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Abstract River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley‐scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence‐ and abundance‐based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance‐based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley‐scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley‐scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.
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Characterization and spatial variation of the deep-sea fish assemblages on Pioneer Bank, Northwestern Hawaiian Islands
Knowledge of the spatial variation of deep-sea fish assemblages is a critical gap in understanding seamount ecology. Pioneer Bank in the Papahānaumokuākea Marine National Monument (Hawaii, USA) has a history of hook-and-line fishing but not trawling; thus, it is a good location to further describe deep-sea fish assemblages. From replicated autonomous underwater vehicle transects at 300, 450, and 600 m on 3 sides of Pioneer Bank, we observed 4190 fish representing 81 species. Fish assemblages were dominated by Gadiformes, Perciformes, and Stomiiformes. The relative abundance of fish was significantly different among sides of the seamount and the interaction of side and depth, with the NW side having the highest relative abundance at 450 m. Species richness, rarefaction estimates of expected species richness, Shannon diversity, and Simpson dominance showed significant differences by side, but not by depth. These differences were between the S and NW sides, with the S side having the lowest diversity and high dominance. The structure of the fish assemblage was significantly different among both sides and depths, with depth as the most important factor. Fish assemblage structure was most strongly correlated with salinity, % rugosity, chlorophyll a , and mean direction of substrate. These scales of spatial variability both with depth and across short horizontal distances on a single seamount are similar to those found on nearby Necker Island, which reaffirms the spatial heterogeneity in deep-sea fish assemblages on seamounts. This study provides an ecological baseline for the management and conservation of seamounts.
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- Award ID(s):
- 1851365
- PAR ID:
- 10342924
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 692
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 99 to 118
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps14071
