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.