Local-scale resource partitioning by stingrays on an intertidal flat

The partitioning of dietary resources is a potential mechanism by which competing species can coexist. We examined local-scale dietary partitioning among 3 sympatric stingrays, Neotrygon kuhlii, Dasyatis fluviorum and Himantura toshi, from an intertidal flat in Moreton Bay, Australia, and compared their diets to the benthic prey items at the site. Ordination of stomach contents revealed that the species' diets differed significantly from each other and from the composition of potential prey items in their habitat, suggesting dietary partitioning among these species (ANOSIM, p < 0.001, R-statistic = 0.874). According to the index of relative importance (IRI), polychaetes were the most important prey for N. kuhlii (90.0% IRI), while D. fluviorum preferred brachyuran crabs (52.6% IRI) and H. toshi preferred carid shrimp (65.2% IRI). Size-related shifts in diet were investigated for N. kuhlii, and a weakly significant effect was detected, due to a decrease in importance of polychaetes and increased importance of carid shrimp and teleost fishes with increasing body size (ANOSIM, p < 0.001; R-statistic = 0.253). Jaw morphology was compared between D. fluviorum and N. kuhlii; D. fluviorum had a larger gape and a more molariform dentition than N. kuhlii, which may relate to preferences for epifaunal and infaunal prey, respectively. The results of this study suggest that N. kuhlii, D. fluviorum and H. toshi partition food resources at a local-scale within Moreton Bay, which likely facilitates their coexistence in this area.