Figure 1.
The predicted relationship between nitrogen stable isotope discrimination between predator and prey consumed (∆15N) and the prey stable nitrogen isotope composition (dietary-δ15N) estimates for each shark species based on the widely reported ∆15N-dietary δ15N relationship
Figure 2.
Illustration of the expected relationship between stable isotope values of a predator and its’ prey in mixing space [27,28], employing the Bayesian approach of Jackson et al. [29], centered on multivariate ellipse based metrics.
In choosing discrimination factor (∆15N and ∆13C) values, it would be expected that the δ15N and δ13C values of the predator after adjustment to specific ∆15N and ∆13C values should overlay or fall within the range of δ15N values of the PP it consumes (see Table 2), indicating a best-fit scenario between predator and prey [ellipses represent prey (black) and predator (gray) respectively]. Black points represent δ13C and δ15N values of a predator, gray points (light and dark) represent adjusted-δ13C and adjusted-δ15N values with two different ∆15N and ∆13C values. White shapes represent mean (± variance) of prey species.
Figure 3.
Box plots representing the δ15N values of all of the PP derived from stomach content data of the bonnethead Sphyrna tiburo, Atlantic sharpnose Rhizoprionodon terraenovae, bull Carcharhinus leucas, and white Carcharodon carcharias shark.
Figure 4.
Dual-plot of individual predator (■) and mean (± SD) δ13C and δ15N values of the PP for each predator ((a), (f), (k), (p); see Table 1).
Standard ellipse areas corrected for sample size (SEAc) of sharks (solid black) and PP functional prey groups (Crustacean, dashed light gray; Mollusk, dotted light gray; Teleost, dashed dark gray; Elasmobranch, solid dark gray; Mammal solid light gray), and the broader diet (dotted black) following Jackson et al. [29]. Note different scales on the x- and y-axes in each species.