Shifts in Functional Traits of Aquatic Insects along a Subtropical Stream in Taiwan

along a subtropical stream in Taiwan. Zoological Studies 51(7): 1051-1065. Despite an increasing interest in the study of functional diversity, there have been no attempts to link aquatic insect traits, habitat variations, and community structure in subtropical Asian streams. We examined relationships between habitat characteristics and aquatic insect traits at 7 sites along a subtropical stream in Taiwan by an RLQ analysis and fourth-corner analysis. The habitat was described by the slope, mineral substrate size, and water chemistry, while aquatic insect traits were described using 40 categories of 9 functional traits. The 1st axis of the RLQ analysis explained 96.5%, suggesting a strong longitudinal environmental gradient structuring the characteristics of sites and aquatic insect assemblages. The most influential habitat variables were the slope, mineral substrate size, conductivity, and alkalinity, which reflected both natural variations and human impacts along the stream. The main covariations between traits and habitat were a shift from organisms with combining features, such as crawlers, a large body size, a flat body form, and low body flexibility to organisms which are swimmers, possess high body flexibility and a small body size, and feed on fine detritus and microinvertebrates. In the results of the fourth-corner analysis, 18 of 40 trait categories were significantly correlated with environmental variables. In particular, traits relating to flow, such as body form, attachment to substrate, body flexibility, and food type, showed the strongest correlations with environmental variables. Longitudinal gradients of aquatic insec