The Role of Elevation, Connectivity and Land Cover on Migratory and Non‐Migratory Fish Communities in an Amazonian Riverine System

Dams and deforestation are key drivers of freshwater biodiversity loss in the Amazon, as they alter river connectivity, water quality and habitat structure. This study investigates how connectivity (Reach Connectivity Index—RCI), elevation and natural land cover influence the diversity and composition of fish assemblages in a highly fragmented Amazonian river network. Based on their distinct life‐history traits, we analysed migratory and non‐migratory species separately, hypothesizing differential responses to these environmental gradients. Generalized linear models (GLMs) were used to evaluate the effects of RCI, elevation and land cover on species richness (alpha diversity) and the Local Contribution to Beta Diversity (LCBD, a measure of community uniqueness). Additionally, we examined the influence of these variables on community composition using distance‐based RDA and hierarchical partitioning. We found that species richness for both groups was higher at lower elevations. However, only non‐migratory species richness increased with greater connectivity (RCI), whereas migratory species richness was unaffected by RCI. For community uniqueness (LCBD), values for migratory species were higher in areas with more conserved land cover. In contrast, non‐migratory species had higher LCBD at less connected sites. Community composition analysis revealed that non‐migratory species were strongly influenced by elevation, while migratory species composition showed no significant relationship with the environmental variables analysed. Our results confirm distinct ecological responses between migratory and non‐migratory species to fragmentation, supporting our initial hypothesis. These findings underscore the critical importance of considering species' life‐history traits when planning conservation strategies and river connectivity restoration in the Amazon.