Ecological features, populations traits and conservation status of Helianthemum caput-felis along its distribution range

Understanding factors limiting populations’ growth and persistence is crucial to evaluate the current conservation status and possible future management of plant populations. This Ph.D. thesis focussed on ecological constraints related to population trends and the conservation status of Helianthemum caput-felis Boiss., characterized by a highly fragmented areal isolated from the distribution centre. In particular, the specifics aims of the thesis were: (1) to analyse the distribution range, population size, the reproductive traits, the effect of human disturbance and identify the threats affecting the persistence of H. caput-felis in Sardinia following the IUCN regional protocol; (2) to investigate flowers and fruits phenology, ecological traits (geomorphology, substrate, slope and human trampling intensity) affecting reproductive outputs (as fruit and seed sets) and the presence of two ecological gradients along the entire European distribution range of the species; (3) to discover the population dynamics by the analyses of populations vital rates, both at global level than a local scale; (4) to evaluate the risk of extinction of H. caput-felis at global level, and then to assess the global conservation status of the populations, together with an accurate analysis of the global area of occupancy of the species, following the IUCN protocol. The thesis results indicate relevant aspect regarding the ecology, population dynamics, distribution and conservation traits of the species. In Sardinia, the species preferably grows in lowland areas with deep structured soil, due to the amount of water and resources available and morphological stability. H. caput-felis shows the highest reproductive output in garrigues, habitat that represents its ecologically optimum. The high seed production indicates that this is not a limiting factor for this plant, in contrast to seedling establishment, which represent its main critical stage. Surprisingly, in Sardinia, human trampling enhanced the plant size and the rate of fruits production, suggesting that reproductive plants of H. caput-felis are tolerant to direct damage, and probably benefit from the reduction of inter-specific and intra-specific competition. Comparing the phenology and reproductive output along the entire European distribution range of this species over a two year temporal context indicate that the general phenological pattern of H. caput-felis was similar among Sardinian and Majorcan regions, whereas, in the eastern Iberian populations (the western part of the distribution range), the southern population (Cabo Roig) showed a higher inter-annual variability and an early flowering period. Those differences could be related to a longitudinal aridity gradient for this plant: the aridity decreases from western to eastern localities. Plants growing at the eastern edge of the distribution range (Sardinia) produce more viable fruits, fruits per plant and seeds per fruit than the other two regions, while plants growing in arid substrate (as in the sandy habitat of Sa Ràpita, Majorca) are the least productive, confirming that sandy substrate is negatively correlated with fruits production and viable fruits, as well as lowland geomorphology. Hence, these analyses underline that the Abundant Centre Model assumptions, by which reproductive traits should be higher at the centre of species distribution, is not confirmed for H. caput-felis, maybe because the central populations, represented by the largest distribution area along the Iberian’s coasts, appear strongly fragmented mainly by human disturbance. Demographic traits of H. caput-felis population were analysed, by using demographic surveys, integrated by Matrix and Integral Projection Models (MPM and IPM, respectively). Plant performance and population dynamics were investigated in plants sampled along the comprehensive and representative part of the European distribution range in which the species occurs. The global population showed a general stability in the first year transition, after which it declined. This trend was probably due to the higher shrinkage of plants in the last year of study, which correlates negatively with reproductive traits, in agreement with the frequent increase in reproductive outputs with plant size. Despite this decline, stochastic population growth rate highlighted as H. caput-felis population oscillated around the equilibrium. Elasticity analysis indicated the higher importance of large individuals and the determinant role of the survival-growth transitions for the population growth rate. Moreover, plants reached high generation times and mean long life span, which, with the limited seedling recruitment rate and the presence of a consistent seed bank, reflect patterns that are typical both of many long-lived plants and of calcareous rupicolous Mediterranean species. IPM methods were found to be more accurate than MPM to monitoring species with restricted range, as H. caput-felis. At local level, the pattern of typical long-lived Mediterranean plants was also confirmed; in fact, populations were mainly composed from large individuals, characterized by slow growth. H. caput-felis showed vital rates and population dynamics varying among populations: the Sardinians’ seems to have greater equilibrium than Spanish populations. The high population growth rates of Moraira and Colònia de Sant Jordi were strongly influenced by the fecundity parameters. Plants growing in Moraira show a uniform shrinkage of individuals, probably due to a more intense fragmentation of the population. The different population dynamics observed among the analysed localities of H. caput-felis should be correlated to particular microclimate and ecological conditions, i.e. the high aridity of Cabo Roig and the sand substrate of Sa Ràpita, which probably affected the relationship among size and vital rates. On the contrary, H. caput-felis populations in demographic equilibrium, as the Sardinians’, could be locally adapted to ecological and microclimate conditions. Finally, population dynamics models were applied to analyse the extinction risk and then assess the global conservation status of H. caput-felis, together with an accurate analysis of the global area of occupancy of the species, following the IUCN protocol. This research highlighted that H. caput-felis should be considered an Endangered (EN) plant at global level, according to the formula B2ab (ii,iii,iv,v) + E. H. caput-felis suffered a continuing decline in AOO, quality of its habitat, number of localities and number of reproductive plants. This decline rate was mainly due to the habitat loss and the expansion of infrastructures detected in the last decades. Hence, effective future conservation measures could be focussed on protecting the single localities where H. caput-felis grows, in order to avoid further species decline. In this contest, conservation efforts primarily aimed to protect established individuals (mature plants) against disturbances, as suggested for other long-lived species. The results of this thesis gave new findings for the ecology and conservation of H. caput-felis, and demonstrate the importance to considerate both global than local level in demography and phenology studies.