Lichen fungi in the Atlantic rain forest of Northeast Brazil: the relationship of species richness with habitat diversity and conservation status

Although lichens develop their highest biomass in cool-temperate climates, lichen fungi may form highly diverse assemblages in tropical lowland rain forests. The reasons for such high species richness are not well known. The present study tested the hypothesis that lichen diversity in the northern Atlantic rain forest mainly depends on habitat diversity and conservation status of forest fragments. To this end, the known lichen biota of 23 forest remnants in the region was analyzed. We identified 784 species, with 11 taxa newly reported from Brazil and 44 from Bahia. The vast majority (711) are principally corticolous, while 53 are saxicolous and 20 terricolous. The most frequent species in terms of site occurrence were found at 13 sites, whereas over half of the taxa (462) were only found at a single site. This coincides with an overall low average sampling score, with only six sites being moderately well to well sampled. The number of species per site varied between 5 and 371. Multiple linear regression of species richness with the parameters, site extension, habitat diversity, sampling effort, conservation status, and elevation, was strong and highly significant, with site extension, habitat diversity, and sampling effort being the best predictors for species richness. Site ordination based on species composition suggested a correlation with conservation status and species richness, as well as site extension and habitat diversity. There was no overall correlation between species composition and geographical location of sites along a north-south gradient, but an underlying pattern was detected, suggesting some species turnover along a macroecological gradient. A predictive model using a combined score from the five parameters resulted in a strong and highly significant linear correlation with observed species richness. Using a quantitative, site-based method, we predicted a minimum of 44 and a maximum of 583 species per studied site and we estimated the overall richness for the northern Atlantic rain forest to be 1017 species. Traditional estimators (Chao 1, Chao 2, Jackknife 1, Jackknife 2, Bootstrap) resulted in predicted values ranging between 971 and 1527 species overall. The results of the study are relevant for conservation priorities, as they show that well-conserved areas with a higher habitat diversity (e.g., including transitional forest types and open areas) are an important component preserving the original diversity of the Atlantic Rain Forest, accounting for a large part of the extant biodiversity of this biome.