Table 1.
A comparison of SIMM assumptions and features among commonly used SIMMs.
Figure 1.
Isotopic mixing space for FC black bears sampled in Yosemite National Park.
Isotope values (δ13C and δ15N) for male bears (open circles) captured in YNP and their estimated food sources. Estimated means for source aggregates (100% plant diet [green circle], 100% animal diet [orange circle], 100% human food diet [blue circle]) and process error (1 SD; dashed ovals) were estimated by IsotopeR and defined the vertices of the dietary mixing triangle; the shape of each source aggregate illustrates the degree of estimated isotopic correlation of observations used to define each source (see Fig. 4). Variations in dietary contributions (%) of plants (P), animals (A), and human food (HF) are shown along the edge of the mixing triangle (solid gray line) that connects estimated source means; labels denote the contribution of diet when consumers lie at the intersection of the mixing triangle edge and gray dashed iso-diet lines (within the triangle). The black dashed triangle illustrates the approximate total mixing space at 1 SD. Measurement error (not shown) was also estimated by IsotopeR and applied to each source observation when estimating source aggregates and to each bear in the mixing space. The inset illustrates the isotopic mixing space if concentration dependence was not included in the analysis.
Table 2.
Bear food sources.
Figure 2.
Means and 95% credible intervals (denoted by error bars) calculated by IsotopeR (blue circles) and other Bayesian (orange circles) models. The blue dashed line and gray bar indicates the estimated mean and 95% credible interval for the full IsotopeR model, respectively. Frequentist (open black circles with confidence intervals) and data cloning estimates (open green circles) are also illustrated.
Figure 3.
Dietary estimates generated by IsotopeR and the Semmens et al. model.
Proportional dietary estimates (marginal posterior probability distributions) for individual bears (n = 11) estimated by IsotopeR (blue lines) and the Semmens et al. model (orange lines). Dotted lines denote population-level dietary estimates.
Figure 4.
Isotopic correlation of δ13C and δ15N in each aggregated source.
Orange circles indicate accepted draws from IsotopeR's MCMC chains; these values are used to estimate isotopic correlation and other source parameters. Black circles denote observed values.