Study Species
The gopher tortoise is the only native tortoise found east of the Mississippi River (Auffenberg and Franz 1982, Bury and Germano 1994, Edwards et al. 2016). Its range spans the southeastern United States, from Louisiana to South Carolina and south into Miami-Dade County and Cape Sable in Florida (Kushlan and Mazzotti 1984, Enge et al. 2004, Waddle et al. 2006). Gopher tortoises support over 350 commensal animal species that use their burrows (Diemer 1986, Lips 1991) and are known to forage on over 1000 plant species across their range (Ashton and Ashton 2008).
Many studies have investigated the diet and foraging ecology of this species (McRae et al. 1981, MacDonald and Mushinsky 1988, Mushinsky et al. 2003, Ashton and Ashton 2008), classifying it as an herbivore that engages in frugivory (Birkhead et al. 2005, Hanish 2018, Richardson and Stiling 2019a, 2019b). As such, it is a widely-recognized seed disperser by ingesting the seeds of fleshy-fruited (Hanish 2018, Richardson and Stiling 2019a), and “foliage is the fruit” species (Carlson et al. 2003, Birkhead et al. 2005, Figueroa et al. 2021), oftentimes enhancing seed germination (Falcón et al. 2020). The tortoises in this study serve as a model for investigating how frugivory might fluctuate in a seed-dispersing herbivore (Marques Dracxler and Kissling 2022, van Leeuwen et al. 2022), providing an opportunity to quantify which fleshy fruits are an important part of its diet, and whether its functional role as a seed disperser changes temporally.
The tortoises in the study site are found in three aggregations which we refer to as the East, South, and West sites – named after the cardinal directions in which they are located across Zoo Miami’s pine rocklands (see Fig. 1). These tortoises aggregations are due to a combination of the species’ social behavior (Guyer et al. 2012), as well as the geology of this ecosystem (Hoffmeister et al. 1967), which can limit the availability of deep sandy soils that facilitate burrowing (Whitfield et al. 2022). During the study, no tortoises migrated from one site to another, as we regularly tracked individuals via radio telemetry, so each site has a perfectly nested subset of individuals that occupy it. While formal surveys were not conducted, the plant communities in both the South and West sites were representative of healthy pine rockland while the East site had a greater presence of invasive plant species such as Burma reed (Neyraudia reynaudiana), showy rattlebox (Crotalaria spectabilis), and shrub verbena (Lantana camara).