Integrating dark diversity and functional traits to enhance nature conservation of epiphytic lichens: a case study from Northern Italy

Abstract

Mountains provide a timely opportunity to examine the potential effects of climate change on biodiversity. However, nature conservation in mountain areas have mostly focused on the observed part of biodiversity, not revealing the suitable but absent species—dark diversity. Dark diversity allows calculating the community completeness, indicating whether sites should be restored (low completeness) or conserved (high completeness). Functional traits can be added, showing what groups should be focused on. Here we assessed changes in taxonomic and functional observed and dark diversity of epiphytic lichens along elevational transects in Northern Italy spruce forests. Eight transects (900–1900 m) were selected, resulting in 48 plots and 240 trees, in which lichens were sampled using four quadrats per tree (10 × 50 cm). Dark diversity was estimated based on species co-occurrence (Beals index). We considered functional traits related to growth form, photobiont type and reproductive strategy. Linear and Dirichlet regressions were used to examine changes in taxonomic metrics and functional traits along gradient. Our results showed that all taxonomic metrics increased with elevation and functional traits of lichens differed between observed and dark diversity. At low elevations, due to low completeness and harsh conditions, both restoration and conservation activities are needed, focusing on crustose species. Towards high elevations, conservation is more important to prevent species pool losses, focusing on macrolichens, lichens with Trentepohlia and sexual reproduction. Finally, dark diversity and functional traits provide a novel tool to enhance nature conservation, indicating particular threatened groups, creating windows of opportunities to protect species from both local and regional extinctions.

Observed and dark diversity dynamics over millennial time scales: fast life-history traits linked to expansion lags of plants in northern Europe

“…Those consequences include accelerating nutrient cycling, increasing productivity and biomass turnover, as well as herbivory and sensitivity to drought events, affecting ecosystems services and functioning [89,90]. Although focused on millennial time scale patterns, our results are in line with recent evidence suggesting dark diversity as a promising tool to assess and foreseeing biodiversity change in the Anthropocene [8,11,91].…”

“…For example, taxonomic dark diversity is expected to be low under harsher conditions, such as the Late Glacial period, because just a few species in the region would be able to cope with the extreme environmental conditions (i.e. low suitability) [8]. As soon as conditions become more favourable (e.g.…”

“…Comparing the traits in observed and dark diversity enables us to understand why these species are suitable but absent and how the filtering process operates from regional to local scales (i.e. favouring or jeopardizing certain set of traits) [6][7][8]. Since global changes alter the dispersal and suitability of species and traits across space and time, quantifying and foreseeing biodiversity change using taxonomic and functional species pool dynamics is crucial but still incipient in ecology [9][10][11].…”