How the morphology of two closely related riverine sympatric species are reflected in ecological niche overlapping? A case study of two Capoeta species

This study investigated morphological differences, habitat preference, and ecological niche overlap in two sympatric Capoeta species i.e., Capoeta. damascina and Capoeta umbla collected from the Sirvan river drainage. Ten environmental factors, including pH, temperature, electrical conductivity (EC), total dissolved solids (TDS), river width, river depth, flow velocity, altitude, slope, and dissolved oxygen (DO) were measured during sampling time. A total of 17 morphometric characteristics were measured using digital calipers for traditional morphometrics (TM). For the geometric morphometric method (GM), 2D pictures were taken from the left side of the fresh samples, by tpsDig2 software, and 16 landmark points were defined and digitalized to extract body shape data. The data were analyzed using t-test, Mann–Whitney, principal component analysis (PCA), and discriminant function analysis based on the P-value of Hotelling’s T-squared. The ratio of the common area under the graph to the total area of habitat suitability indices was defined as the ecological niche overlap. The results showed significant differences in eye diameter, predorsal, caudal peduncle length, preanal, preventral, ventral-pectoral, body depth, and caudal peduncle depth traits (P < 0.05) in TM, and those differences in the GM were related to the position of the snout, head and body depth and caudal peduncle length i.e., C. damascina had the deeper body shape and head, and anterior the snout and caudal peduncle length. Based on the results, C. damascina prefers areas with higher pH and temperature and by increasing other studied factors, its habitat suitability decreased. The preference for C. umbla with increasing river depth and DO was increased. These two species showed low niche overlap i.e., they avoid competition in their habitat by opting for different areas in terms of river width, flow velocity, and temperature that have more depth with higher slope microhabitats.