How do alligators benefit prairie iris?

By Chelsie Vandaveer

March 31, 2004

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The Dixie or prairie iris (Iris hexagona Walter) is an inhabitant of low ground—swamps, prairies, and marshes. The plants tolerate both fresh and brackish waters, growing on seasonally wet to permanently inundated soils. Like other irises, the prairie iris reproduces vegetatively (the growing and branching rhizome) and sexually (the production of seed). The quality of the water affects how the plant will mostly reproduce.

In an experiment with prairie iris, Peter Van Zandt, Mark Tobler, Edmund Mouton, Karl Hasenstein, and Susan Mopper found that slightly increasing the salinity of the water caused the plants to reallocate their resources.
Plant of the Week 03/29/2004

Prairie Iris (Iris hexagona Walter)
Plant of the Week 03/29/2004

With fresh water, the plants used most of their energy growing more plant--leaves and rhizomes—creating larger colonies.

In mildly saline water, the plants were smaller, the nutrients and energy going into seed production. Highly saline water went beyond the iris's tolerance, the plants senesced and died. ("Positive and negative consequences of salinity stress for the growth and reproduction of the clonal plant, Iris hexagona", Van Zandt, Tobler, Mouton, Hasenstein, and Mopper, Journal of Ecology 91, 2003)

In later experiments, the scientists discovered that there was also a maternal effect on the seeds. In response to saline-induced stress, the mother plant creates more abscisic acid (ABA), a hormone that regulates growth. Seeds with high ABA levels have increased germination rates. Slightly saline-stressed plants are more likely to successfully reproduce by seed.

American Alligator Eats its Prey on Floridas Gulf Coast

The deer learned to browse on plants that are away from the water's
edge where their major predator, the alligator, may be lurking.
American Alligator Eats its Prey on Floridas Gulf Coast Photographic Print
Klaus Nigge
Buy Photographic Print at AllPosters.com

On Marsh Island where the prairie irises were studied, white-tailed deer browse on the flowers preventing seed production. The deer learned to browse on plants that are away from the water's edge where their major predator, the alligator, may be lurking.

Since the plants away from the water are better at colonizing, the deer inadvertently aid their vegetative growth which helps prevent erosion. The plants at or in the water are more likely to have saline-stress effects due to tidal influences. The alligator aids the survival of the flowers and seeds that will disperse to grow in new areas. ("Alligators, deer, and the evolutionary ecology of a native Louisiana iris", S. Mopper, C.J. Criner, K.H. Hasenstein, E. Mouton, M.A. Tobler, Y. Wang, and P.A. Van Zandt, Presentation Abstracts, Allen Press, 2000)

The Atlas of Florida Vascular Plants, Institute for Systematic Botany, University of South Florida has numerous photographs of the prairie iris showing the variations found in the species. To view the photographs, click on the link:

http://www.plantatlas.usf.edu/main.asp?plantID=3156

Click on the Images tab and on the thumbnails to enlarge the images.

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