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Caulotrupis parvus is endemic to Santa Maria (Azores, Portugal). It has a very small extent of occurrence (EOO = 8 km²) and area of occupancy (AOO = 8 km²). There is a continuing decline in the EOO, AOO, extent and quality of habitat as well as the number of mature individuals as a result of the invasions of non-native plants. The species occurs only at two locations. Therefore, it is assessed as Critically Endangered (CR).
Caulotrupis parvus is a single island endemic species from Santa Maria (Azores, Portugal) (Borges et al. 2010), where it is restricted to the highest elevations of the island (310 to 550 m Asl) and to the unique native primary forests. However the species was also found recently by Meijer et al. (2011) in a Cryptomeria japonica plantation, which is to be cut down soon. The size of its remaining native habitat is 0.09 km², but the AOO is 8 km². Its extent of occurrence (EOO) is therefore also 8 km².
The species is very rare and only known from a single sustainable subpopulation, since the second known location is a Cryptomeria japonica plantation threatened by deforestation. A continuing decline in the number of mature individuals is inferred from the ongoing habitat degradation due to invasions of alien plants in the main native forest patch, and deforestation of production plantation of Cryptomeria japonica.
The species occurs in the native forests of the Azores, surrounded by plantations of exotic trees and pastures, but also found in a Cryptomeria japonica plantation. This species has an range between 310 and 550 m Asl. It feeds on dead wood.
In the past, the species has probably strongly declined due to deforestation. The most important ongoing threat to this species is the spread of invasive plants (Hedychium gardnerianum and Pittosporum undulatum) that are changing the habitat structure in the main native forest, namely decreasing the cover of bryophytes and ferns in the soil and promoting the spread of other plants. Based on Ferreira et al. (2016) the habitat will decline as a consequence of climate change (increasing number of droughts), which may drive this species to extinction, because it is depending on humid forests.
The species is protected by regional law (RAA 2012). Its habitat is in a regionally protected area (Santa Maria Natural Park). The Santa Maria Natural Park administration is currently starting control measures of the invasive plants. Further spread of invasive plants needs to be stopped in order to avoid any future declines of the species. Degraded habitats should be restored and a strategy needs to be developed to address the future threat by climate change. A habitat management plan is needed and anticipated to be developed during the coming years. Further research is needed into its ecology and life history in order to find extant specimens and obtain information on population size, distribution and trends. It is also necessary an area-based management plan and a monitoring plan for the invertebrate community in the Pico Alto native forest and surrounded areas of non-native habitat in order to contribute to perform a species potential recovery plan. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2011).