Journal Article

Swan foraging shapes spatial distribution of two submerged plants, favouring the preferred prey species

Sandsten, Håkan, Klaassen, Marcel

2008

Overview

Compared to terrestrial environments, grazing intensity on belowground plant parts may be particularly strong in aquatic environments, which may have great effects on plant-community structure. We observed that the submerged macrophyte, Potamogeton pectinatus, which mainly reproduces with tubers, often grows at intermediate water depth and that P. perfoliatus, which mainly reproduces with rhizomes and turions, grows in either shallow or deep water. One mechanism behind this distributional pattern may be that swans prefer to feed on P. pectinatus tubers at intermediate water depths. We hypothesised that when swans feed on tubers in the sediment, P. perfoliatus rhizomes and turions may be damaged by the uprooting, whereas the small round tubers of P. pectinatus that escaped herbivory may be more tolerant to this bioturbation. In spring 2000, we transplanted P. perfoliatus rhizomes into a P. pectinatus stand and followed growth in plots protected and unprotected, respectively, from bird foraging. Although swan foraging reduced tuber biomass in unprotected plots, leading to lower P. pectinatus density in spring 2001, this species grew well both in protected and unprotected plots later that summer. In contrast, swan grazing had a dramatic negative effect on P. perfoliatus that persisted throughout the summer of 2001, with close to no plants in the unprotected plots and high densities in the protected plots. Our results demonstrate that herbivorous waterbirds may play a crucial role in the distribution and prevalence of specific plant species. Furthermore, since their grazing benefitted their preferred food source, the interaction between swans and P. pectinatus may be classified as ecologically mutualistic.

• Publisher: Berlin/Heidelberg : Springer-Verlag,Springer,Springer-Verlag,Springer Nature B.V
• Subject: Analysis of Variance / Animal and plant ecology / Animal, plant and microbial ecology / Animals / Anseriformes / Anseriformes - physiology / Aquatic birds / Aquatic environment / Aquatic plants / Biological and medical sciences / Biomass / Biomedical and Life Sciences / Bioturbation / Community structure / Deep water / Demography / Ecology / Food Preferences / Food Preferences - physiology / foods / Foraging / Fundamental and applied biological sciences. Psychology / General aspects / Grazing / Grazing intensity / Herbivores / Herbivory / Hydrology/Water Resources / Intermediate water / Life Sciences / Pectinatus / physiology / plant communities / Plant Sciences / Plant species / Plant-Animal Interactions - Original Paper / Plants / Population Density / Potamogeton pectinatus / Potamogetonaceae / Potamogetonaceae - physiology / rhizomes / Rivers / Sediments / Spatial distribution / Spring / Stuckenia pectinata / submerged aquatic plants / Submerged plants / Summer / Swans / Terrestrial environments / Tubers / underground parts / Vegetation / water birds / Water depth