Seed Consumption by Gopher Tortoises (Gopherus polyphemus) in the Globally Imperiled Pine Rockland Ecosystem of Southern Florida, USA

Abstract. Turtles have been identified as key dispersers of seeds in many ecosystems; however, seed dispersal by turtles (chelonochory) has received far less attention than seed dispersal by birds or mammals. We assessed the role of gopher tortoises (Gopherus polyphemus)—a keystone species—as potential seed dispersers by analyzing the seed composition of their diet in a globally imperiled ecosystem: the pine rockland ecosystem of South Florida. The pine rocklands contain high numbers of both endemic and invasive plant species that may be dispersed by tortoises. We collected scat samples from wild gopher tortoises living in the pine rockland habitats in the Richmond Tract (Miami-Dade County, Florida, USA) and examined the samples to identify seeds consumed. We extracted 2484 seeds from 53 samples from at least 10 individual tortoises. Of the 2484 individual seeds, we distinguished 33 morphospecies and identified 23 to the species taxonomic level. The 14 most abundant seed species in the scat constituted > 90% of all seeds eaten by the tortoises. Three of the 14 most abundant seeds were from nonnative plants, but none were among the most disruptive invasive species. Tortoises consumed mostly herbaceous ground cover and fibrous grasses. Given that the tortoises were consuming several ground cover plants and contained a high density of those seeds in their scats, they seemed to be consuming the seeds as bycatch rather than selectively feeding on them, therefore supporting Janzen's “foliage is the fruit” hypothesis. The prevalence of many seeds and a variety of seed species in the tortoise scat suggests that gopher tortoises may be serving the ecological role of a seed dispersal agent for some of the plants they consume within the pine rocklands.