Patterns of density dependence in growth, reproduction and survival in the invasive freshwater snail Pomacea canaliculata in Japanese rice fields

1. Patterns of density dependence in growth, reproduction and survival are important for predicting the population dynamics of a species. The patterns may change with environmental factors, such as the harshness of winter, but very little is known about such patterns and their mechanisms in unmanipulated natural populations of invasive animal species. 2. We studied the extent of density dependence in the growth, reproduction and survival of an invasive freshwater snail, Pomacea canaliculata, in rice fields in Nara (cold district) and Kumamoto (warm district), Japan, over 2- and 1-year periods, respectively. 3. In both areas, growth was negatively density dependent within the same generation, and the density of snails in the parental generation negatively affected the growth of offspring. The number of eggs per unit area was independent of adult density, suggesting eggs per adult female were few at high densities. Survival over the cold winter of 2005-2006 was independent of density in Nara. However, survival over the warm winter of 2006-2007 in both Nara and Kumamoto was negatively density dependent. 4. Irrespective of the various negative density-dependent patterns, population density tended to show positive correlations with the density of the previous generation. This appears to reflect the substantial capacity of this snail to resist extremely low densities due to the various negative density-dependent patterns rather than indicating susceptibility to extinction at low densities.