SSI radiating populations have larger craniofacial trait values than Caribbean or SSI generalist-only populations.
The results of Bayesian mixed-effects model suggest that on average the SSI radiating group has larger trait values (mean trait value: 0.06, 95% HDI: 0.03, 0.09) than either the Caribbean (mean trait value: -0.09, 95% HDI: -0.13, -0.05) or SSI generalist-only groups (mean trait value: -0.07, 95% HDI: -0.11, -0.03; Figure 3). Model estimates for each trait indicate that this pattern was reflected in 13 of the 18 traits, while 5 of the 18 traits showed no significant differences between groups (Appendix Table D1).
We also included species as a fixed effect in this model to account for the expected differences in trait values between species. We found that on average generalists (mean trait value: 0.039, 95% HDI: 0.020, 0.058) had larger trait values than both snail-eaters (mean trait value: -0.11, 95% HDI: -0.17, -0.046) and scale-eaters (mean trait value: -0.031, 95% HDI: -0.075, 0.013; Appendix Figure D1.A), however, this pattern is variable depending on the trait. For instance, scale-eaters have larger estimates of lower jaw length and lower estimates of maxillary head protrusion compared to both generalists and snail-eaters (Appendix Table D2).
Finally, we investigated the effects of population in our model and found that populations did not have significantly different trait value estimates (Appendix Figure D1.B). We also examined the variability of estimates due to population ID for each craniofacial trait. The standard deviation reported for 16 of the 18 traits was below 0.1 indicating that populations generally have similar trait values. The exceptions being maxillary head height and nasal tissue protrusion, which had higher standard deviations of 0.25 and 0.16 respectively (Appendix Figure D1.C).