Emerging pantropical patterns
The observed compositional differences among geographic regions indicate
a relatively high level of endemism even within different parts of the
Neotropics. Because our sampling of the hyperdiverse mycota in these
regions is incomplete, it is possible that more shared taxa will be
identified through the accumulation of more field data in the future.
Nonetheless, regional endemism is widespread in fungi, as many species
in low- to mid-latitudes show dispersal limitation and pronounced
phylogeographic patterns (e.g., Geml 2011; Peay et al . 2012;
Branco et al . 2015), resulting in differences in the composition
of regional species pools.
Despite the low number of shared species, environmental variables are
still at least as important drivers of community composition of tropical
fungi as geography (i.e. biogeographic history). Almost two-thirds of
the putatively pantropical OTUs were indicators for an elevational zone.
This suggests that even among fungi with widespread geographic
distributions, many are habitat specialists for a certain elevational
forest type. This observation is in agreement with the importance of
abiotic factors in shaping the distributions of the most common fungi on
a global scale (Větrovský et al. 2019).
Fungal communities in upper montane forests are particularly rich in
taxa with high specificity and fidelity to their habitat, as shown by
indicator species analyses. The upper montane forest likely represents a
unique habitat with a higher proportion of species specialized to the
characteristic environmental conditions there (i.e. lower temperature
and pH, increased OM accumulation, higher relative humidity and cloud
formation).
Likewise, the similarity of proportional richness of the functional
groups among the three regions is remarkable (Fig. S5). We hypothesize
that functional niche proportions may be driven by similar mechanisms of
environmental filtering along elevation gradients throughout Neo- and
Paleotropical forests, resulting in relatively predictable
representations of the functional guilds in lowland forests: saprotrophs
representing ca. 35-40%, plant pathogens 11-17%, wood decomposers
6-15%, animal pathogens 2-4%, and mycoparasites 1-2% of the OTUs (as
calculated for the whole community including fungi with currently
unknown function). In addition, ECM and non-ECM root-associated fungi
represent 1-2% and 1-5% of OTUs in Neotropical and 4-8% and 1-2% in
Paleotropical lowland rainforests, and reach 4-12% and 2-4% of OTUs in
Neotropical upper montane forests, respectively.