Survival among critically endangered partulid tree snails is correlated with higher clutch sizes in the wild and higher reproductive rates in captivity

Endemic Pacific Island land snails are among the planet's most endangered taxonomic groups and many have fallen victim to misguided biological control programmes involving the rosy wolf snail, Euglandina rosea. The family Partulidae has been heavily impacted but a recent study of Tahitian species found that survivors had differentially higher clutch sizes. Here, we further tested the inference that higher fecundities may promote survival of Partula species by incorporating historical field demographic data from additional island populations (Guam, Saipan and Moorea) that collectively span the range of the family, as well as complementary demographic data from captive populations sourced from these islands and from Tahiti. Our primary result broadly corroborated the earlier study: species with higher reproductive output, whether measured by historical field clutch sizes or by reproductive rates in captivity, are more likely to have survived. However, this generality does not apply to all island populations and it is unlikely to be the sole determining factor in any of these cases. Detailed ecological and behavioural studies of extant wild P. radiolata (Guam), P. gibba (Guam and Saipan), P. taeniata (Moorea), P. hyalina and P. clara (Tahiti) populations, and of their co-occurring introduced predators, are urgently required.