Consumption of lichens by native (Philomycus sp.) and non-native
(Arion sp.) slugs and the most common snail species present, Discus
catskillensis, and Amber snails, Succinidae, was evaluated using
feeding trials. After collection from the boards, gastropods were fed
with lettuce in outdoor shaded conditions prior to the start of the
feeding trials. Lichen species used in the main feeding trial (Trial
1) were: Hypogymnia physodes, Lobaria pulmonaria, Myelochroa
aurulenta, and Puntelia rudecta. All lichens were selected for their
abundance and relative ease of collection at the HBEF except for L.
pulmonaria, which was shipped from Maine where it is much more common.
Lichen thalli were removed from their substrate, dried at 40°C for 48
hours, and weighed prior to the start of the feeding trials. Ten
trials were run for each of the four gastropod groups. Gastropods were
weighed and distributed into plastic, rectangular food-storage
containers. Several small holes were punctured through the lids of the
containers for air exchange. The bottom of each container was covered
with wetted unbleached paper towel. The lichens were equidistant from
the gastropods upon placement of the gastropods into the center of the
containers. Containers were kept in natural light conditions in a
shaded outdoor location. The feeding trials lasted for four days and
containers were sprayed to maintain humidity at least every eight
hours. At the end of the trials, gastropods and fecal matter were
removed from the remaining lichen scraps which were then dried at 40°C
for 48 hours and re-weighed.
A second set of feeding trials (Trial 2) was conducted for the slugs
(only) with three additional lichen species, Flavoparmelia caperata,
Platismatia glauca, and Usnocetraria oakesiana; also, P. rudecta was
included in these trials for reference to check comparability of the
results with the previous trials. For these trials, lichens were not
completely cleaned of their substrate. These trials were conducted in
the laboratory using 12 hours of light, and slugs were not fed
overnight prior to starting the experiment. In all other respects
these trials were identical to the first.
