Scat Collection and Dissection
We conducted this study over a 1.5-year period with scat collection
beginning on May 11th, 2021, and ending on November
9th, 2022. We tracked wild gopher tortoises at the
Richmond Tract twice weekly via radio telemetry. If an individual
defecated during handling, we collected the sample labeled it with the
tortoise’s ID number, location, and the date. Sometimes, we encountered
fresh fecal samples belonging to unknown tortoises and thus collected
them. For these samples, we GPS marked, dated, and labeled them with a
unique identifier that indicated it came from an unknown individual.
Fecal samples were either dissected on the same day of collection or
frozen for dissection at a future date. We performed scat dissections
with forceps over laminated graph paper (29.59cm x 21.01cm) containing
5mm x 5mm grids as a static background reference, and we used this
background reference to compare the relative contributions of food items
to the total fecal volume. All food items recovered from fecal samples
were identified to the lowest taxonomic unit or qualified as their own
category (e.g., fur/hair was recovered from multiple species and
subsequently categorized as mammal fur).
After dissecting fecal samples and separating contents over the
laminated graph paper, we then visually estimated the relative
contributions of each food category to the total scat volume was; this
approach has been compared with other methods resulting in its
acceptance for dietary studies (Klare et al. 2011). We quantified the
contribution of five functional food categories – Grasses, Legumes,
Other Plants, Fruit, and Animals – to the total fecal volume as either
0.01, 0.05, or in increments of 0.05 all the way to the total scat
volume proportion of 1.00. If a value less than 0.05 remained after
quantifying the relative contribution of all food items, we would
allocate the amount to the most abundant food category in the sample.
Additionally, we identified all seeds extracted from fecal samples to
the lowest taxonomic unit using dichotomous keys, online references, and
consultations with local botanists (Gann et al. 2001, 2002, Wunderlin et
al. 2016). Seeds were then counted and the dispersal syndromes were
recorded using criteria from Ridley (1930) and Van der Pijl (1982) to
distinguish species with the endozoochory syndrome from all other
syndromes (Table 1).
Quantifying the Strength of Frugivory through Time
While other studies have used activity budgets to quantify the strength
of frugivory (Pavelka and Knopff 2004), we directly measured the
proportion of total fecal volume comprised of fruit. This measure was
used as the response variable in all subsequent analyses on frugivory.
As our predictor variables, we used indices of time in the form of
calendar days to cover the whole calendar year and in a separate
analysis, we used an interaction term between the season in which the
sample was collected with the number of days elapsed within that season.