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.