title: Persistence and extinction of local populations of the garden snail Helix aspersa in unfavorable environments.
abstract: In southern California, previously disturbed but currently uncultivated habitats are unfavorable environments for the introduced snail Helix aspersa. In these habitats, snails were often distributed in small, local populations only a few meters apart. Migration between neighboring populations was minimal because the snails have strong homing tendencies. Local micro-environmental differences produced differences in the demographic properties of 4 adjacent populations during studies spanning 5 years.The major unfavorable feature of these habitats was 6-8 months annual drought which caused slow and intermittent population growth. Snails nested successfully only 3 times in 5 years, but juveniles from only 2 of these cohorts reached sexual maturity. Most growth was restricted to the spring and snails were up to 4 years old when they matured, except for one population where additional water during dry weather enabled snails to mature in 6-8 months.At least 74% of deaths were caused by small mammals, and one population went extinct when adverse physical conditions prevented recruitment during a period of heavy mortality. Adverse physical conditions alone did not lead to population declines or extinctions.
authors.affiliation: Department of Biological Sciences, University of California, Santa Barbara, California.|Department of Environmental Biology Research School of Biological Sciences, The Australian National University, P.O. Box 475, Canberra City, A.C.T., Australia.
authors.forename: D C
authors.initials: DC
authors.lastname: Potts