Zoological Studies

Vol. 51 No. 7, 2012

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

Sen-Her Shieh1,*, Ling-Kuo Wang2, and Wen-Feng Hsiao2

1Department of Ecological Humanities, Providence University, 200, Sec. 7, Taiwan Boulevard, Shalu Dist., Taichung 433, Taiwan
2Department of Biological Resources, National Chiayi University, 300 University Road, Chiayi 600, Taiwan

Sen-Her Shieh, Ling-Kuo Wang, and Wen-Feng Hsiao (2012) 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 fourthcorner 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 insect assemblages corresponded to a gradual shift from aquatic insects that preferred larger and more stable mineral substrates (rubble) to those that preferred still waters in lowlands with finer substrates.  The results suggested that the low substrate heterogeneity and stability at downstream sites led to a simpler but less stable functional organization, and that functional traits should be sufficiently sensitive to detect changes in environmental variables and can be used for biomonitoring streams in Taiwan. 

Key words: Life history traits, Habitat templet hypothesis, RLQ analysis, Fourth-corner analysis.

*Correspondence: E-mail:shshieh@pu.edu.tw