Introduction: Considering the rising the need to estimate optimal conditions and species tolerance limits in management planning compared to the past, understanding species responses to gradual environmental changes has become more important. Therefore, the focus of this study is on understanding the response of benthic invertebrate communities to limiting factors in their distribution and examining their habitat preferences along rivers and when occupying new habitats. Such analyses can greatly assist in predicting community changes due to stressors and prioritizing conservation areas.
Materials and Methods: This study was conducted over a 50-kilometer range of the Jajrood River basin, with sampling at 10 sites simultaneously on a single day during the autumn season of 1403. Thirteen environmental parameters and biological variables were systematically measured and analyzed. To assess the similarity of stations, hierarchical clustering with Euclidean distance was employed, and correlation matrices were used to identify variables affecting community structure formation. Multiple regression analysis was used to examine the statistical significance of the correlation and to investigate habitat selection behavior by plotting behavioral response curves based on habitat selection indices, and in addition to these analyses, a complementary method for identifying functional feeding groups was employed to better interpret the findings.
Results: The analysis revealed that among the seven identified families, Caenidae, Chironomidae, and Hydropsychidae contributed the most to the changes. The Chi-Square test confirmed the significance of biological distribution differences along the river. PCA results analysis showed that temperature, depth, elevation, electrical conductivity, and discharge played the most significant roles in station differentiation. The BEST analysis also identified the best environmental combination with nine variables having a 0.78 correlation. Habitat selection curves often exhibited a doubly exponential and sometimes a triply exponential pattern, indicating complex relationships between biological and non-biological variables, and ultimately, a high count in the abundance of foraging and filtering dietary groups downstream was noticeable.
Discussion: Species distribution modeling is an effective approach for analyzing complex ecological data and assessing habitat suitability. Analysis of multiple regression and the shapes of response curves indicate that there is no significant correlation between the pattern of spatial distribution of these families and these environmental variables, and essentially complex and non-linear relationships govern. Analyses showed that elevation, along with other variables, accounts for approximately 50% of the changes, but non-linear, exponential, and sometimes cubic response curves indicate the influence of unidentified factors including competition and land-use changes. Despite all the above, access to food resources acted as the primary determinant of species distribution during the study period. For instance, the high abundance of collector and filter feeding groups downstream, resulting from the transfer of organic matter from upstream agricultural lands following autumn rainfall, can be noted. In general, it can be concluded that classical linear approaches are insufficient alone to explain complex distribution patterns, and the use of behavioral curves provides a more accurate analytical framework. This integrated approach enabled a comprehensive assessment of environmental factors and species responses, offering important insights for ecological interpretation and guiding effective conservation and management programs in aquatic ecosystems.