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

Caddisflies occupy a great variety of habitats, have diverse trophic preferences, and are very sensitive to environmental changes [17]. In Ecuador, 314 species are currently recorded, but estimations predict that this may only represent about 50% of the true diversity. From these species records, the majority of them occur below 2000 m asl [18]. In an era of climate and land-use change, it is essential to know the actual diversity, distribution, and life history of cad- disflies in the Neotropics due to their sensitivity to environmental changes [19]. In this con- text, our goal was to assess which effect environmental variables have in shaping Trichoptera species and genera distribution and community assemblages along an elevation gradient in the equatorial Andes. We expected: (1) a decrease in species and generic diversity with increasing elevation, and (2) an increase in caddisfly community composition dissimilarity as the eleva- tion and geographic distance increase. Thus, our objectives are: (1) to determine the variation in the number of species and genera of Trichoptera along the elevational gradient starting at the foothills of the Pichincha volcano (3,500 m a.s.l.) and following the Guayllabamba water- shed down to 600 m a.s.l., (2) to evaluate the role of environmental variables in Trichoptera community composition, and (3) to assess the importance of geographic proximity and eleva- tion in explaining the composition of caddisflies assemblages and community composition turnover (β-diversity) patterns along these gradients. Materials and methods Study area

The study area is in the remnant montane cloud forest on the western flank of the Pichincha volcano in the Ecuadorian Andes. This study took advantage of a long-term forest biodiversity and carbon monitoring transect established in 2015 by Pinto & Cuesta [20]. The permanent transect spans 3,000 m of elevation, from the piedmont forest (619 m a.s.l.) to upper montane forest (3,464 m a.s.l.). The transect captures four ecosystem types (Piedmont Forest (PMF), Lower Montane Forest (LMF), Montane Forest (MF), and Upper Montane Forest (UMF) [21] that reflect changes in environmental conditions related to environmental gradients in mean annual temperature (7.2–21.6˚C), relative air humidity (96.1%– 99.8%), and mean annual pre- cipitation (1,580–2,448 mm; [22, 23]) We selected 7 locations along the monitoring transect associated with second-order streams (Fig 1, Table 1). Locations were selected based on the following criteria: (1) a second-order stream was located at less than 1 km from the permanent forest plot, (2) the selected locations were distributed approximately every 600 meters, allowing to capture the variations of the microenvironmental conditions found along the elevation gradient (see [22])., (3) the riparian ecosystem was in good condition and did not show human impacts (S1 Fig). Although the Intillacta location has a considerable amount of agricultural land in its drainage area (15%), the riparian forest is well preserved and the stream water quality is good. Moreover, the Intil-

lacta location is embedded in a private reserve that protects a montane forest fragment of 250 hectares. Collecting methods At each locality, adult caddisflies were attracted to black (UV) fluorescent lights (F8T5/BL, 8 watts) placed across white plastic pans filled with 96% ethanol as a preserving fluid [19]. One pan trap with a black light was placed on the riverbank per locality each night. Sampling was conducted from 6 to 8 pm during three consecutive nights, from late June to early August 2017 (dry season; S1 Table). The dates were as far away from the full moon as possible to maxi- mize the effectiveness of the traps [19]. All collected material was preserved in 96% ethanol until sorting and identification. PLOS ONE Elevational biodiversity gradients of Neotropical caddisflies PLOS ONE | https://doi.org/10.1371/journal.pone.0272229 August 5, 2022 3 / 17