Gopher tortoise herbivory increases plant species richness and diversity
Mammalian herbivores often alter plant species richness and diversity, but such impacts have not been much investigated in reptiles. This study examined the effects of gopher tortoise (Gopherus polyphemus) herbivory on species richness, Gini-Simpson diversity, and dominance, plant abundance, and biomass. Tortoise herbivory was eliminated in five areas through the use of exclosure plots for a period of two years and was compared to five similar areas where tortoises were allowed to feed. Cafeteria feeding trials were also used to quantify dietary preference. Tortoise exclosure plots had lowered species richness, and significantly lowered diversity, but significantly higher dominance than in controls. Heliotropium polyphyllum, the most highly preferred local species by tortoises, was the most dominant plant in exclosure and control plots and became even more dominant in exclosure plots. The abundance and biomass of the next two most common plant species, Fimbristylis cymosa and Polypremum procumbens, which are not preferred by tortoises, were reduced in the exclosures, probably due to increased competition with Heliotropium. Several rare plant species were eliminated in the exclosure plots. We conclude that tortoise herbivory may directly influence plant community assembly by reducing preferred plant species and promoting the growth of non-preferred species.
KeywordsVertebrate herbivory Plant diversity Plant communities
Thanks to Tom Watson and the rest of the Egmont Key State Park staff for keeping an eye on things; Alison Gainsbury, Chris Grimaldi, Stephen Hesterberg, Elizabeth Salewski, Keith Stokes, and Jake Zydek for field assistance; and the Lowry Park Zoo Herps department for use of their tortoises. This study was funded by The Odessa Garden Club and USF Provost’s Office. This research was conducted under USF IACUC permit 739.
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