Countries of Occurrence:
Portugal - Madeira
Henriques, S. & Russell, N.
Facilitators / Compilers/s:
Xysticus grohi is known from the islands of Deserta Grande and Bugio, Portugal. This species is assessed as Critically Endangered (CR) since it has a very restricted geographic range (extent of occurrence (EOO) and area of occupancy (AOO) are both only 24 km²) and there is a continuing decline in the number of mature individuals and habitat area and quality, based on the introduction of an invasive species. Due to this threat the number of locations is only one. More research is needed into the distribution, ecology and threats. The habitat of this species should be properly managed to avoid any future declines.
This species is possibly restricted to the islands of Deserta Grande and Bugio (Wunderlich 1987, Wunderlich 1992, Crespo et al. 2013, unpublished) where it is known from three sites but probably extends across the entire islands given the adequate microhabitat (steep slopes). The extent of occurrence (EOO) can be calculated with reasonable confidence.
No population size estimates exist. The introduction of the invasive X. nubilus seems to have originated the extirpation of X. grohi from most of the islands. This invasive process may continue in the future to the current refuge of the endemic species, the steep coastal slopes, and the population is therefore assumed to be declining.
This species is possibly restricted to rocky areas, now only on coastal slopes. Xysticus grohi is an ambush hunter of small insects over rocks and possibly low vegetation.
The introduction of the invasive species X. nubilus, first detected in 2011, seems to have originated the extirpation of X. grohi from most of the islands. This invasive process may continue in the future to the current refuge of the endemic species, the steep coastal slopes. The number of locations is therefore estimated to be only one.
No specific conservation measures are in place for this species, but all of the species range is inside the Desertas Nature Reserve. The invasive X. nubilus should be eradicated from the island. As this task is probably impossible, ex-situ conservation with eventual re-introduction and recovery might be the only feasible measure to prevent the species extinction. The current distribution of the species and possible threats from the invasive congener should be thoroughly studied. X. grohi should be the target of a species conservation plan with consequent area management actions. Monitoring of population trends should be conducted to confirm the species status.