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United States Department of Agriculture

Agricultural Research Service

Title: Competition between Salvinia minima and Spirodela polyrhiza mediated by nutrient levels and herbivory.

item Tipping, Philip
item Bauer, Laurie
item Martin, Melissa
item Center, Ted

Submitted to: Aquatic Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2008
Publication Date: 4/1/2009
Publication URL:
Citation: Tipping, P.W., Bauer, L., Martin, M.R., Center, T.D. 2009. Competition between Salvinia minima and Spirodela polyrhiza mediated by nutrient levels and herbivory.. Aquatic Botany. Vol. 90, Issue 3, pps. 231-234.

Interpretive Summary: Floating plants like Salivinia minima (‘salvinia’) and Spirodela polyrhiza (‘spirodela’) compete for space, light, and nutrients along a gradient of biotic and abiotic factors. The dynamic nature of their growing medium (water) complicates attempts to predict their assemblages and densities under natural conditions. In controlled experiments the final biomass produced by both species growing together was influenced by fertility, herbivory, and their starting biomass. However, fertility influenced spirodela but not salvinia, while herbivory influenced salvinia but had no secondary effect on spirodela. Despite the fact that herbivory usually eliminated salvinia, spirodela biomass did not increase. These data suggest that salvinia may dominate low fertility sites and spirodela more eutrophic sites. Ultimately, all of these factors coupled with the mosaic of wetland environments in Florida likely promotes a continuum of competitive outcomes between salvinia and spirodela, thereby ensuring their continued coexistence.

Technical Abstract: We investigated the effects of initial biomass, nutrients, herbivory, and competition with Spirodela polyrhiza on Salvinia minima biomass and density. Salvinia minima populations were subjected to two levels of herbivory from the weevil Cyrtobagous salviniae and various levels of competition from Spirodela polyrhiza, while growing in high or low nutrient conditions. The top-down influence of herbivory was the most important factor in S. minima biomass production while bottom up factors like competition or fertility had no measurable impact. In contrast, S. polyrhiza biomass was mediated primarily by nutrients, not competition. There was no herbivory treatment for this plant. Spirodela polyrhiza was superior to S. minima at converting nutrients to biomass but this did not give it a competitive advantage since S. minima biomass was unchanged when herbivory was absent. Salvinia minima can generally overtop S. polyrhiza which, in turn, can form multiple layers within its mat. These characteristics may act to lessen competition between these species at certain times, thereby permitting their mutual usage of the same resources. However, the variety and interactions of biotic and abiotic factors likely complicates predictions of the trajectory and outcomes of competitive interactions between these floating macrophytes.

Last Modified: 06/26/2017
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