Elevational biodiversity gradients in the Neotropics: Perspectives from freshwater caddisflies (Insecta: Trichoptera)

Trichoptera diversity patterns across the elevation gradient Most of the species were recorded at a single locality, reflecting a high degree of rareness. Of the 69 species found across the elevation gradient, 53 species (77%) occurred at only a single locality, and at least 10 of those species are endemic to the western ridge of the Ecuadorian Andes, an area strongly influenced by the Choco´ bioregion in terms of species composition (S2 Table). The ordination analysis segregated the study localities into two clearly distinguishable groups along the elevation gradient (second ordination axis)—the low elevation localities located on the left-hand side of the diagram and the mid to high elevation localities, placed at the center and on the right-hand side, where T˚ min was the main variable related to this con- figuration (Fig 3). However, the resulting groups showed very low similarity (8%), suggesting high species turnover among localities (see below). Since we observed that locality Mashpi T had a very high richness of species and genera compared with the other localities, we repeated all the ordination and cluster analyses without this outlier, and results were similar to those observed with all localities (S1 Fig). Geographic distance, elevation and community composition The matrix correlation analysis between community genus level composition and geographic distance showed a strong correlation (Rho = 0.624; p = 0.016). However, the community com- position similarity at the species level was not significantly correlated with geographic distance (Rho = 0.321; p = 0.2874).

The overall community turnover between Trichoptera assemblages across the elevation gra- dient, independent of geographic distance, was higher for species compared to genera (Whit- taker’s indices: 4.03 and 1.89, respectively; S2 and S3 Tables). Along the elevation gradient, β- Table 3. SIMPER analysis between generic cluster groups (high and low altitude clusters) at localities across an elevation gradient (600–3,500 m a.s.l.), Volca´n Pichincha, western Ecuador. Genus High Low Average Distance/S % Contribution Cumulative % (average abundance (average abundance Distance Leptonema 0 4.86 13.24 2.81 16.16 16.16 Chimarra (Chimarra) 0 4.27 11.17 2.09 13.63 29.79 Wormaldia 0 2.69 9.4 11.34 11.47 41.26 Nectopsyche 3.14 1.62 7.18 1.05 8.76 50.02 Smicridea (Rhyacophylax) 1 3.89 6.74 1.25 8.22 58.24 Atopsyche 1.9 1.73 5.12 1.41 6.24 64.49 Helicopsyche 1.63 0.93 4.32 1.01 5.27 69.76 Rhyacopsyche 1.14 0 3.61 2.23 4.4 74.16 Chimarra (Curgia) 0 1.04 3.05 1.29 3.72 77.88 Smicridea (Smicridea) 0 1.4 2.57 0.95 3.14 81.02 Chimarrhodella 0 1.6 2.15 0.55 2.83 83.65 Mortoniella 0 0.71 1.69 0.8 2.07 85.72 Polycentropus 0.33 0.43 1.59 0.77 1.94 87.66 Phylloicus 0.33 0.5 1.4 0.84 1.17 89.36 Amphoropsyche 0.47 0 1.27 0.82 1.55 90.91 https://doi.org/10.1371/journal.pone.0272229.t003 PLOS ONE Elevational biodiversity gradients of Neotropical caddisflies PLOS ONE | https://doi.org/10.1371/journal.pone.0272229 August 5, 2022 9 / 17