Date of this Version
Published in Aquatic Botany 102 (2012) 23– 27. DOI:10.1016/j.aquabot.2012.04.005
Populations of the floating macrophyte, Salvinia minima Baker, were assessed over a 39-month period at four sites in southern Florida in order to elucidate the abiotic and biotic factors that influenced their density. These factors included the abundance of other plant species, changes in water depth, water quality, and herbivory by insects. Abiotic factors like temperature, pH, DO, and conductivity varied among sites and, more importantly, over time. The same was true for S. minima biomass, coverage, and condition. Principal component analysis identified four components which together explained 64% of the variability in S. minima biomass. The first component correlated strongly with herbivory from Cyrtobagous salviniae Calder and Sands and Synclita obliteralis (Walker) as well as the abundance of the duckweed Spirodela polyrrhiza (L.) Schleid. Temperature effects were strongly represented in the second principal component. A stepwise regression model that best predicted S. minima biomass incorporated conductivity, insect herbivory, and interspecific plant abundance. Broader dry vs. wet season influences were apparent and linked to temperature, water depth, and conductivity that covaried with S. minima biomass. Sites where water depth changed the most had the least S. minima. Insect herbivory did not increase under more stagnant conditions when plant populations were less mobile. Overall, S. minima populations cycled in southern Florida in response to a shifting array of abiotic and biotic factors. The relative importance of these factors was less clear although the influences of herbivory, temperature, and the presence of other plants were significant.