Effect of size on the relationship between habitat suitability index and niche overlap in Namak chub (Squalius namak Khaefi et al., 2016) in Jajrood River, Namak Lake basin

The habitat suitability index can be applied to predict the distribution of living organisms in the aquatic ecosystem i.e. it can reveal their correlation with environmental factors. By examining the relationship between the habitat suitability index and the ecological niche of a species, important findings can be obtained from the functional aspects of ecological niche theory and intra-species competition. In this study, using traditional morphometric data and k-mean clustering, 103 samples of Squalius namak were grouped based on two groups of small and large fish. Then, to calculate the habitat suitability index, a non-parametric smoothing method was used to draw the relationship between each environmental variable and the number of fish in each station. A polynomial equation was then fitted to the data predicted by the smoothes. The ratio of the common area below the plots to the total area was used as the niche overlap. Finally, using linear regression, the relationship between the habitat suitability of each parameter and the amount of niche overlap obtained from the same parameter was investigated for both size groups. The height and slope of the two linear regressions were analyzed using the analysis of covariance. The results showed that there was no significant difference in the height and slope of the two fitted regression lines, indicating the same changes in the habitat suitability index on the niche overlap of small and large river fish. The average of niche overlap of small and large samples was 52%. Therefore, other parameters are likely to be effective in the competition of two different size of S. namak species.