Interspecies trophic niche differences and spatial–temporal adaptations found in Cultrinae fishes

It has been debated whether interspecies niche differences may follow niche conservatism, whether niches are becoming specialists, whether generalists and specialists are maintained in a balance, and how the realized niche may adapt to local or temporal environments. In the present study, by using stable isotope analysis to evaluate the trophic niche of seven Cultrinae species, we investigated niche conservatism among these species from 10 sites of the Yangtze River by testing the Mantel test of trophic niche variables [trophic position (TP), δ13C, and trophic niche breadth]. We also comprehensively investigated the fundamental niche differences as well as spatial and temporal adaptations of the realized niche of these seven Cultrinae species by calculating trophic niche breadths, overlap, and TP. The results showed that TP and fundamental trophic niche breadth exhibited phylogenetic conservatism, while the fundamental trophic niche breadth of the three Hemicultrine species tended to become generalists and four Cultrine species tended to become specialists. Moreover, the realized trophic niche of the same species would exhibit different adaptation at different sites as well as in different seasons. In the wet season, trophic niche breadths of the seven species were significantly larger than that in the dry season with great overlaps between species, while in the dry season, trophic niche separation was found among the seven species due to competitive exclusion of niches. We believe that these findings will contribute to future theoretical and empirical niche investigations.