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Calacalles droueti is an endemic species present in Flores, Faial and Pico islands, but considered extinct in Flores (Azores, Portugal). It has a relatively small extent of occurrence (EOO = 113 km²) that does not include Flores island and a small area of occupancy (EOO = 28 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 seven locations and is associated with an endemic rare plant (Euphorbia stygiana subsp.stygiana). Therefore, we suggest as future measures of conservation: (1) regular monitoring of the species; and (2) control of invasive species namely Hedychium gardnerianum. Based upon the small area of occupancy and continuing decline of its habitat area and quality, it is assessed as Endangered.
Calacalles droueti is an endemic species present in Flores, Faial and Pico islands, but considered extinct in Flores (Azores, Portugal) (Borges et al. 2010), known from Natural Forest Reserves of Caldeira do Faial (Faial) and Lagoa do Caiado (Pico). The extent of occurrence (EOO) is 113 km² and the maximum estimated area of occupancy (AOO) is 28 km².
The species is very rare and only known from a single subpopulation in Faial island and several subpopulations in Pico island. A continuing decline in the number of mature individuals is inferred due to host-plant rarity (Euphorbia stygiana subsp. stygiana). This species is assessed here as severely fragmented as at least 50% of its population can be found in subpopulations that are 1) smaller than would be required to support a viable population, and 2) separated from other habitat patches by a large distance. In fact, the species occurs in fragments that are isolated in a matrix of pastures.
The species occurs in native forests of high altitude in the Faial and Pico islands (Azores), with an altitudinal range between 600 and 1200 m. Adults and larvae are nocturnal herbivores and feed of plant tissues of Euphorbia stygiana subsp. stygiana.
In the past, the species has probably strongly declined due to changes in habitat size and quality (Triantis et al. 2010, Terzopoulou et al. 2015). Currently invasive plants (Hedychium gardnerianum) are changing some of the areas and decreasing the quality of the habitat, since are changing the habitat structure, 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 further decline as a consequence of climate change (increasing number of droughts and habitat shifting & alteration). Other important threat is the extreme rarity of the host plant.
The species is protected by regional law (RAA 2012). Its habitat is in regionally protected areas (Natural Parks of Faial and Pico). A habitat management plan is needed and anticipated to be developed during the coming years. The conservation of the host plant is critical. Since this species occurs in relict native Azorean forests and associated also with a very rare plant, it is suggested that some awareness measures should be put in practice. Further research is needed into its ecology and life history in order to find extant specimens in other sites with the host plant, 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 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).