Step 4: Locustberry (Byrsonima lucida)/Saw Palmetto Ratio
The final pair of fruit species that accounted for the greatest logratio variance was locustberry/saw palmetto. Locustberry is a tropical plant species that is known to be consumed by the Florida box turtle (Terrapene carolina bauri ) (Liu et al. 2004, Platt et al. 2009). This fleshy fruit-bearing tropical shrub led the rest of the logratios when paired with saw palmetto to explain an additional 2.81% of total variance. After this logratio, the total amount of logratio variance explained equaled 96.96% (Supp. Table 1), at which point we stopped selecting additional logratios.
To illustrate the interrelations between the five fruit species comprising the four logratios, we created an acyclical graph where each edge connects two of the fruit species corresponding to one of the logratios we selected (Supp. Fig. 1). In total, five fleshy-fruited species contributed to the observed shift toward frugivory – three of which were native palms and two were state threatened species in Florida (Table 4). Subsequently, the LRA biplot illustrates the analysis of the full 16-species dataset whereas the PCA biplot depicts the ordination of the 4 logratios (Fig. 5). While not visually obvious, the LRA biplot analyzes all 120 logratios – which can be thought of as the connections between all 16 pairs of fruit species.
In contrast, the PCA was performed only on the four logratios selected in the stepwise LRA (Fig. 5; right panel), which shows a very similar pattern in the spread of the points as in the LRA biplot (Fig. 5; left panel). Fall and summer samples have greater spread in them than winter and spring samples and South and West samples are more spread out than East’s samples. To estimate the strength of these correlations, we calculated a Procrustes correlation of 0.976, indicating strong agreement between the two ordinations. The concordance between the LRA and PCA biplots indicate that the spatiotemporal patterns in frugivory are indeed captured by the subset of four logratios we selected out of the 120 possible. This suggests that saw palmetto, silver palm, sabal palm, prickly pear, and locustberry are important fruit resources for the gopher tortoise that drive its frugivorous dietary habit. Of the four logratios selected, the most variance-explaining species when paired with saw palmetto are each of the following: eastern prickly pear, locustberry, sabal palm, and silver palm (Supp. Table 2). These results suggest the most important fruit species in the diet of tortoises in our study are saw palmetto, eastern prickly pear, locustberry, sabal palm, and silver palm in that order.