Flood Regime Structures Small Mammal Assemblages in Riparian Forests Along the Upper Paraguay River

ABSTRACT

The diversity of small non‐volant mammals is shaped by multiple environmental factors, with habitat structure as a key driver. Horizontal and vertical heterogeneity influence shelter, food, and movement, guiding how species with different locomotor and dietary traits partition space. Across a~200 km riparian corridor in the Upper Paraguay River, Brazil, we aimed to: (1) examine richness, abundance, and functional group composition, primarily among terrestrial and scansorial small mammals in riparian forests; (2) relate species richness and abundance to local habitat and hydrological conditions; and (3) evaluate species composition along environmental, hydrological, and geographic gradients. We sampled 24 sites distributed across six riparian forest landscapes along the Upper Paraguay River using live traps placed at ground level and in the lower understory, supplemented by ground‐level pitfall traps. We also assessed flood‐pulse and vegetation‐structure variables at each site. We analyzed the data using a rarefaction approach, generalized additive models (GAMs), and ordination analysis. Flood duration was strongly associated with species composition. Scansorial species dominated (62.3% of captures), even in ground traps, suggesting possible reliance on vertical refugia during floods and flexibility across strata. Terrestrial species, however, were associated with sites experiencing shorter and shallower inundation and were absent from the most extensively inundated areas. Canopy height was negatively associated with richness, whereas flood duration, elevation, dense forest cover, and tree density were associated with species composition. These patterns may be further influenced by recent large‐scale disturbances such as wildfire, highlighting the vulnerability of vertically structured habitats in floodplain systems.