Urban land use homogenizes fish assemblages across mesohabitats in headwater streams

Anthropogenic land use profoundly affects stream environmental conditions and fish assemblages. However, significant knowledge gaps remain regarding how land use influences fish species composition across different mesohabitats. To address this, we sampled riffles, runs, and pools in rural and urban streams, analyzing how land-use types shape environmental conditions, species composition, and the distribution of fish body shapes across mesohabitats. We hypothesized that urban streams would exhibit degraded environmental conditions, reduced fish diversity, and homogenized species composition and body shape distribution across mesohabitats. Our findings confirmed that urban streams had more degraded conditions and lower fish diversity. Additionally, fish body shape distribution and species composition were homogenized across mesohabitats in urban streams. These results highlight the need for stream management and restoration strategies, emphasizing that diverse mesohabitats alone may not counteract the homogenizing effects of urbanization on fish assemblages.