Atractylis arbuscula Svent. & Michaelis (Asteraceae): Two insular endemics from the Canary Islands with different conservation scenarios

Plants from arid environments can prevail with low fecundity, high survival and long lifespans. However, climate change may have an important impact on endangered species. In order to assess the effect of climatic fluctuations and change, we studied demographic processes in the narrow-range Canary Islands endemic Atractylis arbuscula Svent. & Michaelis. It is considered a threatened taxon of arid ecosystems on the islands of Lanzarote (A. arbuscula ssp. arbuscula) and Gran Canaria (A. arbuscula ssp. schizogynophylla (Svent. and Kahne) Marrero Rodr. & Caujape acute accent ). Monitoring was initiated in 2011 and conducted annually for six consecutive years to study population dynamics. Deterministic simulations showed that the population subjected to greater aridity (ssp. arbuscula) underwent an expansive trend. In contrast, the Gran Canaria population, presenting decline, seems not to benefit from higher annual precipitation. Spring precipitation is a good predictive variable that best explains the finite rate of population increase (lambda) variability, determining "good years " with wet springs and "bad years " with dry springs. With the climate projections for the 21st century of the spring precipitation for the stations closest to the studied populations, we obtained for each year of the period 2017-2100 a random vector that determines the probability with which each of the five matrices can be selected. The stochastic projections carried out reveal that ssp. arbuscula may experience a slight decline under two scenarios based on different Representative Concentration Pathways (RCPs): RCP45 and RCP85, although the probability of extinction is zero in both. However, ssp. schizogynophylla could decline much faster, especially in scenario RCP85, reaching a 100% probability of extinction by the end of the century. In conclusion, the population stability of ssp. arbuscula and its being included in a protected area of Lanzarote guarantees its conservation to a certain extent. However, the decline in ssp. schizogynophylla makes prompt conservation measures advisable on Gran Canaria.