Fresh perspectives on the River Continuum Concept require trophic ecology approaches focussed on food web structure and energy mobilisation routes

Abstract

Stream‐dwelling communities are expected to show a gradual replacement of the dominant feeding types following the type of resources found along the river continuum. Yet, the underlying longitudinal gradients in food web structure and energy flow‐paths remain poorly understood. Here, I synthesise novel research on the River Continuum Concept (RCC) and identify promising areas for future research linked to longitudinal changes in food‐chain length and energy mobilisation routes. For example, feeding links and connectance should reach maximum values in mid‐order rivers and then decrease to river mouths following uncovered longitudinal diversity patterns. Regarding energy mobilisation routes, a gradual replacement in the food web fuelling between allochthonous (leaf litter) and autochthonous (periphyton) resources should be expected. Beyond longitudinal changes in primary basal resource to consumer paths, other allochthonous (e.g. riparian arthropod inputs) and autochthonous (e.g. fish prey) inputs subsidising higher level consumers may show longitudinal changes, that is, terrestrial invertebrates decreasing but piscivory increasing downstream. However, the role of these inputs, that can alter predator niche variation and have indirect community‐based effects, on both food web structure and energy flow‐paths along the river continuum is not clear yet. Incorporating energy mobilisation and food web structure into RCC principles is necessary for a broad understanding of ecosystem functioning and trophic diversity in riverine systems, driving the emergence of novel insights. How function and structure of riverine food webs adapt to longitudinal changes in physical and biological environments represent a challenge for next generation of stream ecologists.

No effects of macroconsumer exclusion on macroinvertebrate functional composition in Brazilian karst streams along a gradient of riparian forest loss

“…The absence of inputs of wood from the riparian forest can also alter habitat complexity and retention of organic matter that provides food for different detritivores (Baker et al, 2016;Sitati et al, 2021). These changes in riparian cover can often affect the abundance of functional feeding groups (FFG) of the benthic invertebrates by decreasing the allochthonous organic matter inputs (e.g., leaves, fruits, woody materials, and terrestrial insects) that constitute important food resources and substrates for specific benthic invertebrates (Allan et al, 2021;Sánchez-Hernández, 2023;Webster et al, 1983). Overall, the loss of key macroconsumers can substantially affect benthic communities and stream ecosystems (Dangles & Guérold, 2001;Hildrew & Giller, 2023;Marshall et al, 2012) as well as influence the effectiveness of biotic indices for water-quality analyses (Brasil et al, 2020).…”

“…The potential for changes in benthic invertebrate populations and communities following the loss of riparian vegetation can depend on the type of ecosystem, degree of food-web connectivity, dispersal, and the species pool as well as the type and intensity of the riparian alterations in the buffer-zone along the stream channel (Dudley et al, 2021;Feijó-Lima et al, 2019, 2023 and the landscape composition (Dala-Corte et al, 2020). Understanding if the loss of vegetation around streams can influence trophic relationships as well as the composition of the FFG benthic invertebrates remains an important area of research for many ecosystems facing increasing anthropogenic pressures, especially in different types of tropical streams, where intensive modification of forest to agriculture is a widespread and increasing environmental problem Dudgeon, 2010;Foley et al, 2011).…”