Network topology mediates freshwater fish metacommunity response to loss of connectivity

Abstract

Changes in connectivity regimes affect patterns of diversity and species richness. In riverine ecosystems, factors that vary through space and time, such as flow, the presence of barriers to movement, and network topology determine connectivity, and in turn shape patterns of diversity and richness.While the effects of network topology and changes in spatiotemporal connectivity regimes on patterns of species richness have been studied in isolation, they have not been studied simultaneously. We used a discrete-time logistic growth metacommunity model to analyze the role of spatial and temporal functional connectivity in determining patterns of local (patch level) species richness in freshwater fish metacommunities. Our modeling suggests that:(1) the effect of spatial loss of connectivity on local species richness is mediated by network topology and where richness is measured in the system and (2) increasing temporal autocorrelation in connectivity results in increasing temporal autocorrelation in patch occupancy. Spatial and temporal loss of connectivity is a ubiquitous issue for river ecosystems, making understanding and predicting its effects of fundamental importance to both improving theory and guiding river management. Our findings highlight the importance of network topology (and hence context dependency) in shaping metacommunity response to changing connectivity regimes.

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

“…We require novel approaches to examine dynamics and functioning of ecosystems along longitudinal environmental gradients integrating meta‐ecosystem, meta‐community and river network concepts (Doretto et al, 2020 and references therein), as flow connectivity across longitudinal and lateral (aquatic–terrestrial linkage) dimensions aligns well with meta‐ecosystem and meta‐community perspectives (Humphries et al, 2014). Network topology is crucial to understand response of meta‐community to changing connectivity by altering dispersal patterns (Carraro & Altermatt, 2022; Lee et al, 2022), but also changing connectivity regimes impact on species richness as local species richness is mediated by spatial loss of connectivity (Lee et al, 2022). As already pointed out, food web structure and energy mobilisation routes may respond to biodiversity patterns along the river continuum (Figure 2).…”