Fish communities respond to environmental factors over a range of spatial and temporal scales within the riverine landscape. The perceived influence of these factors depends on the scale at which the investigation is carried out, thus, a hierarchical approach is essential. This study uses established frameworks to analyse the fish community structure of refugial waterholes of the Lower Balonne System, south-eastern Australia, in relation to hydrological and physical habitat features characterised at different spatial and temporal scales. Results demonstrate that different features of hydrological character operating at various spatial and temporal scales influence fish community structure at different levels of ecological organisation. Long-term hydrological character at a river-system scale was correlated with fish communities at the level of the species assemblage; whereas short-term hydrological character at a waterhole-scale was correlated with fish communities at the population size-structure level. Physical habitat characteristics were correlated with fish assemblages; however, the strongest correlations between environmental variables and fish assemblages were derived from combinations of physical habitat variables and hydrological variables, highlighting the importance of hydrology as an over-arching driver of fish community structure. The role of hydrology and the biological response it initiates needs to be considered at both long- and short-term scales in order to determine ecological requirements for native fish communities and maintain critical refugial habitats of dryland rivers.
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