Landscape and hydro-climatic drivers of fish communities in floodplain wetlands

Floodplain wetlands are characterised by dynamic hydrological regimes and seasonal patterns of wetting and drying. Floodplain wetlands support distinct communities of fish many of which are adapted to dynamic and variable conditions. This study aimed to evaluate how broad-scale landscape and temporal environmental drivers of wetland ecosystems and biological traits of wetland fishes can determine occurrence patterns in floodplain wetlands fish assemblages.We analysed inundation and environmental data spanning 37 years (1986–2022) across floodplain wetlands in the southern Murray–Darling Basin (MDB). The data were gathered from open access sources such as: Atlas of Living Australia (ALA) https://www.ala.org.au/ ; Victorian Biodiversity Atlas https://www.environment.vic.gov.au/biodiversity/victorian-biodiversity-atlas ; Wetland Insight Too lhttps://knowledge.dea.ga.gov.au/notebooks/DEA_products/DEA_Wetlands_Insight_Tool/; Australian Hydrological Geospatial Fabric - Surface Catchments, Environmental Variables GEOFABRIC; https://digital.atlas.gov.au/maps/digitalatlas::australian-hydrological-geospatial-fabric-surface-catchments/about. Fish occurrence records for 14 species (10 native and 4 introduced) were sourced from public databases and combined with remotely sensed estimates of inundation frequency and land-cover data to assess species-environment-relationships. To better understand the potential influence of biological determinants of habitat use (i.e. biological traits and species interactions), we also incorporated species-specific traits related to life history, trophic levels and resilience, as well as phylogenetic relatedness. We applied Joint Species Distribution Models (JSDMs) to evaluate how environmental and biological factors jointly shape wetland fish community structure. Fish assemblages were primarily structured by environmental conditions, with inundation regime, water temperature, and wetland area acting as key drivers. Species-specific responses to these environmental filters were heterogeneous. Biological traits, including life history, trophic level, and resilience, collectively explained 26% of the variance in species occurrences, highlighting their role in habitat use. Spatial effects, accounting for variation among wetland locations and catchments, also contributed significantly to community structure. Phylogenetic relatedness did not influence species co-occurrence. After accounting for environmental, trait-based, and spatial factors, residual species associations suggested the potential for biotic interactions such as competition or facilitation acting at different scales.