

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Arachnida
  • Order: Araneae
  • Family: Oecobiidae
CR Critically Endangered
IUCN Red List Status:

Countries of Occurrence:
Portugal - Madeira

Archipelago(s):
Madeira

Assessor/s:
Luis Crespo
Mario Boieiro
Paulo A.V. Borges
Pedro Cardoso
Cardoso, P., Crespo, L.C., Silva, I., Borges, P. & Boieiro, M.

Reviewer/s:
Henriques, S. & Russell, N.

Contributor/s:

Facilitators / Compilers/s:


Assessment Rationale:

Oecobius selvagensis is probably restricted to two caves on the Selvagem Grande Island (Portugal). This species has a restricted geographic range, with an extent of occurrence (EOO) and area of occupancy (AOO) of only 4 km². The major threat is the spread of the invasive congener O. navus, which may be outcompeting the species in part of its range. Due to this threat, Oecobius selvagensis occurs in only one location and there is a continuing decline in EOO, AOO, number of mature individuals and the extent of the habitat. This species is therefore assessed as Critically Endangered (CR). More research on the distribution and threats is urgently needed. The habitat and the species should be protected and properly managed to avoid any future declines.

Geographic Range:

The species is probably restricted to the Selvagem Grande Island (Portugal) between Madeira and the Canary Islands, where it was found in an unnamed erosion coastal cave in 1958 (Denis 1963, Rambla 1978, Wunderlich 1992). Two caves are now the entire known range of the species. The extent of occurrence (EOO) and area of occupancy (AOO) are both 4 km².

Regions:
Portugal - Madeira
Extent of Occurrence (EOO):
4 (km2)
Area of Occupancy (AOO):
4 (km2)
Elevation Lower Limit:
0 (m)
Elevation Upper Limit:
160 (m)
Biogeographic Realms:
Palearctic
Presence:
Extant
Origin:
Endemic Madeira
Seasonality:
Resident

Population:

No population size estimates exist, but the population is assumed to be declining due to the threat of invasive species.

 

Habitat and Ecology

This species is only known from two caves. It is probable that this is a species that lives underground due to the two known localities being inside of caves and it being largely depigmented. Congeners build small flat webs where they hunt for small insects.

Major Threat(s):

The cosmopolitan congener O. navus is now commonly seen, even in caves, after being detected on the island for the first time before 1978. It is possible that there is a gradual replacement of one species by the other, although this, for now, is only suspected. Therefore the cosmopolitan O. navus may be outcompeting the species in part of its range.

Conservation Actions

No specific conservation measures are in place for this species, but the island of Selvagem Grande is part of the Selvagens Nature Reserve. If competition is confirmed, the invasive O. navus should be controlled. As this task is probably impossible, ex-situ conservation with eventual reintroduction and recovery might be the only feasible measure to prevent further reduction of O. selvagensis. The current distribution of the species and possible threats from the invasive congener should be thoroughly studied. If outcompeted, O. selvagensis should be the target of a species conservation plan with consequent area management actions.