Species

BackTheba macandrewiana (L. Pfeiffer, 1853)

Theba macandrewiana (L. Pfeiffer, 1853)

  • Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Gastropoda
  • Order: Pulmonata
  • Family:
NT Near Treatened
IUCN Red List Status:

Countries of Occurrence:
Portugal - Madeira

Archipelago(s):
Madeira

Assessor/s:
Dinarte Teixeira

Reviewer/s:
Cameron, R., Seddon, M.B. & Groh, K.

Contributor/s:

Facilitators / Compilers/s:


Assessment Rationale:

This species is endemic to Portugal, where it is restricted to the three Selvages Islands, in the Atlantic Ocean. It is assessed as Near Threatened (NT), as it is only known from three locations and it has a restricted range. There are possible threats in the longer term due to climate change. However now the habitats have been restored and the predatory invasive species were removed during the early 2000s, hence the population is now stable. There is an active habitat management programme, hence whilst the species at present is considered not to be threatened, the Near Threatened assessment reflects the possible change in conservation status in the longer term. 

Geographic Range:

This species is endemic to Portugal, where it is restricted to the three Selvages Islands, in the Atlantic Ocean (Backhuys 1972, GBIF 2007, Abreu and Teixeira 2008). The species is particularly found at Ilha Selvagens Grande (Gran Salvage), Ilha Selvagem Pequena (Gran Piton), and Ilhéu de Fora (La Salvajita, Little Piton). On Ilha Selvagens Grande it is only found living on the southeastern side (D. Teixeira pers. comm. 2016).

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

Population:

The subpopulations on the three Selvagens Islands remain stable, with no extreme fluctuation detected on the period between 2008 and 2014 (D. Teixeira pers. comm. 2016). Living animals have been found together with many empty shells.

Habitat and Ecology

This species is the only non-marine gastropod species known from the Selvagens Islands (Gittenberger and Ripken 1987). It occurs on rocky and sandy soils, beneath rocks or associated to grasses. 

Major Threat(s):

There are possible soil erosion events after rainstorms, that may locally cause population fluctuations, mainly at Selvagem Grande. All rabbits and mice have now been eradicated from the islands. Native lizards may predate on the eggs. Possible threats are landslides, which could partially affect the marginal subpopulations on Selvagem Pequena, as well as continuous droughts and flooding (D. Teixeira pers. comm. 2016). In the longer term the species could be threatened by increased frequency of droughts and sea level changes. 

Conservation Actions

Habitat restoration and recovery were successfully implemented in 2000 on Selvagem Grande, eliminating the tobacco tree (Nicotiana glauca), mice (Mus musculus) and rabbits (Oryctolagus cuniculus) from this island. Currently there are no known conservation actions for this species and none are considered necessary.