Selective waterfowl herbivory affects species dominance in a submerged plant community

Abstract

I used a field experiment to test the hypothesis that waterfowl affect not only the abundance, but also the composition of submerged plant communities. A simple community was chosen for this purpose, composed of two taxa with contrasting distributions along a depth (shore-centre) gradient. I compared exclosures and grazed,reference plots' at the point in the depth gradient where Potamogeton pectinatus L. (dominant at deeper areas) co-exists with Zannichellia spp. (dominant at shallower areas). Results indicated that selective waterfowl foraging may affect community composition, through a variety of effects that include: (a) a reduction in the standing crop of Zannichellia, which was selectively foraged and (b) indirect effects on the survival of asexual propagules (tubers) in the less-foraged species, P. pectinatus, mediated by changes in tuber size and burial depth. [KEYWORDS: macrophytes, waterfowl grazing, enclosure, competition, Zannichellia, Potamogeton]