Mollusc grazing limits growth and early development of the old forest lichen Lobaria pulmonaria in broadleaved deciduous forests
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This study aims: (1) to quantify mollusc grazing on juvenile and mature thalli of the foliose epiphytic lichen Lobaria pulmonaria, and (2) to test the hypothesis inferring a herbivore defensive role of lichen depsidones in forests with indigenous populations of lichen-feeding molluscs. Lichens were transplanted in shaded and less shaded positions in each of two calcareous broadleaved deciduous forests, one poor in lichens, one with a rich Lobarion community. Preventing the access of molluscs significantly reduced the loss of juvenile L. pulmonaria, particularly in the naturally lichen-poor forest. Molluscs also severely grazed mature thalli in the lichen-poor forest, especially thalli placed under the more shading canopies. Furthermore, reducing the natural concentration of depsidones by pre-rinsing with acetone increased subsequent grazing significantly, showing that lichen depsidones function as herbivore defence in natural habitats. Our results suggest that mollusc grazing may play important roles in shaping the epiphytic vegetation in calcareous deciduous forests, and that recently established juvenile L. pulmonaria thalli seem to be particularly vulnerable.
KeywordsAcetone rinsing Development stage Depsidones Herbivore defence Lichenized fungi
Thanks to Dr Torstein Solhøy for identifying mollusc species and giving useful advice on practical means to exclude snails and slugs, to Monica Slåttum, Dr Knut Asbjørn Solhaug, Annie Aasen, Dr Vidar Selås, John Gunnar Dokk and John Wirkola Dirksen assisting in various ways in the set up of the field experiment. Dr Line Nybakken is thanked for collecting mature thalli. Thanks also to Dr Håkon Holien and Dr Olga Hilmo for information on collection localities for the juvenile thalli. We are also indebted to Professor Mikael Ohlson for some financial support through the project 15442/720 funded by the Research Council of Norway. All experiments conducted in this study comply with Norwegian Law. A permit was issued allowing us to temporally transplant the thalli at Jordstøyp Nature Reserve.
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