DISCUSSION
In the present study, we quantified a temporal shift toward frugivory in
a population of gopher tortoises, where fruit consumption increased with
seasonal precipitation. This seasonal precipitation spurs the production
of fleshy fruits in the pine rocklands of south Florida (Snyder et al.
1990, Lodge 2017), allowing this species to shift its foraging strategy.
As the temporally limited fleshy fruits become increasingly available
over the wet season, the gopher tortoise gradually incorporates these
resources into its diet, becoming more frugivorous intra-annually.
These temporal shifts toward frugivory coincided with the calendar
seasons, demonstrating that fruit consumption increased through the
spring and summer, and decreased through the fall and winter. Seasonal
patterns of frugivory have been documented in many other species (Koike
et al. 2008, Takahashi et al. 2008), including other folivores such as
the western lowland gorilla (Remis 1997). Although gopher tortoises are
efficient hind-gut fermenters (Bjorndal 1987), engaging in frugivory
might confer energetic and nutritional benefits that benefit life
history processes such as growth and reproduction.
All three native palm species in this ecosystem facilitated the observed
shift toward frugivory, along with eastern prickly pear and locustberry.
Eastern prickly pear has been documented to benefit from seed dispersal
through the gopher tortoise (Richardson and Stiling 2019a), while the
other four species have yet been tested. However, palms are known to be
widely dispersed by turtles (Falcón et al. 2020, Marques Dracxler and
Kissling 2022), and saw palmetto in particular benefits from seed
dispersal by the Florida box turtle in the pine rocklands of south
Florida (Liu et al. 2004). If the gopher tortoise is found to enhance
germination in the other four fruit species, seasonal shifts toward
frugivory may translate to increased plant recruitment for these
fleshy-fruit bearing plants.
On this note, we found that as frugivory increased, so did the dispersal
of species with fleshy fruits, suggesting that as the gopher tortoise
switches foraging strategies from folivory to frugivory, so might its
functional role as a seed disperser. This alternation between folivory
and frugivory can be described as a shift along the mutualism-antagonism
continuum (van Leeuwen et al. 2022), by more frequently interacting with
the fruits of endozoochorous species and subsequently dispersing their
seeds. With the gopher tortoise being a well-known seed disperser
(MacDonald and Mushinsky 1988, Carlson et al. 2003, Birkhead et al.
2005, Figueroa et al. 2021) – known to enhance seed germination for
both fleshy and non-fleshy-fruited species (Hanish 2018, Richardson and
Stiling 2019a) – this study documents not only a temporal shift toward
frugivory, but a shift in its functional role as a seed disperser for
plants with the endozoochory syndrome (Ridley 1930, Van der Pijl 1982),
although endozoochorous dispersal of plants without fleshy fruits is
widespread even in the gopher tortoise (Figueroa et al. 2021, Green et
al. 2021).
Considering the high degree of endemism in the pine rockland plant
community (Trotta et al. 2018), and the diversity of state-threatened
species dispersed by the gopher tortoise (Table 1), the importance of
seed dispersal by the gopher tortoise for plant conservation is a
promising avenue for research. Conversely, the dispersal of invasive
plants by the tortoises in this study raises the question of how gopher
tortoises affect germination and colonization of new habitats by
invasive plants, which are already widespread in south Florida (Rodgers
et al. 2014).
To further unravel how endozoochorous seed dispersal varies
intra-annually and how individuals of the same species may provide
unique dispersal services, we encourage future studies that identify
which plant species are dispersed by different individuals and how
patterns of seed dispersal vary seasonally. With appropriate sampling
(Jordano 2016), and using well-defined network indices (Bascompte et al.
2003, Blüthgen et al. 2006, Bascompte and Jordano 2007, Vázquez et al.
2007, Dormann et al. 2009), future research can reveal in great detail
the functional differences between individuals as seed dispersers
(Bolnick et al. 2011, Zwolak 2018), and what the implications of
seasonality are for plants exhibiting different dispersal syndromes.