Rapid population growth countered high mortality in a demographic study of the invasive snail, Melanoides tuberculata (Müller, 1774), in Florida

摘要

Melanoides tuberculata , an exotic thiarid snail that originated in the Middle East, eastern Africa, and Southeast Asia, has invaded subtropical and tropical areas worldwide. This study provided a detailed picture of the characteristics of a population in central Florida. We collected 40 specimens of Melanoides tuberculata from a cool spring and cultured them and 54 of their offspring in the laboratory for 7 and 10 months, respectively. For both the adults and their F1 offspring, weekly or bimonthly measurements of individuals and counts of offspring produced estimates of growth, age at first reproduction, offspring production, and survival. From these measurements, we produced estimates of birth and death rates and a growth curve using a monomolecular model. We estimated predation rates on the snails with a three-day incubation of small (1–4 mm) M. tuberculata with crayfish in the laboratory. Finally, we produced a static life table from measurements of ~2,200 specimens of M. tuberculata collected from the spring. Growth and reproduction measurements from the laboratory indicated that the snails grew rapidly and were prolific. Only initial size significantly explained any variation in the growth of individuals and only first clutch size explained any variation in fecundity. Nonpredatory mortality in the laboratory was low, but crayfish-induced mortality was high. The life table analysis suggested that the spring population was stable and that mortality was extremely high on the smallest individuals, such as those used in the crayfish predation rate measurements, and on the largest individuals. Therefore, the potential of M. tuberculata to invade new habitats and quickly establish populations may be the result of its high population growth rate, but its population growth may be checked by local predators, such as crayfish and perhaps snail-eating turtles and raccoons.