Functional Convergence Across Contrasting Ecosystem Disturbances Following the Destruction of the Kakhovka Reservoir

Environmental disturbances alter the taxonomic and functional structure of soil communities, yet whether different disturbances produce common patterns of functional convergence remains unclear. We investigated soil nematode assemblages across habitats with distinct disturbance histories on Khortytsia Island, Ukraine, where the destruction of the Kakhovka Dam in June 2023 triggered major hydrological and ecosystem transformations. A total of 120 soil samples representing eight habitat–ecosystem state combinations yielded 39 nematode taxa. Non-metric multidimensional scaling (NMDS), redundancy analysis (RDA), and canonical correspondence analysis (CCA) were used to identify community variation associated with ecosystem states and nematode maturity. The Maturity Index of free-living nematodes (coloniser–persister classes 2–5) provided an ecological reference for interpreting ordination gradients as community responses to disturbance-associated environmental stress. Functional convergence and divergence were assessed using Rao's quadratic entropy and null-model randomisation, alongside variation in morphological, trophic, and life-history traits. Significant functional convergence was detected for combined traits, body size, feeding strategies, and coloniser–persister and plant-parasite classifications, but not body shape. No significant functional divergence was detected. Relationships between convergence and ordination gradients differed among methods: NMDS revealed nonlinear responses, whereas RDA and CCA generally indicated stronger convergence towards higher axis scores. Increasing scores associated with declining community maturity coincided with reduced community-weighted body size and coloniser–persister values, fewer omnivores, and shifts in trophic composition. Morphological traits also differed among ecosystem states. These findings identify functional convergence as a recurring feature of nematode community responses across habitats with distinct disturbance histories, consistent with environmental filtering during community assembly. Integrating multivariate ordination, maturity indicators, functional traits, and null models offers a framework for distinguishing shared and disturbance-specific patterns of functional restructuring during ecosystem transformation.