How much matching there is in functional, phylogenetic and taxonomic optima of epiphytic macrolichen communities along a European climatic gradient?

Adopting an integrative approach that explicitly includes the different facets of biodiversity is crucial to assess the response of biological communities to changing environments. The identification of the optimal climatic conditions where communities maximize their functional, phylogenetic and taxonomic diversity is useful to compare whether the optima of the different facets of biodiversity match. Using a wide climatic gradient across Europe, we quantified the functional, phylogenetic and taxonomic diversity of epiphytic macrolichen communities, which are valuable early-warning ecological indicators. We ordinated 22 environmental variables and simultaneously illustrated non-parametric regressions of the diversity metrics against the climatic space using the 'hilltop plot' method to detect the climatic conditions in which the different diversity facets peaked and to compare the match between them. Functional diversity predicted at least part of the peaks of phylogenetic and taxonomic diversity, but phylogenetic and taxonomic hotspots did not overlap. Epiphytic macrolichen communities maximized their functional and phylogenetic diversity in the southernmost forests, with the Mediterranean region appearing as a biodiversity hotspot. Regarding the studied traits, photobiont type and growth form showed clearly defined optima while the quantitative physiological traits and families' optima did not show this pattern in response to climate. The different facets of biodiversity were not surrogates of each other highlighting the need for an integrative approach to assess the effect of environmental changes on communities and to establish conservation priorities. As functional traits mediated the response of lichen communities to climate, preserving high functional diversity might indirectly preserve high phylogenetic and taxonomic diversity. Relevant ecological indicators useful to develop rapid assessment methods to evaluate the effects of climatic changes include the photobiont type and growth form. The lack of relation between quantitative traits and climate call for further research to unveil their role as ecological indicators of small-scale variables or as effect traits.