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

patterns have been documented along elevational gradients in the tropical Andes for other taxa such as rodents [42], bats [8], ferns and lycopods [5, 43], epiphytes [44], and trees [45– 47]. Our data suggest that the decline in Trichoptera richness at high elevations is related to low air temperature (Fig 2a & 2b). Cold temperatures are associated to longer life cycles, that can affect diversity [45]. Another possibility is that with low air temperatures adults are less likely to fly to black lights. However, studies with sticky and Malaise emergence traps, along different seasons have found the same low richness and abundance in high altitude tropical streams [48, 49]. Localities up to 1,800 m a.s.l. have higher minimum temperatures (20.25˚C—14˚C) than the upper localities (7.3–3.7˚C). The most abundant genera at the lowland localities (Table 3) are mainly collector-gatherers (Chimarra, Wormaldia, Leptonema, and Smicridea). The com- munities at localities above 2,200 m a.s.l. showed lower species and generic richness but higher functional feeding diversity (less functional redundancy). Atopsyche is mainly a predator, Rhyacopsyche and Helicopsyche are primarily scrapers, and Nectopsyche is a shredder [50, 51]. This also suggests high functional feeding diversity agrees with resource changes along rivers at different altitudes [52]. Also, this suggests that the harsher climatic conditions of the high Andes might be acting as a strong environmental filter for low elevation taxa restricted to

below 2,000 m a.s.l. [13]. Recent studies in similar ecosystems and with similar taxa [53, 54] Table 4. Species (A) and generic (B) β-diversity dissimilarity (Whitaker), mean null models (1000 interactions), and the SES score along the elevation gradient. Bold numbers are significant values according to SES. Elevation range (m asl) Observed Null SES (A) 619–903 0.55 0.82 -2.62 903–1028 0.76 0.81 -0.56 1028–1874 0.87 0.82 0.58 1874–2281 0.83 0.81 0.2 2281–2325 0.62 0.81 -1.91 2325–3464 0.88 0.81 0.64 (B) 619–903 0.33 0.67 -2.35 903–1028 0.63 0.66 -0.27 1028–1874 0.42 0.67 -1.79 1874–2281 0.5 0.66 -1.14 2281–2325 0.23 0.67 -3.051 2325–3464 0.4 0.67 -2.01 https://doi.org/10.1371/journal.pone.0272229.t004 Table 5. Species and generic β-diversity dissimilarity (Whitaker), mean null models (1000 interactions), and the SES score along sites grouped by elevation. Elevational Groups Elevation range (m asl) Observed Null SES Species Low-elevation 619–1028 0.855 0.63 2.78 Intillacta (mid-elevation) 1029–1874 0.881 0.628 3.185 High-elevation 2281–3464 0.882 0.633 3.181 Genera Low-elevation 619–1028 0.455 0.468 -0.13 Intillacta (mid-elevation) 1029–1874 0.55 0.472 0.87 High-elevation 2281–3464 0.58 0.466 1.06 https://doi.org/10.1371/journal.pone.0272229.t005 PLOS ONE Elevational biodiversity gradients of Neotropical caddisflies PLOS ONE | https://doi.org/10.1371/journal.pone.0272229 August 5, 2022 11 / 17