The life cycle of the apple snail Pomacea canaliculata was monitored over 2-and 1-year periods in Nara (cold district) and Kumamoto (warm district), respectively. The life cycles were similar in both districts: most hatchlings appeared after August, and although some had grown to Ն20 mm by autumn, the majority of juveniles remained Ͻ20 mm. The survival rate over winter was very low (Ͻ1%) in Nara, and moderately low (9%) in Kumamoto. After winter, survivors grew rapidly with low mortality, reproduced actively in summer, and most died during the following winter. The survival rate during mid-term drying (drying of fields for about 2 weeks in summer) in Nara was high (ca. 90%) in both years. In Nara, snail density after winter decreased to 1/43 of that in Kumamoto, but survivors in Nara grew larger and laid more eggs. Due to these effects, egg density in July, and also snail density in September, in Nara recovered to ca. 1/3 of that in Kumamoto.

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Summary 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. 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. 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. 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.

SummaryOverwintering of two social halictine bees, Lasioglossum duplex (Dalla Torre) and L. problematicum (Blüthgen), was studied. In L. duplex many females stay near the old nests, each female preparing a hibernaculum separated from the natal nest. In L. problematicum most females overwinter communally within the natal nest. This difference in overwintering habits relates to the social structure in the next spring. L. duplex is nearly always solitary in spring although later becoming eusocial, whereas many nests of L. problematicum are polygynous, beginning in early spring. L. duplex overwinters much deeper () in the soil than does L. problematicum (), but both species are safe from drops in soil temperature, which is above 0°C even in midwinter, and the bees' supercooling points are lower than −6°C. This cold resistance and the storage of sufficient food in the crop are reflected in the winter survival, which is much higher (79%) than the rate of successful nests in the spring active phase (25%).