Structural and Functional Variations of the Macrobenthic Community of the Adige Basin along the River Continuum

Abstract

Since the publication of the River Continuum Concept (RCC), the capacity of the longitudinal dimension to predict the distribution of species and ecological functions in river networks was discussed by different river theories. The taxonomic structures and functional attributes of macrobenthic communities were investigated along the river continuum in the river Adige network (Northern Italy), with the aim to test the reliability of RCC theory and clarify the relation between structural and functional features in lotic systems. Distance from the spring was found to be most representative proxy among environmental parameters. The analysis highlighted the decrease of biodiversity levels along the river continuum. The decrease of taxonomic diversity corresponded to the loss in functional richness. The abundances of predator and walker taxa, as well as semelparous organisms, declined along the longitudinal gradient, suggesting variations in community complexity and granulometry. Regression models also depicted the presence of disturbed communities in the central section of the basin, where intensive agricultural activities occur, that affected environmental gradients. Overall, results offered evidences that the river continuum may predict macrobenthic community structures in terms of taxonomic diversity, thus confirming the general validity of RCC. Nonetheless, the functional analysis did not provide equally clear evidences to support the theory. After four decades from its postulation, the RCC is still a reliable model to predict the general macroinvertebrates distribution. However, community functions may respond to a number of local factors not considered in RCC, which could find a declination in other theories. The relations between structural and functional features confirmed to be complex and sensitive to disturbances and local conditions.

Functional trait responses to different anthropogenic pressures

“…In theory, a decrease of taxonomic diversity corresponds to loss in functional richness, but this is not necessarily the case for the other functional indices (Gaglio et al, 2021). A loss in species richness does not imply an uneven distribution of functional attributes, a dimension computed in both functional evenness (FEve) and Rao's quadratic entropy (RaoQ) indices.…”

Fish functional gradients along a reservoir cascade

“…The concept is applicable to interpret clinal patterns in lotic geomorphology, hydrology, and ecology. Applications of the concept have been expanded into numerous aspects of stream ecology including trophic ecology (Gaglio et al, 2021; Greathouse & Pringle, 2006), reproductive ecology (Aarts & Nienhuis, 2003; Gaglio et al, 2021), and biodiversity with a heavy focus on macroinvertebrates (Tornwall et al, 2015). The RCC has also been adapted to recognise longitudinal physical gradients and habitat distributions along rivers (Gaglio et al, 2021; Rice et al, 2001; Torgersen et al, 2006).…”

“…Applications of the concept have been expanded into numerous aspects of stream ecology including trophic ecology (Gaglio et al, 2021; Greathouse & Pringle, 2006), reproductive ecology (Aarts & Nienhuis, 2003; Gaglio et al, 2021), and biodiversity with a heavy focus on macroinvertebrates (Tornwall et al, 2015). The RCC has also been adapted to recognise longitudinal physical gradients and habitat distributions along rivers (Gaglio et al, 2021; Rice et al, 2001; Torgersen et al, 2006). The RCC has encouraged developments of various alternative concepts including: (1) the River Ecosystem Synthesis (Thorp et al, 2006), Hierarchical Patch Dynamics (Poole, 2002), and Process Domains (Montgomery, 1999) to account for the patchy nature of river systems moulded by factors such as local climate, physiography, geomorphic processes, and distribution of tributaries and floodplains; (2) Network Dynamics to account for the dendritic nature of river ecosystems (Altermatt, 2013; Benda et al, 2004; Osborne & Wiley, 1992); (3) the River Wave Concept to account for the temporal characteristics of energy and nutrient storage and transport (Humphries et al, 2014); and (4) the Serial Discontinuity Concept to accommodate the discontinuities created by dams and impoundments (Ward & Stanford, 1983).…”