Feio, M.J., Almeida, S. & Aguiar, F.C. (2017) Functional associations between microalgae, macrophytes and invertebrates distinguish river types.Aquatic Sciences, 79, 909-923. DOI:10.1007/s00027-017-0541-4 (IF2017 3,622; Q1 Limnology)
Contemporary large-scale river ecology is grounded on the existence of patterns in the distribution of aquatic communities, structured by prevailing abiotic conditions. Here, we investigated the existence of functional consistent associations of traits (i.e., traits appearing consistently together at different sites and the same river type) between different biological elements of the aquatic community, assuming that species traits confer them advantages for certain environmental conditions but also within the aquatic community. If this is true, these trait associations should be consistently found in water bodies with similar characteristics (river types), defining different types of ecosystem functioning. To test this, 79 least-disturbed sites, belonging to five well-defined Portuguese river types and covering the longitudinal river gradient were used: headwaters of semi-arid streams, mountainous streams and northern-Atlantic climate streams, middle reaches and lowland large rivers. For each river type, we analyzed the strongest associations (via the Bray–Curtis coefficient) between diatoms, benthic invertebrates and macrophytes and traits that could be relevant to their interactions (e.g., invertebrate trophic groups, mobility/fixation ability of diatoms, macrophyte affinity to water) against a priori predictions. The strongest associations of traits changed over the river continuum with an increase in their complexity (number of associations) from headwaters to middle reaches and a decrease in lowland large rivers. These changes were not related to total richness, which was similar for all river types and over the continuum (ca. 100 taxa). In the three types of headwaters, there were also clear differences in associations among aquatic elements. The importance of riparian trees in small streams was not as high as expected while instream macrophytes were more relevant than predicted. This study revealed the existence of predictable functional associations that could serve as a basis for the functional assessment of running waters.