COS 13-1 - The effects of gopher tortoise herbivory on plant community composition

Monday, August 7, 2017: 1:30 PM
D133-134, Oregon Convention Center
Jason Richardson and Peter Stiling, Department of Integrative Biology, University of South Florida, Tampa, FL

Consumption of plants by vertebrates may affect plants on an organismal level through direct mortality, on a community level by changing species composition or by altering rate of succession, and at whole ecosystem levels by altering nutrient cycles. In regards to community ecology, the majority of scientific literature on herbivory has focused extensively on the role mammals play in affecting plant populations and communities. Attempts to quantify the effects on plants and plant communities through folivory and frugivory by reptiles is lacking, despite the prevalence of some form of herbivory in many reptile groups. This study examined the effect of gopher tortoise (Gopherus polyphemus) herbivory on plant community composition. Exclosures were set up for two years which were compared seasonally to areas where tortoises were able to feed. We also evaluated the effect of gut passage and presence of scat on seed germinability using a fully factorial ANOVA that included passage through the gut and scat fertilization as main effects.


Areas where tortoises are prohibited from feeding had lowered diversity than control plots. The community assemblage remained fairly consistent across time in the control plots, but shifted considerably in the exclosures. Gut passage averaged 46 days across all tortoises. Percentage of seed germination, but not germination rate, changed in all species after gut treatment. The presence of scat was largely unimportant in changing germinability. Seeds from fruits with fleshy outer coating germinated faster and at higher percentages. While seed germinability is not always enhanced, the long passage time provides opportunity for seed dispersal. We conclude that gopher tortoises can exert strong pressures on plant community assembly. These pressures are probably a combination of selective dietary preference and altered seed germination rates and percentages.