Competition among Small, Free-floating, Aquatic Plants

• Published in: The American midland naturalist 1998-07, Vol.140 (1), p.55-67
• Main Authors: Dickinson, Matthew B, Miller, Thomas E
• Format: Article
• Language: English
• Subjects: Aquatic life; Aquatic plants; Autumn; Azolla caroliniana; Biological competition; Biology; Buoyancy; Contents; Emergent plants; Mathematical minima; plant communities; Plant competition; Plant growth; Plants; Salvinia minima; Spirodela punctata; Summer; Swamps
• ISSN: 0003-0031; 1938-4238
• DOI: 10.1674/0003-0031(1998)140[0055:CASFFA]2.0.CO;2

The surface cover of three species of small, free-floating, aquatic plants in a beaver swamp was monitored for 1 yr. Simultaneous experiments at the same site quantified competitive relationships among these species in different seasons. In the summer competition experiment, Salvinia minima grew rapidly and had negative effects on the relative change in cover of both Azolla caroliniana and Spirodela punctata. Relative change in cover of S. minima increased when it was grown with S. punctata, but only when A. caroliniana was not present. A negative correlation in the swamp between cover of S. minima and S. punctata, the two most abundant species during the summer, is consistent with the strong competitive effects of S. minima in the summer competition experiment. During the autumn competition experiment, S. minima had a negative effect on A. caroliniana's relative increase in cover. This effect, however, was not competitive and was caused by an herbivore of S. minima that switched to A. caroliniana as S. minima's growth slowed in the autumn. Total cover of small, floating, aquatic plants was lowest in the autumn. Salvinia minima, the best competitor for surface space during the summer experiment, is also the largest species, the most difficult to sink and the most buoyant once submerged. Competition has an important, but limited, role in this community. The effects of competition on surface area were seasonal, and the striking gains in cover of Salvinia minima during the summer were reversed by its relative intolerance of winter conditions and its higher reduction in cover during floods. Apart from late summer, cover of S. punctata was by far the highest throughout the study period, despite S. minima's competitive ability.