Demographic Studies on Hawaii's Endangered Tree Snails: Partulina proxima

Abstract

Populations of the tree snail Partulina proxima, endemic to higher elevations of Molokai, Hawaiian Islands, were studied for 3 years. Analyses of the data derived from 17bimonthly mark-recapture events determined that each tree harbors a small, mostly nonmigratory population of 8-26 snails of which 2-4 are adults; the snails average 4.2 mm long at birth and 21.3 mm long when growth stops; growth is slow, with maturity reached in 5-7 years; annual fecundity averages 6.2 offspring per adult; and mortality is about 98% over the first 4 years of life. Given the high rate of juvenile mortality, adult snails must reproduce for at least 12 years to replace themselves. From this we calculate a minimum maximal life-span of 18-19 years. We conclude that the current high rate of unexplained juvenile mortality, combined with lat e age at first reproduction and low fecundity, place this species at very high risk to any sort of perturbation, particularly any selective predation on adults.