Gastropod grazing of epiphytic lichens in Western Newfoundland

Flores, Katherine (2021) Gastropod grazing of epiphytic lichens in Western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Overgrazing by introduced gastropods has been identified as a potential threat to some rare or threatened epiphytic foliose lichens; however, gastropod grazing severity has not been evaluated within Newfoundland. Lobaria pulmonaria is locally abundant in Newfoundland but considered rare and threatened in parts of the U.S.A and Europe. To evaluate gastropod grazing severity and describe the tree-climbing gastropod community we conducted lichen diversity and lichenivory surveys and used two methods of gastropod sampling. To determine how lichen species diversity affects lichen grazing of L. pulmonaria, we conducted cafeteria feeding experiments using native and introduced snail species and common lichen species from our study area. We found that within the study area, some lichens including L. pulmonaria were severely overgrazed, and that tree-climbing gastropod abundance increased with greater grazing severity. We found that lichenivory severity was driven by tree-level factors and identified the most common tree-climbing slugs within the study area. Feeding experiment results showed that snails consumed greater lichen biomass with greater species diversity; however, distinct preferences for specific lichen species were apparent. Grazing severity of L. pulmonaria decreased with greater lichen species diversity, which suggests that L. pulmonaria may be more resistant to gastropod grazing in forests with higher foliose lichen species diversity.

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