Unveiling patterns of vulnerability across habitats in heterogeneous mountain landscapes

Héctor Miranda Cebrian, María B. García and Manuel Pizarro Gavilán, Pyrenean Institute of Ecology, Spanish National Research Council, Zaragoza, Spain, Héctor Miranda Cebrian, Rey Juan Carlos University, Madrid, Spain, Xavier Font, University of Barcelona, Spain, Cristina Roquet, Autonomous University of Barcelona, Spain

Background/Question/Methods: Biodiversity is being severely affected by global change worldwide. In order to better assess and compare differences in vulnerability of sites or habitats, and consequences in terms of loss of biodiversity, we need first to understand the way different components distribute and the vulnerability of the species they shelter. Here, we explored the patterns of alpha taxonomic (richness) and phylogenetic diversity (PD) across a mountain range in southern Europe, the Pyrenees (400-3400 m a.s.l.), a complex landscape sheltering a very diverse flora of more than 3400 plants. More than 18,000 plant surveys spanning multiple habitats were analyzed. In addition, we classified plant species according to three kinds of rarity, and estimated their frequency among habitats as a proxy for vulnerability. Then, we asked which habitats (1) shelter the highest diversity in terms of species richness and PD; and (2) could be more vulnerable due to the type and frequency of rare species. Mixed effect models were used for the analyses.
Results/Conclusions: Richness and phylogenetic diversity varied greatly among habitats, although the overall correlation between both measures was negative. Grasslands harbored the greatest number of species but were poor in PD, while habitats such as rocky cliffs, screes or water bodies contained fewer species but were more phylogenetically diverse. Deciduous, evergreen and Mediterranean forests showed both high species richness and PD. Rare species accounted for half of the regional species pool, represented an average of 22% of the species in each habitat, and were more abundant in habitats with fewer species and higher PD. Different habitats were characterized by different rates and types of rarity, but surface water bodies, inland cliffs and screes had much higher proportions of rare species than the rest. In this study, we provide valuable insight on how different metrics of diversity distribute across habitats in heterogeneous landscapes. Metrics often show opposite tendencies, emphasizing that they are not interchangeable. Our results highlight the theoretical vulnerability of rocky and inland water related habitats due to the abundance of rare species, which are assumed to be more vulnerable. However, these findings should be combined with future research exploring how different global change drivers such as climatic and land use change, affect each particular habitat too.