The impact of land-use intensity on the community dynamics of colonial volvocine algae in the Yangtze River Basin

Colonial volvocine algae (CVA), which range from four-celled to complex multicellular forms, are vital for understanding life evolution. This study aims to quantify the impacts of human land-use intensity on CVA communities across the Yangtze River Basin and explore how anthropogenic changes drive CVA ecological niche dynamics and assembly processes. Findings reveal that increased land-use intensity reduces forest cover, expands construction land, and elevates water nutrients, thereby worsening water quality. This environmental shift provides elevated nutrient resources for CVA, expanding their ecological niche width (<i>P</i> < 0.01) and reducing competition (interspecific niche overlap network simplified), particularly benefiting larger-bodied colonial volvocine algae, such as <i>Volvox carteri</i>. However, morphological similarity among CVA species, such as <i>Eudorina elegans</i> and <i>Colemanosphaera charkowiensis</i>, results in niche overlap and intensified competition. Notably, CVA complexity does not substantially correlate with distribution patterns, indicating that factors other than basic morphological characteristics play a role in determining their ecological success. On the other hand, CVA community assembly in the Yangtze River Basin, analogous to eukaryote and prokaryote, was initially dominated by stochastic processes at low land-use intensities (β-NTI mostly ranges between -2 and 2). Increased intensity enhances environmental filtering, leading to community homogenization (β-diversity decreased from 0.9119 ± 0.2236 under low HAILS to 0.8974 ± 0.2332 under high HAILS, <i>P</i> < 0.001), which diminishes biodiversity, alters ecological processes, and reduces ecological stability, ultimately affecting ecosystem integrity and sustainability. This study highlights that land-use intensification-induced environmental changes restructure CVA community dynamics, niche relationships, and assembly processes. These findings provide critical insights for sustainable land management and freshwater biodiversity conservation.IMPORTANCEThis study underscores the importance of colonial volvocine algae as a model for understanding how human land-use intensification reshapes freshwater biodiversity, ecological niches, and community assembly, offering key insights for sustainable ecosystem management.