Potts D C
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.
Oecologia. 1975 Dec;21(4):313-334. doi: 10.1007/BF00345824.
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.
在南加利福尼亚，先前受到干扰但目前未开垦的栖息地对于引进的蜗牛——散大蜗牛来说是不利的环境。在这些栖息地，蜗牛常常仅以相距仅几米的小的局部种群形式分布。相邻种群之间的迁移极少，因为蜗牛具有很强的归巢倾向。在为期5年的研究期间，当地微环境差异导致了4个相邻种群在人口统计学特征上的差异。这些栖息地的主要不利特征是每年有6至8个月的干旱，这导致种群增长缓慢且断断续续。蜗牛在5年中仅成功繁殖了3次，但只有其中2个种群的幼体达到了性成熟。大多数生长仅限于春季，蜗牛成熟时年龄可达4岁，不过有一个种群在干旱天气期间因额外的水分供应，使得蜗牛在6至8个月内就成熟了。至少74%的死亡是由小型哺乳动物造成的，而且有一个种群在一段高死亡率时期因不利的物理条件阻碍了补充个体的产生而灭绝。仅不利的物理条件并不会导致种群数量下降或灭绝。
