Poster

         Pteridology

Coexistence of two congeneric species of bracken (Pteridium) in a zone of overlap

Presenting Author
Jeffrey Dosdall
Description
Congeneric species whose ranges overlap often encounter each other in the same habitat, but theory suggests that for a stable coexistence they should differ at least subtly in their microhabitat preferences. Southern Florida represents a zone of range overlap between two closely related bracken (Pteridium) species, the tropical P. caudatum and the temperate P. aquilinum ssp. pseudocaudatum. This zone of overlap presents an opportunity to investigate the coexistence of congeners in a genus with ecological significance and a worldwide distribution. We surveyed bracken populations from seven sites at Archbold Biological Station and measured microhabitat variables. We compared microhabitats among three classifications of plots (P. caudatum dominant, P. a. pseudocaudatum dominant, and controls with no bracken present) using a multinomial baseline-category logit model. We found that the bracken species co-occurred at three of seven sites. Both species preferred areas with high litter cover. Pteridium caudatum favored lower canopy cover than control plots, while P. a. pseudocaudatum favored lower fire frequency. Pteridium caudatum grew in higher densities and had greater biomass per stipe than P. a. pseudocaudatum. These results suggest both bracken species occupy similar yet distinct microhabitats, which might help explain their coexistence in Florida.