Summary
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.
Similar content being viewed by others
References
Allard, R. W.: Genetic systems associated with colonizing ability in predominantly selfpollinated species. In: Genetics of colonizing species, (H. G. Baker, G. L. Stebbins, eds.), p. 49–75. New York: Academic Press 1965
Anderson, P. K.: Ecological structure and gene flow in small mammals. Symp. zool. Soc. Lond. 26, 299–325 (1970)
Rasinger, A. J.: The European brown snail in California. Calif. agric. exper. Stn. Bull. 515, 1–22 (1931)
Boycott, A. E.: The oecology of British land Mollusca, with special reference to those of ill-defined habitat. Proc. malac. Soc. Lond. 18, 213–224 (1929)
Boycott, A. E.: The habitats of land Mollusca in Great Britain. J. Ecol. 22, 1–38 (1934)
Boycott, A. E.: The relation of slugs and snails to man in Britain. Proc. Cotteswold Nat. Field Club 26, 73–82 (1936)
Cadart, J.: Les escargots (Helix pomatia L. et Helix aspersa M.). Biologie, élevage, parcage, histoire, gastronomie, commerce. Paris: Paul Lechevalier 1955
Cain, A. J., Sheppard, P. M.: The effects of natural selection on body colour in the land snail Cepaea nemoralis. Heredity 6, 217–231 (1952)
Carpenter, P. P.: Report on the present state of our knowledge with regard to the Mollusca of the west coast of North America. Report of the B.A.A.S. for 1856, p. 159–368 (1856)
Comfort, A.: The duration of life in molluscs. Proc. malac. Soc. Lond. 32, 219–241 (1957)
Cotton, B. C.: These snails may invade your garden. J. Dept. Agric. South Aust. 52, 561–565 (1949)
Ehrlich, P. R.: The population biology of the butterfly Euphadryas editha. II. The structure of the Jasper Ridge colony. Evolution 19, 327–336 (1965)
Ehrlich, P. R., Breedlove, D. E., Brussard, P. F., Sharp, M. A.: Weather and the “regulation” of subalpine populations. Ecology 53, 243–247 (1972)
Ehrlich, P. R., White, R. R., Singer, M. C., McKechnie, S. W., Gilbert, L. E.: Checkerspot butterflies: a historical perspective. Science 188, 221–228 (1975)
Forbes, E.: On the species of Mollusca collected during the surveying voyages of the Herald and Pandora, by Capt. Kellett, R.N., C.B., and Lieut. Wood, R. N. I. On the land-shells collected during the expedition. Proc. zool. Soc. Lond. 1850, 53–56 (1850)
Frank, P. W.: Shell growth in a natural population of the turban shell, Tegula funebralis. Growth 29, 395–403 (1965)
Hanna, G. D.: Introduced mollusks of western North America. Occ. pap. Calif. Acad. Sci. 48, 1–108 (1966)
Ingram, W. M.: The European brown snail in Oakland, California. Bull. So. Calif. Acad. Sci. 45, 152–159 (1946)
Kerney, M. P.: Snails and man in Britain. J. Conch. Lond. 26, 3–14 (1966)
Lamotte, M.: Polymorphism of natural populations of Cepaea nemaralis. Cold Spr. Harb. Symp. Quant. Biol. 24, 65–86 (1959)
Lewis, H.: Catastrophic selection as a factor in speciation. Evolution 16, 257–271 (1962)
Morton, J. E., Machin, J.: A key to the land snails of the Flatford area, Suffolk. Field Studies 1, 57–71 (1959)
Potts, D. C.: Population ecology of Helix aspersa, and the nature of selection in favorable and unfavorable environments. Ph.D. thesis, University of California, Santa Barbara (1972)
Southwood, T. R. E.: Ecological methods. London: Chapman and Hall 1966
Stearns, R. E. C.: On Helix aspersa in California, and the geographical distribution of certain west American land-snails, and previous errors relating thereto, etc. Ann. N.Y. Acad. Sci. 1, 129–139 (1881)
Stearns, R. E. C.: Exotic Mollusca in California. Science 11, 655–659 (1900)
Taylor, J. W.: Life histories of British helices. Helix (Pomatia) aspersa Müll. J. Conch. Lond. 4, 89–105 (1883)
Taylor, J. W.: Monograph of the land and freshwater Mollusca of the British Isles. Leeds: Taylor Bros. 1894–1921
U.S. Weather Bureau: Monthly climatological data. Wash. D.C.: U.S. Govt. Printing Office 1965–1969
Wells, G. P.: The water relations of snails and slugs. III. Factors determining activity in Helix pomatia L. J. exp. Biol. 20, 79–87 (1944)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Potts, D.C. Persistence and extinction of local populations of the garden snail Helix aspersa in unfavorable environments. Oecologia 21, 313–334 (1975). https://doi.org/10.1007/BF00345824
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00345824