2.3 Species trait measure
Choosing the appropriate functional traits could provide valuable insights into the relationships between environmental changes, fish functional diversity, and ecosystem (Villéger et al., 2017; Troia & McManamay, 2020). As habitat alteration and fragmentation associated with low-head dams can potentially affect the habitat guilds and trophic structure of fish assemblages in headwater streams (Helms et al., 2011; Fencl et al., 2017; Smith et al., 2017), we estimated the functional diversity of each community by measuring the most commonly available traits of fish species related to feeding, locomotion, and habitat preferences (Albouy et al., 2011). We measured a series of traits of fish in the laboratory and used them to calculate seven morphological ratio traits: (1) eye size; (2) oral gape position; (3) oral gape shape; (4) gut length; (5) caudal peduncle throttling; (6) body transversal shape; and (7) body depth (Appendix S1). At least 20 adult specimens of each species were used to measure the traits, and all adult specimens were measured when the species contained < 20 adult individuals.