Diversity, Environmental Drivers, and Niche Overlap of Native and Invasive Gastropods in Southern Iraq’s Freshwater Ecosystems

This study assesses the diversity, distribution, and ecological interactions of freshwater gastropod communities across eight sites in southern Iraq, spanning marshes, rivers, and canal systems within the Tigris-Euphrates basin. Diversity indices (Shannon–Wiener H′ and Pielou’s evenness J) were calculated to evaluate community structure, and a revised stacked bar chart of relative abundances revealed widespread dominance by species such as Melanoides tuberculata and Physella acuta, which frequently exceeded 50% of local assemblages. While P. acuta is an established invasive species, M. tuberculata is now considered native or long-established in the region. Species interactions were examined using Pianka’s niche overlap index, and null model testing (999 permutations) revealed only a few statistically significant overlaps (p < 0.05), suggesting that species co-occurrence is shaped more by environmental filtering than direct competition. To directly examine the influence of environmental drivers on species composition, Multiple Factor Analysis (MFA) was performed. MFA revealed patterns of association between dissolved oxygen, salinity, and species assemblages, suggesting these abiotic factors may influence community structure. To our knowledge, this study is the first in Iraq to use null models, constrained ordination, and MFA to investigate community assembly of freshwater gastropods, ultimately producing novel insights regarding the interactions between environmental stressors and aquatic biodiversity patterns. The results of this study highlight the need for long-term ecological monitoring and conservation in marshland habitats important for the resiliency of native species.