When family matters: an analysis of Thelotremataceae (Lichenized Ascomycota: Ostropales) as bioindicators of ecological continuity in tropical forests

We analysed patterns of habitat and microhabitat preferences of 19 families (comprising 135 genera and 950 species) of crustose, corticolous lichens in Costa Rica (Arthoniaceae, Arthopyreniaceae, Coenogoniaceae, Graphidaceae, Lecanoraceae, Letrouitiaceae, Monoblastiaceae, Pertusariaceae, Physciaceae, Pilocarpaceae, Porinaceae, Pyrenulaceae, Ramalinaceae, Roccellaceae, Strigulaceae, Teloschistaceae, Thelenellaceae, Thelotremataceae, Trypetheliaceae), in order to test whether Thelotremataceae are suitable predictors of undisturbed tropical rain forest and can be used as bioindicators of ecological continuity. The dataset consisted of 12,215 specimen samples and six environmental parameters recorded for each sample (altitude, degree of seasonality, vegetation type, disturbance level, substrate nature, light exposure), which were analysed by a multivariate approach using principal component analysis (PCA). The analysis showed that three of the 19 families, Letrouitiaceae, Porinaceae, and Thelotremataceae, showed significant preferences for undisturbed primary to old growth secondary forest, fully shaded to semi-exposed microhabitats, and the bark of mature tree trunks, parameters assumed to be correlated with ecological continuity of closed rain forest habitats. Thelotremataceae had broader altitudinal range than Letrouitiaceae and Porinaceae and significantly higher genus and species diversity (16 genera, 130 species) compared to Porinaceae (4 genera, 40 species) and Letrouitiaceae (1 genus, 5 species). Our results support the hypothesis that Thelotremataceae perform best as predictors of undisturbed dry and lowland to montane rain forest and are the most suitable lichen bioindicators of ecological continuity in these ecosystems. In contrast, Lecanoraceae, Pertusariaceae, Physciaceae, and Teloschistaceae, were found to be predictors of disturbed and pioneer (micro-)habitats. We also found that, among a variety of parameters tested, the Index of Ecological Continuity (IEC), adapted to the use of Thelotremataceae in tropical forests, performs best in terms of predicting disturbance levels and site history. A semi-taxonomic approach identifying morphotypes rather than genera or species yielded the same results, making this method suitable for a broader spectrum of potential users.