SD: Standard Deviation
Figure 1. A) Maps of study sites in the Izu Peninsula.Euhadra peliomphala simodae is distributed on the Izu Peninsula
(mainland) and the Izu Islands including Niijima Island. The survey was
conducted on both the Izu Peninsula and Niijima Island. B, C) The
cross-section of the Izu Peninsula and Niijima Island from the west
side. In the Izu peninsula, E. p. simodae is inhabited only in
southern part of it.
Figure 2. Frequency shell colour distribution on marked snails
in A) the Izu Peninsula and B) Niijima Island (modified from Ito and
Konuma, 2020). Shell colour was quantified using the luminance value\(Y\) using a photograph of the snail, with higher values representing
brighter colours. In the Izu Peninsula, the distribution showed unimodal
and mainly bright shell colour existed whereas it showed bimodal, dark
and bright shell colour existed in Niijima Island.
Figure 3. Images of predated empty shell and the large Japanese
field mouse Apodemus speciosus . A) the scene that A.
speciosus predated a living snail which was tethered using sting in
front of a trail camera. B) the shell left after a trail camera captures
a scene that A. speciosus preyed on a snail. C) empty shells
predated by A. speciosus found in mark-recapture survey. It has
characteristics the splitting of the apex or the shattering of the
shell.
Figure 4. The relationship between survival rate and shell
colour in A) the Izu Peninsula and B) Niijima Island (modified from Ito
and Konuma, 2020); I) is juvenile, II) is adult. This shape represents
the natural selection worked on shell colour. In the Izu Peninsula, the
natural selection was estimated after excluding predation effects. The
solid and dashed lines indicate the median and the 95% Bayesian
confidence interval, respectively, in the posterior distribution
obtained from Markov chain Monte Carlo simulations.